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CN 11-1958/O4
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Perpendicular magnetic anisotropy in the CoFeB/Pt multilayers by anomalous Hall effect
Liu Na, Wang Hai, Zhu Tao
Acta Physica Sinica, 2012, 61 (16): 167504
Research on enhanced perpendicular magnetic anisotropy in CoFe/Pd bilayer structure
Zhu Yun, Han Na
Acta Physica Sinica, 2012, 61 (16): 167505
Effect of light path folding on the properties of electron transport in dyesensitized solar cell
Liu Wei-Qing, Kou Dong-Xing, Hu Lin-Hua, Dai Song-Yuan
Acta Physica Sinica, 2012, 61 (16): 168201
Acta Physica Sinica  
  Acta Physica Sinica--2012, 61 (16)   Published: 20 August 2012
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Design and simulation of a cross split ring lefthanded materials unit structure

Yang Chen, Zhang Hong-Xin, Wang Hai-Xia, Xu Nan, Xu Yuan-Yuan, Huang Li-Yu, Zhang Ke-Xin
Acta Physica Sinica. 2012, 61 (16): 164101 doi: 10.7498/aps.61.164101
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In this paper, we present a novel compact left-handed material unit, which can generate the equivalent negative permittivity and negative permeability in the two-dimensional direction only by etching one side of the dielectric substrate. We propose a new formula for calculating the field and circuit to analyze the equivalent permittivity and the equivalent permeability that are used to explain the principle of the left-handed characteristic of the unit. In the simulation, the equivalent permittivity and permeability are calculated by the Nicolson-Ross-Weir method, and the negative refraction is verified by the prism experiment. The experiments show that the cross-ring structure unit can present left-handed properties with frequency bands appearing at 6.8–6.9 GHz in the two-dimensional incidence. The left-handed material can be used to design microwave field for its simple fabrication process.

The design of tank coating based on photonic crystal

Li Wen-Sheng, Luo Shi-Jun, Huang Hai-Ming, Zhang Qin, Fu Yan-Hua
Acta Physica Sinica. 2012, 61 (16): 164102 doi: 10.7498/aps.61.164102
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In order to reduce the infrared radiation of tank in actual combat, characteristics of tank barrel radiation after low speed firing are analyzed. Common SiO2 and Si are selected as the mediums according to the barrel radiation characteristic wavelength of 8–12 μm. With the consideration of the dispersion relation, an insulating coating with photonic crystal structure is designed. Mathematical computation indicates that when the two mediums each have 4 layers and their geometric thicknesses are 1330 nm and 825 nm respectively, there will be a strict band gap of 8–12 μm. When the geometric thicknesses of the two mediums increase, the band gap will have red shifts and the width will increase, and vice versa. As long as the geometry thickness variations of the two mediums are less than 10%, the original band gap will always exists. When the mediums are of 7–8 layers, the coating form a strict band gap in the above mentioned wavelength range. With the medium layer number increasing, there will be no substantial change with the band gap. The band gap structure is not sensitive to the change of incidence angle.

Simulation and experimental confirmation on the reconstruction of Bessel beams

Fan Dan-Dan, Zhang Qian-An, Cheng Zhi-Ming, Zheng Wei-Tao, Wu Feng-Tie
Acta Physica Sinica. 2012, 61 (16): 164103 doi: 10.7498/aps.61.164103
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The reconstruction property of the Bessel beam plays a significant role in the application of multi-plane micro-manipulation. We analyze the principle of the generation and the reconstruction of Bessel beam according to the Hankel wave theory; we also discuss the reconstructions of circular and square obstacles on-axial and off-axial of system in detail respectively. The generation of Bessel by axicon and the self-reconstruction property of Bessel beam after different kinds of obstacles are simulated by optical design software ZEMAX. Experimental result is used to confirm the simulation model, and it accords with the simulation very well. Therefore, we obtain a conclusion that the software ZEMAX can quickly and intuitively simulate the reconstruction of Bessel beam generated by axicon with high veracity.

Operation principle of optical waveguide isolator based on TE-TM mode conversion

Zeng Wei-You, Xie Kang, Chen Wei, Mao Shu-Zhe
Acta Physica Sinica. 2012, 61 (16): 164201 doi: 10.7498/aps.61.164201
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According to the perturbation theory, the theory of self-phase compensation is developed for the optical waveguide isolator based on the TE-TM mode conversion. The operation principle of such a device is explained in terms of synchronization of phase and power conversion. The effect of balancing phase mismatches of the two convertors on achieving a proper percentage of mode conversion is revealed. The simulation results confirm the self-phase compensation theory.

A novel method of improving coupling effiency of laser diode based on synthesized lens with graduaed index fiber

Yan Feng-Ping, Liu Peng, Tan Zhong-Wei, Tao Pei-Lin, Li Qi, Peng Wan-Jing, Feng Ting, Tan Si-Yu
Acta Physica Sinica. 2012, 61 (16): 164202 doi: 10.7498/aps.61.164202
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In this paper, a novel method of improving coupling effiency of laser diode to single mode fiber based on synthesized lens with graduaed index fiber is provided. The output beam with large astigmatism from laser diode is shaped and focused via synthesized lens and graduaed index fiber, and then couplied into single mode fiber. Analysis using Jones matrix theory indicates that the power coupler effect of 86% is obtained from output port of the single mode fiber. The tolerances for fiber length of graduaed index fiber, radial offset and tilt degree are 60 μm, 30 μm and 2.4 degree respectivily for 1 dB insert loss. This method can be used for improving the quality of optical beam and increasing output power for laser diode to single mode fiber with a large output optical power.

Analysis of absorption property for pumping laser with double cladding rare earth doped fiber

Yan Feng-Ping, Liu Peng, Tao Pei-Lin, Li Qi, Peng Wan-Jing, Feng Ting, Tan Si-Yu
Acta Physica Sinica. 2012, 61 (16): 164203 doi: 10.7498/aps.61.164203
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In this paper, a pump laser absorption model for double cladding rare earth doped optical fiber is established by using the finite difference beam propagation method combined with complex refractive index profile, and the absorption properties are analyzed in detail for some typical inner cladding structures by using this model. The results can be used to design the double cladding rare earth doped optical fiber.

Theoretical analysis of coherent perfect absorption in one-dimensional anti-laser

Shen Yun, Yu Guo-Ping, Fu Ji-Wu
Acta Physica Sinica. 2012, 61 (16): 164204 doi: 10.7498/aps.61.164204
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Detailed analyses and the correlations of coherent perfect absorption (CPA) in single-channel and two-channel structures are performed by the transfer matrix and scattering matrix method. The results show that there are many possibilities for single-channel and two-channel structures to satisfy the occurring of CPA. Moreover, with the same incident wavelength and refractive index of dielectric, the length of dielectric for two-channel CPA is twice that for single-channel. For instance, it is 3.701 μm/7.402 μm for single-/two-channel CPA as 756 nm wavelength is incident on Si material. Our results facilitate the application of CPA in optical modulator, switches, detector, etc., and they are also of significance for Si-based integration of optical circuits in optical communication and computer.

Wavelet transform of coherent state

Yu Hai-Jun, Du Jian-Ming, Zhang Xiu-Lan
Acta Physica Sinica. 2012, 61 (16): 164205 doi: 10.7498/aps.61.164205
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Two new mother wavelets are constructed on the basis of the quantum mechanics of classical wavelet transform. Based on that, the wavelet transform of coherent state and particle number state is studied with the technique of integration within an ordered product, and the wavelet transform from coherent state to particle number state is obtained by numerical calculation.

Theoretical and experimental study on femtosecond enhancement resonator

Han Hai-Nian, Zhang Jin-Wei, Zhang Qing, Zhang Long, Wei Zhi-Yi
Acta Physica Sinica. 2012, 61 (16): 164206 doi: 10.7498/aps.61.164206
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The femtosecond enhancement resonator has important applications in the fields of nonlinear optics, precision spectroscopy, etc. In particular, it has been become a powerful tool of generating ultraviolet optical frequency comb at a high repetition rate in recent years. In this paper, we analyze the characteristics of enhancement and dispersion in the femtosecond enhancement resonator by use of the circulating stable electric field method. The relations between enhancement multiple and fineness and between, resonance bandwidth and fineness as well as intracavity dispersion are obtained. Finally, we experimentally realize the resonance enhancement of 15 fs laser from a Ti:sapphire oscillator at a repetition rate of 175 MHz. The enhanced magnification is about 10.

The effects of shape and position on field distribution of discontinuous crack

Zhang Chun-Lai, Liu Chun-Ming, Xiang Xia, Wang Zhi-Guo, Li Li, Yuan Xiao-Dong, He Shao-Bo, Zu Xiao-Tao
Acta Physica Sinica. 2012, 61 (16): 164207 doi: 10.7498/aps.61.164207
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Elliptic paraboloid model is established, and three-dimensional finite-difference time-domain method has been employed to simulate the field distribution of discontinuous crack with different shapes and positions in fused silica output subsurface under 355 nm laser incidence. Results show that both electric field intensity and the number of enhanced points (with |E|≥ 2.0 V/m) follow a trend of first increasing and then decreasing with the increase of collinear axis length of ellipsoid. The light intensity enhancement factor reaches a maximal value when the axial ratio is 1.1 to 1.2. If parallel collinear axis length of ellipsoid increases, the electric field intensity first increases gradually, and then becomes stable when the axial ratio is 0.53. At the same time, the number of enhanced points grows rapidly.

Optical polarization rotation in a rubidium vapor

Cao Ming-Tao, Qiu Shu-Wei, Guo Wen-Ge, Liu Tao, Han Liang, Liu Hao, Zhang Pei, Zhang Shou-Gang, Gao Hong, Li Fu-Li
Acta Physica Sinica. 2012, 61 (16): 164208 doi: 10.7498/aps.61.164208
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We theoretically and experimentally study the effects of Faraday rotation, optical polarization of self-rotation, and their overlapping rotation. In our theoretical simulation, we set up a simple and effective theoretical model for the three kinds of rotations. In our experiment, the atomic vapor is placed in a magnetic shielding cavity to shield the earth magnetic field. Doppler-free spectrum configuration is used and the F=2 → F'=3 transition of 87Rb D2 line is chosen. We observe the three kinds of rotations, separately. Experimental results and theoretical simulations are in good agreement.

Effective radius of curvature of truncated laser beams with amplitude modulation and phase fluctuation

Shao Xiao-Li, Ji Xiao-Ling
Acta Physica Sinica. 2012, 61 (16): 164209 doi: 10.7498/aps.61.164209
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Usually, high-power laser beams are amplitude modulated and have phase fluctuations (PFs). The analytic formula of the effective radius R of curvature of truncated laser beams with amplitude modulations (AMs) and PFs propagating through atmospheric turbulence is derived by using the statistical optics method. It is shown that the R in free space increases with the increases of the phase fluctuation parameter, the intensity modulation parameter and the truncated parameter. And the influence of turbulence on the R also increases with the increases of the three parameters. Furthermore, the R of Gaussian beams is largest in free space, but it is most affected by turbulence. Therefore, in turbulence the R of truncated laser beams with AMs and PFs is even larger than that of Gaussian beams when the propagation distance is large enough. In particular, the relative effective radius Rr of curvature varies non-monotonically with propagation distance, and there exists a minimum at a propagation distance where the influence of turbulence on the R is largest. In addition, the position where the Rr reaches its minimum increases with the increasees of intensity modulation and phase fluctuation.

Magneto-optical Faraday rotation effect enhancement of a thick metal Ag

Dong Li-Juan, Du Gui-Qiang, Yang Cheng-Quan, Shi Yun-Long
Acta Physica Sinica. 2012, 61 (16): 164210 doi: 10.7498/aps.61.164210
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In order to more comprehensively know and understand the physical properties of the metal Ag, its magneto-optical characteristics are investigated. By using light tunneling mechanism, we study the transmission and magneto-optical Faraday rotation effect of a thick metal Ag sandwiched between two dielectric photonic crystals. The results show that the transmission and magneto-optical Faraday rotation effect of a thick metal Ag can be enhanced, owing to the localized electromagnetic field at the interface between the metal Ag and photonic crystal.

Emissivity study of the array shaped blackbody in the microwave band

Jin Ming, Bai Ming, Miao Jun-Gang
Acta Physica Sinica. 2012, 61 (16): 164211 doi: 10.7498/aps.61.164211
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Different from that in the optical band, the blackbody in the microwave band is constructed in a coated cone array structure. The blackbody of this type can be used in calibrating microwave radiometers with standard brightness radiations, and needs to have a uniform surface thermal distribution and high emissivity. The emissivity study of such a blackbody can be performed based on the Kirchhoff's law of thermal equilibrium, in a reflection determination routine. The emissivity characteristics varying with frequency have been intensively studied, but their variations with direction and polarization have not received much attentions. Starting from the Floquet mode analysis, a reflection evaluation scheme for the blackbody is presented, which is more robust than that based on the back-ward RCS determination. Based on the presented scheme, the trends of emissivity varying with frequency, direction, polarization are studied, for a microwave blackbody design. Results show that the emissivity rises as the frequency rises in a range from X band to Kα band; and in the low frequency band, the trend of the vertical polarization emissivity varying with elevation angle is different from that of the horizontal polarization emissivity, and there exists an obvious phenomenon that the vertical polarization emissivity declines with the increase of elevation angle. These phenomena are related to the electromagnetic absorption characteristics of the coating layer.

Recording and numerical reconstruction of single digital tomographic hologram

Zhou Wen-Jing, Hu Wen-Tao, Qu Hui, Zhu Liang, Yu Ying-Jie
Acta Physica Sinica. 2012, 61 (16): 164212 doi: 10.7498/aps.61.164212
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In this paper, we study the single tomographic hologram (STH). We first define the STH and analyze the frequency spectrum of the STH containing three projections, then perform the simulation analysis including the digital recording, information separation and numerical reconstruction of the STH, and finally we rebuild an experimental setup to record the single tomographic hologram from three projections. A phase grating with 100 μm period is used as a test sample. The reconstructed period error of grating is between 4%-5%. Both simulation analyse and experimental results demonstrate the feasibility and validity of the STH. In the next work, the improvement of the reconstruction quality for single digital tomographic hologram will be discussed.

Noise annoyance from a mixture of multiple single sources: rating and prediction

Yan Liang, Chen Ke-An, Ruedi Stoop
Acta Physica Sinica. 2012, 61 (16): 164301 doi: 10.7498/aps.61.164301
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In this paper, noise annoyance from a mixture of multiple single sources is studied with emphasis on subjective evaluation and objective prediction. From 10 subjects, annoyance values for all single and artificially combined noise samples are collected using the semantic differential method with a suitable verbal scale. We propose a novel method to determine the utility weights of a multivariate linear regression model by comparing the total annoyance αT of the combined noise sample to every single annoyance αi from its componential single sound sample. This method predicts αT on the premise of given αi. Our results demonstrate that the multivariate linear regression model and the calculated utility weights provide a good and conceptually simple framework to predict the total noise annoyance.

Effects of envelope modulation rate and carrier frequency on auditory temporal modulation detection

Meng Qing-Lin, Yuan Meng, Mou Hong-Yu, Chen You-Yuan, Feng Hai-Hong
Acta Physica Sinica. 2012, 61 (16): 164302 doi: 10.7498/aps.61.164302
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The effects of envelope modulation rate (below 300 Hz) and pure-tone carrier frequency (below 8 kHz) on auditory temporal modulation detection ability (TMDA) are investigated through psychophysical experiments. The stimuli are sinusoidal amplitude-modulated signals with pure tone carriers. Two-alternative-forced-choice procedure with adaptive step is used. The temporal modulation transfer functions with different carrier frequencies are measured. Twenty-two normal-hearing subjects (22 to 29 years old) are recruited for this study. Experimental results show that both envelope modulation rate and carrier frequency have significant effects on TMDA. When carrier frequency is below 2 kHz, TMDA improves with the increase of modulation rate. When carrier frequency is above about 3.5 kHz, TMDA is influenced by the variation of carrier frequency, but without significant monotonic trend. When modulation rate is between 10 and 100 Hz, carrier frequency does not affect TMDA. When the modulation rate is between 150 and 300 Hz, TMDA decreases with the increase of carrier frequency until the carrier frequency is above 3.5 kHz.

Fractal analysis of Herschel-Bulkley fluid flow in a capillary

Yun Mei-Juan, Zheng Wei, Li Yun-Bao, Li Yu
Acta Physica Sinica. 2012, 61 (16): 164701 doi: 10.7498/aps.61.164701
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A fractal model for Herschel-Bulkley fluid in a capillary is proposed based on the fractal theory. The proposed model relates flow rate, velocity, starting pressure gradient and effective permeability to the rheological characteristics of fluid and the structural parameters of capillary, and all parameters in the proposed expressions have clear physical meanings. The analytical expressions reveal the physical principle for Herschel-Bulkley fluid flow in a capillary.

Numerical studies of unsteady ignition of pulverized magnesium particle cloud

Yang Jin-Zhao, Xia Zhi-Xun, Hu Jian-Xin
Acta Physica Sinica. 2012, 61 (16): 164702 doi: 10.7498/aps.61.164702
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A one-dimensional unsteady magnesium particle cloud ignition model with finite influencing sphere is established. The behavior of ignition of magnesium particle cloud is numerically simulated. The result shows that when the reaction is speeded up on the surface of magnesium particle, the temperature of the particle phase rises rapidly up to ignition temperature, while the surrounding air is much slower in temperature rising than particles; the gas temperature rising is unconspicuous in the whole sphere in the ignition process, albeit it is significant near the particle surface. The effects of the interior parameters and the environmental parameters on the ignition of the magnesium particle cloud are analyzed. With the increase of particle concentration, the particle cloud becomes easier to be ignited, and reduction in its ignition time delay can be seen. However, when the particle concentration has increased to some specific extent and its further increase will be adverse to the ignition of the particle cloud. The influence of the environmental pressure on the ignition of particle cloud is insignificant, and the ignition performance of the particle cloud almost keeps constant in a range of 1-5 atm. The oxygen concentration in the gas phase also has a weak effect on the ignition performance of particle cloud, but when the oxygen concentration is very low, the effect will significantly increase. The particle size, the initial temperature of the gas/particle and the radiant source have all great influences on the ignition performance of the particle cloud. Small particle and high temperature are helpful for speeding up the ignition process. The tendency obtained by numerical simulation coincides well with that of the experimental results from the literature.


Threshold-voltage and hole-sheet-density model of quantum well Si/SiGe/Si p field effect transistor

Li Li, Liu Hong-Xia, Yang Zhao-Nian
Acta Physica Sinica. 2012, 61 (16): 166101 doi: 10.7498/aps.61.166101
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The low hole mobility restricts the application of Si complementary metal-oxide-semiconductor in high frequency fields. In this paper, the SiGe p-metal-oxide-semiconductor field-effect-transistor (PMOSFET) is studied. By numeric modeling and analysis, the vertical potential distribution of the device is obtained through solving one-dimensional Poisson equations, and the threshold-voltage model is established. The effects of Ge-profile, thickness of Si buffer layer, thickness of Si cap layer and substrate doping on the threshold-voltage are discussed. In SiGe layer, the quantization effect of the potential well in valence band is taken into account. When the gate voltage is large enough, the holes in SiGe channel layer will transit to the Si/SiO2 interface due to band bending and energy level splitting, causing the degradation of device performance. Thus, the hole-sheet-density model in quantum channel of SiGe PMOSFET is established, and the concept of the maximum operating gate voltage is proposed, moreover the channel saturation induced by gate voltage is calculated and analyzed. The results show that the threshold voltage and the maximal operating gate voltage are related to Ge-profile, and a proper increase of Ge-profile can extend the range of the operating gate voltage effectively.

Melting behavior of Au-Pd eutectic nanoparticle: A molecular dynamics study

Wang Zhi-Gang, Huang Rao, Wen Yu-Hua
Acta Physica Sinica. 2012, 61 (16): 166102 doi: 10.7498/aps.61.166102
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In this paper, we present an investigation on thermal stability of Au-Pd eutectic nanoparticle by using molecular dynamics simulation with embedded-atom potential. The results show that the melting point of Au-Pd eutectic nanoparticle is remarkably higher than that of pure Au one but lower than that of Pd one. By the analyses of Lindemann index, it is found that Au atoms first melt, then induce the melting of Pd atoms. The temperature range of melting is broader for Au-Pd eutectic nanoparticle than that for Au and Pd nanoparticles.

Solidification behaviors of undercooled Ni-P alloys

Huang Qi-Sen, Liu Li, Wei Xiu-Xun, Li Jin-Fu
Acta Physica Sinica. 2012, 61 (16): 166401 doi: 10.7498/aps.61.166401
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In order to gain an insight into the primary phase selection and solidification structure formation while undercooled eutectic alloys solidify, Ni100-xPx (x=18, 19, 19.6, 20, 21, atomic percent) alloy melts are undercooled to different temperatures below the equilibrium liquidus. The recalescence behavior associated with rapid solidification is monitored by a high-speed infrared pyrometer, and the solidification structure is analyzed systematically. When α-Ni/Ni3P regular eutectic forms as the primary phase during rapid solidification, single recalescence event takes place. In the resulting anomalous eutectic, fine granular grains of α-Ni are distributed uniformly in the Ni3P matrix. When the primary phase is one of the eutectic phases, however, there is a second recalescence event following the first one, resulting from nucleation of the other phase in the remaining liquid and the subsequent rapid eutectic growth. In this case, there are two types of granular grains whose sizes are significantly different from those in the anomalous eutectics. Finally, a coupled growth zone of eutectics is determined. At large undercoolings, α-Ni rather than Ni3P solidifies as the primary phase even in the Ni-P hyper-eutectic alloys due to its rapider growth kinetics.

Bootstrap percolation on bipartite networks

Wan Bao-Hui, Zhang Peng, Zhang Jing, Di Zeng-Ru, Fan Ying
Acta Physica Sinica. 2012, 61 (16): 166402 doi: 10.7498/aps.61.166402
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Bootstrap percolation was first used in statistic physics to study the phenomenon that magnetic-order goes down and disappears because of the disturbance of nonmagnetic impurity. With the development of complex network, the application of bootstrap percolation in network has attracted much attention. In the real world, many systems naturally exhibit the two-branch structure. And bipartite network is one of important networks in complex networks. In this paper, we use the dynamics equation and computational simulation to study the bootstrap percolation in bipartite networks. The parameters we focus on are the node initial active ratios f1 and f2 and active thresholds Ω1, and Ω2. We draw the conclusion that the ratio of active nodes has discontinuous transition, which will gradually disappear with parameters varying. We also prove the consistency between the dynamic equation and simulation results.

The study on the mechanism of liquid surface in interior corner and the applicability of Surface Evolver

Xu Sheng-Hua, Wang Lin-Wei, Sun Zhi-Wei, Wang Cai-Xia
Acta Physica Sinica. 2012, 61 (16): 166801 doi: 10.7498/aps.61.166801
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The study on the fluid behavior under microgravity condition is of great importance for the investigation of the fluid behavior caused by surface tension, the prediction and control of the liquid location at microgravity, the fluid management in space, etc. In this study, we analyze the relationship between the contact angle and the direction of the contact line in interior corner of container, and compare it with the Concus-Finn theory. The mechanism of mutual correlation among the direction of contact line, the contact angle and the geometric shape of container, and the physical meaning of relevant theory by Concus and Finn etc. are also analyzed. By comparing the theoretical results with the numerical results calculated by Surface Evolver, we find that the Surface Evolver program can predict the contact line and the liquid surface in interior corner with angle smaller than 180°, simply by the automatically partitioned grid. However, when the angle of the interior corner is larger than 180°, the results given by Surface Evolver can have a remarkable error with the automatically partitioned grid. In order to reduce the error, it is necessary to manually partition the surface to reduce the singularity of grid. And the results from Surface Evolver should be tested quantitatively at the interior corners for complicated containers. The theoretical analysis and the numerical results calculated by Surface Evolver in this study will be helpful for understanding the characteristics and mechanism of liquid surface in interior corner, choosing the applicable parameters for Surface Evolver program, and the future study on the behavior of liquid in interior corner, especially under microgravity condition.

Investigation of the electronic and mechanical properties of Al2O3-AlN solid solution by virtual crystal approximation

Wang Ying, Lu Tie-Cheng, Wang Yue-Zhong, Yue Shun-Li, Qi Jian-Qi, Pan Lei
Acta Physica Sinica. 2012, 61 (16): 167101 doi: 10.7498/aps.61.167101
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Based on the density functional theory within plane-wave pesudopotential method, the band structure and elastic properties of spinel Al(64 + x)/3(8-x)/3O(32-x)Nx (x=2, 5, 8) and α-Al2O3, AlN are calculated. The spinel Al(64 + x)/3(8-x)/3O(32-x)Nx (x=2, 5, 8) are calculated by using the 'virtual crystal approximation'. The results prove it possible to study the Al(64 + x)/3(8-x)/3O(32-x)Nx (x=2, 5, 8) by this approximation. The calculated elastic constants and hardness features accord well with the experimental results. The five structures in the Al2O3-AlN solid solution region all show brittle features and the Al23O27N5 shows the lowest brittleness. High hardness and low brittleness reflect that Al23O27N5 has a great flexural strength. Elastic property analysis confirms the mechanical stability, it also reveals that AlON has highly elastic anisotropy. Band structure analysis shows that the spinel AlON and α-Al2O3, AlN are both direct bandgap materials. Hybridizations take place between Al-3p, 3s and O, N-2p orbitals near the Fermi level in the AlON. The calculated results are consistent with relevant experimental results, which provides a theoretical method and reference for the further study.

First-principles study on the effects of high Al doped on the band gap and absorption spectrum of ZnO

Hou Qing-Yu, Dong Hong-Ying, Ying Chun, Ma Wen
Acta Physica Sinica. 2012, 61 (16): 167102 doi: 10.7498/aps.61.167102
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According to the density functional theory, using first-principles plane-wave ultrasoft pseudopotential method, we set two different kinds of Zn1-xAlxO supercell models of substituting Zn atom with Al atom and optimige the geomertries for the two models. The total density of states and the band structures are also calculated. The results show that in a range of high doping concentration, when the doping concentration of Al atoms increases, the band gap will be decrease, blue shift will decrease, which accords with the experimental results.

First-principles study on the electronic structures and absorption spectra of Sm-N codoped anatase TiO2

Li Cong, Hou Qing-Yu, Zhang Zhen-Duo, Zhao Chun-Wang, Zhang Bing
Acta Physica Sinica. 2012, 61 (16): 167103 doi: 10.7498/aps.61.167103
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Based on first principles within density-functional theory, we establish three models of N doped anatase TiO2, Sm doped anatase TiO2 and Sm-N codoped anatase TiO2 by using the plane-wave ultrasoft pseudopotential method. We calculate their densities of states, band structures and absorption spectra. Their results show that although the N doped anatase TiO2 takes the best redshift, the Sm-N codoped anatase TiO2 makes better lifespan of electron and the Sm-N codoped anatase TiO2 is more stable.

The physical characteristic study on luminance uniformity and temperature for power GaN LEDs chip

Chen Huan-Ting, Lü Yi-Jun, Gao Yu-Lin, Chen Zhong, Zhuang Rong-Rong, Zhou Xiao-Fang, Zhou Hai-Guang
Acta Physica Sinica. 2012, 61 (16): 167104 doi: 10.7498/aps.61.167104
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In this paper, we study the relationship among current density distribution, heat and temperature based on current continuity equation, ohm law and three-dimensional heat transfer model. The relationship between luminance distribution and current spreading of GaN blue light emitting diode (LED) is studied. Luminance distribution is proved to be an effective method of distinguishing the performance of current spreading. Because of the close relationship among temperature, luminance distribution and current density, a qualitative method of optimizing electrode structure and current spreading is proposed. With different currents and heat sink temperatures, the current non-uniformity and the luminance distribution of LED are analyzed. Temperature or current density crowding results in heat accumulation, increase of non-radiative recombination and the restriction of the emitting photons, hence thermal flux is an important factor influencing the luminance distribution. Through carrier transport mechanism, the reason for the temperature influence on luminance distribution is explained. Optimized contact electrode structure can improve current spreading and luminance uniformity, also considerably increase the reliability of high power LED.

Suppression of visible light emission of ZnO nanostructures by Ga-doping

Shen Qing-He, Gao Zhi-Wei, Ding Huai-Yi, Zhang Guang-Hui, Pan Nan, Wang Xiao-Ping
Acta Physica Sinica. 2012, 61 (16): 167105 doi: 10.7498/aps.61.167105
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Ga-doped ZnO nanostructures with various doping concentrations are prepared by using carbon thermal reduction reaction and in situ doping method. X-ray diffraction measurement reveals only wurzite structures existing in Ga-doped ZnO nanostructures. Scaning electron microscopy observations show that with the increase of Ga doping concentration, the morphology of ZnO nanstrucuture varies gradually from nanorods to nanocones. From the photoluminescence, we find that the visible light emission of ZnO nanostructures can be suppressed obviously and even disappears with the increase of Ga doping concentration. Moreover, the suppression of visible light emission is correlated well with the behavior, and X-ray photoelectron spectroscopy measurement reveals that the vacancy oxygen in ZnO nanostructure decreases drastically with the increase of Ga doping concentration. This result offers a new strong evidence for the mechanism that the visible light emission of ZnO nanostructures is caused by the oxygen vacancy defects. This work also demonstrates that a little Ga incorporation into ZnO nanostructures can effectively reduce the oxygen vacancy defects occurring.

Influence of sintering temperature on thermoelectric properties of La0.1Sr0.9TiO3 ceramics

Sun Yi, Wang Chun-Lei, Wang Hong-Chao, Su Wen-Bin, Liu Jian, Peng Hua, Mei Liang-Mo
Acta Physica Sinica. 2012, 61 (16): 167201 doi: 10.7498/aps.61.167201
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Ceramic samples of La0.1Sr0.9TiO3 are synthesized by conventional solid state reaction technique at 1440℃, 1460℃, 1480℃ and 1500℃, respectively. Their thermoelectric properties are investigated. X-ray diffraction characterization confirms that the main crystal structure is of perovskite. Scanning electron microscope images indicate that all ceramic samples are dense and compact, and that the average grain size increases with the increase of sintering temperature. Electrical resistivity and Seebeck coefficient of samples are measured in the temperature range between room temperature and 800℃. In general, with the increase of sintering temperature, the electrical resistivity first increases, and then decreases. With the increase of sintering temperature, the absolute Seebeck coefficient first increases, and then decreases. A maximal power factor 21 μW·K-2·cm-1 is obtained at 165℃ for the sample sintered at 1480℃ because of its reletivly high absolute Seebeck coefficient and reletively low electrical resistivity.

Theoretical analysis on the upper critical field of superconductor NbS2

Huang Hai, Lu Yan-Yan, Wang Wen-Jie
Acta Physica Sinica. 2012, 61 (16): 167401 doi: 10.7498/aps.61.167401
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From the two-band Ginzburg-Landau theory, we study the temperature dependence of upper critical field on the layered superconductor NbS2. The temperature dependence of the anisotropic parameter for upper critical filed is also obtained. All the results fit the experimental data well in a broad temperature range. Thus our results show strong evidence that two-gap scenario is better to account for the superconductivity of NbS2. The anisotropic parameter of the upper critical field for NbS2 starts to decrease from 5.0 K, and this behavior is similar to those of MgB2 and NbSe2. However for NbS2 this number is about 7.3, which is much greater than the ones in MgB2 and NbSe2. The results also show that the band with the larger gap exhibits that the effective mass ratio between the in-plane and out-of-plane direction is about 54, and the other band indicates that the effective mass ratio is almost isotropic.

Ferromagnetic resonance phenomenon of magnetic thin film under a perpendicular field

Gu Wen-Juan, Pan Jing, Hu Jing-Guo
Acta Physica Sinica. 2012, 61 (16): 167501 doi: 10.7498/aps.61.167501
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Regarding ferromagnetic resonance frequency as a function of the perpendicular external magnetic field, the ferromagnetic resonance phenomenon is investigated. The results show that for the case where the external magnetic field is parallel to the its plane and the magnetic thin film has a perpendicular uniaxial magnetiocrystalline anisotropy, magnetic resonance frequency is divided into two categories, i.e., low frequency branch and high frequency branch, their specific relation depends on the magnetic anisotropy of the magnetic film; when external magnetic field is perpendicular to the systemic plane, the magnetic resonance frequency displays only a branch with the change of external magnetic field. In general, the magnetic resonance frequency decreases with the increase of the external magnetic field nonlinearly and monotonically. However, when the ratio between the cubic magnetocrystalline anisotropic field Hk1 and uniaxial magnetocrystalline anisotropic field Ha is about 2/3 < Hk1/Ha < 1, the magnetic resonance frequency increases with the increase of external magnetic field, which is in good agreement with the experimental results. The results show that through magnetic resonance spectrum, the vertical magnetic anisotropy in magnetic thin film can be distinguished.

Investigation of positron annihilation in Fe52Co34Hf7B6Cu1 amorphous alloy treated by intermediate frequency magnetic pulse

Zhang Yan-Hui, Li Yan-Long, Gu Yue, Chao Yue-Sheng
Acta Physica Sinica. 2012, 61 (16): 167502 doi: 10.7498/aps.61.167502
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The effect of intermediate frequency magnetic pulse treatments on Fe52Co34Hf7B6Cu1 amorphous alloy prepared by melt-spun technique is investigated. The microstructure and structural defects of the treated specimens are investigated by TEM, Mössbauer spectroscopy and position annihilation lifetime spectra. The results show that the treated specimens by intermediate frequency magnetic pulse are partially crystallized, the content of the crystallization phase increases with the increase of the magnetic pulse frequency, and the crystalline volume fraction is 33.1% at a frequency of 2000 Hz. For the as-quenched amorphous alloy, the annihilation lifetime τ1 is 150.5 ps in the monovacancy-like free volume, and the relative intensity I1 is 77.7%. The annihilation lifetime τ2 is 349.7 ps in the microvoid, and the relative intensity I2 is 22.3%. With the increase of the magnetic pulse frequency, the values of τ1 and τ2 of the treated specimens decrease, I1 increases, I2 and τ decrease compared with the as-quenched amorphous alloy.

Effect of Pt spacers on interface exchange coupling in ferromagnetic/antiferromagnetic bilayers

Wang Yi-Jun, Liu Yang, Yu Guang-Hua
Acta Physica Sinica. 2012, 61 (16): 167503 doi: 10.7498/aps.61.167503
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By inserting a Pt spacer between ferromagnetic (FM)/antiferromagnetic (FeMn) coumpling systems or by doping Pt element in the AFM layer, the depth dependence of Pt spacer and the thickness dependence of Pt doping layer on exchange bias (Hex) and coercivity (Hc) are investigated. The results indicate that the number of uncompensated spin moments (UCSs) of NiFe/FeMn(dPt)/Pt/FeMn increases as a result of inserting Pt spacer, which enhances Hex and Hc of the system. Also, the distribution depth about 1.3 nm of UCS of FeMn in NiFe/FeMn system is inferred. Besides, by doping Pt element in FeMn near the FM/FeMn interlayer, we find that the Hex of the system is enhanced efficiently, which is caused by the huge increase of the number of UCSs in the system.

Perpendicular magnetic anisotropy in the CoFeB/Pt multilayers by anomalous Hall effect Hot!

Liu Na, Wang Hai, Zhu Tao
Acta Physica Sinica. 2012, 61 (16): 167504 doi: 10.7498/aps.61.167504
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The perpendicular magnetic anisotropy (PMA) in as-deposited [CoFeB/Pt]n multilayer is studied by using anomalous Hall effect. A clear PMA is observed in the ultrathin (~ 0.5 nm) amorphous CoFeB layer sandwiched by Pt. The PMA in as-deposited [CoFeB/Pt]n multilayers is strongly dependent on the thicknesses of CoFeB, Pt, and the number of CoFeB/Pt bilayers. With the increase of the number of CoFeB/Pt bilayers (n ≥ 5), the hysteresis loop changes from rectangular to bow-tie shaped, and then the net moment approaches to zero in the remnant state. Moreover, the coercivty of [CoFeB/Pt]n multilayers is much low, which meets the requirement for free perpendicular electrode in the future spintronic device.

Research on enhanced perpendicular magnetic anisotropy in CoFe/Pd bilayer structure Hot!

Zhu Yun, Han Na
Acta Physica Sinica. 2012, 61 (16): 167505 doi: 10.7498/aps.61.167505
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A series of CoFe/Pd bilayer thin films is fabricated by introducing a native oxide layer to the interface or to the inside of CoFe layer in this paper. The results indicate that the magnetic anisotropy of the film is transformed from in-plane to out-of-plane after annealing by introducing the native oxide layer. For the samples with the introduction of native oxide layer into CoFe layer, the strong perpendicular magnetic anisotropy is maintained in a wide range of the effective thickness (1.2–2 nm) of magnetic layer. For the perpendicular magnetic films, the thickness of CoFe layer in this special bilayer structure is at least 1.4 nm, thicker than in common CoFe/Pd multilayer structure. The results in this paper are beneficial for the fabrication of the electrodes in perpendicular magnetic devices with high thermal stability.

Study on magnetic domain deflection in Tb0.3Dy0.7Fe2 alloy

Li Li-Yi, Yan Bai-Ping, Zhang Cheng-Ming, Cao Ji-Wei
Acta Physica Sinica. 2012, 61 (16): 167506 doi: 10.7498/aps.61.167506
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The characteristics of magnetic domain deflection and permeability under piezomagnetic and magnetoelastic effects in Tb0.3Dy0.7Fe2 alloy are studied in this paper. Based on the minimal value principle of Stoner-Wolhfarth model, the curve of free energy versus domain deflection angle is analyzed, and the angle deflections of magnetic domain under differ compressive stresses and magnetic fields are discussed. The calculational and experimental results of permeability under stress and magnetic field loads are used to confirm the analysis of domain deflection in ally. These results indicate that the magnetic domains [111] and [111] each have a transition effect of angle deflection with the increase of stress and magnetic field, which can be used to explain the huge magneticostrictive mechanism of Terfenol-D. Also, permeability has a negative relation with stress and magnetic field, and the influence of magnetic energy on permeability is greater than the stress energy effect, especially under small loads. The experimental results of permeability are in a good agreement with the calculations confirming the validity of calculation and analyzsis. The above computations have a significant guidance for analyzing and studying the magnetic domain deflection model and hysteresis in Terfenol-D.

Effects of the annealing temperature on microstructure and room-temperature ferromagnetism of N+ ion-implanted ZnO: Mn thin film

Yang Tian-Yong, Kong Chun-Yang, Ruan Hai-Bo, Qin Guo-Ping, Li Wan-Jun, Liang Wei-Wei, Meng Xiang-Dan, Zhao Yong-Hong, Fang Liang, Cui Yu-Ting
Acta Physica Sinica. 2012, 61 (16): 168101 doi: 10.7498/aps.61.168101
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The Mn-N codoped ZnO thin films are fabricated on quartz glass substrates using the radio-frequency magnetron sputtering technique together with the direct N+ ion-implantation. The effects of annealing temperature on microstructure and room-temperature ferromagnetism of the thin films are investigated. The results indicate that both divalent Mn2+ and trivalent N3- ions are incorporated into ZnO lattice. As the annealing temperature increases, the lattice distortion induced by N+ ion-implantation can decrease, and the N3- may escape from the film, which results in the reducing of acceptor (NO) concentration. Ferromagnetism is observed in the (Mn,N)-codoped ZnO thin film at 300 K and found to be the sensitive to the acceptor concentration. The mechanism of room-temperature ferromagnetism in the ZnO:(Mn, N) is discussed based on the bound magnetic polaron model.

Research on the shape memory effect and thermalelasticity of a novel intellectual damping material

Hong Jie, Liu Bao-Long, Zhang Da-Yi, Ma Yan-Hong
Acta Physica Sinica. 2012, 61 (16): 168102 doi: 10.7498/aps.61.168102
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In this paper, we introduce a novel intellectual damping material–shape memory alloy metal rubber (SMAMR), which is made from the shape memory alloy through the process similar to that for metal rubber. The shape craft, shape memory effect and mechanical properties are tested and discussed. The results show that the SMAMR has the combination properties of both shape memory alloy and metal rubber, such as high elasticity and damping capacity, low density, designable porosity, shape memory effect, and temperature dependent mechanical properties. The SMAMR not only has modulus and loss factor varying linearly with temperature during the phase transformation between Martensite and Austenite, which is quite available in the active control of vibration; but also has the modulus and loss factor large enough to be used as bearing structure. So the SMAMR is a significant integration of both functional material and structural material, and is quite attractive in active vibration control.

A molecular dynamics study of silica cluster cutting single crystalline silicon asperity

Si Li-Na, Guo Dan, Luo Jian-Bin
Acta Physica Sinica. 2012, 61 (16): 168103 doi: 10.7498/aps.61.168103
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The molecular dynamics simulation method is used to study the process of silica particle cutting the roughness surface at various cutting depths. The conditions of the asperity and the particle, force bearing state of particle, the distributions of coordination number and temperature in the asperity are investigated. The simulation results show that the material removal rate is small when the cutting depth is smaller than 0.5 nm, and the removed atoms sticking to the silica particle are in single atom or atom cluster form. When the cutting depth is larger than 1 nm, the material removal rate becomes larger; meanwhile a larger scrap is formed. The crystalline silicon is converted into a locally ordered transient structure which is similar to Si-Ⅱ and Bct5-Si with the increases of temperature and pressure in the cutting process; then the transient structure forms amorphous silicon directly as the temperature and pressure decrease after the cutting process.

Effect of light path folding on the properties of electron transport in dyesensitized solar cell Hot!

Liu Wei-Qing, Kou Dong-Xing, Hu Lin-Hua, Dai Song-Yuan
Acta Physica Sinica. 2012, 61 (16): 168201 doi: 10.7498/aps.61.168201
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In this paper, an electron continuity equation with light path folding is developed based on the reflection structure of photoanode in a dye sensitized solar cell (DSC). The characteristics of modulated photocurrent frequency response are calculated, and the effects of light path folding on electron transport property are studied under different absorption and reflection conditions. Intensity modulated photocurrent spectroscopy measurements show that the established model reflectes the actual characteristic of the response to modulated photocurrent frequency when the light path is folded inside the DSC. The kinetic of electron transfer process depends on the light absorption coefficient, film thickness and large particle reflection ability and other factors in DSC with reflector structure. The deep trap is filled and residence time of electron in trap is shortened. It is attributed to the fact that the light path folding reduces the effect of trap/detrap and accelerates the electron transportation.

Linear analysis of open-style dielectric-lined azimuthally periodic circular waveguide

Liu Yang, Wei Yan-Yu, Shen Fei, Xu Xiong, Liu Yang, Lai Jian-Qiang, Huang Ming-Zhi, Tang Tao, Gong Yu-Bin
Acta Physica Sinica. 2012, 61 (16): 168401 doi: 10.7498/aps.61.168401
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A novel slow-wave structure, i.e., an open-style dielectric-lined azimuthally periodic circular waveguide (open-style DLAP-CW) which can be applied to millimeter wave traveling-wave tube, is proposed. The hot dispersion characteristics are derived by the self-consistent relativistic field theory. And the electron beam interaction in the novel slow-wave structure (SWS) is analyzed in a linear frame. The linear gain characteristics of the DLAP-CW is studied analytically for dimensions of the improved SWS and the parameters of the electron beam. The results illustrate that selecting the appropriate dimensions of the metal rods can improve the small-signal gain. Finally, a comparison of the small-signal gain of this structure with a close-style DLAP-CW is made, and the results validate that the novel SWS has an advantage over the close-style DLAP-CW in gain with little influence on the bandwidth, which can potentially improve electron efficiency in the beam wave interaction. The research in this paper will also be a foundation of the theory for open-style dielectric-lined azimuthally periodic circular waveguide traveling-wave tube.

Influence of structure parameters on the performance of p-i-n InGaN solar cell

Zhou Mei, Zhao De-Gang
Acta Physica Sinica. 2012, 61 (16): 168402 doi: 10.7498/aps.61.168402
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The effect of structure parameters on the performance of p-i-n InGaN solar cell is investigated by theoretical calculation. It is found that the short-circuit current decreases while the open-circuit voltage increases with the increase of bandgap of InGaN material. The maximal energy conversion efficiency of p-i-n homojunction InGaN solar cell can be obtained when the bandgap of InGaN is around 1.5 eV. It is also found that the energy conversion efficiency can be improved by appropriately increasing bandgap of p-InGaN p-i-n heterojunction InGaN solar cell, in addition, the efficiency of p-i-n heterojunction InGaN solar cell may be increased further by employing the back electric filed structure. The simulation results suggest that performance of InGaN solar cell can be improved by employing p-i-n heterojunction structure if the appropriate bandgaps of p-InGaN and n-InGaN are adopted.

The lysogeny/lysis switch and entropies of stationary states in λ phage

Feng Wei, Ding Hui, Lin Hao, Luo Liao-Fu
Acta Physica Sinica. 2012, 61 (16): 168701 doi: 10.7498/aps.61.168701
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The system of Escherichia coli infected by λ phage is one of the templates for quantitative study of regulated networks. In this article, according to the characteristics of the interactions between operators and regulators, the probabilities of regulators binding to operators are described by thermodynamic partition function. On the basis of bifurcation analysis of this regulated network, the entropies of stationary states are calculated. Results show that the entropies of both lysogenic state and lytic state are lower than those of saddle-point and bifurcation point states. Moreover, we find that the lysogenic state has lower entropy than lytic state, which proves that the lysogenic state has a higher biological order.

Preliminary analyses on characteristics of sea surface temperatures in Kuroshio and its extension and relations to atmospheric circulations

Wang Shan-Shan, Guan Yu-Ping, Li Zhi-Jin, Chao Yi, Huang Jian-Ping
Acta Physica Sinica. 2012, 61 (16): 169201 doi: 10.7498/aps.61.169201
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A sea surface temperature (SST) based index, denoted as KI, is designed to characterize the holistic feature of Kuroshio east of the Tokara-kaikyo and its extension on the purpose of predict its SST trend. The KI is calculated on the base of the Hadley Center's monthly SSTs during the period 1941-2009. The wavelet analysis showed that the KI displays inter-annual and inter-decadal oscillations, dominated by quasi-triennial, quasi 7-yr and 20-yr time scales. In addition, the KI is shown to be phase-locking to seasonal cycles. It is found that there are significant temporally-lag correlations between the KI and the Pacific decadal oscillation (PDO) index as well as between the KI and the ENSO index. A set of composition analyses using the NCEP/NCAR reanalyses indicate that when the KI shows a positive anomaly, the SST becomes abnormally warm in the equatorial eastern. Pacific, the Hadley circulation is intensified, and consequently the transportation of the westerly momentum is enhanced. The enhanced Hadley circulation and transportation of the westerly momentum give rise to the deepened Aleutian low pressure, then cool the Kuroshio extension and the north Pacific basin and cause the KE extend east. The above " ENSO-PDO-Kuroshio" process need some response time, that is to say, we can forecast the SST variation on the Kuroshio on the basis of the ENSO and PDO, which is very significant to predict the climate in China.

The development and dissemination characteristic of disturbance in weak tropical cyclones

Tao Jian-Jun, Hu Xiang-Hui
Acta Physica Sinica. 2012, 61 (16): 169202 doi: 10.7498/aps.61.169202
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The cyclone disturbance in tropical lower atmosphere is the necessary condition of typhoon forming. Satellite cloud imagery and diagnostic analysis both show that the convection represents separate cloud cluster or mesoscale systems in the disturbance. Whether these disturbances can become the typhoon depends on the strength of the convection heating in the mesoscale systems and close degree of the cloud area. This paper deals with the development and mobile of wave driven by conditional instability of second kind (CISK) mechanism through discussing frequency equation and using numerical method. The results show that the mesoscale CISK wave can occur in the tropics weak cyclone. Vertical shear of basic vortex circulation can significantly strengthen unstable effect of this wave to make fluctuation quickly develop. Vertical shear of basic vortex circulation can also make the wave move toward the center of basic vortex circulation and its group velocity points to the center too. The numerical calculation and the examples show that the disturbance will develop rapidly and move towards the center too.

Latitudinal distribution of landing tropical cyclones over mainland China

Zhang Han, Guan Yu-Ping
Acta Physica Sinica. 2012, 61 (16): 169203 doi: 10.7498/aps.61.169203
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Landfall location is an important research topic in studies of tropical cyclones. For tropical cyclones that made landfall over mainland China during 1951-2010, in this work, we analyze the temporal variations in the annual landfall frequency. We first study the distribution and temporal variations in the landing latitude. To avoid the inaccuracy associated with using a single dataset, in this work we adopt three best track datasets from China, the USA, and Japan and summarize meaningful common phenomena in the three datasets: the annual landfall frequency of tropical cyclones over mainland China in the Chinese dataset is 1 more than in the other two datasets on average. Since 1970, the landfall frequency in the three datasets has shown little change, whereas the landfall latitude has shown a relatively consistent northward movement (prior to 1970, the three datasets showed different trends in frequency and latitude). The landfall frequency data, assigned to different latitude bins, show that the most tropical cyclones made landfall below 30°N and that landfall frequency decreased with latitude increasing. An anomalously large (small) number of tropical cyclones made landfall over the latitude zone of 21°N-23°N (23°N-24°N and 20° N-21°N).

Multi-parameter fusion applied to road traffic condition forecasting

Ma Qing-Lu, Liu Wei-Ning, Sun Di-Hua
Acta Physica Sinica. 2012, 61 (16): 169501 doi: 10.7498/aps.61.169501
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In view of the chaotic characteristic in road traffic flow and the actual traffic condition that cannot be comprehensively reflected by single traffic parameter, a fusion algorithm of multi-parameters for traffic condition forecasting, with the consideration of the relationship between multiple parameters, is proposed. This algorithm is based on the reconstruction of phase space. According to Bayesian estimation theory, the multiple traffic parameters are optimally fused into phase points in the same phase space. Accordingly, the phase space information increases and the phase points are closer to dynamical behavior of the traffic system. On the basis, by using the multi-parameter chaos prediction method, the tendency of dynamic systems from different aspects is described, with reference to the method of predicting single parameter chaotic time series. The experimental results confirm that more features of real traffic condition are reflected by fusing multiple traffic parameters. The multi-parameters forecasting algorithm reduces the prediction error and improves the equalizer coefficients compared with the results generated from single parameter prediction. That is to say, the prediction method used in this paper is effective and accurate for predicting traffic condition based on multiple traffic parameters.

Prediction of smoothed monthly mean sunspot number based on chaos theory

Tang Jie, Zhang Xiong
Acta Physica Sinica. 2012, 61 (16): 169601 doi: 10.7498/aps.61.169601
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Long-term prediction of sunspot activity is of great importance for the space activity, communication, disaster prevention and so on. Cumulative error is main shortcoming of weighted one-rank local-region forecasting model for multi-steps prediction of chaotic time series. The radial basis function neural network forecasting model based on phase reconstruction is presented for chaotic time series prediction. The model is applied to the prediction of smoothed monthly mean sunspot numbers for the 22nd and 23rd sun cycles, and compared them with the observations. The results indicate that the mean absolute errors are 5.47 and 2.82, 15 to the maximum in absolute errors, and the mean relative errors are 5.45% and 4.60%, 15.00% to the maximum in relative errors. These results show that this prediction method can be successfully used to predict the smoothed monthly mean sunspot numbers. The predicted maximal smoothed monthly mean sunspot number is 104.77 that will appear in January 2013 for 132 months of cycle 24 from January 2009 to December 2019.

Dynamic stochastic shortest path algorithm

Zhang Shui-Jian, Liu Xue-Jun, Yang Yang
Acta Physica Sinica. 2012, 61 (16): 160201 doi: 10.7498/aps.61.160201
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The static shortest path problem has been solved well. However, in reality, more networks are dynamic and stochastic. The states and costs of network arcs and nodes are not only uncertain but also correlated with each other, and the costs of the arcs and nodes are subject to a certain probability distribution. Therefore, it is more general to model the shortest path problem as a dynamic and stochastic optimization problem. In this paper, the dynamic and stochastic characteristics of network nodes and arcs and the correlation between the nodes and arcs are analyzed. The dynamic stochastic shortest path is determined. The dynamic stochastic optimization model of shortest path is provided, and a shortest path genetic algorithm is proposed to solve dynamic and stochastic shortest path problem. The effective and reasonable genetic operators are designed according to the topological characteristics of the network. The experimental results show that this algorithm can be used to effectively solve the dynamic stochastic shortest path problem. The proposed model and algorithm can be applied to the network flow optimization problem in transportation, communication networks, etc.

Research on electromagnetic scattering computation and synthetic aperture radar imaging of ship located on two-dimensional ocean surface

Ji Wei-Jie, Tong Chuang-Ming
Acta Physica Sinica. 2012, 61 (16): 160301 doi: 10.7498/aps.61.160301
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The electromagnetic (EM) scattering computation and the synthetic aperture radar (SAR) imaging of three-dimensional conductor object located on ocean surface are studied. The EM scatterings of object, ocean surface and the interaction between them are computed based on the geometric optic, the physical optic, the shooting and bouncing ray. The method of equivalent current is used to calculate the diffraction by object edges. The shadowing effect is also included, and the tapered incident wave is chosen to reduce the truncation error. The Pierson-Moskowitz random sea surface is generated by using Monte-Carlo method, and numerical results are provided to validate the approach through the computation of radar cross section for cube and ship objects located on ocean surface. The backscattering electric field data of different frequencies and angles are computed quickly by using this approximate method. Combining the backscattering data and SAR images technology, the images of cube and ship located on ocean surface are obtained. The method introduced in this paper has important theoretical significance in realistic ocean remote sensing and detection of military targets located on ocean surface.

Radiation power of electric diople in magnetic anisotropic medium

Hong Qing-Quan, Zhong Wei-Bo, Yu Yan-Zhong, Cai Zhi-Shan, Chen Mu-Sheng, Lin Shun-Da
Acta Physica Sinica. 2012, 61 (16): 160302 doi: 10.7498/aps.61.160302
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Under the framework of classical electrodynamics, the electromagnetic radiation in magnetic anisotropic medium is studied in the present paper. The radiation power expression for electric dipole in magnetic anisotropic medium is deduced. The obtained expression in isotropic medium accords with that in the literature, and its validity is therefore proved. The radiation effect of electric dipole in magnetic anisotropic medium can be estimated by the obtained results. It has practical significance for further research electromagnetic property in magnetic anisotropic medium and effective development and utilization of magnetic anisotropic medium.

Quantum process neural networks model algorithm and applications

Li Pan-Chi, Wang Hai-Ying, Dai Qing, Xiao Hong
Acta Physica Sinica. 2012, 61 (16): 160303 doi: 10.7498/aps.61.160303
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To enhance the approximation and generalization ability of process neural networks (PNNs), by studying the quantum implementation mechanism of information processing of process neuron, a new idea of designing quantum process neuron is proposed in this paper, based on the quantum rotation gates and the quantum controlled-non gates. In the proposed approach, the discrete process inputs are expressed by the qubits, which, as the control qubits of controlled-non gates after being rotated by the quantum rotation gates, control the target qubits to reverse. The model outputs are described by the probability amplitude of state |1> in the target qubits. Then the quantum process neural networks (QPNNs) are designed by the quantum process neurons for the hidden layer and the normal neurons for the output layer. The algorithm of QPNN is derived through the quantum computing. The proposed approach is utilized to predict the smoothed yearly mean sunspot numbers, and the results indicate that the QPNN has higher prediction accuracy than the normal PNN, thus it has a certain theoretical meaning and practical value for the complex prediction.

Effect of the Stark shift on entanglement in a double Jaynes-Cummings model in thermal environment

Hu Yao-Hua
Acta Physica Sinica. 2012, 61 (16): 160304 doi: 10.7498/aps.61.160304
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Considering a double two-photon Jaynes-Cummings (J-C) model, we study the effects of Stark shift and mean photon number on entanglement between two two-level atoms when the atoms are initially in a maximally entangled state and the fields are in the single-mode thermal fields. The results show that the two atoms evolve periodically into a disentangled separable state when Stark shift is not considered. However, in the presence of Stark shift, the two two-level atoms are no longer disentangled and long-lived entanglement can be obtained. For a larger value of the Stark shift parameter and a smaller mean photon number, the two atoms can remain in a stationary entangled state. These properties show that the Stark shift can be used to control entanglement in the double two-photon J-C model under the influence of thermal environment.

Characterization of gravitational waves from spinning compact binaries

Wang Yu-Zhao, Wu Xin, Zhong Shuang-Ying
Acta Physica Sinica. 2012, 61 (16): 160401 doi: 10.7498/aps.61.160401
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Some characterizations of gravitational waves emitted from the 2.5 post-Newtonian order Lagrangian dynamics of spinning compact binaries including the next-order spin-orbit contribution and the radiative reaction are detailed. The relationship between the regular and chaotic dynamics and the gravitational waveforms is also described. When the radiative reaction term does not appear in the equations of motion, the gravitational waves are periodic/quasi-periodic for an order conservative binary system, but they seem to be typically irregular for a chaotic one. On the other hand, the binary systems become dissipative and should coalesce if the radiative reaction term is added to the equations of motion. In the dissipative case, the original ordered conservative system can still give regular gravitational waveforms in such a long time before the occurrence of the merging orbits. However, the coalescence time of the binary system corresponding to its original chaotic conservative system is too short to obtain enough information about the characterization of the gravitational waveforms.

Theory and experiment research on a Piecewise-linear model based on stochastic resonance

Wang Lin-Ze, Zhao Wen-Li, Chen Xuan
Acta Physica Sinica. 2012, 61 (16): 160501 doi: 10.7498/aps.61.160501
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We propose a new piecewise-linear model. The principle of stochastic resonance in the new piecewise-linear model is introduced, and the formula of the signal-to-noise ratio (SNR) is deduced. It is proved that stochastic resonance characteristics can be utilized to realize the conversion of noise energy into periodic signal energy. The results clearly show the enhancement of the SNR of the output signal. The model characteristic that the weak periodic signal can be detected from noise background is investigated by the numerical simulation. The stochastic resonance system based on the model is built by using a circuit. The behaviors of stochastic resonance are studied when the circuit is driven by noise and period signal. The simulation and experimental results show that the model can effectively detect weak periodic signal, and enhance the SNR prominently.

Simulation study on the stochastic resonance of single-mode laser system

Yang Ming, Li Xiang-Lian, Wu Da-Jin
Acta Physica Sinica. 2012, 61 (16): 160502 doi: 10.7498/aps.61.160502
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Single-mode laser systems with modulated signals are studied by the method of numerical simulation. The signal-to-noise ratio, the output signal power, and the background noise power are analyzed near and far from the threshold. It is found that when the laser works near the threshold, the signal-to-noise ratio is present and the behavior of stochastic resonance takes place as the quantum noise increases, no matter whether the quantum noise is correlated with the pump noise. The correlation between the two noises, however, will increase the signal-to-noise ratio. And when the laser works far from the threshold, only when the two noises are correlated can the behavior of stochastic resonance appear. It is also found that the output signal power can be influenced by the noises. What is more, the simulation results are compared with those obtained by the method of linear approximation.

Stability analysis of equivalent series resistance of output capacitor in fixed off-time controlled Buck converter

Zhang Xi, Bao Bo-Cheng, Wang Jin-Ping, Ma Zheng-Hua, Xu Jian-Ping
Acta Physica Sinica. 2012, 61 (16): 160503 doi: 10.7498/aps.61.160503
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Based on the power simulation software, the reason of the output voltage phase lagging behind the inductor current phase is analyzed qualitatively, and the mechanism to cause the pulse bursting phenomenon in fixed-off-time (FOT) controlled Buck converter is explained. The way to choose the equivalent series resistance (ESR) of output capacitor to eliminate these complex nonlinear phenomena is discussed. The critical ESR to ensure the state operation of FOT controlled Buck converter is obtained. The study results indicate that the ESR has a great effect on the operation state of FOT controlled Buck converter. When the ESR is smaller than the critical value, the output voltage phase lags behind the inductor current phase, resulting in the pulse bursting phenomenon; while when the ESR is larger than the critical value, the output voltage variation keeps in phase with the inductor current variation, the pulse bursting phenomenon disappearing. In addition, the describing function method is used to obtain the transfer function from the reference voltage to the output voltage. By using the Routh-Hurwitz criterion, it is indicated that the critical ESR is the condition of destabilizing FOT controlled Buck converter.

Small target detection in the background of sea clutter using fractal method

Xing Hong-Yan, Gong Ping, Xu Wei
Acta Physica Sinica. 2012, 61 (16): 160504 doi: 10.7498/aps.61.160504
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Because the detecting of the small target in the background of sea clutter is strongly dependent on sea condition, in this article we use fractional Brownian motion to model IPIX sea clutter and combine multifractal detrended fluctuation analysis (MF-DFA) to determine the fractal parameters for analyzing fractal and multifractal property of IPIX sea clutter. Based on the fact that Hurst parameter and fractal dimension can reflect the fractal property of data, a new parameter named fractal differential which has difference when the sea clutter with or without target is defined, thereby solving the problem of small target in sea clutter background. By comparing the multifractal parameters of two sea clutter, the experimental results show that H(q) is a special value which is bigger than zero when the sea clutter has a small target but smaller than zero when the sea clutter has no target if q is bigger than ten. Another method is proposed by using the difference of H(q). Two methods in this article can solve the problem of strong dependence of detecting the small target in different sea conditions on sea condition.

Frequency enhancement and control of chaos in two spatial coupled semiconductor lasers using external light injection

Yan Sen-Lin
Acta Physica Sinica. 2012, 61 (16): 160505 doi: 10.7498/aps.61.160505
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We present a novel system of oscillation frequency enhancement and control of chaos in two spatial coupled semiconductor lasers due to external light injection. We study the characteristics of frequency enhancement and control of chaos in the system and give a static frequency detuning formula. We find three regimes of chaotic enhancement when external light is injected into single laser, in which, strong light injection can result effectively in frequency enhancement in the injected laser, but the frequency weakens slowly in the other. And large detuning can result effectively in frequency enhancements in both lasers while the frequency can be enlarged 3.5 times more than the intrinsic frequency of the laser 1. Chaos-control region is found in low injection levels. In this region, lasers can be controlled to single -cycle, dual-cycle, cycle-4, cycle-6 and other quasi-cycles. When the dual-injection is present, strong light injection or large detuning can result effectively in frequency enhancements in both lasers while the frequency can be enlarged 3.5 or 2.65 times more than the intrinsic frequency of the laser 1 or 2. Chaos-control region is also found in large injection levels. In this region, both lasers can be controlled to single-cycle, cycle-3, cycle-6 and other quasi-cycles. We point out in detail a path from single-cycle to quasi-cycle to frequency enhancement of chaos when the single-injection is present. We find another reverse path from chaos to quasi-cycle to single-cycle when the dual-injection is present.

Adaptive synchronization of a class of fractional-order chaotic systems

Ma Tie-Dong, Jiang Wei-Bo, Fu Jie, Chai Yi, Chen Li-Ping, Xue Fang-Zheng
Acta Physica Sinica. 2012, 61 (16): 160506 doi: 10.7498/aps.61.160506
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In view of chaos synchronization of a class of fractional-order chaotic systems, a novel adaptive controller and adaptive updating law are designed based on the quasi-Lyapunov stability theory for fractional-order systems. The derived method has some advantages such as simple structure, low control cost and high generality compared with the existing results. Furthermore, the method can be applied to most typical fractional-order chaotic systems. Finally, numerical simulations are used to illustrate the effectiveness of the proposed synchronization method.

Sliding mode tracking synchronization of an uncertain complex network

Liu Shuang, Lü Ling, Li Gang
Acta Physica Sinica. 2012, 61 (16): 160507 doi: 10.7498/aps.61.160507
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The problem of tracking synchronization for an uncertain complex network is proposed. By selecting an appropriate sliding surface, designing parameter identification laws and sliding mode controllers, the tracking synchronization between the network and output signal is achieved. The simulation results show that all the state variables in the network can track target orbit strictly, which shows that the method is effective.

Thermodynamic analyses of dewetting instability in thin films

Wei Qi, E Wen-Ji
Acta Physica Sinica. 2012, 61 (16): 160508 doi: 10.7498/aps.61.160508
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The dewetting instabilities in thin films under the boundary slip condition are studied using the thermodynamic approach. The general form of characteristic dewetting length scale is obtained from. The dewetting instability in thin film without Marangoni effect and that with Marangoni effect are compared.

Analysis of the stability and solitary waves for multi-velocity difference car-following model of traffic flow

Yuan Na, Hua Cun-Cai
Acta Physica Sinica. 2012, 61 (16): 160509 doi: 10.7498/aps.61.160509
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This article deals with the characteristic of the multiple velocity difference car-following model. We obtain the stability conditions of the model by using the linear stability analysis, and find that the stable region is apparently enlarged by adjusting the information about the multi-velocity difference. We study the nonlinear characteristics of the model by applying the reductive perturbation method. We obtain the Burgers equation and the modified Korteweg-de-Vries (mKdV) equation around the critical point and the Korteweg-de-Vries (KdV) equation near the neutral stability line in the stable region and the unstable region and the metastable region. The soliton solution of Burgers equation, the kink-antikink solution of mKdV equation, and the solition solution of KdV equation describe the traffic jams.

A new method for projective synchronization of different fractional order chaotic systems

Huang Li-Lian, Ma Nan
Acta Physica Sinica. 2012, 61 (16): 160510 doi: 10.7498/aps.61.160510
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Based on the Lyapunov theory as the breakthrough point, and based on the fractional order system stability theory and properties of fractional nonlinear system, a kind of fractional-order chaotic system is proposed to determine whether the new theorem is stable, and the theory is used for fractional order control and synchronization of chaotic systems, and gives a mathematical proof process to strictly ensure the correctness of the method and general applicability. Then the proposed stability theorem is used to achieve the projective synchronization of fractional Lorenz chaotic system with fractional order chaotic Liu system, as well as the projective synchronization of four-dimensional hyperchaos of fractional order systems of different structures. In the stability theorem solving the fractional balance point and the Lyapunov index are avoided, therefore a control law can be easily selected, and the obtained controller has the advantages of simple structure and wide range of application. Finally, the expected numerical simulation results are achieved, which further proves the correctness and universal applicability of the stability theorem.

Studies on the optimization of terahertz emission based on the field ionization current model

Zhang Kai-Yun, Du Hai-Wei, Chen Min, Sheng Zheng-Ming
Acta Physica Sinica. 2012, 61 (16): 160701 doi: 10.7498/aps.61.160701
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Based on the theoretical model of field ionization current for terahertz (THz) emission in laser-gas interaction, the parameter optimization for strong THz emission via the two-color laser scheme is explored. It is found from numerical calculation that the ionization current is due mainly to the first-order ionization process and the contribution from high-order ionization is ignorable. In order to produce stronger THz emission, the ionization current can be enhanced by adjusting the amplitude ratio between the fundamental and its second harmonic laser pulses as well as their relative phase difference. The ionization current can also be increased by use of laser pulses at mid-infrared and by changing the gas species. Under the same laser pulse and gas density conditions, the ionization current from the Helium gas is almost twice that from the Neon gas.

Experimental study of X-ray phase contrast imaging without absorbing grating

Yang Qiang, Liu Xin, Guo Jin-Chuan, Lei Yao-Hu, Huang Jian-Heng, Niu Han-Ben
Acta Physica Sinica. 2012, 61 (16): 160702 doi: 10.7498/aps.61.160702
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According to the theoretical analysis of X-ray differential phase-contrast imaging system based on one-dimensional spatial-coherence X-ray source with multi-line structured anode, a scintillator functioning as an absorption grating, and a phase grating fabricated by photo-assisted electrochemical etching technique developed by us, we construct a non-absorption grating X-ray differential phase-contrast imaging system, conduct the experiments on some biological samples prepared with the above system, and finally obtain some phase-contrast images with more structural information than the ones obtained by conventional X-ray absorption method. Consequently, out system can be considered as a feasible imaging system and can have potential applications in hospitals and laboratories.


The implementation of the three-dimensional numerical simulation of the coaxial magnetically insulated transmission line with helical inductor

Liu La-Qun, Liu Da-Gang, Wang Xue-Qiong, Zou Wen-Kang, Yang Chao
Acta Physica Sinica. 2012, 61 (16): 162901 doi: 10.7498/aps.61.162901
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According to the actual device size, a three-dimensional numerical simulation model of the coaxial magnetically insulated transmission line with a helical inductor is developed. The diode with an appropriate distance between anode and cathode is selected as a load of the transmission line. Setting the device parameters, the device is simulated. Comparing the simulation results with the experimental data, the reliability of the simulation is proved. By combining with the corresponding experimental data, the transmission efficiency of the coaxial magnetically insulated transmission lines with adding the structure of helical inductor is analyzed.

The numerical simulation of the electronic energy deposition and temperature variation in post-hole convolute of magnetically insulated transmission lines

Liu La-Qun, Liu Da-Gang, Wang Xue-Qiong, Yang Chao, Xia Meng-Zhong, Peng Kai
Acta Physica Sinica. 2012, 61 (16): 162902 doi: 10.7498/aps.61.162902
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In this paper, we introduce the numerical simulation theory and method to achieve the energy deposition and temperature variation produced by the high-energy electron bombarding the anode surface. A simple beam launch model is developed. The accuracy of the numerical calculation of the anode surface electronic energy deposition is primarily validated. Then, selecting the magnetically insulated transmission line in post-hole convolute as a model, the energy deposition and the temperature variation in the anode produced in the process are simulated. Also by comparing the simulation results with the results given in the literature, the simulation accuracy is further proved. Finally, the simulation results are analyzed and the physical mechanism produced by the simulation results is also discussed.


The ab initio and potential energy curve of OH, OCI and HOCI(1A')

Han Xiao-Qin, Xiao Xia-Jie, Liu Yu-Fang
Acta Physica Sinica. 2012, 61 (16): 163101 doi: 10.7498/aps.61.163101
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The possible ground state structures of OH, OCI and HOCI are optimized by using some methods included in Gaussian 09. Among them, the methods QCISD/6-311G(2df) and B3P86/6-311+G(2df) are the most suitable for the calculation of OH(X2Π) and OCI(X2Π) the spacings between eguilibrium nuclei ROH=0.09696 nm and ROCI=0.1569 nm, and harmonic freguencies ω(OH)=3745.37 cm-1 and ω(OCI)=892.046 cm-1 are calculated respectively. The calculation results are in good agreement with experimental results, Each potential energy curve obtained via scanning the single point energies of OH and OCI is well fit with the four-parameter Murrell-Sorbie function, according to which spectral data and force constants are deduced. The ground state of HOCI molecule is of 2A1' state, and the parameters of structure are ROH=0.0966 nm, ∠HOCI 102.3°, ω1(a1)=738.69 cm-1, ω2(b2)=1260.25 cm-1, De=2.24 eV with QCISD(T)/D95(df,pd). The present calculation results are in excellent agreement with the experimental values, and they are better than those given in the literature. And the force constants are calculated at the same time. The potential energy function of HOCI is derived from the many-body expansion theory. In the symmetric-stretch potential energy diagram, there is a saddle point in reaction channel H+OCI → HOCI, and a stable HOCI molecule could be formed only when H atom crosses an energy barrier of 1.74 eV. However there is no clear energy barrier in the reaction channel Cl+OH → HOCI, therefore a stable HOCI molecule can form easily.

Research on the opacity of Fe M-shell unresolved transition array

Dong Fu-Tong, Wang Fei-Lu, Zhong Jia-Yong, Zhao Gang
Acta Physica Sinica. 2012, 61 (16): 163201 doi: 10.7498/aps.61.163201
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M-shell unresolved transition array of iron is an important diagnostic tool of the X-ray spectrum of active galactic nuclei. This array is measured in the laboratory, and compared with several theoretical models. In the present paper, we introduce a detailed line counting model. With this model, we simulate the experimental spectra, and the comparison shows a good agreement. We also calculate the absorption spectra in a temperature range of 10–50 eV.

Measurement and theoretical calculation for Stark energy and electric dipole moment of Cs Rydberg state

Li Chang-Yong, Zhang Lin-Jie, Zhao Jian-Ming, Jia Suo-Tang
Acta Physica Sinica. 2012, 61 (16): 163202 doi: 10.7498/aps.61.163202
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Rydberg atoms has been one of the hot current research subjects in the field of physics becasue of its large volume, long life, easy polarization and energy levels easily controlled by external electric field. In this paper, the Stark energies and electric dipole moments of 15P3/2 and 16P3/2 of atomic cesium are measured experimentally. The empirical analytic equations of dipole moments and Stark energies for these two states are presented. We also numerically solve the Schrödinger equation and obtain Stark energies, dipole moments, and electron probability density distributions. The probability density distribution accords with the calculated dipole moments. The Stark energies and dipole moments are consistent with our experimental results. To the best of our knowledge, the measurement and calculation methods for dipole moments presented in this paper are reported for the first time.

The dynamic process of two-electron atom irradiated by intense laser pulse using time dependent quantum Monte Carlo method

Guo Fu-Ming, Song Yang, Chen Ji-Gen, Zeng Si-Liang, Yang Yu-Jun
Acta Physica Sinica. 2012, 61 (16): 163203 doi: 10.7498/aps.61.163203
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We investigate the electron dynamic process of a one-dimensional two-electron atom irradiated by strong laser pulse using the improved time-dependent quantum Monte Carlo (TDQMC) scheme. By comparison with the scheme for solving the time-dependent Schrödinger equation by using the accurate numerical integration, the dynamic variation of particle in a quantum ensemble, corresponding to the calculated wave-packet, is consistent with the evolution of time-dependent wavepacket. The computation efficiency of the TDQMC is more largely enhanced than that of the time-dependent integration method. According to the dynamic evolution behaviors of the calculated classical particle ensemble, we analyze the excitation, ionization, recombination of electron and other non-linear processes in a strong laser field.

Polarization induced ultra-high electron concentration up to 1020 cm-3 in graded AlGaN

Li Shi-Bin, Xiao Zhan-Fei, Su Yuan-Jie, Jiang Jing, Ju Yong-Feng, Wu Zhi-Ming, Jiang Ya-Dong
Acta Physica Sinica. 2012, 61 (16): 163701 doi: 10.7498/aps.61.163701
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Carrier concentration and mobility of materials are key factors affecting device performance. Hall tests at different temperatures demonstrate that the carrier concentration and mobility in impurity-doped AlGaN decrease with temperature decreasing. However, carrier concentration and mobility obtained by polarization-induced doping are independent of temperature. Using quasi-insulating GaN as substrate, the electron concentration obtained in the linearly graded AlGaN film through impurity-doping is only 10-17 cm-3 or less. In this study, using unintentional impurity doped (n-type, 10-16 cm-3) GaN template, graded AlGaN film is grown by molecular beam epitaxial, in which polarization induced ultra-high electron concentration is up to 1020 cm-3 in graded AlGaN film without using any dopant. Using quasi-insulating GaN as substrate, only the surface of the free electrons serves as polarization dopant, while unintentionally doped GaN template is used as a substrate, in addition to free electrons on surface/interface, it is also reasonable to surmise more negative charges attracted by polarization electric field to be the source of polarization doping, in the unintentional doped GaN template, thereby achieving an ultra-high carrier concentration via polarization induced n-type doping.


Computer simulation of the glow discharge characteristics in magnetron sputtering

Shen Xiang-Qian, Xie Quan, Xiao Qing-Quan, Chen Qian, Feng Yun
Acta Physica Sinica. 2012, 61 (16): 165101 doi: 10.7498/aps.61.165101
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In this paper, the process of glow discharge in magnetron sputtering is studied by the particle-in-cell with Monte Carlo collision method. The proposed model is a two-dimensional and self-consistent approach. The results show that the discharge mode transits from the negative space-charge-dominated mode to positive space-charge-dominated mode with working pressure increasing or magnetic field weakening. At the transition state, working pressure and magnetic field are 0.67 Pa and 0.05 T, respectively. Discharge current increases as the cathode voltage increases. When pressure increases, discharge current first increases and then tends to balance. When the pressure is higher than 2.5 Pa, current begins to decreases with the increase of the pressure.

Ultra-short ultra-intense laser guiding and its influence on electron acceleration

Wang Guang-Hui, Wang Xiao-Fang, Dong Ke-Gong
Acta Physica Sinica. 2012, 61 (16): 165201 doi: 10.7498/aps.61.165201
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Simulations and analyses of ultra-short ultra-intense laser propagting in plasmas with uniform and parabolic density profiles, as well as the electron injection into the wake field and the electron spectra in the stable transmission state are performed by using a particle-in-cell code. Fixing the incident laser focal spot size but changing the plasma density in a range of (0.4–2)×1019/cm3, comparative analyses are carried out of the evolutions of the laser beam spot during the propagation of the laser pulse in the plasmas with aforementioned two density profiles, with the normalized laser intensity ranging from 1 to 6. The results show that a plasma channel with a parabolic density profile can realize a good guiding of an ultra-short ultra-intense pulse, which is beneficial for high energy electron acceleration. However, at higher densities, self-guiding can be realized by relativistic self-focusing in uniform plasma, which is conducive to simplifying the experiment and to producing more accelerated electrons.

Experimental investigation of radiation charactristics of Ti wire X-pinch X-ray source on Yang accelerator

Zhou Shao-Tong, Li Jun, Huang Xian-Bin, Cai Hong-Chun, Zhang Si-Qun, Li Jing, Duan Shu-Chao, Zhou Rong-Guo
Acta Physica Sinica. 2012, 61 (16): 165202 doi: 10.7498/aps.61.165202
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The X-ray radiation properties of titanium wire X-pinch are investigated on the Yang accelerator at 500–800 kA peak current with a rise time of about 80 ns. The radiation power, spectrum and source size of the X-pinch X-ray source are measured and analyzed using X-ray diodes, a transmission grating spectrometer, a crystal spectrometer and a slit camera. The hot dense spot smaller than 15 μm emits 1 J of X-ray with an FWHM of 200 ps and a peak power of 1.5 GW distributed in the range of 1–4 keV. A method to efficiently generate a single X-ray pulse during the X-pinch implosion is demonstrated. The X-pinch presented here is useful for imaging the early stage interior structure of Z pinch as a backlight source.

The study of capacitively-coupled hydrogen plasma at very high frequency

Li Yan-Yang, Yang Shi-E, Chen Yong-Sheng, Zhou Jian-Peng, Li Xin-Li, Lu Jing-Xiao
Acta Physica Sinica. 2012, 61 (16): 165203 doi: 10.7498/aps.61.165203
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In the high rate deposition of device grade microcrystalline silicon films and their solar cells, plasma enhanced chemical vapor deposition excited using very high frequency (VHF) has become a mainstream method. Although, great breakthroughs in the experiment are achieved, the depositional mechanism is still a research hot spot and difficulty point. In this paper, the capacitively-coupled hydrogen plasma discharge at VHF is simulated. A two-dimensional, time-dependent axial symmetry model is adopted at a frequency of 75 MHz, and the influences of pressure and plasma power on hydrogen plasma characteristic are simulated. At the same time, the hydrogen plasma is monitored on-line using the optical emission spectrometry in experiment. The results show that the value of the electronic concentration ne takes a maximum in the middle of the plasma bulk, while the electron temperature Te and the number densities of Hα and Hβ each have a maximal value at the place near the sheath and plasma bulk; the potential decreases with pressure increasing from 1 Torr to 5 Torr, the electron concentration in the plasma bulk first increases with the increase of pressure, then decreases with the further increase of pressure, but the electron temperature first decreases and then keeps stable in plasma bulk; the electron concentrations, Hα and Hβ increase linely with power increasing from 30 W to 70 W, but the electron temperature keeps stable. The experimental results and simulation results are in good agreement.

Investigations of space charge limited effects in diode with Coulomb's law

Zuo Ying-Hong, Wang Jian-Guo, Zhu Jin-Hui, Fan Ru-Yu
Acta Physica Sinica. 2012, 61 (16): 165204 doi: 10.7498/aps.61.165204
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Vacuum diode is a critical component of the apparatus which is the source of electron beams, the emitted electrons from the cathode of the diode have strong space charge limited effects. Based on Coulomb's law, the distributions of electric field in cathode-anode gap for different values of the ratio of radius to gap distance, R/D, are calculated numerically with the model of space charge limited effects in a planar vacuum diode. This method can avoid solving a non-linear differential equation which is used to yield the Child-Langmuir law from Poisson's equation. The results demonstrate that the only difference between the results from Coulomb's law and Child-Langmuir law is a modification factor, which is shown to be related to the potential difference across the gap. The results also show that one-dimensional space charge limited law will be a good approximation for the practical planar diode if the parameter R/D is beyond 10, but it can present a large error if the parameter R/D is small. Therefore it should be cautiously used.
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