Vol. 63, No. 22 (2014)
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER,CLASSICAL MECHANICS, AND FLUID DYNAMICS
2014, 63 (22): 224203. doi: 10.7498/aps.63.224203
We study the steady optical responses of a four-level Tripod cold 87Rb atomic system, which is driven by two mutually perpendicular strong standing-wave laser fields. It is found that satisfying the condition of a proper detuning between two strong fields, one nearly perfect structure of double photonic band-gap, where reflectivity can reach 95%, can be generated along each direction, respectively. Shifting a strong field (two strong fields) to a travelling-wave field (two travelling-wave fields), we can achieve a reflectivity platform and a transmissivity window (two transmissivity windows). Our new findings are beneficial to a novel all-optical switching and routing, which may have applications in complex all-optical information networks.
2014, 63 (22): 224702. doi: 10.7498/aps.63.224702
Some basic thermodynamic relationships are used to develop a theroretical framework for modeling the detonation in explosives, on the assumption that explosive and detonation product are in a local thermodynamic equilibrium state, i.e., their pressures and temperatures are identical. Using this framework, a continuum constitutive model for explosive detonation is composed of a group of ordinary differential equations including the state equations of explosive and its product, simple mixing law, reaction rate equation and energy conservation equation, which are easily solved by a mature computational method such as trapezoidal rule. A group of nonlinear constitutive equations in a generalized Maxwellian form describe the relationship among the time evolution rates of pressure and temperature, the strain rate, and the chemical reaction rate. Coefficients appearing in the constitutive equations are determined only by parameters of the explosive and the product through using simple mixing rule. The continuum constitutive model and the corresponding computational method are verified by simulating the detonation behaviour of PBX9404 impacted by high velocity Cu flyer, and in the simulation the JWL equation of state for unreacted explosive and detonation product and the two-term Lee-Tarver reaction rate equation are adopted.
Wind velocity retrieval and field widening techniques of fringe-imaging Mach-Zehnder interferometer for Doppler lidar
2014, 63 (22): 224205. doi: 10.7498/aps.63.224205
Compared with the traditional Doppler frequency discriminator Fabry-Perot interferometer, Mach-Zehnder interferometer (MZI) has the advantages in high transmittance, linear parallel fringes instead of circular rings and wide field of view. An incoherent Doppler wind lidar system is demonstrated based on a fringe-imaging MZI. The mathematical model of wind velocity retrieval is derived, and the field widening of MZI is also used to optimize the performance of lidar system. The ideal fringe pattern outputs are obtained by numerical simulation, and the SineSqr function fitting method is proposed to determine the high-precision displacement of fringes after a Doppler shift. Furthermore, the field widening of MZI can be realized by field compensation which reduces the effect of the incidence angle on optical path difference. The results show that the wind velocity error obtained by SineSqr function fitting method is less than 0.45 m·s-1 at the line-of-sight wind velocity in a range from -100 m·s-1 to 100 m·s-1, which overcomes the instability of wind velocity retrieval by the gravity method. A full-angle field of view of 1° for MZI frequency discriminator without significant performance reduction is also achieved. These supplied discussion of the application techniques for Doppler lidar based on MZI fringe technique would promote the practical development of Doppler lidar for wind velocity measurement of the middle and upper atmosphere.
Propagation characteristics of seismic waves in shallow soil with the unsaturated three-phase poroelastic model
2014, 63 (22): 224301. doi: 10.7498/aps.63.224301
In order to study the mechanism of acoustic landmine detection, the propagation characteristics of acoustically coupled seismic waves in shallow soil are investigated. Based on the porosity and compressibility of shallow soil, the influences of parameters including soil porosity and water saturation on the propagation properties of seismic wave are discussed with the model of seismic waves in unsaturated three-phase porous medium. The calculation results show that under the given parameters, the propagation velocity and attenuation coefficient of seismic wave increase with the increase of acoustic frequency. The propagation velocities of longitudinal waves and those of transverse waves respectively decrease and increase with the increase of soil porosity. In addition, the propagation characteristics of acoustically coupled seismic waves become complicated with the increase of water saturation. The feasibility of the analysis method is discussed by comparing the calculation results with the experimental data published previously. As a result, a theoretical foundation is provided for the acoustic-to-seismic coupling mechanism and its application in the study of acoustic resonance landmine detection.
2014, 63 (22): 224302. doi: 10.7498/aps.63.224302
The band gap attenuation characteristics of finite and infinite periodic compound plate simply supported along its longitudinal edges are investigated with the wave propagation approach. Base on the boundary continuum condition between two plates, the coupled equations of finite and infinite periodic compound plate are established by transfer matrix and Bloch theorem respectively, and the relations of band gap attenuation characteristics between finite and infinite periodic compound plate are analyzed in detail. It is shown that the frequency band gap of periodic compound plate is related to exciting form and position. The frequency band gap of finite compound plate is coincident with the frequency band gap of infinite compound plate with the same mode vibration if finite compound plate is excited with one mode along its longitudinal edges. If the plate is excited with a point force, the frequency band gap is the intersection of frequency band gap of all participated modes. Besides, the influence of the structural damping on band gap is also analyzed.
2014, 63 (22): 224304. doi: 10.7498/aps.63.224304
Impact damping has been widely used in machine tools, robots, turbine machineries, aircrafts, and launch vehicles. Introducing micro fine particles into impact dampers may bring additional irreversible energy loss such as particle size reduction and plastic deformation for the damping, and carve out a new way to control the motion. For this purpose we use copper particles with an average size of 50 μm in ball impact dampers installed on a cantilever subjected to sinusoidal vibration within 96-hour impacting, and test the damping characteristics. We show that the response of the primary system can be divided into three stages, i.e., increasing, then deceasing, and increasing again. This dynamic feature reflects the deformation behaviors of the micro copper particles in different stages. In the first stage, the copper particles may display elastic behavior, and the sub-harmonic vibration of the steel ball may return part of the energy back to the primary system and enhance the response. In the second stage, the copper particle is forced into its yield point and the plastic deformation exhausts the energy and response of the system decline. In the third stage, hardening effect of the copper particles occurs and the response of system increases again. Our results may be significant to passively control the vibrations and material deformation.
Comparisons among weakly-compressible and incompressible smoothed particle hdrodynamic algorithms for natural convection
2014, 63 (22): 224701. doi: 10.7498/aps.63.224701
Smoothed particle hydrodynamic (SPH) method is used to solve a variety of complex engineering problems. In the literature about SPH, there are two approaches to solving the pressure component of momentum conservation equation, namely incompressible SPH (ISPH) and weakly compressible SPH (WCSPH) methods. In this paper, we present a new comparative study of WCSPH (Lagrange), ISPH (Lagrange) and ISPH (Euler) methods, focusing on heat conduction issue by numerical solutions of natural convection in a square cavity. Temperature distributions, velocity distributions and Nusselt number distributions at different Rayleigh numbers (Ra=104, 105, 106) are provided in the paper. The quantitative comparisons of results show that WCSPH (Lagrange), ISPH (Lagrange) and ISPH (Euler) methods all perform very well at low Rayleigh number. And at high Rayleigh number, SPH (Lagrange) needs shifting particle technology to correct the distribution of particles, ISPH (Euler) performs best because of the motionless particles, WCSPH (Lagrange) performs better than ISPH (Lagrange).
2014, 63 (22): 224703. doi: 10.7498/aps.63.224703
Targeting the flowing of insoluble surfactant-laden film over topography substrate, the lubrication theory is adopted to derive the evolution equations of thin liquid film thickness and interfacial surfactant concentration. The flowing characteristics of the film on topography surfaces, and the influence of topography structure are examined based on the numerical simulation with PDECOL code. The results show that when the thin film of insoluble surfactant flows over periodic grooving topography, the depression appears at the negative step, while the ridge is shaped at the positive step, both of which increase gradually with time going by. Compared with the case of the flat base, the surfactant-laden film spreading speed is enhanced. Increasing the groove depth or reducing the groove steepness leads to the increase of the rupture possibility of the film. Improving the groove width promotes the film flowing. The decrease of the steepness can cause the film to form a ridge feature before entering into the first groove. Gravity has the opposite effects on the up-hilling and down-hilling processes of liquid film flow, which causes the flow stability to deteriorate. Conjoining pressure induced by intermolecular forces can accelerate the film, giving rise to a notable dewetting phenomenon, while disjoining pressure has an adverse effect.
2014, 63 (22): 224103. doi: 10.7498/aps.63.224103
The characteristics of high-order harmonic generation (HHG) driven by 5 fs laser pulses interacting with argon under tightly focused geometry are investigated in this paper. By carefully optimizing parameters like dispersion, gas pressure and gas cell position, the enhanced HHG with nearly one order of magnitude in a range of 60-73 eV is observed. Based on single atom approximation and Maxwell propagation equations, numerical simulation is conducted to compare with the experimental characterization with proper parameter. It is proved that the phase-matching plays a crucial role in this phenomenon showing that the theoretical results are in agreement with the experimental results.
2014, 63 (22): 224202. doi: 10.7498/aps.63.224202
We propose a dark-field digital holographic microscopy (DHM) by using vortex beam illumination. In this paper, the annular illumination of vortex beam and the dark-field DHM imaging system are theoretically analyzed, and the quasi-nondiffracting property of the vortex beam is discussed. A corresponding DHM imaging system is established. The polystyrene spheres each with a size of 690 nm are utilized as objects in the experiment. By comparing the results of reconstructed images under bright-field illumination with those under dark-field illumination DHM, it is proved that the resolution of dark-field DHM under speckle-field illumination is improved and the contrast of its reconstructed image is enhanced accordingly.
2014, 63 (22): 224204. doi: 10.7498/aps.63.224204
In our work we build a high repetition, high peak power and high average power laser which contains three main components: the fiber oscillator, the Nd:YAG regenerative amplifier, and the four-pass amplifier side-pumped by laser diode. The wavelength is 1064 nm. The laser operates at 100 Hz with pulse energies up to 112 mJ. And the average power is 11 W. The pulse width is tunable from 500 ps to 2 ns. The radius of the beam is 6.8 mm. The spatial profile of the beam presents nearly a top hat in the near filed and 1.5× diffraction-limited in the far filed.
2014, 63 (22): 224102. doi: 10.7498/aps.63.224102
A novel high-gain and low radar cross section (RCS) microstrip antenna is designed and fabricated. The proposed antenna obtained broad-band 3 dB gain bandwidth and wide-band, wide-angle low RCS properties after applying the frequency selective surface (FSS) as a superstrate of original microstrip antenna. The FSS cell is composed of two metallic layers separated by a dielectric substrate. A metallic square loop with four resistors mounted on each side of the loop is enched on the top layer and a metallic plane with a central cross slot and four fringe slots is enched on the bottom layer. The four resistors of top layer are mainly used to absorb radar incoming wave and reduce antenna RCS. The patch of bottom layer can constructe a Fabry-Perot resonance cavity with ground plane and improve the antenna gain. The reflection coefficient S22 and transmission coefficient S12 of top layer are all below -10 dB at 5.75-11.37 GHz. The reflection phase gradient of bottom layer is positive and the reflection magnitude value is above 0.86 from 11.21 GHz to 11.54 GHz. Measurement results show that the antenna gain is enhanced by about 3.4 dB at 11.73 GHz, and the half-power beam width of E-plane and H-plane is reduced 16° and 50° respectively. The 3 dB gain bandwidth is about 2.4 GHz which from 10.0 GHz to 12.4 GHz and well cover the impedance bandwidth. The proposed antenan achieved an RCS reduction of more than 3 dB in the normal direction at 4.10-11.30 GHz, the largest reduction reached 23.08 dB in comparison with the original antenna. The monostatic and bistatic RCS reduction are over 3 dB from -20° to 20° and -37° to 37° respectively at 4.95 GHz. The results proved the FSS superstrate can be applied to improve the radiation and scattering performance simultaneously.
2014, 63 (22): 224201. doi: 10.7498/aps.63.224201
Achieving high resolution images is of great importance in ghost imaging. We present a super-resolution image reconstruction algorithm with sparse measurements based on the theory of compressed sensing and the prior knowledge of the point spread function of the ghost imaging system. A computational ghost imaging experimental setup with a digital mirror device is built to verify the effect of this algorithm on increasing the resolution of the ghost imaging system. In addition, we compare the result with that from the traditional ghost imaging algorithm. The experiments show that we can obtain super-resolution images by this algorithm with the sparse measurements. This approach can break through the Rayleigh limit of the imaging system and obtain super-resolution images.
2014, 63 (22): 224303. doi: 10.7498/aps.63.224303
In order to simulate the structural vibration and acoustic field in time domain, we discuss the calculation method of the structural damping and provide an integrated numerical method for impact sound synthesis which is finally well verified experimentally. Firstly, since the damping is considered to be one of the factors influencing the time-varying characteristics of the transient vibration, the detailed information are obtained by both of modal damping calculating methods. Secondly, the vibration and sound radiation of damping impacted plates are simulated in the time domain, showing that they are highly consistent with the results from the finite-difference time-domain method. Finally, the comparison between the impact sound of the finite cylindrical shell and the experimental results is performed, indicating that the two sounds are much the same in the temporal envelope, spectral structure and decay trend. What is more, the results imply that it is quite effective to use the these numerical methods to synthesize impact sounds.
2014, 63 (22): 224101. doi: 10.7498/aps.63.224101
The dispersion equation of the coaxial interlaced disk-loaded waveguide slow-wave structure is derived by the multi-conductor transmission line method. The simulation results by HFSS are in good agreement with the calculation results obtained from the dispersion equation. Influences of structure parameters on dispersion characteristics are discussed. It can be concluded that with the increase of inner conductor and the decrease of the period length, the bandwidth of the slow-wave structure becomes greater. The dispersion characteristics of the coaxial interlaced disk-loaded waveguide and those of the coaxial disk-loaded waveguide are compared. The results show that the coaxial interlaced disk-loaded structure can obtain a wide bandwidth and weak dispersion. This study will be a guide to the research of the coaxial interlaced disk-loaded waveguide slow wave structure used in the traveling-wave tube.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2014, 63 (22): 228201. doi: 10.7498/aps.63.228201
The process of formation or transformation of multi-armed spiral patterns in gas discharge system is investigated numerically by using H.-G. Purwins model with three components. The parameter space is obtained though analyzing the influence of system parameters on system space, where a stable spiral appears. Besides, the formation mechanism and spatiotemporal characteristics of spiral pattern are studied. In addition, the evolution process of pattern from simple hexagon to spiral wave is numerically simulated, and various kinds of spirals are obtained (including two-armed, three-armed, four-armed, five-armed, six-armed, and seven-armed spirals). It is found that the stable spiral only survives in Turing-Hopf space, which is the result of interaction between Turing mode and Hopf mode. Furthermore, the spiral tips constantly rotate for various spiral patterns, and the velocity increases with the number of spiral arm increasing. For the influences of perturbation and boundary conditions, the multi-armed spiral pattern can lose one arm and become a new spiral in the rotating process. In conclusion, the numerical simulation results are in good agreement with those obtained in gas discharge experiment.
Multi-channel wide area adaptive damping control for suppressing low-frequency and sub-synchronous oscillation
2014, 63 (22): 228801. doi: 10.7498/aps.63.228801
A model reference adaptive control scheme is developed based on hyper-stability theory and is proved. Both of reduced order models of the power system and relevant oscillation frequencies are acquired by TLS-ESPRIT algorithm. The band-pass filters (Butterworth) are utilized to decompose oscillation frequencies into different channels and controllers are designed for each oscillation mode based on adaptive control method, thus reducing the influences of the various controllers. Xiangjiaba-Shanghai DC link under island operation condition is simulated using electromagnetic transient program PSCAD/EMTDC to demonstrate proposed control strategy. The results validate that the proposed method is able to suppress low-frequency oscillation and sub-synchronous oscillation simultaneously and the proposed method has better control performance than the traditional PID control. The problem will lead to controller performance deterioration caused signal transmission delay in system and it is resolved by phase compensation.
2014, 63 (22): 228401. doi: 10.7498/aps.63.228401
A reconstruction failure detection method for random demodulator based compressed sampling is proposed, which utilizes the correlation between two consecutive reconstructed supports of the sparse signal. The method is easy to realize because of its low-computational complexity. Simulations show that the proposed method can judge whether the reconstruction is successful with high accuracy and it can reduce the interference probability with primary users when the signal is not that sparse.
Simulations of the interactions between dislocations and solute atoms in different loading conditions
2014, 63 (22): 228102. doi: 10.7498/aps.63.228102
Dynamic strain aging, i.e. the interaction between dislocations and solute atoms, affects the mechanical properties of alloys. In this paper, a 2D-kinetic Monte Carlo model relating to the interaction between dislocations and solute atoms is developed to simulate the motions of edge dislocations in four different conditions. In “single dislocation with constant stress rate” condition, single dislocation is pinned under low stress rate, moves continuously under high stress rate, and moves intermittently under middle stress rates. In “multi-dislocation with zero stress” condition, the solute atoms gather below positive dislocations and above negative dislocations. In “multi-dislocation with constant stress” condition, the influence of solute atoms on dislocation motion becomes stronger with stress decreasing. In “multi-dislocation with constant stress rate” condition, the collective pinning and unpinning result in the stepped curve of total displacement. The simulated results present the process of dynamic strain aging in a microscopic scale and are consistent with theoretical results.
2014, 63 (22): 228501. doi: 10.7498/aps.63.228501
The field-to-voltage transfer coefficient (∂ B/∂ V) is an important parameter of the multi-channel superconducting quantum interference device (SQUID) magnetic detecting system. The SQUID devices and the readout circuits have the inevitable differences among different channels, so the accurate calibration of system channels is rather significant. In this paper, We first used the circular PCB coils for 36-channel MCG system calibration, and the other one is based on a traditional method in which a uniform field is produced by square Helmholtz coil. The calibration data show that the results are basically the same. The calibrated ∂ B/∂ V values using circular PCB coils are in a range from 1.46-1.73 pT·mV-1. And those of square Helmholtz coils are mostly within a range from 1.56-1.64 pT·mV-1.
Macro-micro coupled simulation of competitive dendrite growth in different areas of the welding pool
2014, 63 (22): 228103. doi: 10.7498/aps.63.228103
A macro-micro coupled model is developed to simulate the competitive dendrite growths in different areas of the welding pool in the solidification process. The transient solidification conditions in welding pool are obtained by the three-dimensional (3D) macro-scale FEM model. The thermal conditions used in the micro-scale cellular automata model is obtained from the macro-scale FEM model by using the interpolation algorithm. The simulation results indicate that the micro-scale cellular automata model developed in this paper can simulate the morphologies of dendrites with various growth directions accurately. The solidification conditions in welding pool have obvious effects on the competitive dendrite growth. The dendrites with their preferential orientations parallel to the direction of the highest temperature gradient are more competitive. The morphology of grain structure is determined by the competition among different dendritic arrays. The dendritic arrays with more favorable growth direction can gradually crowd out other dendritic arrays and occupy more space through dendrite branching. The area near the central line of welding pool has a lower temperature gradient, a higher solidification rate, and a higher cooling rate in the solidification process, and such solidification conditions lead to the finer microstructure. The simulation results of the secondary dendrite arm spacing are in agreement with the experimental results under the corresponding solidification conditions.
2014, 63 (22): 228402. doi: 10.7498/aps.63.228402
In the indoor pseudolite positioning system, the effect of the clock offset always leads to a large error in the positioning result. To reduce the effect of the clock offset, a relative localization algorithm for the indoor environment is proposed. In this paper, firstly, the Kalman positioning algorithm is used to obtain the coarse baseline. The model of the indoor relative localization and its operation are shown. Using the Kalman filter, the pseudorange double difference is smoothed by the carrier phase double difference. Then, the accurate baseline and the accurate positioning result of the receiver could be obtained. In order to predict the next state precisely, the Kalman corrected result is replaced by the accurate result. The experimental results show that the proposed algorithm has a good localization accuracy and the positioning error is less than 20 cm.
Measurement uncertainty of metallic ductility in tensile tests: intermediate temperature embrittlement and strain rate embrittlement
2014, 63 (22): 228101. doi: 10.7498/aps.63.228101
International Standard, ISO 6892-2, Metallic Materials-Tensile Testing: Method of Test at Elevated Temperature maintained that the strain rate variations and test temperature variations can induce the measurement uncertainty of mechanical properties in tensile testing, which will imperil the reliability of tension tests. In this paper, the measurement uncertainties of shrinkage rate or elongation rate in tensile testing cross-section, intermediate temperature embrittlement and strain rate embrittlement are first described experimentally. Second, the fundamental results on the microscopic theory of elastic deformation in metals are briefly mentioned. Then the phenomena of the measurement uncertainties are explained based on the microscopic theory. It is expounded that the elastic deformation of tension tests induces the impurities to segregate to grain boundaries and the relative embrittlement which produces the measurement uncertainties of reduction in area. This work gives a theoretical basis for correcting the present standard method of tension testing to avoid the measurement uncertainty of reduction in area.
Pattern transfer and molecular chain orientation modulation by soft template during the nanoimprint lithography
2014, 63 (22): 228104. doi: 10.7498/aps.63.228104
The templates for the nanoimprinting are fabricated usually through a series of steps, such as E-beam lithography, E-beam deposition, liftoff and reactive ion etching. Any mistake during these steps would lead to the failure of the fabrication, so the template is always expensive and difficult to make. Under this circumstance, it is really important to find an effective way to build the template. In this report, the patterned photoresist layer is used as a mother set of the pattern definition of the soft template polydimethylsiloxane. The grating structure of conjugated polymer poly (9,9-dioctylfluorene) film is successfully obtained by this template in the nanoimprinting process. In addition, we also find the anisotropy of molecular chain distribution. Both the transmission electron microscope diffraction pattern and the polarized absorption spectrum are used to prove that this anisotropy is induced by the molecular chain alignment, which would be really helpful in future applications in organic emission equipment. Moreover, this result is also applicable to the poly (9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-2,1',3-thiadiazole) film system.
2014, 63 (22): 228802. doi: 10.7498/aps.63.228802
To study the spectrum allocation problem based on graph coloring model in cognitive radio network, an algorithm to maximize total network revenue is proposed, which is based on artificial physics optimization because of its NP-based features. In artificial physics optimization algorithm, the solution of spectrum allocation problem is mapped into a particle with mass. It establishes the relation between particle mass and its fitness value, and defines the virtual force between the particles by the law of gravity so that the entire group can move to the better direction and achieve population optimization. The detailed spectrum allocation process is given and the particle position updating equation is improved because of its binary coding features. Simulation results show that the proposed algorithm can better maximize network revenue.
2014, 63 (22): 228901. doi: 10.7498/aps.63.228901
Research on the stochastic behavior of traffic flow is important to understand the intrinsic evolution rule of traffic system. On the basis of cellular automata model and traffic flow model with look-ahead potential, in this paper, a novel traffic flow model with weighted look-ahead potential is presented. By introducing the weighting coefficient into the look-ahead potential and endowing the potential of vehicle closer to itself with a greater weight, the modeling process is more suitable for the driver's random decision-making process which is based on the vehicle and enviroment situation in front of him in actual traffic. Complex high-density traffic behavior is reproduced by numerical simulations. The simulation results show that the weighting coefficient has an obvious effect on high-density traffic flux, and the weighted model is more conducive to keeping high traffic flux and road capacity while maintaining a high traffic density.
2014, 63 (22): 220201. doi: 10.7498/aps.63.220201
The consensus problem of heterogeneous multi-agent systems composed of first-order agents and second-order agents in directed graph is investgated. A linear consensus protocol is proposed for solving such a consensus problem. The sufficient conditions for achieving consensus are established by using the graph theory and matrix theory in fixed and switching topology respectively, and these conditions are dependent on control gain and communication topology. Consensus equilibrium point is derived in the fixed topology. It is proved that only root nodes in the interaction topology can make contributions to the equilibrium point. Numerical examples are provided to prove the correctness of the theorems.
2014, 63 (22): 220202. doi: 10.7498/aps.63.220202
The excessive diffusion of multiple unmanned aerial vehicle (UAV) cooperative system may lead to the cooperative failure, but to control the system scale is a potential way to solve this problem. First, macroscopic motion characteristic of multi-UAV cooperative searching system is abstracted, and then motion model of the platform is established. Afterwards, by constructing an appropriate Lyapunov function, the stable control mechanism of this system and its stable control parameters are obtained. Simulation results verify the following two conclusions: 1) the proposed stable control mechanism can not only make multi-UAV system realizes the effective cooperation, but also can ensure the stability of this system; 2) when this system is in a stable state, its scale can be controlled effectively by adjusting the relevant control parameters.
Directional Lyapunov exponent and its application to fault detection of the single input single output system
2014, 63 (22): 220505. doi: 10.7498/aps.63.220505
In this paper, for the fault detection of a single-input single-output (SISO) system, we use chaotic oscillator to generate the excitation of the system under test (SUT), and use non-uniform method to reconstruct the phase space of the output time series. Directional Lyapunov exponent is defined around the equilibrium point in the phase space, and it is used to analyze the eigen-structure of the output phase space around its equilibrium point, thus the fault detection of the SISO system is realized. The simulation results show that parameter changes of the SUT will affect the phase space structure around its equilibrium point, and the directional Lyapunov exponent is sensitive to these changes.
2014, 63 (22): 220503. doi: 10.7498/aps.63.220503
In this paper, the noise-induced dynamics is studied in an asymmetric bistable coupled network system modulated by different signals. According to the Gaussian approximation and the slaving principle, the asymmetric bistable coupled network system is reduced to a low-dimensional model with two potentials, by which the phenomenon of system size stochastic resonance is studied theoretically and numerically. Under the assumption of adiabatic limit, the expressions of signal-to-noise ratio (SNR) are found by virtue of Fokker-Planck equation with respect to cosine signal and rectangle signal, based on which the system size stochastic resonance is investigated. Further, the effects of the noise strength, the asymmetry and the amplitude of the signal on the system size stochastic resonance are well discussed. It is demonstrated that the SNR shows a non-monotonic dependence on the number of coupled systems, which is demonstrated that there is a resonance with respect to the number of coupled systems.
2014, 63 (22): 220205. doi: 10.7498/aps.63.220205
Recently, a new mechanism of secondary electron multipaction, termed “long-term” multicarrier multipactor, was found in wideband high-power systems used in vacuum environments. Due to the long-term accumulation of secondary electrons between consecutive periods of the multicarrier signal, the long-term multicarrier multipactor has relatively low discharge threshold and is difficult to predict, thus causes potential reliability problems in space and accelerator applications. In this paper, we propose a stochastic approach to the analytical analysis of the multicarrier multipactor discharge occurring in inhomogeneous electric fields. By introducing the random walk and Levy walk theory, the probabilistic model of the lateral diffusion of secondary electrons in the process of a multipactor discharge is derived. Based on the derived probability density, the purely theoretical calculation of the accumulation of secondary electrons of a multicarrier multipactor in a rectangular waveguide supporting TE10 mode is given. The theoretical results comply well with the results achieved by the time-consuming particle simulation, with reducing computational time by about one- order of magnitude. The presented probability density of the lateral diffusion of secondary electrons can have applications in high-power electronics and electromagnetism.
2014, 63 (22): 220301. doi: 10.7498/aps.63.220301
Beam splitter (BS) is a basic linear element in quantum optics, which plays an important role in preparation of entangled states and quantum measurement. On the basis of the transformation relation between operators at input ports and output ports, we derive the natural representations in different representations. Using the natural expression rather than SU(2) Lie algebra relation, as well as the technique of integration within ordered product (IWOP) of operator, we can conveniently and concisely derive the normally ordering form and exponential expression of BS operator. Many forms of decompositions for BS operator can also be directly obtained by its natural representation and the orthogonality of coordinate states. Furthermore, the entangled state representation and corresponding Schmidt decomposition can be conveniently obtained.
2014, 63 (22): 220501. doi: 10.7498/aps.63.220501
In this paper, we proposes a cascading failure model for the complex network with hierarchy structure which is common in real networks. This model can be used to optimize the financial or logistic network design. The hierarchy network has a tree-shape backbone and many random hidden linkages. The branches of each node in the backbone follow normal distribution. The attack on the network is from bottom layer under the condition of incomplete information, i.e., on the assumption that the attacker cannot observe the hidden linkages. The load redistribution of the failure nodes takes into consideration the hierarchy heterogeneity, of which the network tends to redistribute extra load to intact nodes of the same or higher hierarchies. Simulation experiment shows that the topology of hierarchy network changes from small world network into random network with the variation of linkage parameters. The size of cascading failure firstly increases and then decreases with the hidden linkage ratio increasing and the network shows higher robustness when the load of failure node is redistributed to the intact node with high hierarchy. The experiments also demonstrate that the linkage parameters play a significant role in the robustness of the network because these parameters can affect the hierarchy distribution of hidden links. Therefore, in order to achieve better robustness of network, we should reasonably choose parameters in topology design and network control strategies.
Adaptive sliding-mode control of chaotic permanent magnet synchronous motor system based on extended state observer
2014, 63 (22): 220506. doi: 10.7498/aps.63.220506
An adaptive sliding-mode control scheme based on extended state observer (ESO) is proposed for permanent magnet synchronous motor (PMSM) chaotic system with some immesureable states. The adaptive sliding-mode control and extended state observer theory are combined in the developed controller, and thus the restriction that all the states in the PMSM should be completely measured is canceled. Through a simple coordinate transformation, the PMSM chaotic model is transformed into a Brunovsky canonical form, which is more suitable for the sliding-mode controller design. In the presence of unknown states and upper bound of nonlinear uncertainty, the ESO is employed to estimate the unknown states and the nonlinear uncertainty. Then, the adaptive sliding-mode controller is designed to ensure that the system states can converge to zero rapidly and stably. Simulation results show that the proposed controller can improve the chattering problem of the sliding-mode control and enhance the robustness of the system.
A deployment strategy for coverage control in wireless sensor networks based on the blind-zone of Voronoi diagram
2014, 63 (22): 220701. doi: 10.7498/aps.63.220701
In this paper, we propose a blind-zone centroid-based scheme (BCBS) for solving the coverage problem of wireless sensor network in two-dimensional monitor area. In BCBS the monitor area is partitioned into several Voronoi polygons by using the Voronoi diagram and then each Voronoi polygon can be covered by one sensor. The next work in the BCBS is to obtain the blind-zone in the Voronoi polygon according to the positions of its vertexes in order to construct the polygon, which is approximately the shape of the blind-zone. The centroid of the polygon is then regarded as the candidate target position for the sensor nodes in order to improve the coverage rate. Experimental results show that the BCBS has advantages in the coverage rate, uniformity of the nodes distribution and the efficiency of the nodes coverage over the centroid-based scheme.
2014, 63 (22): 220302. doi: 10.7498/aps.63.220302
By changing the Rabi frequency of the photoassociation laser and the atom-polymer coupling strength, we investigate the effect of external field shape on atom-polymer conversion efficiency. First, by defining time-index, the external filed shape given in literature is improved. We discuss the influence of time-index on conversion efficiency, and then choose a more optimized external filed shape, it has good parameter robustness. Under the action of the external field, the adiabatic process has almost no oscillation, the adiabatic fidelity is close to 1, and the error of the system is less. The ultracold atom-polymer molecules conversion can be realized stably and efficiently.
Stabilization of matter-wave solitons in Bessel optical lattice by spatial modulation of the nonlinearity
2014, 63 (22): 220303. doi: 10.7498/aps.63.220303
Using variational and numerical solutions of the mean field Gross-Pitaevskii equation, we investigate the stabilities of nonrotating and vortex solitons in Bessel optical lattice by spatial modulation of the nonlinearity(nonlinear optical lattice). It is demonstrated that there exist the stable matter-wave solitons in a combination of optical lattices with linear Bessel optical lattices and nonlinear optical lattice. Using the time-dependent variational approach, we derive the odinary differential equations for the time evolutions of the width and phase of solitons. Through an effective potential, we obtain the stable criteria for all kinds of combinations of the system parameters. We perform direct numerical simulations to support our analytical results, and find that they are in goog agreement.
2014, 63 (22): 220304. doi: 10.7498/aps.63.220304
Based on the quantum error-correction codes and concatenation, quantum logical gates can be implemented transversally, which is called the fault-tolerant quantum computation. Clifford gates can be directly and fault-tolerantly performed, but they cannot reach universal quantum computation. How to implement the non-Clifford gate fault-tolerantly is a vital technique in fault-tolerant universal quantum computation. Here the magic state is selected to help the implementing of the non-Clifford gate transversally. Based on the non-stabilizer state cos θi|0>+sinθi|1>, circuits which can execute 2θi rotation around X-axis and Z-axis fault-tolerantly are proposed. Then new non-stabilizer states in this form are developed and produced from the distilled magic state. By using these states, a number of non-Clifford gates can be performed transversally, which makes profound implication in fault-tolerant quantum computation. We calculate the number of the non-stabilizer states needed for simulating the desired rotation operations, which is less than that in previous protocols.
2014, 63 (22): 220504. doi: 10.7498/aps.63.220504
In this paper, we investigate the coherence resonance of a piezoelectric energy harvester of beam subjected to an axial force. The fractional damping is considered. First, a nonlinear model of the energy harvesting system with fractional damping and random excitation is set up. The coupling equations of dynamics and electrics are derived. Euler- Maruyama-Leipnik method is used to solve the fractional order differential equations. The signal-to-noise ratios, mean responses, and other statistical quantities under the damping forces with different orders are computed. The results obviously show the appearance of coherence resonance. It can be seen that the reduction of fractional order not only reduces the critical value of noise level, thus leading to coherence resonance, but also increases the amplitude on the occurrence of coherence resonance. So it is possible to maximize harvest power for a given density or variance of random excitation by varying system parameters.
2014, 63 (22): 220507. doi: 10.7498/aps.63.220507
In this paper we study the fractal dimensions of wave function for the periodically kicked free top. We find that when kicking strength coefficient is less than or equal to 1 (≤ 1), the motion in classical phase space is regular, the fractal dimension is about 1, and as kicking strength increases, the motion in classical phase space becomes chaotic and the fractal dimension also increases. And we also find that when kicking strength is greater than or equal to 6 (≥ 6), the phase space becomes completely chaotic, the fractal dimension reaches its maximum value 1.5 and will keep this value.
2014, 63 (22): 220305. doi: 10.7498/aps.63.220305
The decoherence time of superconducting qubit is one of the main parameters that determine whether superconducting quantum computation can be realized. This paper mainly focuses on three-dimensional (3D) transmon. The sample is fabricated on SiO substrate, and measured in 10 mK temperature. By measuring Rabi oscillation, energy relaxation, Ramsey oscillation and spin echo, the decoherence time constants of 3D transmon are characterized. The results show that the decoherence time is around several hundred nanoseconds. Based on the relationship of different decoherence time constant, we have the concludes that the possible reason to diminish the decoherence time is the defect in SiO substrate, but not the low frequency noises.
2014, 63 (22): 220502. doi: 10.7498/aps.63.220502
In this paper, the effect of the oscillation of the substrate potential in a one-dimensional Frenkel-Kontorova model is considered. The relationship between the oscillating amplitude, frequency of the substrate and the nanofriction phenomena such as hysteresis, maximum static friction force, super-lubricity are investigated. Similar results are obtained for the two cases in which the ratios of the atomic distance to the period of potential field of the substrate potential field are incommensurate and commensurate respectively. The results show that on one hand, with the appropriate frequency, the area of the hysteresis will decrease while the amplitude increases, and the tendency of the decrease depends on the frequency. In particular, suitable frequency and amplitude give rise to super-lubricity. However, when the frequency is too high, the result is the same as those in the case without oscillation. On the other hand, fixing the amplitude, the area of the hysteresis will increase with the increase of frequency in spite of tendencies being different. At the same time, on a whole, the maximum static friction force has an increasing tendency. Interestingly and importantly, for a certain amplitude, as the frequency increases, the maximum static friction force first decreases to zero (corresponding to super-lubricity), and then increases. That is, there is an optimum oscillating frequency which makes the system have the minimum static friction force. Furthermore, the difference between the above two circumstances lies in that for commensurate interfaces, there are the same start-up velocities for a certain frequency and various small amplitudes, which is different from the incommensurate mating contacts. Hence, it shows that the latter has a more complex dynamic behavior under the same hypothesis.
2014, 63 (22): 220203. doi: 10.7498/aps.63.220203
In this paper, targeting the permanent magnet synchronous motor chaotic system, we consider the system influenced by uncertain factors. We use the method of the exact feedback linearization which is based on differential geometry theory to establish the nonlinear robust control model and design the robust controller for realizing the robust stabilization and output tracking control of the permanent magnet synchronous motor chaotic system. Numerical simulation results demonstrate the effectiveness of the proposed method and the robustness of the controller.
2014, 63 (22): 220204. doi: 10.7498/aps.63.220204
In order to make the cardinalized probability hypothesis density filter well understood, its function is deduced with the Bayes theorem and the total probability theorem based on the physical-space model made by Ozgur Erdin. The derivation is detailed and clear, and the results of the derivation are identical to those in the literature. This paper will provide the theory basis for the application and the performance improvement of the cardinalized probability hypothesis density filter in target tracking.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL,MAGNETIC, AND OPTICAL PROPERTIES
A real-time magnetic localization method of underwater non-cooperative magnetic targets based on unscented particle filter
2014, 63 (22): 227502. doi: 10.7498/aps.63.227502
A real-time magnetic localization method based on unscented particle filter (UPF) is proposed to solve the problem for real-time localization of underwater non-cooperative magnetic targets. The state space model of non-cooperative magnetic targets is set up according to its motion characteristic, and the state is estimated in real time by UPF. In order to improve the observability of the system, the particle state is constrained and magnetic moment is inverted by the least square method. The simulation results and ferromagnetic object localization experimental results show that the method is good in localization precision and real-time performance, which can be applied to the real-time magnetic localization in near field.
2014, 63 (22): 227101. doi: 10.7498/aps.63.227101
In this paper, the site occupations of H under different mole ratios in interstitials of α -Fe and γ -Fe are studied by the first principles method based on the density functional theory. The total energy of the steady state crystal, binding energy, solution heat, density of states, charge density difference and charge population are calculated. The interaction between interstitial H and Fe lattice is analyzed. The influences of hydrogen dissolution on electronic structure of α -Fe and γ -Fe are discussed. The results show that the dissolved hydrogen leads to the lattice distortions of α -Fe and γ -Fe, and the volume expansion ratio increases with the dissolved quantity of hydrogen increasing. The energy analysis indicates that the hydrogen preferentially occupies the tetrahedral interstitial of α -Fe, while in the γ-Fe it preferentially occupies the octahedral interstitial. The analyses of density state, charge density difference and charge population reveal that the interaction between interstitial hydrogen and Fe lattice is contributed by the H 1s orbital and Fe 4s orbital, and this interaction is relatively weak, which is one of the main reasons for lower solid solubility of hydrogen in Fe lattice.
2014, 63 (22): 227301. doi: 10.7498/aps.63.227301
The two lowest single-particle hole states in the vertically coupled Ge/Si double layer quantum dots are investigated numerically by using the single-band heavy hole effective mass approximation and six-band Kronig-Penney model, respectively. The calculated results indicate that within the frame of several-band coupled model, the bonding-antibonding ground-state transition and a bonding-antibonding energy anti-crossover phenomenon are observed with interdot distance increasing. These results have not been observed previously in those single-band model calculations. The analysis of the wavefunction component of bonding-antibonding hole state shows that the contribution ratios of light, heavy and spin-orbital-split-off hole states to the characteristic hole wavefunction vary with the increase of the vertical coupled distance, resulting in the ground state wavefunction changing from bonding states to antibonding ones finally.
2014, 63 (22): 227304. doi: 10.7498/aps.63.227304
Using non-equilibrium Green's function method, the charge and spin transport properties through T-shape double quantum dot molecule Aharonov-Bohm (A-B) interference are theoretically investigated. Resonance or anti-resonance can occur at the same location in conductance spectrum by controlling coupling or uncoupling between two quantum dots in T-shape double quantum dot molecule, which is the basis for designing quantum switches. When two identical T-shaped double quantum dot molecules are embedded in two arms of A-B interferometer, respectively, totally destructive interference can appear by taking appropriate magnetic flux. Spin current through the system can be regulated by adjusting quantum dot level, bias between two electrodes and Rashba spin-orbit interaction.
2014, 63 (22): 227501. doi: 10.7498/aps.63.227501
The magnetic properties of some magnetic materials are influenced by the exchange interaction between magnetic ions and the spin fluctuations of magnetic ions. By use of the exchange interaction-effective field including the spin fluctuations of magnetic ions Hm= n0(1+γ T +β eω T)M, the Zeeman splitting of crystal field energy levels of Pr3+ ions in PrNi2 and the variation of the magnetic moments with the applied field in a temperature range of 3.8 K≤ T ≤ 30 K are calculated. The thermal variation of the reciprocal susceptibility of Pr3+ ions is calculated as well for the applied magnetic field H=5000 Oe. The calculated results are in good agreement with the experimental data. The magnetic entropy changes are obtained theoretically in a magnetic field range of 0H<50000 Oe, and the results are similar to those reported in the literature. It is indicated that the exchange interaction-effective field containing the spin fluctuations is applicable not only to the ferrimagnetic crystals, but also to the paramagnets.
2014, 63 (22): 227802. doi: 10.7498/aps.63.227802
Optical resonator with high Q value can be used as a core component of the resonator optic gyro, with which the miniaturization and integration would be achieved. The coupling system composed of the disk cavity which is made by traditional micro-electro-mechanical system process and the tapered fiber which is drawn by melting method. When the disk cavity is coupled with the fiber at different places of the tapered region, by swapping input and output there is observed the deviation in the output transmission spectrum, also the resonant frequency, coupling efficiency and the Q value are changed, i.e., the non-reciprocity phenomenon appears. Then the distribution characteristics of the tapered fiber evanescent field are simulated with Rsoft software. The reason of the non-reciprocity is analyzed theoretically. According to the statistics of the output data when the disk cavity is coupled with the fiber at different places of the tapered region, it is found that the non-reciprocity can be eliminated effectively when the coupling happens at the center of the fiber tapered region. And this finding can be used to suppress the non-reciprocity noise produced by the coupling system composed of tapered fiber and resonant cavity in the resonator optic gyros application.
2014, 63 (22): 227902. doi: 10.7498/aps.63.227902
In this paper, the periodic semicircle groove disk is investigated to restrain the multipactor phenomenon in high power pill-box window. Through the theoretical analysis, the semicircle groove is proved to avoid the local field enhancement, which always exists in the vicinity of the sharp boundary groove. The proper groove width with a corresponding minimal suppression tangential electric field is achieved by simulating the multipactor procedure with Monte-Carlo algorithm. The effect of normal electric field is also analyzed. This configuration is to be applied to the high power klystron.
2014, 63 (22): 227302. doi: 10.7498/aps.63.227302
In this paper, a new REBULF (reduced BULk field) SJ-LDMOS (lateral double-diffused MOSFET) is proposed with the N type buffered layer based on the buffered SJ-LDMOS for the low loss of LDMOS used in the power integrated circuits. In this structure, the problem of the substrate-assisted depletion, produced due to the P-type substrate for the N-channel SJ-LDMOS, is eliminated by the N-type buffered layer. The charges for the N-type and P-type pillars are depleted completely. Moreover, a new electric field peak is introduced into the surface electric field distribution, which makes the lateral surface electric field uniform. The breakdown voltage is improved for the REBULF SJ-LDMOS in virtue of the ISE simulation results. By optimizing the location and parameters of the N-type buried layer, the breakdown voltage of REBULF SJ-LDMOS is increased by about 49% compared with that of the conventional LDMOS, and improved by about 30% compared with that of the buffered SJ-LDMOS.
2014, 63 (22): 227303. doi: 10.7498/aps.63.227303
The leakage current characteristics of an insulating sample under high-energy electron beam irradiation are simulated by a numerical model with taking into account the electron scattering, transport, trapping and self-consistent field.The leakage current is measured by using a detection platform. Results show that under the continuous electron beam irradiation, the total electron yield decreases evidently; because of electron transport, the sample near the surface is positively charged weakly and its interior is negatively charged strongly; some electrons are transported downward, forming the electron beam induced current and the leakage current under the long time irradiation. Under the irradiation, the leakage current increases to a stable level gradually. The leakage current decreases with the increase of sample thickness, but it increases with beam energy and current.
2014, 63 (22): 227503. doi: 10.7498/aps.63.227503
Nanomagnetic logic has the advantages in low power, non-volatility, and room temperature operation, however, low power on-chip clocking is the requirement of its integration. An on-chip clocking structure for a nanomagnetic logic circuit using exchange interaction is proposed in this work. This scheme is to use the Oersted field generated by current-carrying copper wire to magnetize ferromagnetic film cladding and then to switch the magnetization orientation of nanomagnets by the exchange interaction between magnetic layers. Simulation results demonstrate that the proposed scheme can reduce the power dissipation by 5/6 and the marginal spray field by 2/3 compared with the ferromagnetic yoked clocking that uses the external field to switch the magnetization. Therefore, it can reduce the power consumption and the risk of crosstalk. In addition, micromagnetic simulation verifies that nanomagnetic array laid on the proposed clocking can work functionally.
Effects of high magnetic field on structure and optical properties of metal ions doped modified CaTiO3
2014, 63 (22): 227803. doi: 10.7498/aps.63.227803
In the paper, the changes of structures and optical properties of metal ions doped modified CaTiO3 prepared under different magnetic field intensities (up to 12 T) and 800 ℃ are studied. The results indicate that the photo absorption performances are enhanced with the ions doped concentration increasing and red shift occurs significantly. With the same doped concentration, the photo absorption performances of the samples prepared under magnetic field are improved compared with under no magnetic field, while there are little differences among the absorption curves of these samples prepared under different magnetic field intensities. Furthermore, it is observed that the X-ray diffraction curve peaks of pure CaTiO3 prepared under magnetic field are all left-shifted and cutoff wavelengths of UV-vis are augmented, which indicates that the interplanar spacing and lattice constant are increased while the band gap is narrowed.
2014, 63 (22): 227901. doi: 10.7498/aps.63.227901
A particle model that is based on Monte Carlo particle simulation arithmetic is built up to investigate the multipactor behavior on the surface of cylinder window disk in pill-box window. The regime of multipactor in the inhomogeneous electric field is obtained. The simulation results prove that the interaction between secondary electrons and window disk is sustained by magnetic field force on the upstream side. The multipactor phenomenon acts intensively in the area with a great electric field. The ponderomotive force does not devote any effort to multipactor on the upstream side. On the downstream side, the multipactor cannot be excited without strong enough surface electrostatic field because of the positive magnetic field force. With the increase of transmitting power, secondary electrons can obtain more energies. Due to the effect of ponderomotive force, the multipactor region transfers from the area with powerful electric field to the weak one on the downstream side. Besides, the resistance effect of electrostatic isolation on multipactor is also confirmed in the input port of cylinder waveguide.
Infrared radiation dynamic response and parametric analysis for silicon solar cell using photocarrier radiometry
2014, 63 (22): 227801. doi: 10.7498/aps.63.227801
An analytic mathematical model of modulated laser-induced minority carrier density wave of silicon solar cells is developed, and light-induced carrier recombination radiation luminescence method (photocarrier radiometry (PCR)) is employed to detect the doping concentration, impedance and carrier transport parameters. The double knee characteristics of frequency domain response curve are investigated, and in a small ac signal case, the equivalent circuit topology structure of a solar cell is constructed. Through simulation analysis based on minority carrier density wave mathematical model, the effects of doping concentration, resistance and carrier transport parameters on the PCR frequency domain response are investigated. Donor/acceptor concentration, shunt resistance and carrier transport parameters of Si solar cell are obtained by PCR frequency-scanning experiments and multi-parameter fitting. The results show that the first knee position of PCR-detected large-area solar-cell frequency domain response curve is determined by the capacitive effect. The simplified mathematical model can be used to quantitatively describe and determine the doping concentration, shunt resistance and carrier transport parameters of silicon solar cell.
ATOMIC AND MOLECULAR PHYSICS
In high-temperature high-pressure environment, the measurement precisions of tunable diode laser absorption spectroscopy and other laser spectrum technologies are influenced by spectral overlap because of Doppler and Lorentz broadenings. One of the potential methods to improve precision is to use the second derivative spectral signal, which has less overlap. This paper deals with the second derivative of Voigt function. The integration of its second derivative from negative to positive infinity is proved to be zero. And the analytical results of its second derivative minimum and the maxima or minima of its even-order derivatives are obtained. It is also shown that there is the relationship between the ratio of second derivative maximum point location to zero point location and the ratio of Lorentz half-width to Doppler half-width. These results provide the basis for inversing precision information from second derivative spectral signal.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Radiation effect of deep-submicron metal-oxide-semiconductor field-effect transistor and parasitic transistor
2014, 63 (22): 226101. doi: 10.7498/aps.63.226101
The metal-oxide-semiconductor field-effect transistor (MOSFET) and the parasitic bipolar transistor of domestic complementary metal oxide semiconductor (CMOS) process are irradiated with 60Coγ rays to investigate the failure mechanism of the mixed-signal ICs fabricated by deep submicron CMOS process, caused by total dose radiation. The research results are as follows. 1) The parasitic sidewall and top corner regions contribute to the intra-device leakage. 2) The parasitic bipolar transistor of CMOS process is not sensitive to total dose radiation, which is very different from the conventional bipolar transistor. Preliminary analysis suggests that the difference originates from the differences in the structural and making process. 3) The total dose radiation damage to the parasitic bipolar transistors is not coupled with the damage to the NMOS transistor in the same CMOS process. 4) Based on the above study, the radiation failure mechanisms of the analog and digital module in mixed-signal ICs fabricated respectively by the domestic and commercial CMOS process are investigated. Preliminary analysis suggests that the increase of off-leakage current of MOSFET is responsible mainly for the increase in power consumption of digital module, and the insensitivity of bandgap voltage reference to total dose radiation originates from the radiation resistance of the parasitic bipolar transistor which is the important part of bandgap voltage reference in CMOS mixed-signal ICs.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Analysis of the drought vulnerability characteristics in Northeast China based on the theory of information distribution and diffusion
2014, 63 (22): 229201. doi: 10.7498/aps.63.229201
The drought vulnerability characteristics from 1971 to 2012 in Northeast China are analysed and the risk in Northeast China is calculated based on the theory of information distribution and diffusion, combining with the standardized precipitation index (SPI) and the drought damage index (DDI) in Northeast China, with considering the meteorological factors and social factors. The probability density function (PDF) of DSI is estimated by using the method of information distribution. The vulnerability of the relationship between DSI and DDI is constructed by using the method of two-dimensional normal information diffusion. Then the average risk can be obtained by calculating the sum (discrete distribution) or integral (continuous distribution) of the product of the PDF of DSI and the vulnerability curve. The results show that the introduction of information distribution and diffusion method to analyze the problem of vulnerability for the situation of small sample could render the PDF of DSI smoother. What is more, the vulnerability of the relationship between DSI and DDI through the DSI to obtain the DDI has clearer physical meaning. Therefore the results could be realistic. More significantly, similar results can be obtained with different simple lengths, which means that the method is insensitive to the simple length and it can well overcome the instability of analysis of the small sample.