Vol. 62, No. 15 (2013)
2013-08-05
GENERAL
2013, 62 (15): 150201.
doi: 10.7498/aps.62.150201
Abstract +
In order to enhance complex network connection income and reduce network connection cost, a network topological connection optimization control method was proposed based on network efficiency and average connection degree, which used network efficiency and average connection degree to denote the gain and cost of network connection respectively, and an optimized arithmetic whose time complexity was O(Mpn2) was provided. Experimental analysis shows that the topological connection of complex network can be optimized by some measures, and an average degree threshold existed in small world network and scale-free network which can make the network’s income reach the maximum value.
2013, 62 (15): 150202.
doi: 10.7498/aps.62.150202
Abstract +
Based on the band structure and related theoretical model of two-dimensional electron gas (2DEG), the dependence of the distribution of 2DEG on the thickness of ZnMgO barrier and related Mg content in ZnMgO/ZnO heterostructures has been computed by self-consistently solving the coupled Schrodinger and Poisson equations. Computation results reveal a critical thickness of the ZnMgO barrier for 2DEG formation, with no 2DEG occurring as the barrier thickness is below the critical value. When the thickness is above the value, the density of the 2DEG increases linearly with the thickness of ZnMgO barrier and saturates finally. The density of the 2DEG also shows a strong dependence on the Mg content in the ZnMgO barrier, with an obvious increase obtained as the Mg content enhances. At the same time, we compare the computed results with experimental data reported in the references with a certain degree of consistence obtained. Explanations and discussions of the above comparison have been presented in the study from the views of polarization effects and band structure.
2013, 62 (15): 150203.
doi: 10.7498/aps.62.150203
Abstract +
Focusing on the suspending stabilization problem for the floated inertial platform, the 6-DOF (degree-of-freedom) equation of motion for the stabilized platform is derived based on the disturbance analysis of the platform and the mode of the suspending support system. To solve the disturbance of the external environments, mode parameter uncertainty, unmodeled dynamics and measurement noise, the sliding mode controller based on the extended high-gain observer are proposed. Simulations indicate that the stabilization structure could isolate the external disturbance and improve the anti-interference ability of the platform; the high precision and quick stabilization control are realized by the proposed controller. Compared with the previous research, the dynamic and stabilization performance of the proposed controller is increased by 50%.
2013, 62 (15): 150301.
doi: 10.7498/aps.62.150301
Abstract +
In order to build a quantum signaling network with high survivability, quantum channel survival function and survivability of signaling network have been proposed based on the concept of fidelity. The survival coefficient in optical fiber or free space is analyzed, fidelity in noisy quantum channel with the decoherence mechanisms is calculated and survival function test model is proposed. Simulation analysis shows that, by reducing the quantum state transition rate, controlling fiber attenuation coefficient and atmospheric attenuation coefficient, decreasing the time of quantum states evolution, and setting quantum repeaters, we can construct a high survivability of quantum channel and provide a theoretical foundation for the formulation of quantum entanglement signaling network standard.
2013, 62 (15): 150501.
doi: 10.7498/aps.62.150501
Abstract +
Halbach motors have attracted lots of attention in novel ship propelling and ocean current generators as they have much dominance. Under the condition of ideal ferromagnetic material and slotless stators, randomly magnetized Halbach array is considered as an equivalence of two 90° Halbach (180° Halbach) arrays, and a new analytic method is proposed in this paper to analyze the randomly magnetized Halbach motors. Fourier series of magnetic scalar potential is calculated, and the expression of air-gap flux density of a 90° Halbach motor is given in polar coordinate system. On the basis of calculations above, the magnetization intensity expression of a randomly magnetized Halbach motor in a pole, and the air-gap flux density distribution of randomly magnetized Halbach motor are obtained; and the relationship of air-gap flux density between the numbers of poles, permanent magnet thickness as well as magnetizing angle are analyzed. The finite element method and experimental results verify the effectiveness of the methods above.
2013, 62 (15): 150502.
doi: 10.7498/aps.62.150502
Abstract +
Based on the fractional calculus theory, the transport model of fractional coupled Brownian motors in flashing ratchet potential is established. Using the fractional difference, the numerical solution of the model is obtained, and the directional transport properties at various parameters are investigated. Numerical results show that in fractional ratchet system, the fractional order and spring constant not only affect the transport velocity of the particles, but also reverse the current direction. Moreover, when the fractional order is fixed, the generalized stochastic resonance phenomena are observed in the mean transport velocity as the noise density, spring constant or the depth of the ratchet potential varies.
2013, 62 (15): 150503.
doi: 10.7498/aps.62.150503
Abstract +
In this paper, We have studied the effects of intensity and correlation time of noises on the mean first-passage time in a picecewise nonlinear system driven by multiplicative and additive colored noises with colored cross-correlation. We derived the expression of the mean first-passage time (MFPT) by applying the unified colored approximation method and the steepest-descent approximation. Results show that the MFPT of the system exhibits a mono-peak structure and the “resonance” phenomena enhance with the increase of multiplicative noise intensity. The value of the peak decreases with increasing additive noise intensity and the correlation between the additive and multiplicative noises. However, the MFPT of the system increases with the increase of additive noise intensity. That is, the effects of the additive noise and the multiplicative noise on MFPT are different. Moreover, the negative and passive correlations play different roles in the MFPT.
2013, 62 (15): 150504.
doi: 10.7498/aps.62.150504
Abstract +
By simplifying a substation, a third-order non-autonomous ferromagnetic circuit with single-phase potential transformer has been obtained. Since the voltage is a sine function, by adding a time dimension to the circuit, it becomes a fourth-order autonomous circuit, and some simulation analysis is carried out on it. Studies show the existence of chaotic dynamical behavior in the circuit system, so that we can draw the conclusion that the excitation characteristic of the core has an important influence on the chaotic dynamical behavior of the circuit.
2013, 62 (15): 150505.
doi: 10.7498/aps.62.150505
Abstract +
Inserting the switched-inductor structure into a traditional Boost converter can increase its line-to-output voltage ratio significantly, decrease the current stresses in the switching elements, reduce losses, and improve efficiency at the same time, which makes it find wide applications in prospect. The bifurcation and chaos phenomenon occurring in the hybrid step-up converter with switched-inductor structure is studied for the first time so far as we know. The discrete iterated mapping model under continuous current mode is established, while the effects of circuit parameters on system performance are analyzed by using bifurcation diagrams. Not only period-doubling bifurcation, border collision bifurcation, tangent bifurcation and intermittent chaos are found in this converter, but a special phenomenon can also be observed according to the simulation result. With the decrease of the capacitance C and inductance L2, the circuit experiences roughly a period, double-period and quadruple-period, and during the quadruple period, two of the bifurcation lines will cross, which leads to the system exhibiting a period-3 behavior at that point. Finally, the existence of this special phenomenon is confirmed by the typical time-domain waveforms and phase portraits of the converter. Results obtained indicate that there can be more complicated and diversiform phenomena in the hybrid step-up converter with switched-inductor structure than in the traditional low-dimensional Boost converter as the circuit parameters vary.
2013, 62 (15): 150506.
doi: 10.7498/aps.62.150506
Abstract +
For the control of uncertainty chaos systems, a compensation control method using the polynomial-basis-functions model (PBFM) based on conjugate gradient algorithm (CGA) is studied. In the proposed method, dynamic properties of a chaotic system are first fitted by PBFM, and then feedforward compensation control for the uncertainty chaos system is implemented by using good fitting PBFM. The proposed approach can quickly track any given reference signal without the need of a mathematic model of chaos system. The numerical simulation results show that the proposed control method has not only the fast response speed and high control accuracy, but also a strong inhibitory ability to parameter perturbation and the anti-interference ability for the chaos system.
2013, 62 (15): 150507.
doi: 10.7498/aps.62.150507
Abstract +
The permanent magnet synchronous wind power generator is investigated, and its mathematical model is established in two-phase synchronous rotating coordinates. By a time scaling transformation and a linear affine transformation, the chaos model is obtained, and the chaos phenomena occur when the model parameters are in a certain range and under running conditions. Then, an uncertain nonlinear model of permanent magnet synchronous wind power generator is established, and a fault observer is designed. When faults occur, the fault observer can estimate the fault quickly and accurately. Simulation results show that the fault observer based on linear matrix inequality approach can diagnosis the fault rapidly and accurately.
2013, 62 (15): 150508.
doi: 10.7498/aps.62.150508
Abstract +
In order to simulate the phenomenon that electric shock defibrillation shortens action potential duration, the synchronous repolarization process is introduced into Luo-Rudy phase I model of cardiac tissue. Effects of synchronous repolarization on dynamics of spiral waves and spatiotemporal chaos are investigated. Numerical results show that when the control period is small, the synchronous repolarization can effectively eliminate spiral waves and spatiotemporal chaos. However, the synchronous repolarization can only eliminate spiral waves or spatiotemporal chaos under some control parameters. When spiral waves cannot be controlled, the transition from spiral wave to spatiotemporal chaos or the spiral wave with longer period and wavelength is observed. The control mechanism is analyzed.
2013, 62 (15): 150509.
doi: 10.7498/aps.62.150509
Abstract +
Based on the nonlinear time series local prediction method and the relevance vector machine regression model, the local relevance vector machine prediction method is proposed and applied to predict the small scale traffic measurement data, and the BIC-based neighbor point selection method is used to choose the number of nearest-neighbor points for the local relevance vector machine regression model. We also compare the performance of the local relevance vector machine regression model with the feed-forward neural network optimized by particle swarm optimization for the same problem. Experimental results show that the local relevance vector machine prediction method whose neighboring points have been optimized can effectively predict the small scale traffic measurement data, can reproduce the statistical features of real small scale traffic measurements, and the prediction accuracy of the local relevance vector machine regression model is superior to that of the feedforward neural network optimized by PSO and the local linear prediction method.
2013, 62 (15): 150701.
doi: 10.7498/aps.62.150701
Abstract +
Mode analysis of the terahertz wave generated by 0.14 THz overmoded surface wave oscillator (SWO) (overmoded ratio D/ 3) is theoretically accomplished and experimentally validated. At first, longitudinal field-expansion method for mode analysis is established aiming at overmoded Cherenkov devices. Then this method is used to analyze the theoretical mode content of 0.14 THz SWO in detail based on the simulation results of electric field extracted from a 2.5-dimensional PIC (particle-in-cell) code. Results show that the mode content of terahertz wave in different characteristic regions of the oscillator is varied due to the mode conversion, and it is dominated by TM02 and TM03 modes accompanied by a small quantity of TM04 mode at the output. Finally, the energy distribution in the near-field radiation of 0.14 THz SWO is obtained by image-displaying method. The experimental result is reasonably in accord with the theoretical distribution calculated from the mode analysis results under experimental conditions, testifying the feasibility of longitudinal field-expansion method for the mode analysis and the correctness of its results.
EDITOR'S SUGGESTION
2013, 62 (15): 150702.
doi: 10.7498/aps.62.150702
Abstract +
A beamstop is commonly used in coherent diffractive imaging (CDI) experiments to collect more high-angle diffraction signals. But it causes the low-frequency signals missed, which can make CDI reconstruction unstable or even fail. In this work, a systematic simulation investigation of the effects of the missing low-frequency signals on the quality of reconstructed images of ptychographic CDI (PCDI) is performed using the ptychographic iterative engine algorithm. We found that the robustness of PCDI to the beamstop is much higher than that of the plane-wave CDI, and a smaller incident probe or a larger probe overlap ratio ( 70%) can further decrease the negative influence of missing low-freqency signals on the reconstruction image. The probe scanning position error will be the main degrading factor of PCDI instead of the beamstop in the higher overlap cases, and needs to be corrected in experiments by using high precision motors or adopting the position refinement algorithms. Our results provide quantitative guidelines for the usage of beamstops in ptychographic CDI experiments.
2013, 62 (15): 150703.
doi: 10.7498/aps.62.150703
Abstract +
The feasibility of applying mode propagation analysis (MPA) method in solving single mode- multimode- single mode (SMS) fiber structure is confirmed by comparing the experimental data with the theoretical results. The method of searching for linear response points on SMS based on MPA was proposed, applied to finding a wide-range high-resolution linear response wavelength theoretically, and confirmed in experiment. By using a 104 μ-in-diameter no-core fiber as short as 4.4 mm, we archived a linear transmission variation of 19.10 dB in the refractive index range of 1.326–1.417, which means a refractive index resolution of 4.76×10-5 according to the resolution of common commercial optical powermeter, and realizes a wide-range high-resolution linear response under the direction of the theory.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2013, 62 (15): 151101.
doi: 10.7498/aps.62.151101
Abstract +
Field analysis method is used to deduce the dispersion relation of rising-sun magnetron with sector cavities, which is proved correct by the high frequency field analysis software, and the influence of each structure parameter of the magnetron on the cutoff frequency of π mode and the mode isolation is investigated. The results show that the relative errors between the theoretical values and the simulation values of the dispersion relation are less than 3%, and the relative errors between the theoretical and simulation cutoff frequencies of π mode are less than 1%. Cutoff frequency of π mode is in direct proportion to the cathode radius Rc, anode radius Ra and big cavity angle 2θ1, but in inverse proportion to small cavity radius Rd0, big cavity radius Rd1 and small cavity angle 2θ0. However, these qualitative relationships are not entirely consistent with those of the same cavity magnetron. In radial orientation, the structure parameters, the influence of which on frequency is sorted in descending order, are as follows: anode radius, big cavity radius, small cavity radius and cathode radius. In angular orientation, the influence of big cavity angle on frequency is greater than that of small cavity angle. In addition, mode isolation γ is in direct proportion to big cavity radius Rd1, but in inverse proportion to cathode radius Rc, small cavity radius Rd0, and small cavity angle 2θ0, and it increases first and then decreases with the increase in anode radius Ra or big cavity angle 2θ1.
NUCLEAR PHYSICS
2013, 62 (15): 152801.
doi: 10.7498/aps.62.152801
Abstract +
Three groups of neutron shielding experiments were set up to study the shielding performance of B4C/Al composite, using the Monte-Carlo method. We have made the following changes: the content of boron carbide 20%–40%, neutron energy 200 eV–15 keV, material thickness 0.3–2 cm, so that we can draw the conclusions: the content of boron carbide and neutron transmission coefficient show a linear relation, with a big drop; under the same neutron energy, the neutron-shielding qualities of simulated specimens are for better than polyethylene boron carbide at the same content of B4C and water, copper, and concrete at the same thickness; an exponential decline relationship is exhibited by material thickness and neutron transmission coefficient, which change greatly with the increase in unit material thickness; the content of boron affects the thermal neutron transmission coefficient seriously. In the thermal neutron energy region, the change of per unit neutron energy(100 eV) has a big influence on neutron transmission coefficient. In the slow neutron energy region, the influence is small.
ATOMIC AND MOLECULAR PHYSICS
2013, 62 (15): 153201.
doi: 10.7498/aps.62.153201
Abstract +
Ca5MgSi3O12:Eu2+, Dy3+ was synthesized by solid-state reaction. The luminescence center related to the oxygen vacancies existed in the host matrix. Comparing the fluorescence and phosphorescence properties of samples synthesized under different air condiction, we find that the oxygen vacancies played an important role in the fluorescence and phosphorescence properties. Oxygen vacancies can transfer its energy to the luminescence center. Thermoluminescence spectra were used to characterize the effect of oxygen vacancies on the phosphorescence properties. Ca5MgSi3O12:Eu2+,Dy3+ has a great potential to become a promising candidate to be used as long-lasting phosphors.
2013, 62 (15): 153202.
doi: 10.7498/aps.62.153202
Abstract +
By solving the three-dimensional time-dependent Schrödinger equation, we have theoretically investigated the variation of photoelectron spectroscopy and angular distribution of hydrogen atom with carrier envelope phase (CEP) under the resonant condition. The results show that the intensity of photoelectron spectroscopy is strongly dependent on CEP near the resonant position; and the angular momentum quantum number of resonant initial-ionized state can be determined by further analyzing each partial wave. In addition, we can detect the information of initial phase of multi-cycle pulses with high accuracy by utilizing the information of angular distribution of photoelectron.
2013, 62 (15): 153301.
doi: 10.7498/aps.62.153301
Abstract +
The Raman optical activity (ROA) of (R)-(-)-1,3-butanediol was described through the analysis of bond polarizability and differential bond polarizability, which were elucidated by Raman and ROA spectral intensities, respectively. Analysis shows that during the Raman process, the charge flows from the (six) rings formed by H16 (or H15) O6C3C2C1O5 to the peripheral OH and CH bonds. The analysis also shows that the signs of differential bond polarizabilities associated with the rings inside and outside are opposite. This means that the chiral asymmetry of this molecule is fairly distinct.
2013, 62 (15): 153701.
doi: 10.7498/aps.62.153701
Abstract +
A new scheme of generating the controllable triple-well optical trap is proposed, in which a liquid-crystal spatial light modulator (SLM) is used to fabricate the phase-type blazed grating and be illuminated with coherent monochromatic light. Three optical wells, each of which has the same intensity distribution, can be formed with relative position of the distribution of an equilateral triangle. The relative positions of the optical wells can be changed by simply and conveniently adjusting the phase distribution of the SLM to realize the evolution and reverse evolution from triple or dual wells to single well. The phase grating is designed by simulation according to the technical parameters of the SLM, and illuminated by the laser with ordinary power. The intensity distributions and intensity changes in the adjustment process for the triple wells are calculated. Results show that the controllable triple-well optical trap with very high peak value of intensity and intensity gradient can be obtained. It has many important applications in the experimental study of atomic and molecular optics.
2013, 62 (15): 153702.
doi: 10.7498/aps.62.153702
Abstract +
Considering the stochastic factors and using Monte Carlo method, we have studied the dynamics of two-dimensional (2D) collimated thermal atomic beam of strontium theoretically. Taking into account transverse divergence, initial position of each atom, longitudinal velocity distribution, and isotopes, we show the theoretical transverse distribution and the results of the Monte Carlo method as functions of detuning and power of laser, respectively. The theoretical results agree excellently with the experimental data, showing that the Monte Carlo method has precisely described the dynamics of 2D collimated thermal atomic beam of strontium. The method can provide an analytical tool for precisely controlling the 2D collimated thermal atomic beam and optimizing the atomic clock system.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2013, 62 (15): 154201.
doi: 10.7498/aps.62.154201
Abstract +
Based on correlated imaging with pseudo-thermal light, Wu and Meyers independently experimentally showed that both positive and negative images can be obtained by using a novel algorithm. With the theory of statistical optics, we construct the model of thermal light, and demonstrate the novel algorithm for image reconstruction. To deal with the data attained in the correlated imaging, we reorder the intensity recorded by the bucket detector according to the value of fluctuation. For a given fluctuation range with all the records above or below a specific value, we can obtain either positive or negative images by calculate the correlation between the selected records of the bucket detector and the reference detector. Nevertheless, without correlated calculations, positive or negative images can be also produced by directly averaging the corresponding records of the reference detector with positive or negative fluctuations. Meanwhile, the visibility of imaging is greatly enhanced. This correspondence imaging method further demonstrates the importance of intensity fluctuations in the nonlocal imaging with thermal light. We also experimentally show the images that obtained by the correlation method and the positive-negative correspondence imaging method, respectively. Our results indicate that this novel algorithm has a better visibility than that of the conventional correlated imaging.
2013, 62 (15): 154202.
doi: 10.7498/aps.62.154202
Abstract +
A scanning spectral filter method is proposed for improving the intensity contrast originating from the phase ripple in the femtosecond chains, which is made using the character that the instantaneous frequency varies with the time approximately linearly for the chirped pulse in the time-frequency domain. The scanning spectral filtering for reducing the pre-pulse and post-pulse intensity is analyzed in the time-frequency domain by using the short-time Fourier transformation method. Results show that the coherent intensity pulse contrast can be improved by 0.41F2 for the chirped pulse or the compressed pulse, and the transmission efficiency of the chirped pulse can exceed 90% when the synchronizing time of the jitter ranges from -2 ps to 2 ps and the chirp rate p from 0.9C/T2 to 1.1C/T2.
2013, 62 (15): 154203.
doi: 10.7498/aps.62.154203
Abstract +
LiB3O5 and CsB3O5 are two excellent nonlinear optical borate crystals containing [B3O7] groups. With a difference of aikali metal ions in structure, LiB3O5 and CsB3O5 exhibit different crystallization habits. The former is an incongruent compound, which cannot crystallize from its melt; however, the latter is a congruent compound obtained by cooling its melt directly. In this work, using Raman spectroscopy and ab initio calculation, the structures of LiB3O5 and CsB3O5 melts have been investigated, and then the influence of alkali metal ions on melt structures is discussed, finally, the relationship between crystallization habits of LiB3O5 and CsB3O5 and their melts is proposed. Results suggest that the boron oxide species of LiB3O5 and CsB3O5 melts are in the form of six-membered rings B3Ø7 and B3Ø6 (Ø represents a bridging oxygen); Raman frequency of the symmetric breathing vibration of six-membered rings shifts to low frequency with the addition of BØ4 tetrahedrons in rings; the relatively large amount of BØ4 tetrahedrons is found in LiB3O5 melts. However, Cs+ ions with larger ion radius hinder the formation of BØ4 tetrahedrons, and then reduc, the BØ4/BØ3 ratio of the melt. Finally, considering the growth mechanism of LiB3O5 and CsB3O5 crystals (Wang D, Wan S M et al. 2011 Cryst. Eng. Comm. 13 5239), we propose that the amount of BØ4 tetrahedrons in melts, which is influenced by aikali metal ions, determines LiB3O5 and CsB3O5 crystallization habits, therefore, and suggest the reduction of BØ4 tetrahedrons in melts is an effective way to crystallize LiB3O5.
2013, 62 (15): 154204.
doi: 10.7498/aps.62.154204
Abstract +
Based on the electromagnetic properties of complementary split ring resonator (CSRR), a novel artificial magnetic conductor (AMC), CSRR-AMC, is designed. The comparison of the reflection phase with square patch AMC reveals its features of miniaturization and multiband in-phase reflection, under X- and Y-polarized normal incident waves, respectively. Inspired by the reflection phase difference under different incident conditions, we have designed a wideband low rader cross-section (RCS) reflection screen with a single CSRR-AMC structure. The CSRR-AMC arrays are orthogonally positioned and the backscattering energy is reduced as a result of phase cancellation. Measured results demonstrate that -10dB RCS reduction is achieved in a wide frequency range of 7.38–10.47 GHz and the relative bandwidth is 34.6%, providing a new method for the design of wideband low scattering structure.
2013, 62 (15): 154205.
doi: 10.7498/aps.62.154205
Abstract +
The numerical simulation method for accurately solving the coupled generalized nonlinear Schrödinger equations (C-GNLSE) is essential for describing the dynamic behavior of ultrashort pulse propagating in optical fiber and developing the corresponding nonlinear fiber-optic devices. C-GNLSE in the normal picture is first mapped into the interaction picture by the representation transformation, and then, the two coupled nonlinear partial differential equations in the interaction picture are solved in frequency domain, with synchronous data updating in each iteration step, by using the vector form of Hult’s fourth-order Runge-Kutta iterative scheme. The proposed vector form algorithm of fourth-order Runge-Kutta in interaction picture (V-JH-RK4IP) is verified by using it in simulating the supercontinuum generation in high birefringence photonic crystal fiber. Moreover, the V-JH-RK4IP algorithm also exhibits the highest accuracy and computational efficiency as compared to other classical algorithms.
2013, 62 (15): 154206.
doi: 10.7498/aps.62.154206
Abstract +
The development of real-time single-molecule detection and tracking technology in time and space for multiple bio-molecules in intact cells has important significance for the study on molecular behaviors in life processes. However, limited depth of field is the main drawback of conventional microscopy that prevents observation and tracking of multiple molecules in intact cells. Based on the principle of wavefront coding, the design and fabrication of a novel diffractive optical element (DOE) which combines a distorted diffraction grating with a double-helix point spread function (PSF) phase plate so that it can simultaneously perform multi-plane imaging with double-helix PSF and realize an extended depth of field is presented. Experiments have been carried out on a self-built microscopic system based on the novel DOE, showing that a depth of field can be up to 12 μm. Experimental results are in good agreement with the theoretical predictions, thus proving the feasibility of this method.
2013, 62 (15): 154207.
doi: 10.7498/aps.62.154207
Abstract +
A 101 W all-fiber supercontinuum soure is demonstrated by seeding a piece of photonic crystal fiber with a high-power pulse-repetition-rate-tuning picosecond fiber laser. By performing a series of comparative experiments, influences of the pump pulse repetition rate and the photonic crystal fiber length on the supercontinuum generation process are investigated in detail. How to improve the power level of the supercontinuum soure is analyzed and discussed. The research results will make a contribution to the further development of high-power supercontinuum soure.
2013, 62 (15): 154301.
doi: 10.7498/aps.62.154301
Abstract +
This paper investigates low-frequency acoustic absorption mechanism of a viscoelastic layer with resonant cylindrical scatterers. The viscoelastic layer is 20 mm-thick, and the cylindrical scatterer is a cylindrical cavity coated with a soft rubber layer, with axis in the lateral layer direction. The absorption properties of the viscoelastic layer under the steel-backing condition are studied using the layer-multiple scattering method. Results show excellent absorption performance in the frequency region of 1000–3000 Hz. The absorption mechanism is investigated by analyzing the absorption cross-section of a single scatterer and the multiple scattering of a periodic array of scatterers, together with the displacement field and power dissipation density. Effects of the resonant absorption of a single scatterer and the coupling resonance between the absorption layer and the steel-backing are revealed.
2013, 62 (15): 154302.
doi: 10.7498/aps.62.154302
Abstract +
This paper explores the properties of over-the-horizon propagation of infrasonic wave in the inhomogeneous atmosphere using the nonlinear progressive equation (NPE). It has been calculated for propagation and path transmission loss of infrasonic wave all the year round in Wuhan. Results show that it is obviously influenced due to infrasonic wave propagation with properties of the inhomogeneous atmosphere and winds in the inhomogeneous atmosphere. Refraction in stratosphere is related to the speed of winds and propagation direction of infrasonic wave. The minimum propagation loss is achieved when the main frequency of gauss infrasonic wave source is 0.1Hz.
2013, 62 (15): 154303.
doi: 10.7498/aps.62.154303
Abstract +
The accurate measurements of rainfall distribution with high spatial and temporal resolution have important implications in meteorology, hydrology, agriculture, environmental policies, flood warning and weather forecasting. Based on the rain-induced power-law attenuation equation, a method is presented to reconstruct the rainfall field using rain-induced attenuation data from microwave links, and a tomographic model is formulated. Simutareous itesative reconstruction technigue (SIRT) algorithm and regularization method are employed in the tomographic model separately. The simulated result shows that the tomographic model and iterative algorithms are able to reconstruct the intensity and features of original rainfall field preferably. The distribution of rain rate with high spatial and temporal resolution is also available. Therefore, rain estimation exploiting microwave attenuation measurement data is a useful complement to traditional rain gauge and radar derived estimations.
2013, 62 (15): 154501.
doi: 10.7498/aps.62.154501
Abstract +
In this paper the Lie symmetry and Noether conserved quantity of a discrete difference sequence Hamilton system with variable mass are studied. Firstly, the difference dynamical equations of the discrete difference sequence Hamilton system with variable mass are built. Secondly, the determining equations and the definition of Lie symmetry for difference dynamical equations of the discrete difference sequence Hamilton system under infinitesimal transformation groups are given. Thirdly, the forms and conditions of Noether conserved quantities to which Lie symmetries will lead in a discrete mechanical system are obtained. Finally, an example is given to illustrate the application of the results.
2013, 62 (15): 154502.
doi: 10.7498/aps.62.154502
Abstract +
In seismic exploration, propagation of seismic wave in earth medium is very complex. Theory of analytical mechanics has advantages for solving complicated problems. In this paper, with the hypothesis of viewing geological medium as an elastic medium, the Lagrange equations of analytical dynamics are built for homogeneous and inhomogeneous earth media. Then the seismic wave equations of elastic medium are obtained from the Lagrange equations. The results provide the basis to study propagation of seismic wave in earth medium and discuss problems related to seismic exploration using Lagrange analytic dynamics.
2013, 62 (15): 154701.
doi: 10.7498/aps.62.154701
Abstract +
For the drag reduction application of hydrophobic material, the drag characteristic of typical surface with different roughness or different hydrophobicity is studied by a new annulus experiment. The corresponding torque characteristic and drag reduction rate curve are acquired. The experiment indirectly calculate the surface friction of the annulus by measuring the torque of disk driving annulus and breaks through the limitation of scale in traditional microchannel experiment, avoids the drawbacks of too many influencing factors in water-tunnel experiment, and has important significance in macro application of hydrophobic material. The drag reduction effect of hydrophobic surface is proved at low Reynolds number in macroscale; however, at high Reynolds number, it will be weakened or even changed to drag producing effect, and the rapid increase of pressure drag is the major reason for increasing resistance. Through comparative analysis we find that at low Reynolds number, there will be greater effect of hydrophobicity for drag reduction; where as at high Reynolds number, the roughness will play a greater role, and may even be counterproductive to the increasing resistance.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2013, 62 (15): 155201.
doi: 10.7498/aps.62.155201
Abstract +
Domestic scholars are often concerned with the characteristics of the plasma cylindrical antenna and the plasma reflector antenna. However, foreign scholars have begun to study the plasma array antenna and used it to design smart antenna. In order to understand this new design idea, based on the plasma electromagnetic scattering theory, a theoretical and experimental study on the directive circular antenna array with a center element driving is presented. A sixteen-element plasma passive oscillator circular array, the mechanism of whose single-beam and multi-beam is transmitting, is established. And an experimental system is established to test the radiation result of circular antenna array. The measured results of radiation patterns are in good agreement with the computational values, verifying that electromagnetic waves can be directional and multi-beam transmitted in this circular antenna array. The advantages of this antenna array are fast switching of the radiation parameters, rapid reconstruction, radar stealth and so on.
2013, 62 (15): 155202.
doi: 10.7498/aps.62.155202
Abstract +
To achieve desirable plasma density control, supersonic molecular beam injection (SMBI) feedback control system has been developed on EAST tokamak recently. The performance of SMBI is compared with that of gas puffing feedback system. The performance of pulse width mode is better than that of pulse amplitude mode when gas puffing is used for density feedback control. In one-day experiment scenario, the variation of gas input and wall retention can be clarified into two stages. In the first stage the retention ratio is as high as 80%–90%, and the gas input is of about the order of 1022. However, in the second stage, the retention ratio is in a range of 50%–70%. The gas input of a single discharge is small and the net wall retention grows slowly. The result of SMBI feedback control experiment is also analyzed. The shorter delay time of SMBI makes it more quickly to feedback control the plasma density. Result shows that, compared with gas puffing, the gas input of SMBI decreaseds ～ 30% and the wall retention is reduced ～ 40%. This shows SMBI’s advantage for the long pulse high-density discharges in EAST.
2013, 62 (15): 155203.
doi: 10.7498/aps.62.155203
Abstract +
The Z-pinch dynamic hohlraum (ZPDH), as implemented on qiangguang-1 facility at NINT, is composed of an annular tungsten plasma that implodes onto a coaxial foam convertor. The collision between tungsten Z pinch and foam convertor launches a strong shock. The shock generates a strong radiation pulse, referred as the first radiation power peak, then the radiation is trapped by the tungsten Z pinch. As pinch diameter decreases, the second radiation power pulse rises and acts as the main power peak. The radiation and dynamic characteristics do not show obvious difference between the 8 mm and 12 mm wire array configurations. Hence, it is important to notice that the foam reduces the influence of global instability generated by MRT instability on stagnated pinch, especially reduces the growth of m=0 and m=1 MHD instability.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2013, 62 (15): 156101.
doi: 10.7498/aps.62.156101
Abstract +
Based on the resonating valence bond theory, the linear combinations of the main orbits occupied by liquid hydrogen electrons are selected as the basis sets to construct the Jastrow antisymmetrized geminal product. The resonating valence bond (RVB) wave function which takes into consideration electron correlation effects provides lower energy than the local density approximation (LDA) function. In order to improve the nodal accuracy of the variational trial wave function, the backflow correlations are suggested to be employed whenever rs1.75 or T 15000 K, the improved wave function has about 1 mHa/atom decrease in local energy with respect to the one without backflow effects at the VMC level, and has a lower variance simultaneity. After combining the coupled electron-ion Monte Carlo (CEIMC) method with the RVB wave function, the simulation results we have obtained are in good agreement with the experimental and other ab-initio ones; the deuterium principal Hugoniot curve passing through the error bars of various existing experiments conducted via different high-pressure technologies has a maximum compression of 4.48 at about 50.3GPa, but the phenomenon of apparent increase in compression ratio along the Hugoniot between 100120 GPa has not been found. The RVB wave function discussed in this paper when adopted the CEIMC method is not only quite suitable for the simulation of liquid hydrogen within a wide range of density and temperature (1.0 rs2.2, 2800 K T60000 K), but also can give some more applicable thermodynamic properties of hydrogen under shock loading.
2013, 62 (15): 156102.
doi: 10.7498/aps.62.156102
Abstract +
It has been reported that incoherent 3 boundaries play an important role in the evolution of grain boundary characteristic distribution in the low to medium stacking fault energy in face-centered cubic metals. In order to ascertain the characteristics of incoherent 3 boundaries with varied (h1k1l1)/(h2k2l2) interface matching, the structural stability of [0 1 1] tilt incoherent 3 grain boundaries in pure copper, at temperatures ranging from 700 to 1100 K and under the normal pressure, was studied by molecular dynamics (MD) simulations. Long-range empirical potential (LREP) was used in the simulation in which the time-step was chosen to be 5 10-15 s (5 fs). Simulation results show that the structural stabilities of [0 1 1] tilt incoherent 3 grain boundaries are different from one another. The general trend is that the larger the angle () by which the grain boundary plane deviates from the ideal (1 1 1)/(1 1 1) twin boundary plane, the smaller the grain boundary matching value and thus the more unstable the incoherent 3 boundary. With the smallest angle, (2 5 5)/(2 1 1) is stable and almost no structural change is observed during annealing processes. With increasing angle, the incoherent 3 boundaries will not be stable any longer. They are usually changed into the meta-stable step-like boundaries during annealing by the mechanisms in which every three atomic layers in the high Miller-index side will merge into one atomic layer, or each atomic layer in the low Miller-index side decomposes into three atomic layers. Some of the steps of these boundaries are located at the exact {111}/{111} planes. As the annealing temperature increases, such step-like boundaries will change completely into straight and stable {111}/{111} coherent twin boundaries.
2013, 62 (15): 156103.
doi: 10.7498/aps.62.156103
Abstract +
By using the density functional theory, six structures of oligopeptides chain configuration, consisting of glycine and tryptophan alternatively, are optimized at the B3LYP/6-31 G(d) level. The average binding energy and IR spectrum are calculated. Results show that the stability of oligopeptides grows monotonously with the peptide chain growth. The vibration infrared spectrum analysis show that with the growth of oligopeptides peptide chain, the vibration frequency of one functional group shows blue shift or even-odd shift; while coupling vibration of the same functional group shows red shift, and steady frequencies at the end of chain appear on the infrared spectrum, that is to say, coupling effect, parity effect and size effect exist when, glycine tryptophan oligopeptides, consisting of glycine and tryptophan alternatively, change with peptide chain. The result is significant in measuring the length and number of residue of peptide chain.
2013, 62 (15): 156104.
doi: 10.7498/aps.62.156104
Abstract +
This article presents a simple and efficient method for preparing silicon nanopit arrays structure using laser interference lithography (LIL). Highly ordered nanopit arrays in two dimensions were fabricated on 2 inch Si (001) substrate by LIL and in combination with dry etching and wet etching processes. Dot arrays were directly etched to nanopit arrays with this method, which omitted the necessary steps of metal deposition and lift off in pattern reversal process. Forming a fluorocarbon organic polymer layer on silicon surface after dry etching, which can be used as a wet etching mask, and producing a thin silicon mesa layer under the SiO2 dot arrays by slight over-etching in dry etching process, are two key steps for this method. SEM images show the uniform and controllable pit arrays were prepared; the period of the arrays is 450 nm, the length of the pit is 200280 nm. The pit arrays are composes of square and inverted pyramids, and the four facets of the inverted pyramid correspond to four crystal planes (111) of Si substrate.
2013, 62 (15): 156105.
doi: 10.7498/aps.62.156105
Abstract +
Based on the Geant4 program-the package for simulating particle transportation in materials, simulations of the irradiation by neutrons with 1 MeV energy in zirconium were conducted The two adjacent elastic collisions between injected neutron and target atoms produce numerous primary knock-on atoms (PKA). It is found that the average distance of adjacent collisions is 29.47 mm, and the kinetic energy of most PKAs ranges from 1 keV to 15 keV. The damaged area induced by the PKAs is in nanometer scale, which is far less than the distance between the two PKAs. According to the fact that, the subsequent cascade collisions caused by the two PKAs can be considered as a set of independent processes, it is reasonable to study the cascade collisions of the PKAs by means of molecular dynamics method. The cascade collision progress of PKAs with different energies was performed, and the number of interstitial atoms and the size of the damaged regions in the material were extracted. Through the combination of Monte Carlo method and molecular dynamics simulation, a complete physical picture of the primary damage caused by the 1 MeV neutrons in the zirconium was obtained.
2013, 62 (15): 156106.
doi: 10.7498/aps.62.156106
Abstract +
High-current pulsed electron beam (HCPEB) technique was applied to irradiate the samples of pure zirconium. The microstructures and defects of the irradiated surface are investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD results show that the high value of stress (GPa order) is introduced within the irradiated surface layer, while the formation of {0002}, {1012}, {1120} and {1013} textures are present after HCPEB irradiation. Microstructure observations demonstrate that the surface craters are rarer, and almost no craters are present after multiple pulses HCPEB irradiation, which is evidently different from the case of other metal materials irradiated by HCPEB. Moreover, a large number of ultrafine grains are formed on the irradiated surface. Martensitic transformation occurs and severe plastic deformation is also induced due to the superfast melting and cooling processes. After one- pulse irradiation, the dislocations are the dominant defects, while the amount of twins is less. After five pulses, the dislocation density and the number of deformation twins increase evidently, whereas dense deformation twins are the central microstructures after ten-pulse irradiation, coupled with the appearance of secondary twins occasionally. The formation of these deformed structures results in a significant effect both on the evolution of surface textures and on grain refinement. It is suggested that HCPEB technique provides an impactful approach for hardening of zirconium and zirconium alloys.
2013, 62 (15): 156107.
doi: 10.7498/aps.62.156107
Abstract +
Ferroelectric random memory was irradiated and annealed by 60Co-rays, total ionizing dose (TID) failure mechanism and annealing characteristics of the device were analyzed. DC, AC and function parameters of the memory were tested in radiation and annealing by very large scale integrated cicuit (VLSI) test system, the radiation-sensitive parameters were obtained through analyzing the test data. Ionizing radiation produced a large number of oxide trapped charges, leading MOS transistor threshold to the negative drift in memory peripheral control circuit. Additional electric field was introduced in the ferroelectric film, and leakage current was produced since the Schottky emission or space-charge-limited current occurred. The number of shallower levels and metastable state oxide trapped charges are more than the deep level oxide trapped charge, so that the device functions and the radiation-sensitive parameters were restored in the annealing.
2013, 62 (15): 156301.
doi: 10.7498/aps.62.156301
Abstract +
The dispersion law of a one-dimensional diatomic lattice with on-site potential cross on its dispersion relation is solved under the harmonic approximation with quantized invariant eigen-operator method (IEO) and the influences of on-site potential and force constant are discussed. It is shown that due to the existence of on-site potential the lattice vibration spectra induced are shifted. Under certain conditions, the point of intersection exist between optical branch and acoustic branch in the boundary of Brillioun zone, which means the frequency gap between optical branch and acoustic branch is zero.
2013, 62 (15): 156401.
doi: 10.7498/aps.62.156401
Abstract +
The phase separation process in a three-dimensional lattice gas model with a low volume ratio c=0.01 was studied. Using Monte Carlo simulation, the evolution behaviors of sc, fcc, bcc lattices, and 5 relative temperatures T/Tc=0.450.85 were simulated. It was found that the structure factor functions did not satisfy the scaling relationship, and the growth index was 1/6, less than the value of Lifshitz-Slyozov theory.
2013, 62 (15): 156801.
doi: 10.7498/aps.62.156801
Abstract +
W(Mo, 9.8 at.%)/Cu nanometer multilayer films of different individual layer thickness were prepared by RF magnetron sputtering, which were irradiated by 60 keV He+ ions at ion fluence from 0 to 51017 He+/cm2. Microstructures of nanometer multilayer W(Mo)/Cu films were investigated by high-resolution transmission electron microscope (HRTEM) and X-ray diffraction (XRD) before and after irradiation. Experimental results indicate that: (1) The phase transformation of -W (A-15) into steady state -W can be attributed to the bombardment effect of energetic He ions on the surface of films, leading to phase-transition temperature during irradiation. (2) The irradiation tolerance of W(Mo)/Cu multilayer film was found to depend on the individual layer thickness. (3) At the fluence of 51017 He+/cm2, the HRTEM results reveal that the behavior of helium cluster/bubble in the W(Mo) film is obviously different from that in the Cu film. It is interesting that the distribution of helium cluster/bubble is related to the grain orientation of W(Mo) film and tends to distribute along W (211) plane. However, Cu film is completely amorphized and helium cluster/bubble is evenly distributed in it.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2013, 62 (15): 157101.
doi: 10.7498/aps.62.157101
Abstract +
Based on the density functional theory (DFT), and using the first-principles plane-wave ultrasoft pseudopotential method, we set up models for a pure ZnO and four different concentrations of Ga-doped ZnO, and the geomertry optimization for the four modes was carried out. The total density of states (TDOS), the band structures (BS) and absorption spectrum were also calculated. Results show that the range of Ga doping amount is limited to 2.08 at% to 6.25 at% in this paper; when the doping concentration of Ga increases, the volume change of the system is not obvious; however, when is energy increases, the system will be unstable, the Burstein-Moss effect of its optical band gap will increase, and the absorption spectrum will shift to high energy. The results of calculation agree with the experimental data.
2013, 62 (15): 157102.
doi: 10.7498/aps.62.157102
Abstract +
Based on the density functional theory (DFT), using first-principles plane-wave ultrasoft pseudopotential method, the models for the unit cell of pure ZnO and Zn1-xTMxO (TM=Al, Ga, In) supercells at the same doping concentration were constructed, and the geometry optimization, total density of states, band structures for all models were carried out. The calculation results show that, In-doped ZnO has the best conductivity at the same doping concentration of 3.125 at% of (Al, Ga, In) high doped in ZnO, the calculation results agree with the experimental results.
2013, 62 (15): 157201.
doi: 10.7498/aps.62.157201
Abstract +
An inversion-channel electron mobility model for InxGa1-xAs n-channel metal-oxide-semiconductor field-effect transistors (nMOSFETs) with Al2O3 as gate dielectric is established by considering main scattering mechanisms of bulk scattering, Coulomb scattering of interface charges and interface- roughness scattering of the Al2O3/InxGa1-xAs interface. The simulated results are in good agreement with the experimental data. Analyses by using the model indicate that the total electron mobility is mainly limited by the Coulomb scattering of interface charges under weak and medium effective fields and by the interface-roughness scattering under strong effective fields. Therefore, the effective approaches of enhancing the inversion-channel electron mobility are to reduce the interface-state density and roughness of the Al2O3/InxGa1-xAs interface, to properly increase the in content and control the doping concentration of the InxGa1-xAs channel to a suitable value.
2013, 62 (15): 157202.
doi: 10.7498/aps.62.157202
Abstract +
In order to study the degradation mechanism of leakage current in AlGaN/GaN high electron mobility transistors (HEMTs), we have fabricated AlGaN/GaN heterojunction Schottky diodes having equivalent structure and characteristics to AlGaN/GaN HEMTs. Step stress tests were then performed to compare the leakage current changes at different gate voltages. The transport mechanism of leakage current before and after degradation was validated based on the current-voltage and capacitance-voltage measurements. The light emission from the device surface was examined by emission microscopy (EMMI) to investigate the time-dependent degradation of leakage current. Experimental results show that the leakage current increases with increasing time and is accompanied by a large noise when the applied gate voltage exceeds a critical value. After introducing the polarization field into the current-field dependence, log(IFT/E) exhibits a good linear relationship with E both before and after degradation, indicating that the leakage current is dominated by the Frenkel-Poole (FP) emission. The slope of log(IFT/E)-E curve decreases after degradation, and the hot spots corresponding to defects are directly observed by EMMI at the gate edge of the degraded device, suggesting that the degradation mechanism is: New defects are induced by high electric field in the AlGaN layer, and the increase of defect density leads to the increase of FP emission current.
2013, 62 (15): 157203.
doi: 10.7498/aps.62.157203
Abstract +
For quantitative study of time constant and degradation ratio of degradation parameters which correspond to different failure mechanisms in pseudomorphic high electron mobility transistor (PHEMT) gate current degradation process, a PHEMT gate current degradation model is established based on the relationship between reaction volume concentration and reaction rate in the process of degradation. The degradation law of PHEMT electrical parameters is obtained using online experiment method. The parameter degradation law with the time is analyzed and the failure mechanism which affects gate current degradation in different time period is obtained. Meanwhile, based on the gate current parameter degradation model, time constant and degradation ratio of degradation parameters, which correspond to different failure mechanisms, are also obtained.
2013, 62 (15): 157301.
doi: 10.7498/aps.62.157301
Abstract +
By solving Schrodinger equation and Poisson equation self-consistently, we have calculated the electronic structure for Si-doped GaAs/AlGaAs quantum well system at T=0 in the effective mass approximation. We studied the influence of the doping concentration and the thickness of the doping layer on the subband energies, eigen-envelope functions, Hartree potential, density distribution of the electrons, and the Fermi energy. It is found that at the given doping concentration, the subband energies decrease with the increase of the doping thickness, the width of the self consistent potential well increase, the deepth of the well decrease, the distribution of the electron density becomes wider, the peak value reduced. At the given thickness of the doping layer, with the increase of the doping concentration, the subband energies and Fermi energy monotonically increase, the self consistent potential well becomes narrower and deeper, the peak of the electron density distribution becomes higher, and concentrated around the center of the well.
EDITOR'S SUGGESTION
2013, 62 (15): 157302.
doi: 10.7498/aps.62.157302
Abstract +
This paper uses the first-principles and the tight-binding methods to study the electronic structures of twisted bilayer graphene for different angles. The band structures and density of states of twisted bilayer graphene in different angles are calculated. Our analysis points out that there is a linear dispersion relation in a twisted bilayer graphene, which is similar to a monolayer graphene, and the Fermi velocity of twisted graphene is lower and lower with reducing angle. Furthermore, gaps appearing at M point of certain angles, in which the width of gap depends on the twist angle, this gap would strengthen the Raman mode intensity of twisted bilayer graphene, as was confirmed by experiment. The comparison of moire patterns and the location of density of states both certify that AB region of moire patterns is the reason of gap at M point.
2013, 62 (15): 157501.
doi: 10.7498/aps.62.157501
Abstract +
The behaviors of lattice distortions in the spin 1/2 antiferromagnetic XY model with Thue-Morse quasiperiodic modulation are investigated by the method of exact diagonalization. It is found that the lattice distortion at each site has the character intermediate between the periodic and random systems. For weaker or stronger quasiperiodic modulation, the lattice distortion may increase or decrease with strengthening of the modulation amplitude, respectively. The results also indicate that the energy gaps of ground states are strongly affected by the quasiperiodic modulation
2013, 62 (15): 157502.
doi: 10.7498/aps.62.157502
Abstract +
Mn70Fe30-xCox (x=0, 2, 4) alloys were prepared using non-consumable vacuum arc furnace smelting followed by subsequently solution treatment. The effect of Co content on the property of magnetic-field-induced strain (MFIS) was studied by means of X-ray diffraction (XRD), photomicrograph, differential scanning calorimetry (DSC), and resistance strain gauge method. Result shows that Mn70Fe30-xCox (x=0, 2, 4) alloys are of singe phase at room temperature. With the increase of Co content, the Nel temperatures of alloys decrease, which are all higher than room temperature, i.e., the alloys exhibit antiferromagnetic austenite microstructure at room temperature after quenching from high temperatures. Alloys possess much larger MFIS with the increase of Co content, and taking Mn70Fe26Co4 as an example, when the magnetic field strength is 1.1 T, the MFIS is at its maximum, 610-5.
EDITOR'S SUGGESTION
2013, 62 (15): 157801.
doi: 10.7498/aps.62.157801
Abstract +
By investigating the difference between the analytic solutions obtained from commonly used two-dimensional effective medium theory and the numerical solutions, we found that any analytical solution was quite accurate only at its right normalized cycle, determined by its own effective range. Thus, one should solve the problem that there was no closed-form solution for the effective permittivity of a two-dimensional zero-order grating, and expand the applied scope of the effective medium theory to the boundary of zero-order diffraction. Secondly, by using the two-dimensional analytical solution, we have designed a nanowires anti-reflection layer in silicon, which fully meet the needs of the design that reach zero reflectance at 650 nm; and the spectrum averaged reflection from 310-1120 nm is 8%, lower than silicon nitride anti-reflection layer 9.9%. Stavenga formula can be used to design a large normalized period antireflective microstructure, while the Maxwell-Garnett formula can be used to design a small normalized cycle antireflective microstructure. Design of antireflection structure by two-dimensional closed form solution directly is viable, which have huge potential application value.
2013, 62 (15): 157802.
doi: 10.7498/aps.62.157802
Abstract +
A series of Ba1.99-x/2-2ySiO4:Eu0.012+, Lix+y2+, Euy3+ green phosphors were synthesized by one-step calcination process with precursor prepared by chemical precipitation. X-ray diffraction (XRD) and fluorescence spectrophotometry were employed to characterize the crystal structure and luminescent properties, respectively. The results show that co-doping of Eu2+, Li+ or Er3+ do not change the crystal structure. The excitation band of green phosphors Ba1.99-x/2-2ySiO4:Eu0.012+, Lix+y2+, Euy3+ extends from 270 to 440 nm, with peaks appearing around 288 and 360 nm, thus the phosphors can be excited effectively by InGaN chip which produces ultraviolet light in the range of 350410 nm. The emission spectrum excited by 360 nm shows a characteristic wide band with a peak at about 500 nm, which can be attributed to the typical 4f65d14f7 transition emission of Eu2+. The emission spectrum intensity of Ba1.99-x/2SiO4:Eu0.012+, Lix2+ first increases with increasing Li+ doping concentration, and then decreases. The strongest emission intensity occars when Li+ doping concentration is 0.1. Two additional peaks appear in the emission spectrum of Ba1.99-x/2-2ySiO4:Eu0.012+, Lix+y2+, Euy3+ green phosphors around 488 nm and 530~nm separately when the phosphors are co-doped with Li+ and Er3+ from 0 to 0.012, which are attributed to the 4F7/24I15/2 and 2H11/24I15/2 translation emission of Er3+, the energy transfer effect from Eu2+ to Er3+ is also analyzed.
2013, 62 (15): 157901.
doi: 10.7498/aps.62.157901
Abstract +
We have measured secondary electron emission yields in forward and backward directions from the carbon foils with different thicknesses, which are penetrated by Ne2+ ion of an energy from 2 to 25 keV/u. In the experiment, the contributions of projectile potential energy deposition, electronic energy loss and recoil atom to the forward and backward electron emission yields have been studied systematically by changing the projectile ions energy. Results show that the ions potential energy deposition only have the impact on the backward electron emission yield, while the forward and backward electron emission yields increase approximately linearly with the increase of the electron energy loss at the exit and entrance surfaces of the thin film respectively. When the electron energy loss is low, the impact of recoil atoms on the electron emission cannot be neglected.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2013, 62 (15): 158101.
doi: 10.7498/aps.62.158101
Abstract +
The influences of oxygen ion dose and annealing temperature on the microstructural and photoelectrical properties of microcrystalline diamond films with Si-V luminescence centers were systematically investigated. Results show that high temperature annealing prefers to increase the Si-V luminescence intensity in oxygen-ion-implanted microcrystalline diamond films. With oxygen ion dose increasing from 1014 to 1015 cm-2, the Si-V luminescence intensity of the films enhances. Hall effects measurement show that the resistivity of the films becomes lower after annealing. At different annealing temperatures, the oxygen-ion-implanted microcrystalline diamond films with stronger Si-V luminescence intensity exhibit larger resistivity, indicating that the Si-V luminescence centers are not favorable to the enhance ment of the conductivity of films. Results of Raman spectroscopy show that the increase of defects in films will enhance Si-V luminescence intensity and decrease the conductivity of the films.
2013, 62 (15): 158102.
doi: 10.7498/aps.62.158102
Abstract +
In this paper, we present the design, simulation, and experimental demonstration of a miniaturized low-frequency metamaterial absorber based on the broadside-coupled spiral structures. The tested results indicate that the metamaterial absorber can achieve a miniaturized narrowband absorption with a peak absorption of 98% at 1.39 GHz. Both of the unit cell size and the total thickness of the metamaterial absorber are 6.8 mm that is approximately 1/32 of the working wavelength. Since the spiral structures of the metamaterial absorber are arranged in rotational symmetry, the absorber is polarization-insensitive to the normal incident electromagnetic wave. Additionally, the metamaterial absorber can strongly absorb the obliquely incident electromagnetic wave for both transverse electric and transverse magnetic polarizations, even at 60° angle of incidence.
2013, 62 (15): 158103.
doi: 10.7498/aps.62.158103
Abstract +
Tantalum-doped TiO2 thin films were deposited on glass substrates by pulsed laser deposition (PLD). Their optoelectrical properties were studied. The optical band gap was found varying between 3.26 and 3.49 eV when the oxygen partial pressure increases from 0.3 to 0.7 Pa. The dependence of electrical property of the films on temperature was measured to identify the dominant conduction mechanism. It was found that thermally activated band conduction was the dominant conduction mechanism in the temperatures range of 150 to 210 K. Whereas, in the temperature region of 10 to 150 K, the dependence of the conductivity on temperature followed Mott’s variable range hopping (VRH) model. Moreover, the temperature dependence of resistivity for the films can be described by～ exp(b/T)1/2 at temperatures from 210 to 300 K.
2013, 62 (15): 158104.
doi: 10.7498/aps.62.158104
Abstract +
Flower-like copper monosulfide (CuS) hierarchical nanostructures composed of nanoplates were successfully synthesized by means of a simple solvothermal process, using CuCl2·2H2O as Cu-precursor, CS2 as S-source and ethylene glycol (C2H6O2) as the solvent. The morphology and structure of the product were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The optical properties of the copper monosulfide hierarchical nanostructures were investigated by UV-visible absorption spectra. In addition, the photocatalytic activity of the flower-like CuS hierarchical nanostructures were evaluated by the degradation of methyl orange solution under natural light. Results demonstrate that the as-prepared flower-like CuS hierarchical nanostructures possess high photocatalytic performance, the degradation rate is up to 100% after 90 min degradation under the irradiation of natural light, which is much higher than bulk CuS powder. The formation mechanism of flower-like CuS hierarchical nanostructures was preliminarily analysed, alss.
2013, 62 (15): 158105.
doi: 10.7498/aps.62.158105
Abstract +
Using the self-consistent mean field theory, we have studied the self-assembly behavior of AB/CD block copolymers blend. Simulation results show that the hierarchical structural transitions from lamellar structures on different spatial scales to core-shell structure were caused by the increase of the fusion degree between components B and D. When the mutual fusion degrees between components B and D, between A and B, and between C and D are equal, the structure will change from macro-lamellar to micro-lamellar. In addition, the variation of free energy with the interaction between B and D were also calculated to deepen the understanding about the structural transition.
2013, 62 (15): 158106.
doi: 10.7498/aps.62.158106
Abstract +
This paper focuses on the Fe59.5Ni28Al11.5Ta1 memory alloy, in which the effects of different aging treatments on microstructure and properties of the rolled alloy are investigated by metallurgical microscope, X-ray diffraction, SEM, EDS and pressure test machine. Results show that, because of aging treatment, precipitation of γ’ and β’ phase strengthens the austenitic matrix. With the increase of aging time at 600 ℃, the comprehensive analysis of pseudoelasticity curve, shows that the stress-induced martensite critical stress of the aging state of the alloy decreases first and then increases; the alloy compressive strength, the recoverable strain and the hardness increase first and then decrease, Besides, the alloy residual strain is first decreased and then increased. When the aging time is 60 h, the alloy compressive strength is the maximum, up to 1306 MPa, the alloy recoverable deformation is the maximum, reaching 14.9%, the hardness of the alloy is also the largest, but the alloy residual strain is relative minimum. With the increase of aging time, alloy maximum strain decreases gradually, and the plasticity of the alloy also decreases gradually. The properties of the shape memory alloy are influenced by the particle size, its distribution, volume fraction, of precipitate phase etc.
2013, 62 (15): 158107.
doi: 10.7498/aps.62.158107
Abstract +
CdS films were deposited on corning 9059 glass, FTO, ITO and AZO substrates by r.f. magnetron sputtering, and annealed at 380 ℃ in CdCl2+ dry air. Effects of different types of substrate and thermal annealing on the morphology, structure and optical properties were investigated. Field emission scanning electron microscope shows: the morphology of as-deposited and annealed CdS thin films on different substrates is different, grain size and surface roughness increase significantly with annealing. XRD diffraction patterns show: the structure of as-deposited and annealed CdS thin films on different substrates are mixed phase structure of hexagonal and cubic phases, there is a preferential orientation of the crystallits with the hexagonal (002) and cubic (111) peak for as-deposited and annealed CdS films on corning 9059 glass, FTO, and AZO substrates, for as-deposited CdS film on ITO substrate there is no preferentially oriented diffraction peaks, but has highly oriented with hexagonal (002) or cubic (111) peak after annealing; UV-Vis spectrophotometer spectrum analysis shows: the average transmittance in visible spectrum of CdS thin films deposited on AZO, FTO, ITO and Corning 7059 glass substrates in turn decreases, annealing increases the corresponding substrate of CdS films in visible light transmittance, reduces the optical absorption coefficient; annealing significantly increases the band gap of CdS films on different substrates. Analysis reveals that the performance comes from the result of different types of substrate and annealing process for morphology and structure of CdS thin films, and the band tail states changes, due to variation of doping concentration.
2013, 62 (15): 158201.
doi: 10.7498/aps.62.158201
Abstract +
To understand the thermal effect of polymer Li-ion cells during the discharge process, an electrochemical thermal coupling model was established to investigate the thermal behavior of the cell. The average deviation and variance between the modeling results and the experimental data at 3C discharge rate were 0.57 K and 0.15, thus it was concluded that the modeling results agreed well with the experimental data. Also, the model is used to analyze the temperature distribution affected by discharge rate and cooling condition. The average heat production rate of the cells shows an increasing trend throughout the discharge process; it is increased significantly at both the beginning and the end of discharge. At a high discharge current, the irreversible heating which is proportional to the square of the current density, is the major heat generation source inside the battery. At a low discharge current, the heat production rate is dominated by reversible entropic heat. Improving cooling temperature could lower the average temperature during the discharge process. When the heat coefficient is 5 W/(m2·K), the average temperature rises of the battery cells are 6.46 K, 17.67 K, 27.53 K for 1C, 3C, 5C discharge rates respectively. If the heat coefficient increases to 25 W/(m2·K), the average temperatures of the battery cells are reduced by 2.91 K, 4.68 K, 5.62 K for 1C, 3C, 5C discharge rates, respectively, but the inner temperature difference would be increased.
2013, 62 (15): 158401.
doi: 10.7498/aps.62.158401
Abstract +
Frequency bifurcation is the most typical nonlinear phenomenon in inductive power transfer (IPT) systems. Two stable and one unstable resonant frequencies exist in a bifurcated IPT system while the unstable one lies between the two stable frequencies. To achieve the transition control of the bifurcated frequencies, this paper proposes an orbit shift method through a time delay perturbation, which is applied to the feedback signal. The phase trajectory can be shifted among the stable limit cycle attractors by adjusting the parameters of the time delay perturbation. The operation principle and implementation of the proposed method have been investigated in detail on an example IPT system with series tuned primary and secondary circuits. Both simulation and experimental results have verified the validation of the proposed method. The research results can provide useful theoretical reference for transition control of other similar multiple-attractor bifurcation behaviors.
2013, 62 (15): 158501.
doi: 10.7498/aps.62.158501
Abstract +
Meminductor, a nonlinear device with memory ability and controllable meminductance, was generalized on the basis of the conception of memristor. Currently, meminductor is still unavailable on the market. Therefore, in order to investigate its properties and potential application, designing electronic emulator is of significant importance. In this paper, a flux-controlled memristive emulator using ligh-dependent resistor (LDR) is proposed and the mutator for transferring memristor into a flux controlled meminductor is described, of which the realization is on the basis of two current conveyor chips and operational amplifiers. Results of Pspice simulation and hardware experiments indicate that the current-flux characteristic of the meminductor is a frequency-dependent pinched loop, like an inclined number “8”. To confirm the effectiveness and correctness, the proposed emulator is analyzed theoretically and tested experimentally as it is connected in an RLMC series circuit. The dynamic behaviors of the RLMC circuit are analyzed and observed. All the results manifest that this newly proposed emulator is capable of simulating a nonlinear meminductor and can be applied to the analog circuit design.
2013, 62 (15): 158502.
doi: 10.7498/aps.62.158502
Abstract +
In order to improve the driving current and suppress the SCE and DIBL effect of deep submicron SOI MOSFET, dual material gate strained Si SOI MOSFET structure with asymmetric Halo has been proposed. An impurity with a higher concentration is injected into the channel end near the source and the two materials with different work functions are put together to form the gate. By considering both the characteristics of the new device structure and the influence of strain, the flatband voltage and built-in potential have been corrected. A two-dimensional analytical model for the surface potential and the threshold voltage is proposed by solving Poisson’s equation. The effect of Ge fractions in the relaxed layer on surface potential, surface electric field, and threshold voltage is investigated. The model proposed in this paper takes into account the effects of gate metals length and their work functions. Results show that the novel device can increase carrier transport speed and suppress the SCE and DIBL effects, which provides a valuable reference to the physical parameter design.
2013, 62 (15): 158503.
doi: 10.7498/aps.62.158503
Abstract +
A slotted rectangular single-grating with a cylindrical electron beam was proposed as the beam-wave interaction circuit of a W-band backward wave oscillator (BWO). Analysis on the slow-wave characteristics of the structure was done utilizing three-dimensional electromagnetic field simulation software CST-MWS. Results are as follows: The new structure can have a much larger coupling impedance than traditional one; the bandwidth of the fundamental mode can be broadened and the fundamental mode is unlikely to compete with the high-order mode. The loss caused by the skin effect is reduced. The structure was applied to design a W-band backward wave oscillator whose band center is 94 GHz. A simple slow-wave transition part, and the output coupler and terminal matching attenuator were designed, the parameters of which were optimized to obtain good signal transmission. Using CST-PS’s PIC solver, a three-dimensional large-signal particle simulation was done. After setting a suitable electron current and other parameters, watts scale peak output power was obtained within a wide frequency band by adjusting the working voltage, and the electronic efficiency in the band was greater than 1%.
2013, 62 (15): 158504.
doi: 10.7498/aps.62.158504
Abstract +
We have investigated the light-emitting diodes based on colloidal CdSe quantum dots (QD-LEDs), in which inorganic ZnSnO thin films and organic TPD thin films were used as the electron-transporting layer (ETL) and hole-transporting layer (HTL), respectively. The quantum dots were embedded between the inorganic ETL and organic HTL to form a sandwich structure. ZnSnO ETL was made by magnetron sputtering, while the TPD and QD films were made by spin-coating method. The QD-LEDs display sharp interface and smooth morphology. Optical and electrical characterizations show that QD-LEDs have low turn-on voltage, good monochromaticity, bright electroluminescence and good stability in atmosphere ambient. These characteristics are attributed to the utility of high electron mobility and low carrier concentration of the ZnSnO films used as the ETL. To investigate the devices operation mechanism, the conductivity of ZnSnO was varied during deposition to realize equal injection rate for both electrons and holes, which allows the device to operate optimally.
2013, 62 (15): 158701.
doi: 10.7498/aps.62.158701
Abstract +
The molecular dynamics simulation has been used to study the tribological properties of the seven kinds mixed Langmuir-Blodgett (LB) monolayers, which composed of the fatty acids CnH2n+1COOH and C17H31COOH (n=12,13,14,15,16,17) by the ratio of 1:1, and the monolayers compoesd by C16H33COOH. The results showed that: (1) the shear pressure of mixed LB monolayers decreased as the chain-length of molecules Cn increased. The friction force main come from the coulombic interaction between the monolayers. (2) the arrangement of the two kinds of tails of the molocules influence the friction character. The shear pressure is smaller when all the tails are isotactic-arrangement than anisotactic-arrangemnet, espacilly when the differrence of the chain-length is one C-C bondlength. (3) The shear pressure decreseased as the chainlength decreased, and the friction froce main come from the coulombic interaction, when tails of the up and down isotactic monolayers which are composed of one kind molecule are mirror symmetry, or the friction froce main come from the van der wasls (VDW) interaction when tails are central symmtry.
2013, 62 (15): 158702.
doi: 10.7498/aps.62.158702
Abstract +
The amplitude and phase fluctuations of A-scans, influenced by the galvanometer positioning accuracy, mechanical jitter, and especially the ovement of the sample, may lead to the distortion and degradation of the tissue structure images and the blood flow images within tissue beds in frequency domain optical coherence tomography. The amplitude registration method for A-scans is proposed based on the minimum intensity difference matching criterion, Lorentzian curve fitting method, and compensation of the optical path difference in interference spectrum. The phase differences between A-scans are detected and registered by matching of phase distribution characteristics of A-scans. After the amplitude and phase registration, the complex signal differences between two A-scans are calculated to eliminate the effect of the static tissue on the blood flow imaging. The eye scanning experiments were performed and three-dimensional blood flow images of retina were acquired. Experiment results indicate that the effect of system scanning accuracy and tissue movement on the image quality can be effectively eliminated by the proposed amplitude and phase registration method. The fast and accurate phase registration method can also be used in Doppler OCT, phase microscope, and other phase related applications.
2013, 62 (15): 158801.
doi: 10.7498/aps.62.158801
Abstract +
In order to study intense pulsed emission characteristics of carbon nanotube films (CNTs), CNTs were synthesized on the surface of Cu substrate (Cu-CNTs) by pyrolysis of iron phthalocyanine (FePc). Orientations of CNTs obtained are different from one another. Intense pulsed field emission of CNTs was measured on the 20GW pulse power system using a diode structure. For single pulse emission, the emission current peak of Cu-CNTs increases linearly with pulse field peak, at the applied peak electric field of ～15.5 V/μ; the current peak is ～5.56 kA, and equivalent emission current density is ～0.283 kA/cm2. At the applied peak electric field of ～32.0 V/μ, the current peak can achieve ～18.19kA, and the equivalent emission current density is～0.927 kA/cm2; the ability of emission current of CNTs is obviously better than that reported. In many continuous and similar peak pulse emissions, Cu-CNTs provide with good repeatability of pulsed emission, and present better emission stability.
2013, 62 (15): 158802.
doi: 10.7498/aps.62.158802
Abstract +
High efficiency inverted metamorphic (IMM) GaInP/GaAs/In0.3Ga0.7As(1.0 eV) triple-junction solar cells have been fabricated by growing In0.3Ga0.7As(1.0 eV) sub-cell using step-graded buffer layer, which is 2% lattice mismatch to the GaAs middle cell. The high crystalline quality and low threading dislocation density are confirmed by high resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM). The quantum efficiency and I-V characteristic are measured for the IMM GaInP/GaAs/In0.3Ga0.7As solar cells, as well as for the conventional triple-junction solar cell based on Ge substrate (GaInP/GaAs/Ge). The efficiency of the designed cell with an area of 10.922 cm2 is 32.64% (AM0, 25 ℃), which is 3% higher than the conventional GaInP/GaAs/Ge triple junction solar cell.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2013, 62 (15): 159301.
doi: 10.7498/aps.62.159301
Abstract +
GPS radio occultation observed refractivity is a function of atmospheric temperature and humidity. One-dimensional variational (1DVAR) analysis can be used to retrieve temperature and humidity profiles simultaneously from refractivity data. Profiles derived from 1DVAR method with COSMIC 2011 data occurred in China area are compared with the collocated radiosondes. The background data are ECMWF profiles and the retrieval results show good agreement with radiosondes. The effect of non-ideal gas compressibility on temperature and humidity retrieval errors is focused on in the 1DVAR analysis. Results compared with different months data show that non-ideal gas compressibility has a systematic effect on radio occultation retrieved atmospheric profiles. Including non-ideal gas effect correction the temperature bias to radiosondes is around 0.1 K, while the specific humidity bias is 0.5%. Because radio occultation data can be assimilated into operational numerical weather prediction system without bias correction, taking into consideration non-ideal gas effect is clearly very important. In addition, including this effect in radio occultation retrieval has important impact on climate applications.
2013, 62 (15): 159302.
doi: 10.7498/aps.62.159302
Abstract +
Combined with the multiple solution scheme (MSS) and the rain considered Geophysical model function (GMF+Rain), the two-dimensional variational (2DVAR) ambiguity removal technique is applied to the cyclone wind retrieval under rain condition with QuikSCAT scatterometer data. With the GMF+Rain model, the retrieved wind speed is effectively improved, but large wind direction error still exists when the background is in large error. In this paper, a changeable multi-parameter error model is introduced in the 2DVAR to reduce the wind direction error, and the sensitivity experiments of 2DVAR to its error model parameters are studied with cyclone Yagi QuikSCAT data, to choose the best parameters setting for cyclone wind retrieval with theoretical explanation. Numerical results show that 2DVAR is more effective in wind direction ambiguity removal with the proposed multi-parameter error model when the gross error probability in the multi-parameter error model is set to zero in comparison of the standard setting. The influence of the background is decreased with increasing backround error variance, decreasing the background error correlation length, or decreasing the gross error probabilities in multi-parameter error model.
