Vol. 63, No. 1 (2014)
Generalized Hojman conserved quantity deduced from generalized Lie symmetry of Appell equations for a variable mass mechanical system in relative motion
2014, 63 (1): 010201. doi: 10.7498/aps.63.010201
Generalized Lie symmetry and generalized Hojman conserved quantity of Appell equations for a variable mass holonomic system in relative motion are studied. The determining equation of generalized Lie symmetry of Appell equations for a variable mass holonomic system in relative motion under the infinitesimal transformations of groups is given. The expression of generalized Hojman conserved quantity deduced directly from generalized Lie symmetry for a variable mass holonomic system in relative motion is gained. Finally, the problem of dynamical system with three degree of freedom is studied by using the results of this paper.
2014, 63 (1): 010501. doi: 10.7498/aps.63.010501
We proposed a chaotic secure communication method, namely the partial series of the chaos system for parameter estimation and the other series for secure communications. Parameter estimation could be obtained from the partial series of chaos system with the chaotic ant swarm optimization algorithm, to understand all of the information of the chaos system. In the process of parameter estimation, the introduced parameter space and ant swarm space transformed into each other through space transformation function. Numerical simulation validated the feasibility of the chaos system partial series parameter estimation and the chaotic secure communication method.
2014, 63 (1): 010502. doi: 10.7498/aps.63.010502
Memristor, as a fundamental nonlinear circuit element, is very suitable for realizing new nonlinear circuits that are able to exhibit complex dynamical behaviors. A modified state-controlled cellular nonlinear network (SC-CNN) cell containing memristors, the output nonlinear function of which is implemented with the intrinsic nonlinearity of memristor, is presented in this paper. By using appropriate connection of four modified SC-CNN cells, a SC-CNN based memristive chaotic circuit is developed. In particular, an imitative memristive circuit is developed to experimentally investigate its dynamical behaviors. The resemblance of experimental results with those of numerical simulations shows that the memristive chaotic circuit can be efficiently implemented in terms of SC-CNN scheme.
2014, 63 (1): 010503. doi: 10.7498/aps.63.010503
The dynamical characteristics of super-harmonic resonance of van der Pol oscillator with fractional-order derivative are studied. First the approximate analytical solution are obtained by the averaging method, and the definitions of equivalent linear damping and equivalent linear stiffness for super-harmonic resonance are established. Effects of the fractional-order parameters on the dynamical characteristics of the system are also studied through the equivalent linear damping and equivalent linear stiffness. Moreover, the amplitude-frequency equation and the stability condition for the steady-state solution are analytically presented, and the definitions of equivalent nonlinear damping coefficient and nonlinear stability parameter are also established. Finally, the comparisons of the fractional-order and the traditional integer-order van der Pol oscillators are carried out by numerical simulation. The effects of the parameters in fractional-order derivative on the steady-state amplitude, the amplitude-frequency curves, and the system stability are also analyzed.
2014, 63 (1): 010504. doi: 10.7498/aps.63.010504
A system, which alternates between autonomous and non-autonomous circuit systems observing the time periodic switched rules, is investigated in order to explore its complicated dynamical behaviors. By analyzing the equilibrium point, limiting cycles, and the stability of the autonomous subsystems, as well as deriving the Lyapunov exponents of the switching systems in theory and numerical calculation, we have studied the variation of periodic oscillation behaviors of the compound systems with different stable solutions to the two subsystems. By using the bifurcation diagram of the switched systems and their corresponding largest Lyapunov exponent diagrams, we can observe the complex dynamical behaviors and oscillating mechanism of alternating periodic oscillations, quasi-periodic oscillations and chaotic oscillations with different parameters in the switched systems. Furthermore, dynamical evolutions of the switching system to chaos by period-doubling bifurcations, saddle-node bifurcations and torus bifurcations are observed.
2014, 63 (1): 010505. doi: 10.7498/aps.63.010505
Dual buck full-bridge inverter has the following advantages: it has no shoot-through problem, but receives high-utilization of DC input voltage, high efficiency and optimum selection of the freewheeling diodes, hence it attracts more and more attention in high power applications. In this paper, the bifurcation and chaos in the dual buck full-bridge inverter is studied. The two-dimensional discrete iterated mapping model under proportional control is established and stroboscopic maps in different periods of time are obtained. Effects of the proportional coefficient k on system performance are analyzed by using bifurcation diagram and folded diagram. A simulation model of dual buck full-bridge inverter is established based on Matlab/Simulink and the time domain waveforms and phase-space portraits for different proportional coefficient k are obtained. Besides, the effects of the bifurcation and chaos on the spectrum of the system are analyzed. Finally, the nonlinear behavior in the inverter caused by the variation of other circuit parameters such as input voltage E, inductance L, and the switching period of carrier wave T is discussed through bifurcation diagrams. Results show that the correct choice of circuit parameters of dual buck full-bridge inverter is very important for its stable operation.
Vibrational resonance in a Duffing system with fractional-order external and intrinsic dampings driven by the two-frequency signals
2014, 63 (1): 010506. doi: 10.7498/aps.63.010506
The phenomenon of vibrational resonance (VR) in a Duffing system with both fractional-order external damping and fractional-order intrinsic damping driven by the two-frequency periodic signals is investigated. It is observed that the resonance amplitude Q can be optimized by an appropriate choice of the amplitude of the high-frequency signal. The obtained relationship between VR and the fractional-orders shows that both fractional-order external damping and fractional-order intrinsic damping can induce changes of the shapes of the effective potential function and then lead to more abundant resonance behaviors than in the traditional dynamic systems.
Chaotic synchronization control of Chua’s circuit by injected feedback based on the symbolic function
2014, 63 (1): 010507. doi: 10.7498/aps.63.010507
Due to the inherent property of the Chua’s circuit, it is difficult to obtain the three state variables directly from the circuit, and the general control method is hard to apply to the circuit. For these chaotic circuits which have energy storage elements, a simple circuit is designed to get the state variables. In addition, an injected feedback method to realize the synchronization is proposed, which can control the circuits with unknown differential variables of the state variables. Two chaotic systems which have different motions are investigated using the symbolic function. All results obtained from the circuits are verified by the effectiveness and feasibility of the above method.
2014, 63 (1): 010508. doi: 10.7498/aps.63.010508
In this paper, right-turning vehicle and straight-going bicycle are regarded as the objects for studying the mixed traffic flow characteristics at the intersection. Based on vehicle-bicycle interference characteristics, and the coupling between the vehicle cellular automaton model and the bicycle cellular automaton model, a kind of cellular automaton model (NS-BCA) is presented to analyze the mixed traffic flow of intersection, in which the delay rules of bicycle through vehicle, the gap rules of vehicle through bicycle, and the disposal rules of the occupied conflict zone are taken into consideration. The mixed traffic flow of the right-turning vehicle and the straight-going bicycle is simulated, and the vehicle-non vehicle interference mechanism in mixed traffic flow at the intersection is investigated according to the relationship between traffic volume and arriving rate, transformation of traffic flow phases, the relationship among traffic flow phase, arriving rate and state of mixed traffic flow.
2014, 63 (1): 010701. doi: 10.7498/aps.63.010701
The quality of spectral imaging data will be degraded by the vibrations of satellite platform. We study the methods to correct degraded spectral imaging data in this paper. First, the vibration patterns of satellites and the degradation mechanism of the motion imaging of dispersion imaging spectrometer are introduced. Considering the problems of traditional two-dimensional deconvolution algorithms, and the speciality of push-sweeping mechanism, a sectioned correction method is presented, in which are combined image dividing, dimension rising, and gradual splicing. And the motion deblurring algorithm based on natural image statistics is applied in the correction of degraded spectral imaging data. We implement degradation and correction experiments for various data. Results show that the qualities of spectral imaging data are significantly improved for both the spatials and spectrals. Our method is better than the traditional deconvolution algorithms.
Improvement of the output power of optical pumping THz lasers based on the theory of vibrational relaxation
2014, 63 (1): 010702. doi: 10.7498/aps.63.010702
Based on the semiclassical density matrix theory and vibrational relaxation theory, the present paper studies the influences on optical pumping THz lasers output power due to adding an appropriate proportion of buffer gas and appropriately reducing the waveguide core diameter. Results prove that adding appropriate proportion of buffer gas or appropriately reducing the waveguide core diameter can increase the output of light intensity of THz laser. Optimizing the two parameters at the same time can further improve the efficiency of pumping laser energy into THz laser energy, extend the effective activation area of the working cavity, put off the appearance of the pumping saturation effect, and increase the output power of the THz lasers. This research may have a guiding significance for the THz optical pumping laser in improving energy conversion efficiency, and increasing the output power so as to bring about the miniaturization of THz optical pumping laser.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
Theory and simulations of high frequency characteristics for a staggered double-grating slow-wave structure with step-shaped grooves
2014, 63 (1): 014101. doi: 10.7498/aps.63.014101
Based on a staggered double-grating slow wave structure with step-shaped grooves, the expressions of the electromagnetic field in it have been obtained and the formulae of the dispersion equation and coupling impedance have been solved by means of field matching method. As an example, a staggered double-grating slow wave structure for W band TWT application was used to calculate the characteristics of dispersion and coupling impedance using the formulae and CST-MWS code, and analyze the effect of the step dimension variation on the high frequency characteristics. Results show that the theoretical calculations are in good agreement with the CST-MWS code simulations, and the slow wave structure can improve the dispersion characteristics, enhance interaction bandwidth, while keeping a proper coupling impedance and mechanical intensity, which can to some extent compensate for the deficiency in the staggered double-grating slow wave structure with the rectangular-shaped grooves.
A novel frequency selective surface with stable performance and its application in microstrip antenna
2014, 63 (1): 014102. doi: 10.7498/aps.63.014102
A novel frequency selective surface(FSS) with stable performance is designed and applied to microstrip antenna. The FSS cell is composed of two metallic layers separated by a dielectric spacer. The top and bottom layers connected with metallic cylinders form the fractal dendritic model. By optimizing the geometric parameters of the model, an ultra-thin FSS spatial filter is obtained, whose thickness is only 0.017λ, with wideband, polarization insensitive, wide-incident angle, and miniaturization properties. When applying the radome to microstrip antenna, the bandwidth of the antenna is improved to 40%, the gain is enhanced in the whole operating frequency band, especially at 9.6 GHz, the gain is increased by 6.7 dB; at the same time, the in-band radar cross section(RCS) is reduced significantly, and the largest reduction exceeds 12.7 dB. Experimental results are in good agreement with the simulated ones, which verifies that the novel FSS spatial filter can be used to increase the gain of broadband antenna, enhance the directivity, improve the bandwidth, and reduce the in-band RCS; to sum up, it can be applied to broadband antennas to improve their radiation as well as scattering performance at one time.
2014, 63 (1): 014103. doi: 10.7498/aps.63.014103
This paper presents a novel dual-band magnetic resonance with multi-defect hexagonal structure. Staggered defects double hexagonal metal rings was put on a microwave substrate. So the coupling capacity of the two rings was damaged. Then the dual-band magnetic resonance has been obtained. The traditional structure of dual-band is very complicated. But the new structure is simple and the size is also very easy to control. Finally, we combined the novel structure with metal wires to make dual-band left-handed metamaterials. From the result of the HFSS simulation, this left-handed metamaterials has obtained dual-band at 6.5–7.0 GHz and 8.8–9.3 GHz. The dual-band left-handed structure has a great influence on the microwave filter, antenna, and other microwave devices.
Influence of inner windows on near-field shielding effectiveness of rectangular cavity with apertures
2014, 63 (1): 014104. doi: 10.7498/aps.63.014104
Influence of the inner windows on the shielding effectiveness of a cavity with apertures is investigated by using the adjusted transmission line method (TLM). Electric shielding effectiveness is calculated as a function of the opening width of metal windows. It is shown that the electric near-field shielding effectiveness of a cavity with inner windows and apertures is far inferior to that of far-field. Results also show that the near-filed shielding effectiveness increases with the decrease of the opening width of the inner window, and the capacitive windows may lower the resonance frequency while the inductive windows may enhance. Results of the adjusted TLM are in good agreement with the CST simulation results.
2014, 63 (1): 014202. doi: 10.7498/aps.63.014202
Enhanced Raman scattering can be obtained by the initially prepared atomic spin excitation, or by injecting a seeded light field which is correlated with the initially prepared atomic spin excitation. This paper theoretically calculated the quantum fluctuations of the quadrature components of the two-mode photon-atom quantum interface and found that the enhanced Raman scattering based on coherence can improve the initial photon-atom squeezing slightly in a certain scope, and correlation-enhanced Raman scattering can produce strong two-mode squeezing of photon-atom. Such a strong two-mode squeezed state at the photon-atom interface has very important applications in precision measurement research based on the light field and atomic system.
Dynamic characteristics of 1550 nm vertical-cavity surface-emitting laser subject to polarization-rotated optical feedback：the short cavity regime
2014, 63 (1): 014203. doi: 10.7498/aps.63.014203
Based on the extended spin-flip model (SFM), we investigate theoretically the dynamic characteristics of 1550nm vertical-cavity surface-emitting laser subject to polarization-rotated optical feedback: the short cavity regime. Results show that increasing the feedback strength will result in multiple polarization switching (PS) phenomena, and there will appear rich dynamics under the condition of medium feedback intensity, such as single period, period-doubling, quasi-periodic and chaotic states. At the same time, the increase of injection current will result in the reduction of working area of Y direction polarization mode. As the feedback delay time increases, under the condition of weak optical feedback polarization mode, the hopping phenomenon will take place at a particular frequency; the frequency of mode hopping will increase with the increase of moderate feedback strength, and the laser shows a variety of new dynamic characteristics, such as single period, pulse envelope, quasi-periodic and chaotic states, by taking a beat frequency signal. These dynamic characteristics are very sensitive to the phase change so the beat frequency effect between external cavity modes plays a key role. In addition, the hopping phenomenon between various dynamic states can also be found along with the mode hopping.
Numerical analysis of in-phase supermode selection of seven-core photonic crystal fiber by gain distribution
2014, 63 (1): 014204. doi: 10.7498/aps.63.014204
A model based on propagation-rate equations by considering the multi-transverse mode is constructed to describe the amplifier made from seven-core photonic crystal fibers. The output power of the seven eigenmodes in the amplifier infected by the dopant distribution, coupling coefficient and the pump power is discussed using the split-step Fourier algorithm. Mode selection can be realized by the design of dopant distribution and suitable coupling coefficient without the need of other devices. Mode selection may become more convenient due to this method. Moreover, high pump power can contribute to the improvement of the in-phase supermode. These results are helpful for improving the light quality of the amplifier.
2014, 63 (1): 014205. doi: 10.7498/aps.63.014205
A passively mode-locked Tm:YAG ceramic laser was demonstrated. Employing a 6 at.% Tm3+-doped sample with a length of 2.7 mm, we have realized stable mode-locked pulses with a repetition rate of 109 MHz by a semiconductor saturable absorber. A maximum output power of 116.5 mW was obtained at the central wavelength of 2007 nm. The corresponding pulse duration was determined to be 55 ps by a self-built noncollinear intensity auto-correlation setup. It is shown that Tm:YAG ceramics are excellent laser materials which can be used in ultrafast lasers with high-power and high-efficiency output.
2014, 63 (1): 014206. doi: 10.7498/aps.63.014206
Metal nanoparticle is of great importance for the study of surface plasmon resonance, and its functional assembly can show more excellent overall collaborative performance. We propose an efficient assembly of gold nanoparticles (GNP) through femtosecond laser fabrication without introducing additional modifier, which can not only retains the particle’s surface plasma resonance characteristic, but also realizes the assembling pattern of arbitrary subtle shape. We apply the assembly in microfluidic chip for surface-enhanced Raman scattering detection and achieve a very good enhancement. It provides a new approach for the preparation of plasma devices.
2014, 63 (1): 014207. doi: 10.7498/aps.63.014207
The expressions for the Rayleigh range zR, the turbulence distance zT and the far-field angle θ of Gaussian array beams propagating through non-Kolmogorov turbulence are derived. Influence of generalized exponent factor α of the atmospheric power spectrum and the type of beam combinations on the spreading of Gaussian array beams is studied. It is shown that for both coherent and incoherent combinations, the dependence of zR, zT and θ on α is not monotonic. When α=3.108, zR and zT reach their minima, and θ reaches its maximum. This means that the spreading is largest, and the spreading is enormously affected by turbulence when α=3.108. For the incoherent combination the spreading is larger than that for the coherent combination, but for the incoherent combination the spreading is less affected by turbulence than that for the coherent combination. It may be that, for the small free-space diffraction we have zT zR, i.e., the spreading is affected by turbulence within the Rayleigh range; for the large free-space diffraction we have zT > zR, i.e., the spreading is less affected by the turbulence within the Rayleigh range.
2014, 63 (1): 014208. doi: 10.7498/aps.63.014208
A sodium beacon with bright magnitude can be obtained during backscattering time, by utilizing a long pulse laser with parameters matched with a sending and receiving beacon system. This is helpful to get high SNR in detecting beacon, and to achieve a closed-loop correction at high frequency. Based on a 450 mm telescope and a high-energy long pulse laser, the detection experiment of sodium beacon was carried out, and the backscattering characteristics of sodium beacon were obtained. The intensity data of backscattering light with different launching energy and polarization were collected by CCD and PMT. As high as ～15,000 photons/m2·pulse-1 of backscattering light was detected, and the brightness is close to 4.1 magnitudes during backscattering time. The column density in experiment was derived from analyzing and calculating experimental data. No saturation phenomenon was observed during the whole experimental process. And the feasibility to avoid saturation is verified and a bright sodium beacon is obtained by utilizing a long pulse laser.
2014, 63 (1): 014209. doi: 10.7498/aps.63.014209
The Tm3+-doped fiber is the key of Tm3+-doped fiber laser, which has broad application prospects. In this paper, the silica-based Tm3+-doped fiber preform is manufactured by gas-solution co-doping method in MCVD(modified chemical vapour deposition) and the Tm3+-doped double-cladding fiber is also achieved, the core and cladding diameters of which are 10 μm and 125 μm respectively. We prepare the Tm3+ all-fiber laser using the Tm3+-doped fiber and when the laser is pumped by a 793 nm laser diode, the center wavelength is 2002 nm, maximum output is 31.7 W, and the slope efficiency of the fiber is 59.32%.
Design and performance of mid-IR dispersion in photonic crystal fiber prepared from a flattened chalcogenide glass
2014, 63 (1): 014210. doi: 10.7498/aps.63.014210
In this paper, using the self-made Ge20Sb15Se65 chalcogenide glass as matrix material, we design an infrared octagon dispersion flattened photonic crystal fiber, and the mid-IR dispersion and transmission characteristics are numerically studied using the multipole method. Results show that when we control the duty ratio (d/Λ) in 0.323–0.367, the dispersion and transmission properties in the 3–5 μm range are adjustable. When we set the hole spacing Λ=3.4 μm, hole diameter d=1.1 μm, in the 4.1–4.9 μm band, the fiber dispersion fluctuates between-0.8 ps·nm-1·km-1 and 0.8 ps·nm-1·km-1, and shows single-mode transmission, low loss (LossAeff2) characteristics, thus it is suitable for nonlinear applications in mid-IR band.
A new pulse-coupled device composed of optical waveguide is presented. Its operating mechanism is discussed based on experimental results. Particle nature of light in optical stopping and wave nature of light in mode coupling of branch waveguide are combined in the device operating, then the optical pulse-coupled dynamics between input electrical pulses and synchronous output electrical pulses is realized.
2014, 63 (1): 014301. doi: 10.7498/aps.63.014301
Rayleigh waves propagating in an elastic surface are commonly used for the near surface flaw detection and material characterization. However, unlike the bulk wave case, there are seldom three-dimensional models to be provided for the Rayleigh waves. In the past decade, multi-Gaussian beam models have been gradually developed and perfectly applied to solve many complicated propagation problems of bulk waves. However, up to date they have not been extended to the simulation of the Rayleigh waves. By combining the Rayleigh wave Green function and the multi-Gaussian beam model, a three-dimensional Rayleigh wave model is presented to calculate the beam fields radiated from a rectangular transducer mounted on the Lucite wedge. Furthermore, some simulation results of the provided method are compared to those of a more exacted point source model. It is shown that the multi-Gaussian surface wave model has good capability in both computational accuracy and efficiency.
2014, 63 (1): 014401. doi: 10.7498/aps.63.014401
On the basis of transformation thermodynamics, a thermal conductivity expression for cylindrical thermal cloak with arbitrary cross section is derived. Based on the expression, we design a thermal cloak with a non conformal section profile. Results of full wave simulation show that the cloak possesses heat protection function, since it is capable of guiding heat fluxes to travel around its inner domain, leaving the inner region untouched; meanwhile, the heat fluxes return to their original pathways, resulting in a perfect thermal invisible effect. Arbitrary shaped cylindrical thermal cloak with conformal or non-conformal cross section can be designed based on the derived thermal conductivity expression, and all of them have perfect thermal protection and invisibility functions. It is indicated that the derived conductivity expression is applicable to designing cylindrical thermal cloaks with an arbitrary cross section. The generality of this method has been confirmed, and it may have potential applications in the designing of thermal protection devices for computer chips and satellite, etc.
2014, 63 (1): 014402. doi: 10.7498/aps.63.014402
In this paper, molecular dynamics simulation was performed to predict the thermal conductivities of ordered mesoporous α-Al2O3. A kind of porous structure was proposed to guarantee the electrical neutrality. Based on the Matsui potential, the nonequilibrium molecular dynamics method adapted by Mller-Plathe was used to calculate the lattice thermal conductivity of mesoporous alumina along the axial direction of pore at various temperatures. Effects of pore size and porosity were also investigated. It turns out that with increasing temperature the thermal conductivity of mesoporous α-Al2O3 rises first until the temperature reaches 200–400 K, then decreases almost linearly. In addition, as the pore size gets larger, the specific surface area decreases, and the thermal conductivity increases because the boundary scattering has been weakened. On the other hand, the number of phonons in the pore wall decreases greatly with increasing porosity, thus dramatically reducing the thermal conductivity of the mesoporous material. Range analysis shows that the porosity is more influential than the pore size on the thermal conductivity of mesoporous materials.
The rising motion of grains in a vibrating pipe is studied experimentally and by DEM (discrete element method) simulations. A pipe is partially inserted into a static granular layer. With the pipe initially filled with a certain height of grains, when the pipe is set into vertical vibrations, grains in the pipe will rise along the pipe and the motion will be finally stabilized at a certain height. The rising height and the speed of motion are strongly dependent on the vibration strength. By using a high speed camera and through DEM simulation, the trajectory of individual grains and the force acting on the grains in each vibration cycle can be obtained. A force-based mechanism for this rising motion is proposed. During vibrations of the pipe, the grains in the pipe are compacted and loosened alternately, and the force of the pipe and the grains varies periodically, thus leading to the rising motion of grains. A new possible way of continuously transporting grains is presented in this work.
2014, 63 (1): 014701. doi: 10.7498/aps.63.014701
A novel dual-mode large-mode-area micro-structured fiber is proposed. The characteristics of mode field distribution, effective area of fundamental mode, and bending loss based on FEM (finite element method) are analyzed. And the effects of all structured parameters on the confinement loss and effective area are discussed. Results show that this structure makes the first HOM (LP11) and the second mode(EH11) cut off, and it achieves dual-mode transmission in the fiber by adjusting the structural parameters. The effective area of a fundamental mode is approximately 700 μm2. The dual-mode large-mode-area micro-structured fiber can be used in large-capacity fiber transmission.
2014, 63 (1): 014702. doi: 10.7498/aps.63.014702
The mechanism of blood embolism formation always attracts the attention of researchers. Through calculating rigid particle movement in a bifurcated pipe, the blood flow as well as blood embolism in a bifurcated pipe are simulated preliminarily, and the flow speed and the probability to form thrombus are investigated. We can draw a conclusion that the higher the hematocrit is, the easier the blood is to form embolism, meanwhile, the bigger the pressure difference, the harder the blood is to form embolism. We also find that the embolism tends to occur at the entrance of a bifurcated pipe and bifurcation forming place. Beyond the bifurcation place, the hematocrit of the blood in a big tube is larger than that in a small tube.
2014, 63 (1): 014703. doi: 10.7498/aps.63.014703
Dynamical behaviors of granular piles are systemically investigated by an experimental equipment and imaging and direct particle tracking during quasi-static avalanches and slow flow process. It is found that part of beads slides obliquely downward, meanwhile the other part of beads is almost fixed; layer-structure can be clearly observed, and it include flow-layers and static-layer. The flow-layers lie almost parallel to each other and the angles between the flow-layers and horizonal plane are approximately in the range 4050. Moreover, the slippage of the flow-layers from the static-layer begins to gradually increase linearly. In addition, the positions of initial flow-layer that has different volumes of granular piles tend to be fixed.
2014, 63 (1): 014201. doi: 10.7498/aps.63.014201
In order to meet the further demand of the next-generation electronic devices in the transplantable, lightweight and portable performances, flexible and stretchable inorganic electronics attract much more attention in both industry and academia in recent years. Compared to organic electronics, stretchable and flexible inorganic electronics are fabricated with the integrated structures of inorganic components on complaint substrates, which own the stretchability and flexibility via mechanical design. Thus stretchable and flexible inorganic electronics have the high electron mobility and excellent conformability to non-planar environment subjected to large deformation. This paper reviews the recent progress on principle, design based on mechanics, integration based on transfer printing and the reliability analysis of stretchable and flexible inorganic electronics. Finally, the prospective is also described for future application in bioengineering and medicine.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Effect of H3BO3 on structure and long persistence properties of Y1.98O3：Eu, Dy red long-afterglow phosphor
2014, 63 (1): 016101. doi: 10.7498/aps.63.016101
The phosphor Y1.98O3: Eu0.013+, Dy0.013+ was prepared by high temperature solid reaction method. X-ray powder diffraction (XRD), scanning electronic microscope (SEM), photoluminescence spectra (PL), and single-photon counter system were used to investigate the structure, morphology, luminescent properties, and decay characteristics of the phosphor Y1.98O3: Eu0.013+, Dy0.013+ which was synthesized with different contents of H3BO3. Results show that the structure of the H3BO3-contained phosphors can keep Y2O3 matrix when the content of H3BO3 is below 8%(mol), and the particles size of phosphors increases during the addition of H3BO3. The luminescence of phosphors come from the transition of 5D0→7FJ of Eu3+, the main emission peaks at 612 nm and the intensity is increased linearly with the increase of H3BO3 content. Phosphors show better afterglow characteristics during the increase of H3BO3.The measurement of thermoluminescence(TL) reveals that the addition of H3BO3 increases the trap depth and trap concentration in the host, hence the afterglow characteristics become better.
2014, 63 (1): 016102. doi: 10.7498/aps.63.016102
This paper mainly investigates the total dose irradiation effects on 0.8 μm PD SOI PMOS devices which are exposed to 60Co γ-rays at a dose rate of 50 rad(Si)/s. The channel length dependence of SOI PMOS devices at total dose irradiation is investigated. The result shows that the threshold voltage shift is only a little larger for shorter channel devices at the same total dose. However, the degradation of maximum transconductance for shorter channel devices is more significant. We found that the oxide-trapped charge is the main factor impacting the threshold drift. We may conclude that a short channel device can produce more interface trapped charges by using the subthreshold separation technology.
2014, 63 (1): 016201. doi: 10.7498/aps.63.016201
Metal silver in the nanoscale range is widely used in the fields, such as microelectronics, optoelectronics, catalysis etc., due to its unique electrical and thermal conductivity, especially in nano-electrodes and nano-devices. Tensile deformation behavior of polycrystalline silver nanowires, in various grain size, is simulated using molecular dynamics method. Effect of grain size on elastic modulus, yield strength, and plastic deformation mechanism of polycrystalline silver nanowire is analyzed in detail. Results indicate that polycrystalline silver nanowires show a softening for grain sizes smaller than 13.49 nm, a reverse Hall-Petch relationship. At this stage, the plastic deformation is dominated by ‘sliding’ at the grain boundaries and rotating of grains; moreover, a five-fold twin is formed at the later stage of deformation. While the plastic deformation mechanism changes to dislocation sliding, when the grain size is larger than 13.49 nm, and a large number of twins are formed at the later stage of deformation.
Variation of effective elastic moduli of a solid with transverse isotropy due to aligned inhomogeneities
2014, 63 (1): 016202. doi: 10.7498/aps.63.016202
In this paper the effective or overall moduli of a solid containing aligned ellipsoidal inhomogeneties, are derived by making the scattered displacement field equal to that scattered by a spherical–shaped effective medium in the same matrix. It is shown that the obtained formulae of effective elastic moduli are of second-order accuracy at least. The effective moduli decrease monotonically with porosity, thus excluding the unphysical behavior in Hudson’s model in which there is an increase of moduli with porosity when the porosity goes beyond a certain threshold. By integration of inhomegeneity orientation angle, the effective moduli can be obtained for a solid with randomly orientated inhomogeneities, which are the same as those in the Kuster-Toksöz model. Numerical calculations show that a rock with fluid-saturated inhomegeneities has a higher longitudinal wave modulus in the direction of TI symmetric axis than the modulus for a rock with empty inhomegeneities.
2014, 63 (1): 016801. doi: 10.7498/aps.63.016801
The structural and electronic properties of hydrogenated bilayer boron nitride (BN) were studied by employing the first-principles calculations. Six major polymorphic structures of hydrogenated bilayer BN are considered. Calculated results show that, among them, the AB-BN and AA-BN structures are the most stable ones. The analysis on the energy bands and electronic properties of the two most stable structures are then performed. Structures of AB-BN and AA-BN are both semiconducting with direct band gaps, and the gaps are 1.47 eV and 1.32 eV, respectively, calculated using the GGA method. Since GGA usually severely underestimates the band gap, the hybrid density functional calculations are then conducted, which suggests that the band gaps are 2.52 eV and 2.34 eV for AB-BN and AA-BN structures, respectively. In the most stable structures of AB-BN and AA-BN, B-N bonds show mainly covalent characters, while B-H and N-H bonds exhibit clear ionic characteristics. Moreover, the band gap of hydrogenated bilayer BN atomic sheet can be continuously modulated by biaxial strains. When the lattice constant is compressed by around 8%, the electronic character of the atomic sheet changes from semiconducting into metallic.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Based on the structure of strained Si/SiGe NMOSFET, a unified charge model is presented, in which charge conservation is guaranteed by using the charge as the state variable. The model describes device characteristics from subthreshold to strong inversion as well as from the linear to the saturation operating regions using a smoothing function, and guarantees the continuities of charges and capacitances. Furthermore, capacitance models have been presented using Verilog-A, a language to describe analog behavior. Comparisons between the model and measured data show that the charge model can describe the device characteristics well. The proposed model is useful for the design and simulation of integrated circuits made of strained Si.
2014, 63 (1): 017102. doi: 10.7498/aps.63.017102
Electron paramagnetic resonance (EPR) spectra for Fe3+ in sapphire were measured and studied by Scholz and Buzaré in 2002. Their analysis shows that the ground-state splitting for Fe3+ in sapphire may be associated with two distortion angles Δθ and Δφ. By diagonalizing 252×252 complete energy matrix for the d5 configuration ion in C3 symmetry ligand-field, in this paper a systematic investigation about the ground-state splitting for Fe3+ in sapphire is given. Our results indicate that the 6A1 ground-state splitting are sensitively dependent on the local lattice distortion along the two directions, respectively, which supports the Scholz and Buzaré’s opinion. Meanwhile, by simulating the optical spectra and the EPR spectra for Fe3+ in sapphire, the local lattice distortion parameter Δθi can be obtained.
2014, 63 (1): 017301. doi: 10.7498/aps.63.017301
A nanoscale metal ring resonator with a notch is proposed, in which the propagating characteristics of surface plasmons was studied with the help of finite-difference time-domain method. Influences of the length and position of the notch and the radius of the ring on the transmission properties of the ring resonator have been studied in detail. We found that, compared with the ring resonator without notch, the intrinsic mode of the ring resonator will split when the length and position of the notch satisfy some special conditions. In addition, the split modes will shift toward longer wavelengths as the radius of the ring increases, while the variation of the radius has no influence on the splitting behavior of the intrinsic modes.
2014, 63 (1): 017302. doi: 10.7498/aps.63.017302
Supposing that the quantum well of a superlattice is a periodic potential well of an arbitrary shape, the motion problem of electrons in the superlattice can be reduced into the motion in a periodic field. From the Schrödinger equation and its general solution, the dispersion equation of the system can be derived using Bloch theory and the transfer matrix method in the framework of quantum mechanics; and the electronic transitions of the multi-quantum well for the superlattice can be discussed in parabolic approximation. Results show that the radiation energy is located at the infrared, far infrared or terahertz band.
2014, 63 (1): 017303. doi: 10.7498/aps.63.017303
By using the nonequilibrium Green’s function technique, the charge and spin transport properties through an A-B interferometer that has a parallel-coupled double-quantum-dot molecule embedded in each arm, (named as parallel-coupled double-quantum-dot molecule A-B interferometer) are investigated. In the absence of magnetic flux, as compared with the A-B interferometer with two quantum dots embedded in each arm, electron tunnelling becomes far easier for parallel-coupled double-quantum-dot molecule A-B interferometer. When the magnetic field is introduced, one can observe in the conductance spectrum one Fano resonance and one anti-resonance, both of which will die away simultaneously when the magnetic flux takes a proper value. Besides, spin transport can be manipulated by tuning the bias voltage between the two leads, magnetic flux, and Rashba spin orbit interaction.
2014, 63 (1): 017801. doi: 10.7498/aps.63.017801
Periodic structure is the basic physical model in optical film design. Universal conditions of the reflecting center wavelength are given. With the refractive index dispersion of the layers, the reflecting center wavelength and the band characteristic of equal-thickness and unequal-thickness periodic structures are studied. According to experimental results, in both the equal-thickness and unequal-thickness periodic structures with the refractive index dispersion of the coating layers, the reflecting center wavelength moves towards the longer wavelengths, and the reflective series as well as the relative wave number will depart from linear relation. For the same optical thickness of the film with unequal-thickness periodic structure, when the optical thickness of the high refractive index layer is bigger than that of the low refractive index layer, the departure from linear relation between the reflective series and the relative wave number is higher. For the low reflective series, the bandwidth of unequal-thickness periodic structure is smaller than that of equal-thickness periodic structure. The influence of the layer dispersion on the bandwidth is found to be weak.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Fabrication and optical property characterization of quantum-dot-array diffraction grating with single order diffraction based on focused ion beam
2014, 63 (1): 018101. doi: 10.7498/aps.63.018101
Quantum-dot-array diffraction grating(QDADG), with an area of 200 μm×200 μm, a line density of 500 line/mm, an aperture size of 800 nm and a gold absorber of 500 nm thick, is successfully fabricated by focused ion beams. The diffraction properties and relative diffraction efficiencies of QDADG are measured at different transfer distance for 442 nm laser. It is shown that the high-order diffraction is removed from the spectra with only the ±1 and 0 order diffraction lines reserved. Moreover, in accordance with the calculated values obtained using the grating equation, variations of space between the 1st order and the 0th order increase gradually with the increase of transfer distance.
2014, 63 (1): 018102. doi: 10.7498/aps.63.018102
The template for naoimprint lithography having a nano-sized structure was usually fabricated by traditional lithography such as extreme ultraviolet (EUV) lithography, focused ion beam (FIB) lithography, electron beam (EB) lithography. However, these approaches are always time-consuming and inefficiency which limits the potential application in nanoimprint lithography. To find a simple and low-cost method to fabricate the mold for nanoimprint lithography, and to improve the application in nanoimprint lithography have become the research focus. Instead of being formed by traditional lithography, the anodic aluminum oxide (AAO), with highly regular structures and high pore density, is the mold to achieve periodic structures for nanoimprint lithography. In this work, we successfully transfer a 2D nanoporous array structure to the Si surface via the nanoimprint lithography and AAO. The pore diameter and the interpore distance of the porous silicon (PS) are well consistent with that of AAO template. The interval, the diameter, and the height of the hexagonal array structure are 350–560 nm, 170–480 nm, and 200 nm, respectively. We have tested the Raman spectrum under the excitation by lasers of wavelength 514 nm. According to the results, two samples each exhibits a peak at 520 cm-1 and no frequency shift is observed with the Si characteristic Raman peak, indicating that the PS was not extensively damaged by the ICP etching process. Raman intensity in the structured Si is almost enhanced by a factor of 12 as compared with the case on polished Si, which will greatly benefit the application of Si-based optical devices. Thus, we have realized the replica of the PS template and obtained a nanopillar soft template via the hot embossing lithography.
2014, 63 (1): 018201. doi: 10.7498/aps.63.018201
Helical formation is fairly ubiquitous in nature. Under certain circumstances, entropy may induce polymer chains to form helical structures. In this article, molecular dynamics is applied to illustrate the conformation behaviors of a polymer bottle brush adsorbed onto the surface of a cylinder with infinite length. The helical conformation of a polymer bottle brush is closely related to the number of branch chains as well as the adsorption energy between the polymer bottle brush and the cylinder. Once the adsorption energy is weak, the polymer bottle brush with enough branch chains may form an entropy-induced complete helical structure. Our results may give a deeper insight into polymer helical structural studies.
Nuclear magnetic resonance test and analysis on water phase of the ultra-soft soil under different load level and rate
2014, 63 (1): 018202. doi: 10.7498/aps.63.018202
In large-scale constructions, more and more ultra-soft soil foundation treatments are faced. The treatment purpose is to discharge as much as possible the pore water in the soft soil and make it consolidated, so as to improve its physical and mechanical performances. The static and dynamic drainage consolidation method is tried to use high-energy impact and convert part of the combined water in the ultra-soft soil into free water, and thus achieve more water discharge and effective consolidation. However, it is unclear what level and rate of the impact load could cause the water phase to change. For this, based on the tests with different load level and rate for the ultra-soft soil under simulated engineering condition, water phase test of the soil by nuclear magnetic resonance (NMR) was carried out, in order to explore the rules or conditions under which the combined water in this ultra-soft soil could be converted into free water at typical load level and rate. Our main conclusion is that: (1) corresponding to the engineering usual load, true tri-axial test at low load rate and level (1.6 MPa/s, the 100 kPa), the combined water in the ultra-soft soil cannot be converted into free water; (2) corresponding to the condition of high-speed impact load (a3787 kPa load level per blow and a rate of 631.2 MPa/s) used in the static and dynamic drainage consolidation method, the combined water in the ultra-soft soil could be converted into free water; and the greater the total impact energy, the easier the conversion into free water; (3) the effect of constraint sample confining stiffness on the conversion of combined water to free water can be ignored.
2014, 63 (1): 018301. doi: 10.7498/aps.63.018301
During the scanning of magnetic resonance imaging (MRI) system, the main acoustic noise source comes from the gradient coils. The gradient coils are turned on and off repeatedly, thus producing noise within the coil. With increasing magnetic field strength, the noise also increases. The primary method to reduce the noise is to decrease the distribution of the Lorentz forces. Target field (TF) method is very important for designing gradient coils which have been used in MRI and other applications. Many works based on the Turner’s traditional TF method have been proposed. In this paper, a target field method combined with vibration control has been presented to analyze the deflection of a cylindrical z-gradient coil because of the Lorentz forces. Simulation results via Matlab show that the maximum vibration amplitude can be reduced effectively by the new design method proposed in this paper.
2014, 63 (1): 018401. doi: 10.7498/aps.63.018401
Electromagnetic properties of a two-dimensional metallic photonic crystal in a transmission line is analyzed, and a compact TEM-TE11 high-power microwave mode converter which takes this type of sturcture for phase-shiftting is presented. An L band TEM-TE11 mode converter is optimized using the commercial software cst microwave studio. Its conversion efficiency is 98% at the center frequency of 1.58 GHz. Over the frequency range of 1.56–1.625 GHz, the conversion efficiency exceeds 90%, with a corresponding bandwidth of 4.1%. This mode converter has a gagawatt level power handling capability, thus it is suitable for narrow band high-power microwave application. Using magnetically insulated transmission line oscillator as a high-power microwave source, particle-in-cell simulation is carried out to test the performance of the mode converter. It is found that the proposed mode converter works well with this narrow band high power microwave device.
2014, 63 (1): 018402. doi: 10.7498/aps.63.018402
This paper described a high-order mode oscillation phenomenon, in the simulation of four-cavity intense relativistic klystron amplifier(IRKA). And we have analyzed the cause of this kind of oscillation, and explored the suppression methods for the whole tube. Two-dimensional and three-dimensional electromagnetism simulation software are used to study the influence of parameter’s changes (such as the oscillation frequency of cavities, the cavity Q value, the length of drift tube, and the characteristic impedance) on the high-order mode oscillation. The effectiveness of the high-order mode oscillation suppression methods is verified by simulation. Then, by optimizing the structure of IRKA, we have achieved an output microwave with a power of 2.13 GW, a gain of 60 dB and an efficiency of 26% in simulation, and the high-mode oscillation is avoided effectively. Finally, an output microwave with a power of 1.9 GW, a gain of 61 dB, and an efficiency of 24% is gained in the experiment.
Synergistic effects of total ionizing dose on the single event effect sensitivity of static random access memory
2014, 63 (1): 018501. doi: 10.7498/aps.63.018501
The single event effect sensitivity of static random access memory(SRAM) under different cumulative dose were carried out using 60Co source and heavy ions. The trend of sensitivity was obtained and the radiation damage mechanism was analyzed theoretically. This investigation shows that the variation in single event upset cross section with increasing accumulated dose appears to be consistent with the radiation-induced leakage current originating in the memory cells that affects the parameters such as low-level hold voltage and high-level fall time and induces con-imprint effect. Results obtained support the reliability analysis of the aerospace devices in space radiation environment.
Image reconstruction based on total variation minimization and alternating direction method for Compton scatter tomography
2014, 63 (1): 018701. doi: 10.7498/aps.63.018701
Compton scatter tomography measures samples electron densities utilizing the scattered photons. Compared to traditional transmission imaging models, Compton scatter tomography has the following characteristics, i.e. freedom in construction systems, greater sensitivity for low-density materials, and lower radiation dose. It has been applied in non-destructive testing, medical, and security inspections, and other fields. However, Compton scatter tomography reconstruction is a nonlinear inverse problem, common is ill-posed, and its solutions are very sensitive to noise and erroneous measurements. To tackle the problem, in this paper we propose a novel Compton scatter tomography reconstruction algorithm based on the total variation minimization and alternating direction method. The main idea of our method is to reformulate the reconstruction problems TV function as an optimization with constrains where the objective function is separable, and then minimize its augmented Lagrangian function by using alternating direction method to solve the sub-problems. Numerical experiments shows that the reconstruction quality and efficiency of the proposed method are improved compared to the adaptive-steepest-descent-projection onto convex sets method.
2014, 63 (1): 018702. doi: 10.7498/aps.63.018702
Each stage of cell growth is inseparable from the protein-protein interactions. It is of great significance in studying the function of the cell cycle, regulatory mechanism, and relationships among the proteins involved in the regulation in biological engineering and other fields. This paper studies the function, principle, and self-repairing mechanisms based on the intracellular protein p53 when DNA is damaged by ionizing radiation. We introduce more regulating factors for the proteins to build the networks based on the existing one and simulate a more comprehensive cell cycle progression. Then we analyze the anti-interference and self-repairing system of the regulatory networks using the complex network theory and cell cycle regulation. Numerical simulation results and experimental data show: (1) The protein network shows a stable condition when it suffers a small disturbance, while it shows a poor stability when facing deliberate attack; (2) whether the damaged DNA can be repaired depends on the dynamic behavior of p53 protein, i.e., p53 can transmit the damage signal to the cell cycle regulatory factors through the signal transduction pathway to induce the cell cycle arrest so as to complete the self-repairing processes in the case of the low-damage and the medium-damage. When DNA comes to face the high-damage and the excess-damage, the concentration of p53 shows a periodic oscillation behavior and it can induce apoptosis.
Fabrication of flexible Cu2ZnSnS4 (CZTS) solar cells by sulfurizing precursor films deposited via successive ionic layer absorption and reaction method
2014, 63 (1): 018801. doi: 10.7498/aps.63.018801
Cu2ZnSnS4 (CZTS) precursor thin films were prepared on a flexible Mo foil substrate via ZnS/Cu2SnSx stacked structure using successive ionic layer absorption and reaction (SILAR) method; the precursor thin films were annealed at 550 ℃ in sulfur atmosphere to obtain CZTS absorber layers. The chemical composition,crystallinity and surface morphology were characterized by EDS, XRD, Raman and SEM, respectively, indicating that the annealed films are highly crystallin and have compact morphology. In order to analyse the optical and electrical properties of the films, same processes were implemented on the soda glasses. Results reveal that the band gaps of the annealed films are 1.49 eV, the absorption coefficients are higher than 104 cm-1, and the carrier concentration as well as the electrical resistivity is suitable for fabrication of thin film solar cells. Flexible solar cells with a structure of Mo foil/CZTS/CdS/i-ZnO/ZnO: Al/Ag were fabricated by the above CZTS absorber layers, which demonstrated an efficiency of, 2.42%, the record efficiency of flexible CZTS solar cells as far as we know.
2014, 63 (1): 018802. doi: 10.7498/aps.63.018802
In order to achieve maximum power output, common PV modules will deliberately make a certain angle, but still some light will be reflected from the surface of the common PV modules into the air and waste. This paper presents a reflective plate structure having efficient black silicon solar modules, and multi-angle light-absorbing black silicon components to construct a reflective plate structure that can take advantage of the reflected light. The angle between the reflectors and black silicon component was simulated in this paper, which shows that when the assembly angle of PV module is 34°, the optimum angle of the reflective plate is 16.5°, in this case, the battery’s power generation is increased by about 39% under the same illumination conditions.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Noise suppression for magnetotelluric sounding data based on signal subspace enhancement and endpoint detection
2014, 63 (1): 019101. doi: 10.7498/aps.63.019101
To retain useful information of magnetotelluric low frequency band and improve the capacity of magnetotelluric deep detection in ore concentration area with complex noises, the combined signal subspace enhancement with endpoint detection is proposed based on morphology filtering to secondary signal-to-noise separation processing. Firstly, aimed at noise contour extracted by morphology filtering, we use signal subspace enhancement to separate signal subspace and noise subspace for pretreatment. Secondly, the signal subspace is combined with reconstructed signal and the noise subspace is set to zero. Finally, endpoint detection for post-processing is carried out in order to identify the start and end points of the waveform mutation. Simulated results show that Cagniard resistivity curve in the low frequency band has been improved obviously, and the apparent resistivity value is relatively stable. The proposed method is better to offset the loss of low frequency useful information in the process of the morphological filtering, and the results can even more truly reflect the inherent deep structural information of low frequency components for the measured point itself.
Automatic recognition of mid-altitude radial convergence and study on the relationship between the convergence and strong convective weather based on Doppler weather radar data
2014, 63 (1): 019201. doi: 10.7498/aps.63.019201
To identify the mid-altitude radial convergence of a strong convective weather automatically, we propose a method based on recognition of ‘positive-negative velocity region-pairs’ (region-pairs)in a single elevation angle of the Doppler radar radial velocity image. First of all, according to the principle of the radar detection, this paper explains the phenomenon that the convergence field formed by the airflow must produce a local maximum in positive or negative velocity region in the radial velocity image.The algorithms for recognizing these regions and matching the positive-negative pair are then devised.By searching a set of region-pairs with longitudinal extension, which are obtained from the multiple single elevation radial velocity images, we can judge whether there is a mid-altitude radial convergence in the convective storm, and estimate important parameters, such as the strength and extended thickness of the mid-altitude radial convergence.Finally, we determine the position of optimal section and present the cross-sectional view of the mid-altitude radial convergence. We have tested 384 samples with obvious mid-altitude radial convergence and 365 heavy rainfall samples without obvious mid-altitude radial convergence. Experimental results show that the recognition rate of obvious mid-altitude radial convergence is 100% and the false alarm rate is 0.Compared with the manual way by means of the cross-sectional view, the proposed method in this paper can more rapidly recognize the mid-altitude radial convergence (and reduce the recognition time from minutes to seconds). At the same time, it can present a great deal of quantitative information, including the strength, height, thickness, and position of the mid-altitude radial convergence.Furthermore, it shows the cross-sectional view automatically.We can obtain good results from the comparison between the mid-altitude radial convergence and strong convective weather by using the given parameters.We test and verify the strong correlation between the mid-altitude radial convergence and severe surface wind.Moreover, the height of the strongest mid-altitude radial convergence plays an important role in discrimination of strong hail and torrential rain. Also the strength of the mid-altitude radial convergence can be used to estimate the maximum dimensions of the hail.
2014, 63 (1): 019202. doi: 10.7498/aps.63.019202
Occurrence regularity of chaotic pulse trains (CPT) discharge event in negative cloud-to-ground (CG) lightning during six thunderstorms are analyzed in this paper. Results show that CPT is a common phenomenon throughout the negative CG lightning discharge process, 243 times of CPT discharge events occurs during 323 negative CG lightning, a proportion reaching 75.2%. CPT in negative CG can occur before the first return stroke, between the strokes, and after the last stroke. The proportion of 66.7% of the total subsequent strokes is preceded by CPT, and CPT occurs after 11.5% of the total last strokes. It is also found that there are four distributions prior to subsequent strokes: single CPT-c (CPT connecting with subsequent strokes), single CPT-i (CPT occurring in an interval between CPT and return strokes), CPT-c and CPT-i occur concurrently, and several CPT-is appear concurrently. Single CPT-c is the most common, 39.4% of subsequent strokes are preceded by single CPT-c, and several CPTs are easier to occur before the first and second subsequent strokes, which are respectively the corresponding strokes 9.4% and 7.7% of the total number. With the increase of the order of subsequent stroke, there is a decreasing trend for the occurrence of CPT, and in addition to the previous two subsequent strokes, the number of CPT-c is obviously greater than CPT-i before the others. In addition, CPT-i and CPT-a both occur to add on the negative CG K-change, and some also correspond to the process of J-change in the slow electric field wave.
2014, 63 (1): 019203. doi: 10.7498/aps.63.019203
On the basis of evolutionary algorithm, a novel method for parameter estimation of nonlinear dynamic equations is given in the present paper. Numerical tests indicate that the unknown parameters all can be estimated quickly and accurately whether the partial parameters are unknown or all parameters are unknown in the classic Lorenz equation. However, it is found that the convergence rate of the new algorithm is relatively slow when multiple unknown parameters are estimated simultaneously. To solve this problem, a corresponding improvement of measure is proposed, namely, a constraint mechanism is taken during the variation operation of evolutionary algorithm. The improvement is mainly based on the characteristic that the longer the running time of the evolutionary algorithm, the smaller the range of variation of the estimated parameters. Results indicate that the searching speed of the algorithm is greatly improved by using the improved estimation parameter project.
2014, 63 (1): 019401. doi: 10.7498/aps.63.019401
Dense plasma cloud can be produced by small debris impact on spacecraft surface, with the diffusion of plasma which can induce the electrostatic discharge (ESD) and electromagnetic interference (EMI). By this way, spacecraft will experience electrical anomalies. In this paper, a plasma drag particle accelerator is used to study the characteristics of impact-generated plasma due to crash of small debris with mass 10-5 g. The relation between plasma charge and debris velocity is acquired by analyzing experimental data. In addition, the diffusion velocity of the impact-generated plasma is observed by two retarding potential analyzers. By theoretical analysis, the change law of the electron density with time and dimension is calculated. Experiment results will be helpful to reveal the physical mechanism of spacecraft anomalies by small debris impacts.