Vol. 62, No. 21 (2013)
New infinite sequence soliton-like solutions of (2+1)-dimensional generalized Calogero-Bogoyavlenskii-Schiff equation
2013, 62 (21): 210201. doi: 10.7498/aps.62.210201
This paper will study in detail homogeneous linear ordinary differential equation with constant coefficients of second order and draw new conclusion to construct new infinite sequence soliton-like solutions of high-dimensional nonlinear evolution equations. Step one: the solving of a homogeneous linear ordinary differential equation with constant coefficients of second order is changed into the solving of the quadratic equation with one unknown and the Riccati equation. Based on this, new infinite sequence solutions of homogeneous linear ordinary differential equation with constant coefficients of second order are found by using nonlinear superposition formula for the solutions to Riccati equation. Step two: new infinite sequence soliton-like solutions to (2+1)-dimensional generalized Calogero-Bogoyavlenskii-Schiff equation are constructed using the above conclusion and the symbolic computation system Mathematica.
A modified electromechanical model with one-dimensional abalation model for numerical analysis of the pulsed plasma thruster
2013, 62 (21): 210202. doi: 10.7498/aps.62.210202
The electromechanical model is used widely in simulating the operation process of pulsed plasma thrusters, because of its simplicity. Considering the limitation of the model that the late time ablation mass is assumed to be constant and the ablation process is ignored, we propose a modified mechanical model to serve a one-dimensional ablation model, and then the operation process of LES-6 PPT was simulated by this modified electromechanical model. Simulation results show excellent agreement with experimental data from the LES-6 PPT. This modified model can simulate the ablation process which cannot be completed by using the original electromechanical model. So, this modified model can better reflect the real operation mechanism than the electromechanical model. Besides, this modified model is as simple as the original model, it is of great significance for PPT design.
2013, 62 (21): 210501. doi: 10.7498/aps.62.210501
In this paper we combine stable noise with bistable stochastic resonance to investigate the parameter-induced stochastic resonance in the high-and low-frequency (both for multi-frequency) weak signal detection with different stable noise, and explore the action laws between the stability index (0 2) and skewness parameter (-1 1) of stable noise, and the resonance system parameters a, b on the resonant output effect. Results show that for different distribution of stable noise, the high- and low-frequency weak signal detection can be realized by tuning the system parameters a and b. The intervals of a and b which can induce stochastic resonances are multiple, and do not change with or . Moreover, while detecting the high- and low-frequency weak signal, the action laws of the resonant output effect which are affected by or are the same. These results will contribute to realize a reasonable selection of parameter-induced stochastic resonance system parameters under stable noise, and lay the foundation for a practical engineering application of multi-frequency weak signal detection based on the stochastic resonance.
Study on bifurcation and chaos in single-phase H-bridge inverter modulated by unipolar sinusoidal pulse width modulation
2013, 62 (21): 210502. doi: 10.7498/aps.62.210502
The unipolar SPWM has been widely used in H-bridge inverter because of its superiority for lower switching loss and less electromagnetic interference as compared with bipolar SPWM. However, the nonlinear phenomena in it have not been reported. In this paper, the bifurcation and chaos in the H-bridge inverter modulated by unipolar SPWM is studied. The one-dimensional discrete iterated mapping model under proportional control is established. Effects of the proportional coefficient k on the system performance are analyzed by using bifurcation diagram, folded diagram, and Lyapunov index spectrum. The time-domain waveforms with different proportional coefficients are obtained by Matlab/Simulink, which verify the correctness of theoretical analysis. Finally, the nonlinear behavior in the inverter caused by the variation of other circuit parameters like input voltage E, load resistance R, and inductance L is investigated through bifurcation diagrams. This paper turns the chaotic research of single-phase H-bridge inverter from bipolar SPWM to unipolar SPWM, So that the proposed approach is more practical. The results have important guiding significance and application value for designing and debugging the single-phase H-bridge inverter correctly.
2013, 62 (21): 210503. doi: 10.7498/aps.62.210503
When moving in viscous medium, the mass of a Brownian particle is fluctuant and its damping force depends on the past velocity history. Therefore, in order to investigate the characteristics of Brownian motion in viscous medium, fractional harmonic oscillator is proposed in this paper for the first time so for as we know. First, the Shapiro-Loginov formula is fractionized to solve fractional stochastic differential equation with exponential correlative stochastic coefficients. Then, by using stochastic averaging method and fractional Shapiro-Loginov formula, the analytical expression of a system’s steady response amplitude is presented and the system’s resonant behavior is discussed accordingly. Finally, the reliability of theoretical results is tested by simulation experiments. All the research shows that: (1) Stochastic resonant behavior can be induced by mass fluctuation noise. (2) Parameter-induced resonance can be induced by memory damping force. (3) Under different parameter conditions, the system’s resonant forms are diverse.
Synchronization, antisynchronization and amplitude death in coupled fractional order bistable oscillators
2013, 62 (21): 210504. doi: 10.7498/aps.62.210504
The dynamic behaviors of coupled fractional order bistable oscillators are investigated extensively and various phenomena such as synchronization, anti-synchronization, and amplitude death, etc. are explored. Based on the bistable characteristics of P-R oscillator with specific parameters, effects of initial conditions and coupling strength on the dynamic behaviors of the coupled fractional order bistable oscillators are first investigated by analyzing the maximum condition of Lyapunov exponent, the maximum Lyapunov exponent and the bifurcation diagram, etc. Further investigation reveals that the coupled fractional order bistable oscillators can be controlled to form chaotic synchronization, chaotic anti-synchronization, synchronous amplitude death, anti-synchronous amplitude death, partial amplitude death, and so on by changing the initial conditions and the coupling strength. Then, based on the principle of Monte Carlo method, by randomly choosing the initial conditions from the phase space, we calculate the percentage of various states when changing the coupling strength, so the dynamic characteristics of coupled fractional-order bistable oscillators can be represented by using the perspective of statistics. Some representative attractive basins are plotted, which are well coincident with numerical simulations.
2013, 62 (21): 210505. doi: 10.7498/aps.62.210505
Choosing the current of the front inductor of SEPIC converter as controlled object, the resonant parametric perturbation is applied to control the chaos in SEPIC converter. Through the small perturbations of circuit parameter, chaos control of SEPIC converter is realized, and the results are analyzed by the time domain waveform, power spectrum, and bifurcation diagram. Finally, the results of the circuit experiment demonstrate that chaos control of SEPIC converter can be realized by the resonant parametric perturbation method.
2013, 62 (21): 210506. doi: 10.7498/aps.62.210506
A dynamic threshold value control method is proposed to get control over a chaotic neural network (CNN). The sinusoidal signal, which constitutes the key component of the brain wave, is taken as the control signal to change the threshold value of the internal states of the CNN. The chaos control of the CNN is therefore reached with its outputs of the controlled CNN reciprocating between a stored pattern and its reverse pattern related with the initial pattern. And then the CNN can be applied in information processing, such as pattern recognitionetc. The chaos control method works in a self-adaption way since it does not need to set the threshold value beforehand, which is in accordance with brains’ thinking activities.
2013, 62 (21): 210507. doi: 10.7498/aps.62.210507
There are three kinds of conflicts in a traffic flow at the traffic circle because of track changing. We establish the driver model by regarding each vehicle as an intelligent agent which constitutes the multi-agent system by integrating the cellular automation model at the traffic circle. Besides, we put forward the problem how to eliminate the conflicts between the vehicle agents by priority strategy and dynamic negotiation mechanism. Take the traffic flow at the classic traffic circle of the suburban area of a small-medium city as the sample data to simulate and verify the accuracy of the model, and study the influences of some factors on the flow of motor vehicle, such as the proportion of different driver type and track changing probability, etc. The experimental result shows that the model constructed is consistent with the actual situation. Meanwhile, it is found that the driver characteristics have obvious influences on the flow, and the track changing probability follows, which does not have obvious influences on the fluctuation in the flow.
2013, 62 (21): 210601. doi: 10.7498/aps.62.210601
The concept of shock temperature in the interaction betweer femtosecond laser pulses and a solid target is defined. The relationship between the shock temperature and other physical parameters in the process of femtosecond laser ablation of aluminum and copper targets is discussed. Absolute values of shock temperature are calculated by means of a two-temperature model. Shock temperature is calculated distribution based on the non-Fourier heat conduction model. Result of this investigation plays an important role in the secure femtosecond laser processing of energetic materials.
2013, 62 (21): 210701. doi: 10.7498/aps.62.210701
The material of GaAs/AlGaAs bound-to-continuum terahertz quantum-cascade laser (THz QCL) was grown by gas source molecular beam epitaxy. A THz QCL device was fabricated with semi-insulating surface-plasmon waveguide. Its spectrum and light intensity-current-voltage characteristics were studied. The device emits about 2.95 THz, and yields a maximum temperature of 67 K in pulse mode. In continuous-wave mode, it displays a threshold current density of 230 A/cm2 at 9 K with maximum emitted power of 1.2 mW and lases up to 30 K.
2013, 62 (21): 210702. doi: 10.7498/aps.62.210702
Cone-beam computed tomography (CT) has the notable features, viz high efficiency and high precision, and is widely used in the areas such as medical imaging and industrial non-destructive testing, but the presence of image lag reduces the quality of CT images. By referencing the multi-exponential decay model for the image lag and combining with the actual decay rule of the flat panel detector output signal, a new decay modeling and correction method for the image lag based on multi-exponential fitting is proposed. Firstly, an imaging experiment using cone-beam CT based on flat panel detector is carried out; the results show that the image lag decay of the pixels in the flat panel detector has a good consistency, and is irrelevant to the initial gray value. Then, the rapid image lag correction is achieved according to the image lag decay model, and the comparison of image quality of the projected images and slice images before and after image lag correction indicates that the edge sharpness of the part has been significantly improved after the lag correction. This method does not need to obtain the scintillation compositions and the decay time constants of the detector, and is easily applied to the practical cone-beam CT imaging systems for image lag detection and correction.
ATOMIC AND MOLECULAR PHYSICS
2013, 62 (21): 213301. doi: 10.7498/aps.62.213301
An analytical formula has been proposed to predict the high-lying spectral lines of rovibrational transitions for diatomic systems by Sun et al. who used multiple spectral difference method. This study improves the formula based on their previous work by adding a higher order spectral term Hv. Applications of this new formula to the AuO molecule shows that the accuracy of the P-branch rovibrational transition lines is about one order of magnitude better than the results obtained using the previous formula, and that the contributions of the small quantity Hv to the high-lying rovibrational energies and the transitional lines are shown to be important.
2013, 62 (21): 213601. doi: 10.7498/aps.62.213601
Hydrogen storage capacity of Mg-decorated closo-hexaborate B6H62- has been studied using density functional theory. The binding strength of Mg atom is sufficiently large to ensure the stability of MgB6H62-. Each Mg atom can adsorb six H2 molecules. Moreover, the larger dipole moment combined with enhanced electrostatic field around the Mg atom originates from the charge transfer from B6H62- to Mg, accounting for the higher adsorption capacity of MgB6H62- than that of MgB6H6. Hydrogen storage capacity of MgB6H62- can be up to 11.1 wt% with an average binding energy between 0.23 eV and 0.34 eV. The electrostatic field around the Mg atom can be enhanced by controlling the charge state of the metal-organic complex, thereby significantly improving the hydrogen adsorption capacity.
COMPREHENSIVE SURVEY FOR THE FRONTIER DISCIPLINES
2013, 62 (21): 213401. doi: 10.7498/aps.62.213401
Quantum phase space theory is widely used to investigate physical, and chemical questions. It gives us a powerful tool to study the relations between the classical and quantum world. In quantum phase space theory, entangled molecular dynamics method is developed based on quantum Liouville equation. It is different from classical Hamilton dynamics, the trajectories are entangled i.e. not independent with each other. The quantum effect in the system can be described using the semiclassical theory, and give a vivid physical picture. The quantum tunneling, photodissociation, and self-correlation are investigated using the entangled trajectory. In this paper, we review the recent development in this field.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2013, 62 (21): 214101. doi: 10.7498/aps.62.214101
We have designed and fabricated a broadband low radar cross section (RCS) metamaterial absorber with polarization-independent characteristic based on electromagnetic resonance. The absorbing mechanism is investigated by means of electric as well as magnetic field distributions and retrieval algorithm. Absorbing and RCS properties of this absorber are performed by waveguide experiment and free space measurements, respectively. Theoretical analysis indicates that the absorber can produce electric and magnetic resonances in different locations for fixed frequency, while for different frequencies, it can provide energy losses in different dielectric layers, which effectively lowers the electromagnetic couplings and consequently keep the strong absorbing properties in a wide frequency range. Experimental results show that the designed absorber with 3-layer structure achieves a frequency range which is 4.25 times as that of 1-layer absorber with absorptivity above 90%, its relative bandwidth for RCS reduction above 10dB is 5.1%. The cell size and thickness of the designed absorber are very small, i.e., 0.17 and 0.015 of the working wavelength. Thus the low-RCS property of the absorber is wide-angle and polarization-independent. In addition, the working frequency range of the absorber can be adjusted by properly designing the layers.
2013, 62 (21): 214102. doi: 10.7498/aps.62.214102
The electromagnetic shielding effectiveness (SE) of a metal cavity covered by a material of medium conductivity is investigated theoretically by using an equivalent circuit method based on the transmission line and waveguide theory. The validity of the theoretical model is verified by comparison with the electromagnetic simulation software. The position effect and the resonance effect of the SE are calculated. A method for evaluating the SE of materials is suggested. With this method, the influence of the resonance effect and the position effect can be impaired greatly, also the SE of materials against plane wave can be evaluated directly.
Average capacity of free-space optical systems for a Laguerre-Gaussian beam propagating through non-Kolmogorov turbulence
2013, 62 (21): 214201. doi: 10.7498/aps.62.214201
The propagation of vortex beam in atmospheric turbulence is of great importance in theoretical study and practical applications. Based on the Rytov approximation and extended Huygens-Fresnel integral, the analytical expressions for the spiral spectrum of the Laguerre-Gaussian (LG) beam propagating in a slant non-Kolmogorov turbulence channel have been derived and the average capacity of free space optical system is given. The average capaticy of free space optical system is examined and the effects of exponent parameter, wavelength, zenith angle, inner scale, outer scale, and structure constant on average capacity are also analyzed. Results obtained in this paper may be benefical to optical communication.
2013, 62 (21): 214202. doi: 10.7498/aps.62.214202
To reduce the threshold is an important requirement for utilizing the random laser. RFL (random fiber laser) is a new random laser which user the photonic bandgap of PCF to lower the threshold by filling the random medium into a hollow-core PCF. Theoretical analysis shows that most of the emitted light is concentrated in the core of the fiber because of the controlling of the bandgap, which should enhance the interaction between the random medium and the localized light for the light oscillating back and for the thin core region, therefore the excitation efficiency of the random laser could be improved. However, the band gap of PCF filled with the random medium should be changed, so when choosing fiber to reduce the threshold for RFL, we should consider the matching between the new bandgap of the padded fiber and the gain frequency of the medium, and arrange the fiber and medium in pairs reasonably. If the PCF matches with the medium, the lasing may be enhancedly regulated and controlled and the threshold can be reduced greatly.
2013, 62 (21): 214203. doi: 10.7498/aps.62.214203
The coherence of light source have been employed in many aspects, such as optical processing and optical coherence holography. For this reason it has attracted vast interest in developing quantitative methods for measuring the spatial coherence characteristics of an optical field. We propose a novel method for measuring the spatial coherence degree of optical fields based on the triangular interferometer. Spatially separated twin beams are formed by an interferometer, and the interferogram formed by the twin beams is captured by an image detector. Because the separation of the twin beams is related to the coordinate position of the input beam, a series of positions are sampled by moving a pinhole and corresponding interference patterns are recorded. Then the visibilities of the interference patterns are calculated for measuring the spatial coherence degree. Experimentally measured and theoretically calculated values of spatial coherence degree fit well. The measurement error is 3.8%. Experimental results show the method proposed here is effective, simple, and robust without any special optical elements.
2013, 62 (21): 214204. doi: 10.7498/aps.62.214204
This article describes the variational multi-source image fusion using the structure tensor algorithm, which can keep the image features and details very well. We first narrative the fusion gradient field based on structure tensor, then measure the characteristic graphs of each source image, and thus construct a weight value for the source image gradient according to the characteristic graph. Gradients with high image features are highlighted in the fusion gradient field, and thus image features in the sources are well preserved. By using variational partial differential equation, the fusion image is reconstructed from the target gradient field. From the actual experimental results, the average gradient value and entropy of the fused image are found to be higher than those obtained by using the wavelet transform algorithm, tower decomposition algorithm, and direct gradient fusion algorithm, and the visual effect of the fusion image is good enough to retain the feature of source images and details in it. Therefore, it can give qualified image information for target detection and identification.
Study on the relationship between the population of metastable state and time delay in an erbium-doped optical fiber
2013, 62 (21): 214205. doi: 10.7498/aps.62.214205
The slow light propagation in optical fiber has attracted much attention because of its practical applications. Use of coherent population oscillation to produce slow light propagation has many advantages over other methods. We investigate the reduction of the group velocity propagation by the coherent population oscillation in erbium-doped optical fiber, and also the relationship between the population of metastable state and the time delay by changing the doping concentration, the length of the fiber, the input power, and the pump power. The results show that we can select a high doping concentration of erbium in the fiber, increase the length of the fiber, decrease the pump power and select the appropriate power of the signal light to increases the time delay.
Investigation of bidirectional dual-channel long-distance chaos secure communication based on 1550nm vertical-cavity surface-emitting lasers
2013, 62 (21): 214206. doi: 10.7498/aps.62.214206
Based on the chaos synchronization between two pairs of corresponding linear polarization modes in two 1550 nm vertical-cavity surface-emitting lasers (1550 nm-VCSELs) subject to optical injection of common chaotic signals, a novel bidirectional and dual-channel long-distance chaos secure communication system is proposed. The chaotic synchronization characteristics, bidirectional dual-channel communication performance, and the influences of the fiber channel on the message transmission are numerically investigated. Results show that, driven by a common chaotic signal generated from a driver VCSEL (D-VCSEL), two pairs of responding linear polarization modes in two response 1550nm-VCSELs (R-VCSELs) can be synchronized completely and isochronally. Meanwhile, the synchronization coefficients between the two pairs of responding linear polarization modes in D-VCSEL and R-VCSELs are low. Based on the high quality chaos synchronization between two pairs of responding linear modes in two R-VCSELs, bidirectional and dual-channel chaos secure communication can be achieved. After adopting a single mode polarization-maintaining fiber (or dispersion-shifted polarization-maintaining fiber), for 2.5 Gbit/s messages, the Q factor of the decryption signals after transmitting 60 km (or 200 km) can be more than 6.
2013, 62 (21): 214207. doi: 10.7498/aps.62.214207
The influence of electrolytes on the diffusion properties of polystyrene colloidal particles in dense suspensions is measured by means of phase-modulated fiber optic low-coherence dynamic light scattering. In our experiments, both NaCl and BaCl2 are used as electrolytes. Experiment results show that the diffusion coefficients of the polystyrene colloidal particles increase with the increasing of ion concentration and ion valence when the concentration of electrolyte is below 0.01mol/L and the temperature keeps constant. The diffusion coefficients obtained experimentally show good agreement with the diffusion coefficients obtained by using the Stern model.
2013, 62 (21): 214208. doi: 10.7498/aps.62.214208
CO is an indicative gas of coal spontaneous combustion warning and mine production safety instruction, whose detection process generally requires fiber long-haul transmission. However, currently, the communication fiber windows are mainly in the near-infrared band, so it is very significance to realize highly sensitive CO detection at near-infrared band. Tunable diode laser absorption spectroscopy (TDLAS) technology has advantages of high sensitivity, high resolution, fast response ability and no-contact, which has been widely used in air pollution monitoring, industrial and agricultural production process control, and many other fields. Long-path multi-pass cell can effectively improve the TDLAS detection capabilities, at the same time, the whole system is more compact. In this paper, 1566.64 nm DFB laser and the novel multi-pass cell with an optical path 56.7 m are used to detect different CO concentrations in long-term, while the system stability and linearity are analyzed. In addition, the detection limit is 0.25 ppmv with 30 s integration time by calculating the Allan variance. It means that we have primarily achieved highly sensitive detection of CO in the near-infrared bands.
In-fiber Mach-Zehnder interferometer based on fiber core etched air-bubble and core diameter mismatch for liquid refractive index sensing
2013, 62 (21): 214209. doi: 10.7498/aps.62.214209
A kind of optical fiber liquid refractive index sensor is proposed based on fiber core etched air-bubble and core diameter mismatched in-fiber Mach-Zehnder interferometer. A core etched standard single-mode fiber is spliced to another core etched standard single-mode fiber (SMF) to form an air bubble at the connecting point, and a 20 mm thinned fiber is cascaded (TCF) by fusion splicing method, which is 20 mm apart from the bubble, then a leading-mode fiber is spliced to the thinned fiber to form a structure of SMF-(air-bubble)-SMF-TCF-SMF in-fiber Mach-Zehnder interferometer liquid refractive index sensor. The air-bubble and the two fiber core diameter mismatched points serve as optical couplers for modes conversion. The transmission spectrum of sensor is studied by experiment. Results shows that the peak power changes with respect to surrounding refractive index with good linearity. The sensitivity of the sensor is 142.537 dB/RIU in the range of 1.3511.402 with linearity of 0.996, making it a good candidate for bio-chemical measurements.
Study on the partial gating smart network camera for controlling strong light intensity based on DSP and liquid crystal
2013, 62 (21): 214210. doi: 10.7498/aps.62.214210
Based on the electro-optical characteristics of the transmission-type liquid crystal (LC) and DSP (Digital Signal Processor, chip TMS320DM642) technology, a smart network camera system for partial gating strong light intensity is developed. An LC display driver is controlled by DSP to achieve light intensity transmittance of every single pixel in this system; the light intensity transmittance can be decreased by two orders of magnitude. In addition, the smart camera of video signal processed under a strong light can be transmitted through network transmission and real-time storage to PC by another DSP (chip TMS320DM6437). Thus the LC delay time is about 25.5 ms and the system circuit delay time is about 17 μs, while the storage hard disk capacity requires 8.648 Gbit in 24 h. Experimental images are taken by the prototype to shoot the simulated license plate illuminated by the strong light (greater than 2.2×105 lx). Results show that the imaging problems, viz the ordinary CCD camera may give partially overexposed images and cannot distinguish details under the strong light, are all solved and achieved a high dynamic range imaging by the prototype.
Investigation of the crystal and optical properties of ZnS thin films deposited at different temperature
2013, 62 (21): 214211. doi: 10.7498/aps.62.214211
The crystal and optical properties of ZnS optical coatings deposited at different substrate temperatures are studied in this paper. It is indicated that the substrate temperature has an evident effect on the properties of ZnS films. The XRD varies with the temperature. With the increase of the temperature, the XRD of ZnS film exhibits an obvious (111) orientation. At the same time, ZnS films have different stabilities at different substrate temperatures. At 115 ℃ and 155 ℃, the stability gets worse but at 190 ℃ and 230 ℃, it gets better. The variation of the substrate temperature has also effect on the optical properties of ZnS film, such as optical constants and deposition coefficient. At higher temperatures (190 ℃ and 230 ℃), the refractive index is higher than at lower temperatures (115 ℃ and 155 ℃). But the deposition coefficient gets smaller. Optical constants of ZnS films are calculated at different temperature.
2013, 62 (21): 214212. doi: 10.7498/aps.62.214212
High nonlinear and high birefringent photonic crystal fiber is one of the most effective medium for supercontinuum generation, therefore we select the V-type photonic crystal fiber as the research object. Through the numerical simulation results of multipole theory, we determined that the V-type optical fiber has high birefringent and high nonlinear characteristics. Through experiments, we found that the birefringence of the fiber and the central wavelength of the incident light have great influence on the generation of supercontinuum: when the central wavelength of incident light in the anomalous dispersion region of the fiber, its spectrum is quite wide relatively, and the supercontinuum of the long axis is flat tar than that of the short exis and has more abundant spectral components; at the same wavelength of light, the polarization direction of the former is closer to 45°, the supercontinuum spectrum range is larger. With the increase of the incident pulse power, supercontinuum will spread wider, but will reach a saturation when the power is large enough.
Tapered chirped fiber grating filter is analyzed from the detailed theoretical and experimental studies. The transmission spectrum of tapered chirped fiber grating filter is influenced by the parameters and loss of chirped fiber grating (length, refractive index modulation, chirp coefficient) and taper after examined by the transfer matrix method and resonance theory combined with coupled-mode theory. We study the influence of the chirped fiber grating wavelength reflectivity by tapering, and make the corresponding numerical simulation and experimental verification based on the above theories. Numerical simulation result is consistent with the experimental data.
2013, 62 (21): 214501. doi: 10.7498/aps.62.214501
A gradient representation of the first-order Lagrange system is studied. A condition under which the first-order Lagrange system can be considered as a gradient system is obtained. The stability of the system is discussed by using the property of the gradient system. Some examples are given to illustrate the application of the result.
2013, 62 (21): 214601. doi: 10.7498/aps.62.214601
The inertia effect induced by the motion of heat flow will have a significant impact on the heat transfer, when the heat pulse duration or the device structure has micro-scale characteristics. Based on the thermomass theory, the thermal wave equation is introduced to describe the motion of thermomass, and the generalized thermoelastic dynamic model involved in the thermal inertia is established by combining the constitutive relation of isotropic material. By taking into account the micro-scale characteristics for the transient heat transfer, the one-dimensional problem for the semi-infinite solid with the boundary subject to thermal impact is investigated by an analytic method, where the asymptotic solutions for thermoelastic response are obtained. With these solutions, the propagation of the thermal wave and thermal elastic wave and the distribution of the temperature, displacement and stresses are studied. By comparison with the same predictions of the L-S generalized thermoelasticity, the effect of thermal inertia on the thermal behaviors is revealed. The results show that the spatial thermal inertia induced by the motion of heat flux has an impact on the thermal behaviors, except for the temporal thermal inertia. All the velocities and wavefront locations of thermal wave and thermal elastic wave, and the time of each physical field begin to establish, the peak values of jumps and the intervals of two jumps are influenced by the spatial thermal inertia.
Simulation of two-dimensional droplet collisions based on SPH method of multi-phase flows with large density differences
2013, 62 (21): 214701. doi: 10.7498/aps.62.214701
In this paper, the corrective continuity equation proposed by Ott and the momentum equation improved by Adami combine to solve two-dimensional simulation problems of droplet collisions in air. To effectively improve the calculation accuracy, the artificial viscosity equation and the artificial stress equation are derived which are suited for multi-phase flows with large density differences. This method is validated to be effective via examples of an initially square droplet under surface tension and in evolution process of two droplets in air. Droplet collisions for different Weber numbers (8.8, 19.8) and different impact parameters (0, 0.5) are simulated, all of which are compared with the results of VOF simulation. Through further calculation, distribution map of the two-dimensional droplet collision outcomes in air is obtained, which is in agreement with the experimental results. It is demonstrated that this method can be effective for solving problems of droplet collisions which are involved in multi-phase flows with large density differences, and is easily extended to three-dimensional simulation; thus it lays a foundation for further simulation of the secondary atomization in liquid rocket engines.
2013, 62 (21): 214702. doi: 10.7498/aps.62.214702
In this paper, Layzers model which has a simple velocity potential, and Zufirias model are extended to the case of non-ideal fluids, and the effects of surface tension on Rayleigh-Taylor instability are investigated. Firstly, the analytical expressions for the asymptotic bubble velocity and curvature are obtained in the two models. Secondly, the effects of surface tension on Rayleigh-Taylor instability are studied systematically. Finally, the two models are compared with each other and the comparisons with numerical simulation are made as well. The results indicate that the surface tension depresses the bubble velocity, but does not affect the bubble curvature. The Layzers model with the simple velocity potential gives a smaller bubble velocity than that predicted by the Layzers model with a complex velocity potential. But the bubble velocity predicted by the Layzers model with the simple velocity potential is larger than that obtained by Zufirias model. Both Layzers models lead to the same bubble velocity when the Atwood number is A = 1.
2013, 62 (21): 214703. doi: 10.7498/aps.62.214703
Study on the interaction between bubble and free surface near an inclined vertical wall is carried out in this paper. Firstly, boundary element model for bubble dynamics based on incompressible potential flow is established, and the solid wall is modeled using the images of bubble and free surface. Then, through the numerical model, bubble dynamics near the walls with various inclination angles are studied respectively. We find that the inclination would lead discontinuity of the boundary condition of intersection between free surface and solid wall, which can affect its motion nonlinearly. Finally, the influence of the inclination angle on the bubble and spike dynamics is analyzed.
2013, 62 (21): 214704. doi: 10.7498/aps.62.214704
For the flow of an insoluble surfactant-laden thin film and droplet on inclined random topography, the lubrication theory is used to derive the evolution equations of thin liquid film thickness and interfacial surfactant concentration. Characteristics of thin film flow and droplet spreading, as well as the influence of topography structure are numerically simulated with PDECOL code. Results show that under the action of gravitational component and Marangoni effects, the thin film flow and droplet spreading is accelerated; the capillary ridge emerges at the thin film edge and the droplet center; and at the bottom of the thin film and droplet, the depression is generated. While the deformation of liquid film free surface is more significant due to the effect of random topography. The increasing θ has a role of enhancing gravitational component and Marangoni effects, leading to the enhancement of the capillary ridge and depression. The increase of D promotes the thin film flow and droplet spreading, but causes the deformation amplified; and the increased k0 can induce the evolutions of thin film flow and droplet spreading to slow down and inhibit the formation of capillary ridge and depression. In addition, compared with the thin film flow, the impact of D and k0 on the speed of droplet spreading is relatively weak.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Identification of plastics by laser-induced breakdown spectroscopy combined with support vector machine algorithm
2013, 62 (21): 215201. doi: 10.7498/aps.62.215201
Laser-induced breakdown spectroscopy (LIBS) combined with support vector machine (SVM) algorithm was used to identify 11 kinds of plastics. For each plastic, 100 spectra recorded by the spectrometer system were divided equally into training set and test set, and the former was used to train SVM model while the latter was used to validate SVM model created by the training set. Result shows that 543 of 550 test set spectra are identified correctly with the average correct identification rate 98.73%. However, there are six spectra of PU misidentified as PMMA. This is because the difference of nitrogen content in 11 plastics cannot be reflected by the intensities of N I 746.87 nm and C-N (0,0) 388.3 nm due to the influence of ambient air. Methods and reference data are provided for further study of plastics identification by laser-induced breakdown spectroscopy technique.
A full three-dimensional numerical diagnosis of Japan Atomic Energy Agency 10 Ampere multi-cusp negative hydrogen ion source
2013, 62 (21): 215202. doi: 10.7498/aps.62.215202
This paper develops a full three-dimensional PIC/MCC algorithm, and uses it to conduct a full range of numerical diagnosis of the hot JAEA 10A ion source at home and abroad, explores lateral drift and energy distribution of electrons in the electron energy deposition process, analyzes the influence of the main physical parameters on the electronic deposition. Simulation and analysis results show that electronic horizontal shift (-Y direction) comes from the filtering zone of the magnetic drift. Increasing the filtering field, the magnetic drift increases, and lateral drift is aggravated, and the utilization of electronics increases; improving the discharge of chamber pressure, the electronic collision will be more frequent; thereby increasing lateral non-uniformity can improve the utilization of electronics.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2013, 62 (21): 216101. doi: 10.7498/aps.62.216101
Different concentrations of Er3+ doped in KPb2Br5 powders are prepared by solid-state reaction method. The upconversion spectra under the excitation of 980 nm laser are characterized and show the concentration-related change in emission band. With the doping concentration of 2.5 mol%, the sample exhibits mainly two green emission peaks at 530 nm and 550 nm, which correspond to the transitions of 2H11/2 and 4S3/2 levels to ground state 4I15/2 respectively. When the doping concentration of Er3+ is increased to 5 mol%, the upconversion emission is dominated by 490 nm, related to the transition of 4F7/2 to 4I15/2. Increasing the doping concentration up to 7.5 mol%, the emission quenching is observed throughout and the emission band appears mainly at 690 nm which comes from the transition of 4F9/2 to 4I15/2. The influence of possible substitution of Er3+ on lattice constant and upconversion emission properties of KPb2Br5 are discussed based on the first-principles calculation and Judd-Ofelt theory. The results show that the substitution of Er3+ in KPb2Br5 is dominated for Pb(1) in low concentration. When increasing the Er3+ doping concentration, it may substitute for Pb(2) Pb(1) and Pb(2) sites. The impact of the symmetry of the crystal field on the site-selective doping of Er3+ is proposed to explain the variation of upconversion luminescence spectrum.
Influence of the growth conditions on the transparent conductive properties of ZnO：Al thin films grown by pulsed laser deposition
2013, 62 (21): 216102. doi: 10.7498/aps.62.216102
The influences of aluminum doping, oxygen pressure, and substrate temperature on the transparent conductive properties of ZnO:Al (AZO) films grown by pulsed laser deposition (PLD) were investigated using scanning electron microscope, atomic force microscope, X-ray diffraction, Hall effect measurements, and optical transmission spectrum. When the aluminum doping concentration is over 0.5 wt%, all the PLD grown AZO films are degenerated and the aluminum donors are thermal ionized even at a low temperature of 80 K. As a result, the bandgap of AZO film shows blue shifts due to the Bernstein-Moss effect as further confirmed by optical transmission spectrum. The influences of the oxygen pressure and substrate temperature on the transparent conductive property of AZO films were further studied. When the oxygen pressure is 1 Pa and the substrate temperature is 200 ℃, the best conductivity property of AZO thin film is obtained with Hall mobility of 28.8 cm2/V·s and film resistivity of 2.7×10-4 Ω·cm. Moreover, the light transmittance in the visible range exceeds 85%. However, as the oxygen pressure and temperature continue to increase, the film resistivity will increase.
2013, 62 (21): 216701. doi: 10.7498/aps.62.216701
The effective Lagrangian density function and the quantum fluctuation of the wave function in the form of quantized operators are presented for a quasi two-dimensional Bose-Einstein condensate by means of Madelung transformation. This paper calculates the two-point density-density correlation function of the condensate during its free expansion after its confinement potential is removed. Results show that the two-point density-density correlation function in the long-wave limit is proportional to the wave number k and it tends to be a constant in the short-wave limit.
2013, 62 (21): 216801. doi: 10.7498/aps.62.216801
At a low velocity, the lamellarrod eutectic transition can be controlled by the volume fraction of one eutectic phase only. The factors which affect this kind of transition at high growth velocities are not clear. Based on the competitive growth rule, the criterion for lamellarrod transition is obtained by combining the models of lamellar and rod eutectic growth under rapid solidification conditions. It is shown that for a certain volume fraction, if its value fluctuates around the critical point predicted by the JH Jackson and Hunt model, the increase of the growth velocity or the partition coefficient will lead to the rodlamellar transition. Otherwise, no transition will take place. The lamellarrod eutectic transition at high growth velocity is controlled by the volume fraction variation, which is caused by the increase of the growth velocity.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2013, 62 (21): 217101. doi: 10.7498/aps.62.217101
Silicon boron nitride (SiBN) has been paid attention extensively due to its high melting point and anti-oxidation, which is also the reason that one of the research focus is its physical property of this material at high temperatures. It has been reported that amorphous SiBN ceramics could be modeled based on the the atomic structure of -Si3N4. In this paper, the molecular dynamics and DFT calculation were employed to explore the structural model of SiBN, to reveal the electronic and optical properties of SiBN at high temperatures. It is worth noting that, different from -Si3N4, the absorption of SiBN at visible light and higher frequency decreases at higher temperatures, and the reflectance decreases to 1% or so. Such results could not be found in single crystalline Si3N4. These indicate the possibility of SiBN used as the stealth coating. It also could be a good candidate in the optoelectronic application of amorphous materials in the near future.
Growth of vanadium dioxide thin films on Pt metal film and the electrically-driven metal–insulator transition characteristics of them
2013, 62 (21): 217201. doi: 10.7498/aps.62.217201
High-quality VO2 thin films are deposited on the metal platinum (Pt) electrode buffered by silicon dioxide (SiO2) using radio frequency magnetron sputtering. The effect of the thickness of SiO2 on the the crystal structure, morphology and metal-insulator transition (MIT) performance of the films are discussed. Results show that SiO2 buffer layer with a thickness of 0.2 μm can effectively eliminate huge stress between the VO2 film and the metal film; and the VO2 thin film with the distinct MIT are deposited. When the buffer layer reaches more than 0.7 μm, the VO2 film has a distinct (011) preferred orientation, the smooth surface and compact nanostructure, and the resistance change reaches more than three orders of magnitude. At the same time, Pt-SiO2/VO2-Au sandwiched structure is achieved to test the current versus voltage curves, in which can be seen several distinct steps of current caused by the voltage perpendicular to the plane of a VO2 film. The result confirms the electrically-driven metal-insulator transition. Due to the high-quality VO2 and the flexible device structure, the VO2/Pt-SiO2 can be widely used for large-scale integrated electronic control devices.
2013, 62 (21): 217301. doi: 10.7498/aps.62.217301
In this paper we study theoretically the degradation phenomenon of GaN-based resonant tunneling diode (RTD). The effects of trapping centers on GaN-based RTD are calculated and studied by self-consistently solving the Poisson-Schrödinger aligns when three experimentally obtained deep-level trapping centers are introduced into the AlGaN/GaN/AlGaN quantum well. Results show that the degradations of negative differential resistance (NDR) characteristic in GaN-based RTDs are actually caused by the combined action of the activation energy and the defect density. The deep-level trapping center with high activation energy plays a dominating role in the degradation of NDR characteristics because the probability of ionization is exponentially proportional to the activation energy.
Study on the electronic structures of Iridium-doped SmOFeAs under the strongly correlated electrons effects
2013, 62 (21): 217401. doi: 10.7498/aps.62.217401
Based on the consideration of strong correlation of electrons, we have used density functional theory generalized gradient approximation method SGGA+U to calculate SmFeAsO and Ir doping effects on the lattices and electronic properties. It is found that iridium doping at the Fe site enhances the interaction between FeAs and SmO layers and results in a modification of the FeAs4 tetrahedron. The electronic density of states (DOS) of SmOFe1-xIrxAs is studied by comparing the calculations with the X-ray photoemission spectroscopy experiments (XPS). It is revealed that the Fe 3d and As 4p hybridization orbits dominate the electric properties for SmOFe1-xIrxAs. Ir doping makes the five orbitals of Fe3d all filled. Superconductivity is sensitive to the peak position shifting away from Fermi level. Our VASP SGGA+U calculation provides a better agreement with the experimental results when we use an on-site coulomb energy of U on Fe 3d shell, which is sharply contrasted to the GGA process.
Analysis of the finite-temperature phase transition of Heisenberg antiferromagnetic compound LiVGe2O6
2013, 62 (21): 217501. doi: 10.7498/aps.62.217501
The susceptibility and nuclear magnetic resonance measurements on quasi-one-dimensional spin-1 Heisenberg antiferromagnet LiVGe2O6 indicate that this material shows a phase transition from paramagnetic state to antiferromagnetic Nel state at about 22 K, and there exists a gap in the low-temperature magnetic excitation spectrum. Based on the model Hamiltonian of LiVGe2O6, we propose a low-energy field theoryGinzburg-Landau theory for this compound. From this theory, we study the finite-temperature phase transition induced by spontaneous symmetry breaking and then calculate the finite-temperature susceptibility of LiVGe2O6. All the theoretical calculations are consistent with the experimental results.
2013, 62 (21): 217502. doi: 10.7498/aps.62.217502
Through improvement of Hall probe cryogenic calibration system, a cryogenic remanence measurement system(CRMS) for chunk permanent magnet was built. With a rectangular NdFeB(N50M) permanent magnet (its size is 40 mm×40 mm×10 mm) as example, cryogenic remanence measurement technology for chunk permanent magnet was studied. Results show that main factors affecting cryogenic remanence measurement reliability are Hall probe cryogenic calibration, Hall probe location, temperature drift, and thermal expansion of the material and so on. If the same methods are used for measurement, then the cryogenic remanence measurement repeatability of a permanent magnet is less than 0.1%. The experimental study creates conditions for measurements and research of cryogenic remanence of chunk permanent magnet of high-precision permanent magnet devices, such as cryogenic undulators.
2013, 62 (21): 217503. doi: 10.7498/aps.62.217503
The FeCoAlON thin films were prepared by magnetron sputtering. Effect of element addition of Al, O, and N on magnetic materials was studied. Experiment demonstrated that with increasing Al, O and N, the film structure changed from polycrystalline to amorphous, and the films showed soft magnetism. When N content in the film is high, the films show stripe domain structure. The condition and mechanism for the occurrence of stripe domain structure were discussed in detail, and we found that the frequency response of permeability of the films show characteristics of multi-peak resonance.
2013, 62 (21): 217504. doi: 10.7498/aps.62.217504
Fe- and Mn-doped AlN thin films were prepared on Si substrates by direct current (DC) magnetron co-sputtering method in the atmospher of Ar and N2 mixture. The influences of sputtering currents and the target to substrate distance on the structure of the films were investigated by X-ray diffraction and Raman spectroscopy, respectively. Surface morphology and composition were studied by scanning electron microscope (SEM) with an energy dispersive X-ray spectroscopy (EDS) attachment. The magnetism of Mn- and Fe-doped AlN films was measured by vibrating sample magnetometer (VSM) at room temperature (RT). Processing of the Mn-doped AlN films produces Mn clusters in the samples. Due to the presence of the antiferromagnetism Mn clusters, ferromagnetism is either suppressed or disappears. The Fe-doped AlN films show ferromagnetism at RT, which should arise from the AlFeN ternary alloy. With the increase of the Fe target sputtering current, the Fe concentration is increased from 6.81 at.% to 16.17at.%; the saturation magnetization Ms is reduced from 0.27 emu·cm-3 to 0.20 emu·cm-3, and the coercive force Hc is increased from 57 Oe to 115 Oe, this is because the separation of Fe ions get shorter and the antiferromagnetic coupling is enhanced.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Phase field crystal study on grain boundary evolution and its micro-mechanism under various symmetry
2013, 62 (21): 218101. doi: 10.7498/aps.62.218101
Phase field crystal method is used to investigate the deformation process and mechanism of twined structure of a trigonal phase under uniaxial tensile deformation, and the evolution and corresponding micro-mechanism of low-angle symmetric and asymmetric grain boundaries (GB) as well as high-angle symmetric and asymmetric GB during deformation process are analyzed in detail. The deformation is performed under the condition that the direction of applied stress is parallel to that of initial GB. Results show that low-angle symmetric GB is composed of two kinds of edge dislocations with the angle made by Burgers vectors being around 60 During deformation, two kinds of dislocations in low-angle symmetric GB move along two opposite directions, then meet with the same kind of dislocation emitted from another GB leading to the annihilation of partial dislocations. As to the low-angle asymmetric GB, its only one kind of dislocation first climbs and moves along the horizontal direction of the applied stress, then each dislocation will break down into two dislocations with their Burgers vectors making an angle about 120, finally a perfect single crystal is formed via the movement and annihilation of dislocations. High-angle GBs first keep horizontal shape under the applied stress, then become serrated, and the dislocations are emitted from the cusps in GBs. Finally, the high-angle asymmetric GB will decompose with the movement and annihilation of dislocation, while the shape of high-angle symmetric GB becomes horizontal again. It can be seen that the high-angle symmetric GB is more stable than the high-angle asymmetric GB; this is in agreement with the results of experiments and molecular dynamics.
2013, 62 (21): 218102. doi: 10.7498/aps.62.218102
Synthesizing parameters in the hydrothermal method can affect directly the morphology and the contact angles of ZnO nanowires films, and thus the controllable wettability. In this paper effects of characteristic parameters on the properties of random rough surfaces are simulated, including arithmetical mean deviation of the profile, skewness, kurtosis and correlation length. Batches of ZnO nanowires films with varied morphology were synthesized in different concentrations of seed layer solution and growth solution, as well as growth time spans. Sampling length was determined and characteristic parameters of the profiles of ZnO nanowires films were extracted based on SEM micrographs and specific operators of Matlab software. With vertical and lateral parameters of the morphology introduced into Wenzel model, relationships between synthesizing parameters, morphology, and contact angles of ZnO nanowires films were established. It is conculded that the sampling length was determined to be 5 μm, crystallization between ZnO nanowires occurred as the concentration of growth solution was larger than 0.125 mol/L, resulting in hydrophobic ZnO nanowires films; different concentrations of seed layer solution and growth time spans led to hydrophilic ZnO nanowire films. These results can be used to immobilize various enzymes on ZnO nanowires films and further to improve the property of ZnO nanowires-based bio-sensors.
2013, 62 (21): 218103. doi: 10.7498/aps.62.218103
Eutectic solidification is very important in the development of new materials in which the periodic multiphase structures may have a remarkable or enhanced functionality. The morphology evolution during eutectic solidification is investigated experimentally using slab-geometry slides of succinonitrile-(D)camphor (SCN-DC) transparent organic eutectic material. By specifically focusing on the effect of pulling velocity on microstructure in directional growth, the temperature gradient and the thickness are kept the same in all the experiments. It is found that eutectic seeds first occur in the grain boundary channel or the specimen side-wall groove. And the growth of eutectic seeds is both parallel to the direction of temperature gradient and along the liquid/solid interface at the same time. At a low pulling velocity (0.064–0.44 μm/s), the macroscopic growth morphology is flat, and the inner microstructure is rod-shaped, which is parallel to the growth direction. It is obvious that the eutectic spacing becomes smaller with the increase of pulling velocity. At a high pulling velocity (0.67–1.56 μm/s), the macroscopic growth morphology becomes cellular. However, the inner microstructure is still rod-shaped, but its distribution is radially outward. And the eutectic spacing decreases as pulling velocity increases.
2013, 62 (21): 218401. doi: 10.7498/aps.62.218401
Memristor realized physically is recently a basic two-terminal circuit element with memory property. Based on Taylor series form of φ-q relationship, a charge-controlled memristor equivalent circuit analysis model is built. A charge-controlled memristor model with cubic nonlinearity is taken, as an example, to make a theoretical analysis of circuit characteristics, such as voltage-current relationship, active-passive property, and so on, of the charge-controlled memristor with different parameters. Results indicate that the voltage-current relationship of the charge-controlled memristor has an italic “8” shaped hysteresis loop characteristic, and the charge-controlled memristor shows passivity and activity accompanied with the variations of parameter symbols, resulting in the occurrence of the corresponding variations of circuit characteristics; compared with the passive memristor, the active memristor is more suitable for use as a second harmonic signal generation circuit. An experiment circuit is built based on the equivalent circuit of the charge-controlled memristor characteristic analysis, and the experimental results well verify the theoretical analysis.
Study on control pulse combination of pulse train controlled switching converter and its multi-periodicity analysis
2013, 62 (21): 218402. doi: 10.7498/aps.62.218402
Pulse train control technique is realized through the output voltage regulation of switching dc-dc converter by adjusting the control pulse combination of high-power and low-power control pulses in a control pulse repetition cycle. Once the circuit parameters are determined, the control pulse combination is fixed. The control pulse combination directly affects the steady-state performances of pulse train (PT) controller. In this paper, the control pulse combination of PT control technique is studied by using the continued fraction technique. A one-dimensional normal form of discrete-time map of PT controlled buck converter operating in discontinuous conduction mode is also established in which the steady state performances, such as parameter evaluation of multi-periodicities and output voltage ripple of PT controlled DCM buck converter, are analyzed. The simulation result, experimental result, and the results in the literature are in accordance with the theoretical analysis. This investigation is helpful to obtain a deeper understanding of PT control technique.
Dynamical modeling and multi-period behavior analysis of voltage-mode bi-frequency controlled switching converter
2013, 62 (21): 218403. doi: 10.7498/aps.62.218403
A dynamical model is proposed and the corresponding characteristic aligns are derived for voltage-mode bi-frequency controlled switching converter operating in discontinuous conduction mode. According to the dynamical model, the border-collision bifurcation and multi-period behaviors, such as period-2, period-3, period-4, and so on, are studied using bifurcation diagrams as the circuit parameters are varied. It is found that the converter behaves along the bifurcation route of period-1, multi-period, and period-1, and the change of period state is induced by border-collision bifurcation. Based on the characteristic equation, the converter stability is investigated by the Lyapunov exponent. It is shown that Lyapunov exponent is always smaller than zero with the variation of circuit parameters and the converter operates in stable period state all the time. Also, it is validated that period-3 behavior of voltage-mode bi-frequency controlled switching converter does not predicate its inevitable chaos. Time-domain waveforms, phase portraits, and frequency spectra of voltage-mode bi-frequency controlled switching converter are analyzed by circuit simulation, which validates the feasibility of dynamical model and the correctness of theoretical analysis. Simulation results are verified by experiments in this paper.
2013, 62 (21): 218404. doi: 10.7498/aps.62.218404
Along with the variation of the feedback amplify coefficient, V2 controlled Buck converter exhibits abundant nonlinear dynamical behaviors. By establishing the discrete-time model of the system, this paper has studied the instability phenomena based on the monodromy matrix method. With increasing feedback factor, the analysis indicated that the converter entered from a stable period-one statue into a period-doubling statue. Finally, it showed chaos. Mechanism of the bifurcation generated by the system was fully analyzed based on the monodromy matrix, which showed that as the increase of the feedback coefficient, an eigenvalue of the monodromy matrix went out of the unit circle; this was the reason why the system generated period-doubling bifurcation. Also presented was the sinusoidal voltage compensation method to extend the stability margin based on the monodromy matrix theory, by which the instability behavior was effectively handled. Simulation and experimental results confirmed the analytical method.
2013, 62 (21): 218405. doi: 10.7498/aps.62.218405
The range migration of missile borne synthetic apertare radar (SAR) is very difficult to correct using all the conventional imaging algorithms but the back projection algorithm; however, the large computation burden and the low efficiency are the key problems existing in its practical application. To solve the problems, an extended back projection imaging algorithm for the dechirped missile borne SAR is proposed. Firstly, a new signal model is built for the dechirped missile borne SAR, and the range compression is implemented in the range frequency domain. Secondly, the imaging region is divided into several stripes in range direction, and the raw echo data is back projected to each stripe for coherent integration by using the sub-aperture merging and image splitting technique. Finally, the entire SAR image can be obtained by combining the subimages of all the stripes. The validity of the proposed algorithm is demonstrated by the simulated and real SAR datasets. Testing results indicate that the extended algorithm is appropriate for achieving accurate dechirped missile borne SAR image. Moreover, it can be easily parallelized because the stripe imaging is independent of each other, so that can greatly decrease the computation burden, and improve the computation speed. The method introduced in this paper has important theoretical significance in realistic remote sensing, detection and recognition of military targets and precision guide.
2013, 62 (21): 218501. doi: 10.7498/aps.62.218501
A theoretical model for the noise is derived in this paper to characterize the influence of the noise on quantum dot infrared photodetectors. In this model, the noise current is estimated with the consideration of the common influence of the nanoscale electron transport and microscale electron transport on the activation energy and the contribution of the noise gain. The obtained results show a good agreement with the published experimental values, which illustrates the validity of the model.
2013, 62 (21): 218502. doi: 10.7498/aps.62.218502
A new strained Si MOSFET structure with hetero-polycrystalline SiGe gate was studied, which combines the advantages of “gate engineering” and “strain engineering”. The new structure improved the carrier transport efficiency, suppressed the short-channel effects (SCE), and enhanced the performance on the basis of strain. Then a physically modeling strategy such as quasi-2D surface potential of strong inversion, threshold voltage, and channel current was presented for the strained Si NMOSFET. Finally, the above model was computed and the results were analyzed.
2013, 62 (21): 218503. doi: 10.7498/aps.62.218503
The degradation of a device can be described by the degradation model in the accelerated tests. Because the degradation is closely related to the degradation mechanism, which reflects the intrinsic physical or chemical reactions, the degradation model can be established based on the temperature effect on the reaction rate and the change of reaction volume concentration in the physical/chemical reactions. Different degradation processes can be studied using the degradation model, including both the monotonic and nonmonotonic degradation processes. Moreover, the accelerated test is carried out for the GaN LED, figuring out the parameters for the degradation model, the ratio of different degradation processes, and the time constant.
2013, 62 (21): 218701. doi: 10.7498/aps.62.218701
Transport of anisotropic biomolecules and/or charged Brownian particles in periodic porous media is of great importance in the fields of biomedicine, water treatment, and environmental engineering etc. In this paper, we present the modeling of transport of biomolecules in periodic polar arrays based on a numerical analysis of effective mobility. Anisotropic biomolecules are transformed to point-sized Brownian particles through introduction of configurational entropy, and the effective charge and effective transport parameters are calculated using macrotransport theory. As an example, the mobility of short dsDNA fragments in a nano-polar array is calculated. It is demonstrated that when the sizes of the gaps between the nano-poles are similar to or smaller than the size of biomolecules, the configurational entropy has a significant effect on the effective velocity. Difference in configurational entropy in the confined space dominates the partitioning of the molecules. In addition, as the effect of entropic barrier decreases with the strength of external electric field, relatively low voltage is preferred in order to achieve better selectivity.
Micromagnetic analysis of the maghemite platelet chains in the iron-mineral-based magnetoreceptor of birds
2013, 62 (21): 218702. doi: 10.7498/aps.62.218702
Experiments demonstrate that large varieties of animals have the ability to sense the magnetic field. Especially, some birds can use the geomagnetic field for navigation. According to the avian magnetoreception mechanisms, birds can build magnetic map for orientation and navigation by sensing the intensity and incline of geomagnetic field. However, researches on the magnetoreceptor of birds are still at the stage of discovery and identification, and it is necessary to study the iron-mineral-based structures to know whether they have the physical and magnetic properties to act as magnetoreceptor in living system. In this paper, the maghemite platelet chains in the iron-mineral-based magnetoreceptor have been studied with three-dimensional simulation based on the theories of micromagnetics. The reaction of the maghemite platelet chains with geomagnetic field has been investigated. Result indicates that the maghemite platelet chains with vortex domain can response to the change of the orientation of geomagnetic field.
2013, 62 (21): 218703. doi: 10.7498/aps.62.218703
This paper considers the design problem of observer-based H output feedback control over the nonlinear Takagi-Sugeno (T-S) fuzzy systems with distributed delays．Firstly, delay-dependent sufficient conditions satisfy the H performance, are given for the stability analysis in terms of non-strict linear matrix inequality; then, the equivalent linear matrix inequality stability conditions can be obtained. Based on this, the solvable of the observer-based H output feedback control problem is proposed. Finally, a numerical example is given to illustrate the effectiveness of the design approach here.
The complexity of human brain activity has shown a certain law associated with the difference of age and sex, which can be identified by fMRI (functional magnetic resonance imaging). In this paper, we apply the base scale entropy to 54 groups’ fMRI data of different ages and gender, and then distinguish the different groups through the entropy. Through the base scale entropy with reasonable parameters, fMRI of different people could be distinguished effectively, which provides convenience to further data analysis. Results show that the base scale entropy between men and women of the same age has some differences and the entropy changes correspondingly with the change of age. In order to distinguish different people of different ages, we need to adjust the scale parameter to adapt to the trends in age changes. The fMRI data analysis shows that the base scale entropy could distinguish different populations’ fMRI data characteristics for further facilitating the analysis of complex signals.
2013, 62 (21): 218801. doi: 10.7498/aps.62.218801
The GaInAs/GaNAs super-lattice with a feature of space separation of In and N constituents as an active region, is one of the most important ways to achieve 1 eV GaInNAs-based solar cells. To experimentally realize the high-quality super-lattice structure with the required band-gap, Kronig-Penney model is used to obtain the barrier thickness dependence on the well thickness and its composition. Meanwhile, the strain state of GaInAs/GaNAs SLs with various well choices is also discussed. Results show that when both the GaNAs and GaInAs act as the well layers the super-lattice can achieve 1 eV band-gap, and when the GaN0.04As0.96 is considered to act as the well layer, the entire GaInAs/GaNAs SLs have smaller strain accumulations as compared with the case of Ga0.7In0.3As as the well layer in the super-lattice structure.
2013, 62 (21): 218901. doi: 10.7498/aps.62.218901
The widespread of epidemics bring tremendous losses to the mankind, thus it is very important to prevent the spread of epidemics. In this paper, the differences between individual tendency of vaccination is taken into account to propose a voluntary vaccination model based on the node degree information. Further, the theoretical analysis result shows that if propagation rate exceed a threshold value, the effectiveness of epidemic spreading (the number of infectious nodes) of the model above and the classical model ignoring the difference between the individual vaccination willingness [Zhang et al 2010 New J. Phys. 12 023015] will be the same. Both the permanent vaccination and the temporary vaccination are considered to analyze the process of epidemic spreading for the Barabási-Albert network by using the SIS model. The numerical simulation results are consistent with the empirical ones very well. Experiments prove that when the infection cost and vaccine cost is the same, the model can prevent the spread of the epidemic more effective as compared with the classical one, and the proportion of the infections decreases over 65% than the classical one. In addition, the longer the live of vaccine, the more effective the prevention of the spread of the epidemic using this model (compared with the classical model ignoring the difference between the individual vaccination willingness).
2013, 62 (21): 218902. doi: 10.7498/aps.62.218902
Structural analysis of complex networks has gained more and more concerns, but not enough attention has been paid to the coloring problem in complex networks. In order to understand the relationship between network structure and coloring problem, we investigate the effects of WS, BA networks and different macro-scale parameters on the K-proper coloring. We find that the maximum clique number can generally reflect the trend of K value change, the average degree and the degree correlation have a greater impact on the K value than the heterogeneity and the clustering coefficient. These results are verified on some real-world networks. After coloring the complex networks properly, the independent sets of networks can be obtained. According to the characteristic that any two vertices are not connected in an independent set, we propose a random immunization strategy based on the independent set. Compared with the random immunization, the proposed strategy can make the network more vulnerable, and thus effectively mitigate epidemic spreading. This immunization strategy is simple and practical, which helps to design more efficient immunization strategy.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2013, 62 (21): 219201. doi: 10.7498/aps.62.219201
Lightning information indicates the intensity and the development of severe convection. The characteristics of lightning activity and charge structure of a squall line over Beijing on 13 June 2010 are analyzed by using the SAFIR3000 lightning detection data, Doppler weather radar and precipitation data. Results show that the lightning radiation sources are the major part in the convective leading region with a high reflectivity in front of the squall line, and the number of lightning radiation sources gradually increases in the back of stratiform region only at the dissipating stage. The correlation coefficient between the total lightning and convective precipitation is found to be 0.82, and that of intra-cloud lightning and convective precipitation is 0.76. It is inferred that the lightning is closely related to dynamical and microphysical processes of the squall line. According to the lightning radiation distribution, the charge structure of squall line is also discussed. At the mature stage of the squall line, the lightning radiation sources have two layers with the upper level centered at 11 km and the lower level at 6 km. Based on the bidirectional leader of lightning propagation and by assuming VHF source density maxima being most likely associated with the positive charge region, it is concluded that the squall line is characterized by a tripole charge structure with a middle charge region between the levels of 8 km and 10 km, and the two positive charge regions at the levels of 10 to 12 km and 4 to 7 km above the ground, respectively.
Interannual and interdecadal atmospheric circulation anomalies of autumn dry/wet over the loess plateau and its multi-scalar correlation to SST
2013, 62 (21): 219202. doi: 10.7498/aps.62.219202
The ecological environment is vulnerable and extremely sensitive to climate change in the loess plateau. The interannual and interdecadal variations of dry/wet index are particularly obvious in this region. Up to now, the analisis of the dry/wet variation in the loess plateau has been basically understood during summer, but the autumn dry/wet evolution of the loess plateau and the atmospheric circulation characteristic are still laking in its knowledge. Based on the monthly mean rainfall and temperature of 589 China weather stations, the NCEP/NCAR reanalysis dataset and NOAA extended reconstructed sea surface temperature (SST) data from 1961 to 2010, using the EOF/REOF, bandpass filtering, wavelet technique and regression methods, the autumn dry/wet evolution of the loess plateau and the atmospheric circulation characteristic associated with them, and the multi-scale relationship between dry/wet index and SST were analyzed on the basis of classification of dry/wet over China region in autumn. The continuous wavelet transform shows that the autumn wet/dry index exists has ～4 a and 8 a period over the loess plateau, and the ～8 year oscillation from 1970–1990 is rather obvious. On the interannual scales, the atmospheric circulation anomalies of 500 hPa associated with the wet years exhibit a ’double-blocking’ in the mid-high latitude, and the westerly jet stream turns to be weakened and the jet axis moves to the north significantly. Japan-Okhotsk Sea is featured with anticyclone, and the east wind at the bottom of the anticyclone provides favorable moisture for the middle Loess plateau. On the interdecadal scales, the atmospheric circulation anomalies associated with the wet years show the negative geopotential height anomaly over East Asian, and the East Asian subtropical westerly jet stream of 200 hPa is weakened and moves north too. The vapour of the middle Loess plateau comes from two paths, one is the westerly water vapor transport in the middle latitude, and the other is the southerly water vapor transport from the Bay of Bengal and turns to the north at the Indo-China Peninsula. When the Nino3 index (Nino3I) is in advance of dry/wet index for 5 months, there is a significantly negative correlation between them. When the Bay of Benga and South China Sea SST index (BayI) goes shead of dry/wet index for 3 months, there is a significantly negative correlation between them. On the interannual scales, the cross wavelet transform indicates that both the Nino3I and BayI have significant connections with the dry/wet index (～4 a and 4–6 a cycles). On the interdecadal scales, only BayI has significant connections with dry/wet index (～10 a cycles). By establishing the interannual and interdecadal variations of dry/wet cycle of the loess plateau, recognizing the atmospheric circulation anomalies, and building the relationship between the dry/wet index and SST, this paper reveals the physical mechanism of the dry/wet variation and finds the early waring signals for drought climate change in the region.