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CN 11-1958/O4
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Volume effect in the cyclic segregation of quasi two-dimensional binary granular mixture
Wu Yu-Hang, Zheng Ning, Wen Ping-Ping, Li Liang-Sheng, Shi Qing-Fan, Sun Gang
Acta Physica Sinica, 2011, 60 (2): 024501
Coulomb oscillations effect in dual gate controlled silicon nanowire
Zhang Xian-Gao, Fang Zhong-Hui, Chen Kun-Ji, Qian Xin-Ye, Liu Guang-Yuan, Xu Jun, Huang Xin-Fan, He Fei
Acta Physica Sinica, 2011, 60 (2): 027304
Epitaxial growth of Ge0.975Sn0.025alloy films on Si(001) substrates by molecular beam epitaxy
Su Shao-Jian, Wang Wei, Zhang Guang-Ze, Hu Wei-Xuan, Bai An-Qi, Xue Chun-Lai, Zuo Yu-Hua, Cheng Bu-Wen, Wang Qi-Ming
Acta Physica Sinica, 2011, 60 (2): 028101
Acta Physica Sinica  
  Acta Physica Sinica--2011, 60 (2)   Published: 15 February 2011
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ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

A two-dimensional broad pass-band left-handed metamaterial based on single-sided metallic structure

Chen Chun-Hui, Qu Shao-Bo, Xu Zhuo, Wang Jia-Fu, Ma Hua, Zhou Hang
Acta Physica Sinica. 2011, 60 (2): 024101 doi: 10.7498/aps.60.024101
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Through connecting magnetic resonators and coplanar short metallic wires together, a two dimensional left-handed metamaterial based on single sided metallic structure was proposed. Theoretical analysis and simulated results indicated that this construction exhibited negative effective permittivity and permeability simultaneously in a certain frequency range. Its relative negative refraction pass-band reached 36%. Meanwhile, this construction guaranteed relatively stable tolerance of errors. The resonant frequency and the width of the pass band are insensitive to the change in the width of the short metallic wires, which facilitates its fabrication and is of meaning for designing left-handed metamaterial in infrared or terahertz range.

Transverse superresolution and extended axial focal depth realized by three-zone annular phase pupil filter

Wang Wei, Zhou Chang-He, Yu Jun-Jie
Acta Physica Sinica. 2011, 60 (2): 024201 doi: 10.7498/aps.60.024201
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When linearly polarized light is focused using a high numerical aperture lens with three-zone annular phase pupil filter, vector diffraction method was applied to study the optical intensity distribution in transverse and axial directions. Numerical simulation results show that optical intensity distribution in transverse and axial directions need to be treated simultaneously. When three-zone annular phase pupil filter is added in front of a high numerical aperture lens, transverse super resolution, extended axial focal depth and flat-top focusing can be achieved at the same time. Furthermore, When phase modulation depth is changed, the phenomenon of axial focal shift can be found. The structure of three-zone annular phase pupil filter was optimized and the optimized results were given.

Quantitative relation between "defects" distribution on optics and near-field quality in high power solid-state laser system

Zhou Li-Dan, Su Jing-Qin, Li Ping, Wang Wen-Yi, Liu Lan-Qin, Zhang Ying, Zhang Xiao-Min
Acta Physica Sinica. 2011, 60 (2): 024202 doi: 10.7498/aps.60.024202
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Based on beam propagation theory, the quantitative relation between PSD (power spectral density) of "defects" distribution on optics and that of near field intensity was studied. Its validity was discussed on linear medium, nonlinear medium and spatial filter. The results show that PSD of "defects" distribution on optics and PSD of near field intensity are connected by a system propagation factor when the modulation is weak, which is determined by system architecture and operation state. These results provide a theoretical basis for specifications of "defects" distribution on optics, and also a guidance to enhancing the power of high power solid-state laser system.

Effect of losses for squeezed surface plasmons

Li Wei, Wang Yong-Gang, Yang Bo-Jun
Acta Physica Sinica. 2011, 60 (2): 024203 doi: 10.7498/aps.60.024203
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The surface plasmon polaritons (SPPs) are electromagnetic excitation of electrons in metal surfaces, which propagates in wavelike fashion along the interface between a metal and a dielectric median.Recently Huck et al. reports on the efficient generation, propagation and reemission of squeezed surface plasmons.In this paper, the influence of waveguide loss was discussed for squeezed surface plasmons by means of the heat reservoir theory in quantum optics. Huck’s experimental result is explained theoretically.

Electromagnetically induced transparency in squeezed vacuum

Lü Chun-Hai, Tan Lei, Tan Wen-Ting
Acta Physica Sinica. 2011, 60 (2): 024204 doi: 10.7498/aps.60.024204
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We studied the electromagnetically induced transparency, where the three-level atom of Λ-type is put in two statistically independent squeezed vacuums. We start from the master equation containing the decay of the atom to the squeezed vacuums, and solve the non-diagonal density matrix element analytically, finding that it is strongly dependent on the squeezing degree and the phase of the squeezed vacuum. There is also a dependence on the intensity and phase of the probe beam, which would not appear in the normal vacuum case. By coupling with squeezed vacuums, the atom would not only experience electromagnetically induced transparency and slow group velocity, but also induce a fast group velocity,backward group velocity and a gain in the probe light field. Besides, the absorption and gain can be modulated by the intensity of probe light.

Control of the evolution of an excited atom by using the dynamic Lorentzian reservior

Huang Xian-Shan, Liu Hai-Lian, Yang Ya-Ping, Shi Yun-Long
Acta Physica Sinica. 2011, 60 (2): 024205 doi: 10.7498/aps.60.024205
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We theoretically study the use of a dynamic Lorentzian reservoir environment to realize contro of the evolution of an excited two-level atom. It is found that the change of Lorentzian reservoir leads to the interaction between the electromagnetic modes in the cavity and those outside, resulting in the redistribution of the electromagnetic modes density. When the frequency of reservoir change is consistent with the process of exchange of energy between the atom and environment, a relatively stable coherent evolution can be obtained, and the decay is obviously inhibited.

All-fiber ultrashort Yb3+ doped fiber laser self-started by spectral filter

Zhang Pan-Zheng, Fan Wei, Wang Xiao-Chao, Lin Zun-Qi
Acta Physica Sinica. 2011, 60 (2): 024206 doi: 10.7498/aps.60.024206
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Theory of the passively mode-locked Yb3+ doped fiber ring laser self-starting through spectral filter is presented. The all-fiber Yb3+ doped fiber ring laser generating ultrashort pulses are designed and fabricated. High concentration Yb3+ doped fiber was employed as gain medium, which was pumped by a 980 nm diode laser. In the all-normal-dispersion cavity, a spectral filter was spliced to reduce the large emission peak at 1030 nm of Yb3+ ion and to generate an additional pulse shaping through spectral filtering of chirped pulse. Self-starting and stable mode-locking centered at 1053 nm was achieved by nonlinear polarization evolution along with spectral filtering from the filter. The mode-locking threshold was 300 mW, with the slope efficiency of 18.3%, the maximum output power was 53.07 mW, corresponding to the maximum pulse energy of 3.2 nJ. The center wavelength of the mode-locked pulse was 1053.6 nm, with 3 dB bandwidth of 10.84 nm at the repetition rate of 16.45 MHz. The picosecond mode-locked pulse can be dechirped to 188 fs using grating pair outside the cavity.

Output characteristics of wavelength tunable fiber lasers based on sampled Bragg gratings

Liu Yan, Wang Lei-Shi, Tao Pei-Lin, Feng Su-Chun, Yin Guo-Lu, Ren Wen-Hua, Tan Zhong-Wei, Jian Shui-Sheng
Acta Physica Sinica. 2011, 60 (2): 024207 doi: 10.7498/aps.60.024207
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A simulation model of the fiber DBR (distributed Bragg reflector) laser with two sampled Bragg gratings (SBGs) as reflectors is established, with which the characteristics of the laser are analyzed in detail. The analysis mainly focuses on the change of the laser output characteristics with the wavelength and reflectivity of the front and back sampled fiber gratings. Because of the multi-channel reflection of SBGs, the side mode of such laser is always very obvious. The method for improving the SMSR(side mode suppression ratio) is suggested. And the wavelength tuning mechanism is also studied. Experiment has been carried out to confirm the analysis.

Laser diode-pumped coaxial double crystals yellow laser

Li Bin, Yao Jian-Quan, Ding Xin, Wang Peng, Zhang Fan
Acta Physica Sinica. 2011, 60 (2): 024208 doi: 10.7498/aps.60.024208
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A new configuration of 589 nm yellow laser with a single LD pump source and coaxial double crystal was proposed. When the incidence pump power was 1.5 W, 54 mW yellow laser at 589 nm was obtained, the optical to optical conversion efficiency was 3.6%, and the laser instability was about 5%. A conventional method for 589 nm laser was also tested under the same conditions, only 15 mW yellow laser was obtain. The configuration of single pump source and coaxial double crystals is compact and flexible, which can be used in many sum frequency lasers, such as the 491, 488, 593.5, 555 and 500.8 nm laser, and so on.

Analysis of the effect of phase-mismatch and material absorption on the terahertz-wave generation from GaSe

Lu Jin-Xing, Huang Zhi-Ming, Huang Jing-Guo, Wang Bing-Bing, Shen Xue-Min
Acta Physica Sinica. 2011, 60 (2): 024209 doi: 10.7498/aps.60.024209
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We analyzed the effect of phase-mismatch and material absorption on the terahertz-wave difference-frequency generation from GaSe theoretically. We calculated the best length of crystal and the corresponding terahertz power under four different conditions and the effect of angle-mismatch on phase-mismatch. The result provided a theoretical basis and reference to nonlinear optical difference-frequency experiments.

Metalloporphyrin bonded SiO2 organic-inorganic materials and their strong nonlinear refractive index

Zhang Xiao-He, Wang Dong-Jie, Xia Hai-Ping
Acta Physica Sinica. 2011, 60 (2): 024210 doi: 10.7498/aps.60.024210
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Copper metalloporphyrin was bonded to 3-aminopropltriethoxysilane (NH2(CH2)3Si(OC2H5)3, KH550) by the chemical reaction between the carboxyl group of Cu(Ⅱ) meso-Tertra(4-carboxyphenyl)porphine (Cu(Ⅱ)-TCPP) and amino-group of KH550. The copper metalloporphyrin was connected to gel network after the hydrolysis and condensation of the product. The reaction product of different concentrations was hybridized with 3-glycidoxypropltrimethoxysilane (CH2OCHCH2O(CH2)3Si(OCH3)3, KH560) with sol-gel processing to form sol-gel inorganic material, which has good physical-chemical and optical properties. The cross-linkage of Cu(Ⅱ)-TCPP and KH550 was estimated and confirmed with FT-IR spectroscopy. The state of metalloporphyrin molecules was investiaged by UV/VIS spectra. It was found that the Cu(Ⅱ)-TCPP exists mainly in the state of monomer. Nonlinear optical properties of samples was studied by Z-scan technique using Ti:Sapphire femto-second laser pluses. The nonlinear refractive index n2 reached -1.1161×10-16 m2/W.

Femtosecond optical parametric conversion properties based on the BiB3O

Ma Jing, Liu Ying, Zhang Li-Jun
Acta Physica Sinica. 2011, 60 (2): 024211 doi: 10.7498/aps.60.024211
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Parametric properties in femtosecond optical parametric conversion process based on the new nonlinear crystal BiB3O6 (BIBO) are studied. The phase- matching conditions and effective nonlinear coefficients in the three principal optical planes of the BIBO crystal are calculated, optimum principal optical planes and phase -matching types are determined when using the fundamental frequency and the frequency doubling of the KLM Ti:sapphire laser as pump respectively, and temporal walk-off and spatial walk-off of three waves, and signal parametric gain and bandwidth are analyzed. We thereby provided a theoretical basis and experimental guide for obtaining the light source with high energy, wide tuning range, and short duration with femtosecond optical parametric technology based on the BIBO.

On-line detecting and controlling conception for time-delay measurement in ultrafast laser pulse pump-probe

He Xue-Peng, Liu Yuan-Xing, Liu Shi-Bing
Acta Physica Sinica. 2011, 60 (2): 024212 doi: 10.7498/aps.60.024212
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A novel optical system for detecting and controlling the time-delay value of probe light in the femtosecond pulse pump-probe measurements is presented based on the simultaneous phase-shifting interferometry scheme. The intensity distributions of interference pattern are calculated based on the Jones theory to optimize the optical system, by which the analytical expressions for phase-shifting length between the neighboring interferograms and the relevant phase-delay value are derived. To meet the requirement of practical application, possible latent errors in the process of detecting time-delay are analyzed. In particular, a minimum time-resolution with attosecond level at 800 nm wavelength was achieved. The results show that this system satisfies the requirement of femtosecond pulse pump-probe high-precision measurement.

Stabilizing second harmonic generation output using cascaded crystals

Deng Qing-Hua, Zhang Xiao-Min, Ding Lei, Tang Jun, Xie Xu-Dong, Lu Zhen-Hua, Zhao Run-Chang, Dong Yi-Fang
Acta Physica Sinica. 2011, 60 (2): 024213 doi: 10.7498/aps.60.024213
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Theoretical study and numerical simulation were carried out on the newly proposed way of cascaded second harmonic generation (SHG) to get stable SHG output. The results certify that by way of using cascaded SHG one can obtain stable SHG output. Our results also show that by tuning the angle between k and the optical axis and the distance between the two SHG crystals, the length of the second SHG crystal for most stable SHG can also be tuned. When the length for most stable SHG is tuned to the real length of the second SHG crystal, stable SHG output was be obtained. Both stable SHG output and high SHG conversion efficiency can be got using this new way, and this will help a lot to design the pumping system for the optical pulse chirped amplifying system.

Numerical study of Hermite-Gaussian beams in nonlocal thermal media

Li Shao-Hua, Yang Zhen-Jun, Lu Da-Quan, Hu Wei
Acta Physica Sinica. 2011, 60 (2): 024214 doi: 10.7498/aps.60.024214
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Based on the nonlocal nonlinear Schrdinger equation and Poisson equation of thermal diffusion, using the slip-step Fourier algorithm and multi-grid method, we numerically investigated the propagation properties of Hermite-Guassian beams in the nonlocal thermal media. The results show that low-order Hermite-Gaussian beams can propagate stably, in contrast with the unstable propagation of high-order Hermite-Gaussian beams. The worse the stability is, the higher the order is. The effect of the boundary of the sample with different cross sections on the propagation properties of Hermite-Guassian beam is also discussed in detail. We found that propagation properties in square geometry are in agreement with those in Snyder-Mitchell model. However, in rectangular sample, the evolution of intensity distribution of Hermite-Gaussian beams differs seriously from that in the square sample.

Back conversion in optical parametric process

Liu Jian-Hui, Liu Qiang, Gong Ma-Li
Acta Physica Sinica. 2011, 60 (2): 024215 doi: 10.7498/aps.60.024215
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Back conversion is the key factor that affects the conversion efficiency, the beam quality of the parametric waves, and the stability of the output in the optical parametric process. For the reason of the variation of the back conversion with the distribution in the cross-section and with time, the back conversion cannot be eliminated thoroughly. We analyzed the problem of the back conversion in the optical parametric process, and established the models of the parametric process for the continuous waves and the pulsed waves, which help us study the key factors affecting the back conversion. According to the conclusion of our analysis, the proper length of the nonlinear crystals, the optimal distribution of the energy of the pump beam, and the proper parameters of the resonant cavity ( for optical parametric oscillators ) could reduce the back conversion and help to increase the conversion efficiency. According to the theoretical results, we designed an X-cut KTA (Potassium Titanyl Arsenate) optical parametric oscillator, and obtained the signal light with the energy of 270 mJ and the idler light with the energy of 150 mJ, which decreased the back conversion, and the efficiency reached 43%.

Guidance characteristics correlated to the core refractive index in a hybrid photonic crystal fiber

Cheng Tong-Lei, Chai Lu, Li Yan-Feng, Hu Ming-Lie, Wang Qing-Yue
Acta Physica Sinica. 2011, 60 (2): 024216 doi: 10.7498/aps.60.024216
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The properties of light guiding mechanism and modes relating to the core refractive index in a hybrid photonic crystal fiber (PCF) are numerically investigated by the full-vectorial finite element method. The light guiding mechanism of core mode is the double-bandgap-guiding when the core refractive index is smaller than the effective index of the air-hole cladding in the hybrid-PCF. If the core refractive index is between the refractive indexes of the two kinds of hybrid-claddings, there is a co-operative action of the index-guiding and the bandgap-guiding on the guide mode in the core. Only the total internal reflection guiding occurs in the fiber when the core refractive index is greater than the effective index of the high-index rod cladding. Comparison of these guiding properties in the hybrid-PCF are also carried out. The results provide guidance for the design of hybrid photonic crystal fiber for special purposes.

Fabry-Perot resonance on extraordinary transmission through one-dimensional metallic gratings with sub-wavelength under transverse electric wave excitation

Wang Ya-Wei, Liu Ming-Li, Liu Ren-Jie, Lei Hai-Na, Tian Xiang-Long
Acta Physica Sinica. 2011, 60 (2): 024217 doi: 10.7498/aps.60.024217
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The transmission distribution of transverse electric wave (TE) through one-dimensional metallic gratings with sub-wavelenghth slits with dielectric added in different positions has been simulated by the FDTD (finite difference time domain) method, the extraordinary transmission can be produced at several special wavelengths. The simulation shows that the guided-mode-like resonance theory is the main reason giving rise to the first peak and the second peak. Based on the guided-mode-like resonance theory, from the Maxwell’s equations,we nade sure that the Fabry Perot resonance is the main cause producing the third peak by the effective index mehod. In a word, the guided-mode resonance theory and the Fabry-Perot-like resonance reveal the physical nature of the extraordinary transmission phenomenon which provides a complete theoretical basis for further study of the extraordinary transmission phenomenon of TE-polarized wave.

Characteristics of subluminal for optical resonators

Zhang Jing, Zhang Yun-Dong, Zhang Xue-Nan, Yu Bo, Wang Jin-Fang, Wang Nan, Tian He, Yuan Ping
Acta Physica Sinica. 2011, 60 (2): 024218 doi: 10.7498/aps.60.024218
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The insertion loss of fiber couplers in the two fiber rings waveguide system is studied. The peak power is the same by matching coupler strength of two couplers at the resonant area. The peak transmittance is inversely proportional to the group refractive index regardless of the two reflection values. Group delay increases at the expense of reduction of the peak transmissivity. The three rings waveguide structure manifests the subluminal properties accompanying normal dispersion by doping gain media. Group delay is analyzed in the frequency domain and the time domain, respectively. This study could be regarded as the significant theoretical foundation for applications in the field of controllable light velocity theory, sensors, filters, optical buffers and so on.

Dissonant standing-wave tube and the extremely nonlinear pure standing wave field

Min Qi, Liu Ke
Acta Physica Sinica. 2011, 60 (2): 024301 doi: 10.7498/aps.60.024301
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A standing-wave tube consisting of two tubes with abrupt changing diameters is dissonant, that is, its higher resonance frequencies are not integral multiples of the fundamental one. Using the dissonant property of the said standing-wave tube, the harmonics can be well suppressed and extremely pure nonlinear standing wave can be obtained at the first resonance frequency. Based on the study of the dissonant property of this standing-wave tube and by the straight connection of a high-power loudspeaker, 184 dB extremely pure nonlinear standing-wave field was obtained at the first resonance frequency. Moreover, the nonlinear standing-wave fields were experimentally investigated separately for the second resonance frequency up to the fifth. Relatively regular nonlinear standing-wave field of 180 dB was obtained at the third resonance frequency, and that of 166 dB was obtained at the fourth resonance frequency. The harmonics saturation phenomena and zigzag waveforms were observed at the third and the fifth resonance frequency, respectively.

Volume effect in the cyclic segregation of quasi two-dimensional binary granular mixture Hot!

Wu Yu-Hang, Zheng Ning, Wen Ping-Ping, Li Liang-Sheng, Shi Qing-Fan, Sun Gang
Acta Physica Sinica. 2011, 60 (2): 024501 doi: 10.7498/aps.60.024501
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A systematic study about the cyclic segregation observed experimentally in a vertically vibrated quasi two-dimensional binary granular mixture is reported. The frequency-amplitude phase diagram was obtained, in which the region of cyclic segregation was found. We also measured the period of the cyclic segregation and showed the relationship between the period and total volume of granular mixture. Finally, the competition mechanism of percolation and condensation from Hong’s theory is used to explain the cyclic segregation and volume effect qualitatively.

Analysis and imitation of dynamic properties for rigid-flexible coupling systems of a planar flexible beam

He Xing-Suo, Li Xue-Hua, Deng Feng-Yan
Acta Physica Sinica. 2011, 60 (2): 024502 doi: 10.7498/aps.60.024502
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The finite element method is used for the system discretization and the coupling dynamic equations of flexible beam are obtained by Lagranges equations. The second order coupling terms between rigid large overall motion, arc length stretch, lateral flexible deformation kinematics and torsional deformation terms are included in the present exact coupling model to expand the theory of one-order coupling model. The dynamic response of the present model is compared with that of zero-order approximate model and one-order coupling model. Then the changes of dynamic stiffening terms due to the new coupling terms are discussed according to different models. At the same time, the effect of initial static deformation in the tip is considered to study the vibrant deformation of flexible beam. The difference between zero-order approximate model, one-order coupling model and the present exact model is revealed by the frequency spectrum analysis method and it is concluded that the speed of overall motion is a vital cause for the difference between different models. And we found that the dynamic stiffening phenomenon still exists in rigid-flexible coupling system while the overall motion is free. But the effect of dynamic stiffening in the present exact model is not as severe as that in the one-order coupling model.

A calculating model of sliding friction coefficient based on non-continuous energy dissipation

Gong Zhong-Liang, Huang Ping
Acta Physica Sinica. 2011, 60 (2): 024601 doi: 10.7498/aps.60.024601
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A sliding friction coefficient calculation model was established based on analysis of non-continuous diffusion of energy during the interfacial friction. The results indicated that the sliding friction coefficient is not related with the load and the actual contact area under elastic contact. However, when the actual contact area is close to the nominal contact area, the sliding friction coefficient will increase along with the reducing load. When sliding is slow, the friction coefficient rises slowly with the increase of the sliding velocity, and the influence is more remarkable when the sliding speed is higher. Furthermore, the larger the atomic lattice, the smaller the sliding friction coefficient is. The sliding friction coefficient increases with the rising of the atomic temperature. These results will be used to engineering application and theoretical research.

Equatorial Rossby envelope solitary waves with β effect in a shear flow

Song Jian, Jiang Nan, Yang Lian-Gui
Acta Physica Sinica. 2011, 60 (2): 024701 doi: 10.7498/aps.60.024701
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With a simple model of shallow-water on an equatorial beta plane, the nonlinear equatorial Rossby waves in a shear flow with beta effect are investigated by the asymptotic method of multiple scales. The nonlinear Schrdinger equation, satisfied by large amplitude Rossby envelope solitary waves in shear basic flow with beta effect, is derived. The effects of basic flow shear and beta effect on the nonlinear equatorial Rossby waves are also analyzed.

Experiments on quasi-two-dimensional dipolar vortex streets generated by a moving momentum source in a stratified fluid

Chen Ke, You Yun-Xiang, Hu Tian-Qun, Zhu Min-Hui, Wang Xiao-Qing
Acta Physica Sinica. 2011, 60 (2): 024702 doi: 10.7498/aps.60.024702
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Experiments were carried out in a stratified fluid with a momentum source modeled by a horizontally moving jet. The generation mechanism was investigated and the evolution characteristics were analyzed for the quasi-two-dimensional dipolar vortex streets generated by such a moving momentum source in the stratified fluid. The conditions of different Reynold and Froude number (Re, Fr) combinations under which the dipolar vortex street can be generated by moving momentum source were determined by use of data based on the present series of experiments. Moreover, the dependence of the dimensionless formation time and inverse dimensionless average wavelength of the dipolar vortex street on Fr for different values of Re was obtained. The results show that these parameters are independent of Re and approximately follow some exponential laws of Fr.

Fractal analysis of Casson fluid flow in porous media

Yuan Mei-Juan, Yu Bo-Ming, Zheng Wei, Yuan Jie
Acta Physica Sinica. 2011, 60 (2): 024703 doi: 10.7498/aps.60.024703
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Fractal models for flow rate, velocity, starting pressure gradient and effective permeability for Casson fluid in porous media are proposed based on the fractal properties of porous media and capillary model. The proposed models are expressed as functions of fractal dimension, porosity, maximum pore size and representative length of porous media. All parameters in the proposed expressions have clear physical meaning, and the proposed models relate the properties of Casson fluid to the structural parameters of porous media. The velocity, starting pressure gradient and effective permeability versus different parameters are discussed, and the analytical expressions reveal the physical principles for flow velocity, starting pressure gradient and effective permeability in porous media.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Variable charge molecular dynamics simulation of vitreous silica

Ma Ying
Acta Physica Sinica. 2011, 60 (2): 026101 doi: 10.7498/aps.60.026101
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Variable charge molecular dynamics simulations of vitreous silica have been performed based on the iterative fluctuation charge model. The vitreous silica was formed using the standard melt-quench process. The pair distribution function, angle distribution and frequency spectrum were then obtained. The results are in good agreement with experimental data. More importantly, our results show that the atomic charge in vitreous silica is significantly different from those in the crystalline silica, and larger fluctuations are observed.

Effects of the vacancy point-defect on electronic structure and optical properties of LiF under high pressure: A first principles investigation

He Xu, He Lin, Tang Ming-Jie, Xu Ming
Acta Physica Sinica. 2011, 60 (2): 026102 doi: 10.7498/aps.60.026102
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By using the ultra-soft pseudo-potential approach of the plane wave based on the density-functional theory, the electronic structures and optical properties of LiF with Li-1 and F+1 vacancies are calculated. The results indicate that: (1) the presence of the vacancy causes defective states within the band gap of LiF; (2) the optical absorption of LiF in the visible-light region is not influenced by the vacancy point-defect (absorption coefficients are still zero); (3) in the ultra-violet region, the weak absorption induced by the Li-1 vacancy, appears within ~99—114nm, and the relatively strong absorption induced by the F+1 vacancy exists in the range of 99—262nm; (4) effects of the Li-1 and F+1 vacancy on reflectivity and loss-function show mainly in the ultra-violet region, which is similar to those of optical absorption.

Interpretation of dehydrogenation ability of high-density hydrogen storage materials by density functional theory

Zhang Hui, Xiao Ming-Zhu, Zhang Guo-Ying, Lu Guang-Xia, Zhu Sheng-Long
Acta Physica Sinica. 2011, 60 (2): 026103 doi: 10.7498/aps.60.026103
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A first-principles plane-wave pseudopotential method based on the density functional theory was used to investigate the dehydrogenation properties and its influence mechanics on several high-density hydrogen storage materials (MgH2, LiBH4,LiNH2 and NaAlH4) and their alloys. The results show that MgH2, LiBH4, LiNH2 and NaAlH4 high-density hydrogen storage materials are relatively stable and have high dehydrogenation temperature. Alloying can reduce their stability, but the stability of a system is not a key factor to the dehydrogenation properties of high-density hydrogen storage materials. The width of band gap of hydrogen storage materials can characterize the bond strength basically, the wider the energy gap is, the harder the bond breaks, and the higher the dehydrogenation temperature is. The bonding peak of the valence band top of LiNH2 is attributed mainly to the Li—N bonding, the N—H bond constitutes the low peak, which makes the dehydrogenation temperature of LiNH2 high, though LiNH2 has a narrow band gap in respect to LiBH4 and NaAlH4, which makes the ammonia release in the dehydrogenation process. Alloying makes the band gap narrow, and the Fermi level goes into the conduction band, which improves the dehydrogenation properties. It was found from the charge population analysis that B—H bond in LiBH4 is the strongest, H—N bond in LiNH2 is the weakest, so LiNH2 is relatively easy to release hydrogen. After alloying, the bond strength of X—H is weakened in every hydrogen storage material, and the N—H bond strength in LiMgNH2 is the lowest. Therefore, it is perspective to develop LiNH2 as hydrogen storage from the lowering of dehydrogenation temperature.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Energy band structure of uniaxial-strained silicon material on the (001) surface arbitrary orientation

Ma Jian-Li, Zhang He-Ming, Song Jian-Jun, Wang Guan-Yu, Wang Xiao-Yan
Acta Physica Sinica. 2011, 60 (2): 027101 doi: 10.7498/aps.60.027101
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The strain tensor arising from uniaxial stress along an arbitrary direction on the (001) surface of Si is calculated. With these uniaxial strain tensor, the band structure of silicon material under arbitrary uniaxial stress on the (001) surface is calculated using K ·P perturbation theory coupled with linear deformation potential theory. The relation between energy band structure and stress parameters (type, direction, magnitude) was obtained. Finally, the uniaxial stress induced band structure change, such as that of the conduction band (CB) and the valence band (VB) edge levels, CB and VB splitting energy and the bandgap is demonstrated. Results of these band structure can be used as a guide for the design and the selection of the optimum strain and crystal orientation configuration of uniaxial strained silicon devices.

Drain-induced barrier-lowering effects on threshold voltage in short-channel strained Si metal-oxide semiconductor field transistor

Wang Xiao-Yan, Zhang He-Ming, Wang Guan-Yu, Song Jian-Jun, Qin Shan-Shan, Qu Jiang-Tao
Acta Physica Sinica. 2011, 60 (2): 027102 doi: 10.7498/aps.60.027102
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Based on strained silicon metal-oxide semiconductor field transistor (MOSFET) structure, the distribution of surface potential is obtained by solving two-dimensional Poisson equation, and the threshold voltage model is built. According to calculation results, the dependence of threshold voltage on germanium content of relaxed Si1-βGeβ, channel length, voltage of drain, doping content of substrate and channel are studied in detail, and the influence of drain-induced barrier-lowering on scaled strained silicon MOSFET is obtained, which can provide important reference for the design of strained silicon MOSFET device and circuit.

Preparation of Fe-based thick amorphous composite

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Acta Physica Sinica. 2011, 60 (2): 027103 doi: 10.7498/aps.60.027103
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A thick Fe-based amorphous composite coating (1—5mm) was prepared in situ by tungsten inert gas (TIG) cladding method. The auxiliary cooling system was used to improve the solidification rate of molten alloy and decrease the dilution from the substrates. The microstructure of the composite coating was investigated by X-ray differaction, optical microscope and transmission electron microscope. In addition, the micro-hardness of the coating was also measured. The results show that the composite coating is composed of the amorphous phase and the nano-crystalline grains encapsulated by amorphous transition layer, whose content is more than 50 percent. The composite coatings have been found to have good bonding strength and high wear resistance, the maximum value of the micro-hardness is up to 1600HV0.3. The microstructure of the transition layer with good elastic-plastic properties leads to the higher impact resistance. At last, the relations between the microstructure and micro-hardness properties were discussed in detail, and the main reason for high hardness is the cooperation of the amorphous phase and nano-crystalline phase in the composite coatings.

First principles studies of nitrogen doped tetrahedral amorphous carbon

Gao Wei, Gong Shui-Li, Zhu Jia-Qi, Ma Guo-Jia
Acta Physica Sinica. 2011, 60 (2): 027104 doi: 10.7498/aps.60.027104
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The microstructures and electronic structures of nitrogen doped tetrahedral amorphous carbon (ta-C ∶N) have been simulated and investigated using molecular dynamics within the framework of density functional theory. There are no obvious relation between the coordination of nitrogen and the density of ta-C ∶N. The most common form of nitrogen bonding was found to be three coordinated. Two coordinated and a small quantity of four coordinated nitrogen atoms were also found. The addition of nitrogen caused a big increase in the sp2 fraction of carbon. The states near Fermi level increased in density as the contents of nitrogen atoms increased. Fermi level was not found to shift obviously.

The hole concentration and strain relaxation of ultrathin GaMnAs film

Su Ping, Gong Min, Ma Yao, Gao Bo, Shi Rui-Ying, Chen Chang, Shi Tong-Fei, Cao Xian-Cun, Meng Xiang-Hao, Luo Dai-Sheng
Acta Physica Sinica. 2011, 60 (2): 027105 doi: 10.7498/aps.60.027105
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The hole concentration and strain relaxation degree in the diluted magnetic epitaxial film of GaMnAs are affected by the Mn concentration. The result from Raman scattering spectrum experiment has shown that the hole concentration in ultra-thin GaMnAs sample with Mn concentration of 3% is greater than that in sample with Mn concentration of 2% , while the hole concentration in sample with Mn concentration of 4% is less than that in sample with Mn concentration of 3%. Based on the theory of strain relaxation and investigation by HRXRD, it was indicated the samples with Mn concentration of 2% and 3% are in quasi-coherence or with low relaxation degree, respectively. On the other hand, the sample with Mn concentration of 4% obviously has a greater relaxation degree than that with 3% concentration. Therefore, it is suspected that the status of quasi-coherence or low relaxation degree hardly affects the hole concentration with the change of the Mn concentration. However, the strain relaxation status of large relaxation degree results in more defects in the epitaxial layer which affects the energy band and level thus decreases the hole concentration dramatically.

Theoretical studies on spin-vibronic spectra of CH3 O(X2 E)

Zhang Shi-Yang, Mo Yu-Xiang
Acta Physica Sinica. 2011, 60 (2): 027106 doi: 10.7498/aps.60.027106
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We made an ab initio study of the spin-vibronic couplings in CH3O (X2E) based on diabatic model. The diabatic potential energy curves were calculated at the level of CASPT2/cc-pvtz. The calculated spin-vibronic energy levels are compared with the experimental data, which indicates that the present calculation has higher accuracy than the previously reported ones.

Crystallization and microstructure change of semiconductor active thin layer in polymer organic field-effect transistors

Tian Xue-Yan, Zhao Su-Ling, Xu Zheng, Yao Jiang-Feng, Zhang Fu-Jun, Jia Quan-Jie, Chen Yu, Fan Xing, Gong Wei
Acta Physica Sinica. 2011, 60 (2): 027201 doi: 10.7498/aps.60.027201
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The crystallization and microstructure change of self-organization and the related conduction mechanisms of polymer semiconductor active thin layer in polymer organic field-effect transistors (OFET) are investigated by synchrotron radiation grazing incident X-ray diffraction (GIXRD) for understanding the relationships between polymer self-organization and charge carry. The change of the crystalline microstructure of RR-P3HT clarifies the effect of SAMs for improving the interface between the insulator layer and the organic semiconductor layer. The self-organiztion of RR-P3HT modified by SAMs improves the crystalliztion to pack form the thiophene rings along the perpendicular direction of substrate and results in that the π-π interchains are stacked to parallel the substrate. The two-dimensional charge transport is improved. Furthermore, we find that two-dimensional, conjugated, and self-organized crystalline lamellae are easier to gain with slow grown film than with fast grown film.

Synthesis and thermoelectric properties of thermoelectric materials of the skutterudites In0.3Co4Sb12-xSex

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Acta Physica Sinica. 2011, 60 (2): 027202 doi: 10.7498/aps.60.027202
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Thermoelectric materials of the skutterudites In0.3Co4Sb12-xSex(x=0—0.3) were prepared by melt-annealing and spark plasma sintering. The existence forms of the element In were investigated, and the effect of doping Se in In filled-skutterudites on the structure and thermoelectric properties were also studied systematically. The element In could be filled into the hole structure of skutterudite, and the excessive In exists as InSb in the boundary of grains. After the substitution of Se for Sb, the lattice parameters decrease, and the filling fraction limit of In decreases. All the compounds of In0.3Co4Sb12-xSex(x=0—0.3) show n-type conduction. With the Se doping amount increasing, the carrier concentration and electrical conductivity decrease, and the Seebeck coefficient increases, and the power factor decreases slightly. Since the introduction of Se substitution brings about quality fluctuation and lattice distortion in structure, moderate amount of Se substitution can lower the thermal conductivity largely. The maximum ZT values of both In0.3Co4Sb12 and In0.3Co4Sb11.95Se0.05 samples reach above 1.0.

Preparation and electrical properties of double-doped perovskitestructured conducting ceramics Sm0.9Sr0.1Al1-xCoxO3-δ

Xiang Jun, Guo Yin-Tao, Chu Yan-Qiu, Zhou Guang-Zhen
Acta Physica Sinica. 2011, 60 (2): 027203 doi: 10.7498/aps.60.027203
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A series of new mixed-conducting ceramics Sm0.9Sr0.1Al1-xCoxO3-δ(SSAC, x=0.2, 0.4, 0.5, 0.6) with perovskite structure were prepared by sintering the precursor powders derived from organic gel process. The effects of sintering temperature and Co doping concentration on the crystal structure, phase composition and electrical properties were also discussed in detail. The X-ray diffraction results show that the over-high sintering temperature or Co doping content will lead to the formation of impure phase with a chemical formula of Sm(Sr)CoO3 in sinters, and the solid solubility limit of Co in this system lies in the range of 50 mol%—60 mol%. The partial substitution of Co for Al in Sm0.9Sr0.1Al1-xCoxO3-δ results in an increase in lattice volume. The measurement results of electrical properties reveal that the conductivities of SSAC ceramics are dominated by p-type conduction, and the conduction behavior conforms to the small polaron hopping transport mechanism. With the increasing sintering temperature, the conductivities of as-prepared samples gradually increase. For the SSAC ceramics with Co content lower than the solid solubility limit, it is observed that their conductivities increase with the increase of Co content while the corresponding apparent activation energies decrease. The prepared single-phase Sm0.9Sr0.1Al0.5Co0.5O3-δ ceramic body by sintering at 1200℃ for 10h has a conductivity of 63.4 S/cm and an apparent activation energy of 0.14eV. These novel SSAC mixed-conducting ceramics with good electrical properties can potentially be used in the field of high temperature electrochemistry.

Tunnelling and storage of charges in a-SiNx/nc-Si/a-SiNx structures

Wang Xiang, Huang Rui, Song Jie, Guo Yan-Qing, Chen Kun-Ji, Li Wei
Acta Physica Sinica. 2011, 60 (2): 027301 doi: 10.7498/aps.60.027301
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The a-SiNx/nc-Si/a-SiNx sandwiched structures are fabricated in a plasma enhanced chemical vapour deposition (PECVD) system on n-type Si substrate. The nc-Si layer in thickness of 5 nm is fabricated from hydrogen diluted silane gas by layer-by-layer deposition technique. The thicknesses of tunnel and control SiNx layer are 3 nm and 20 nm, respectively. Conductance-voltage and capacitance-voltage measurements are used to study the charges tunnelling and storage in the sandsiched structures. Distinct frequency-dependent conductance peaks due to charges tunneling into the nc-Si dots and capacitance-voltage hysteresis characteristic due to charges storage in the nc-Si dots are observed in the same sample. The experimental results demonstrate that by controlling the thickness of tunnel and control SiNx layers charges can be loaded onto nc-Si dots via tunnelling and be stored in a-SiNx/nc-Si/a-SiNx structures.

First principles study on structure and property of Si2 CN4(010) surface

Lu Shuo, Zhang Yue, Shang Jia-Xiang
Acta Physica Sinica. 2011, 60 (2): 027302 doi: 10.7498/aps.60.027302
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The structure and property of Si2CN4(010) surface with different terminations were studied systemically by first principles calculation. The calculated cleavage energies of each possible surface showed that the Si—NⅡ bond located at the SiN layer was the strongest,while the Si—NⅠ bond connected with the carbodiimide was the weakest. As a result,the surface with the Si/NⅠ termination was the easiest to form. We have compared the atomic structure and electronic properties of un-optimized and optimized surface models. During the optimization of structure,the unsaturated surface atom,especially the NⅠ atoms at the surface would bond with each other to decrease the surface energies,since there are prominent density of states existing at the Fermi level of NⅠ atom. At the same time,the unsaturated C atoms do not have the tendency of bonding with each other,since their electronic state are more stable than NⅠ atom.

Theoretical investigation of anti-reflection properties of Ag-nanoparticles

Han Tao, Meng Fan-Ying, Zhang Song, Wang Jian-Qiang, Cheng Xue-Mei
Acta Physica Sinica. 2011, 60 (2): 027303 doi: 10.7498/aps.60.027303
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In order to trap more sunlight onto the crystalline silicon solar cell and improve the photo-electric conversion efficiency, it is very important to study the optical scattering properties of silver nanoparticles on silicon wafer. Based on localized surface plasmon effect and MIE scattering theory, using numerical calculation by Matlab, the scattering properties of solar spetra for different radius and density of silver nanoparticle are investigated in theory. The dependence of the optimal optical transmittance on the radius and density of Ag nanoparticle is obtained. Furthermore, it is found that the dipole peaks is redshifted and high mode peaks gradually emerges. Firstly this paper gives the variation of the best Ag nanoparticle density with the radius quantitively, the theoretical method calculating the transmittance of the nanoparticle antireflection film is also established. As a result, the simple functional expression of transmittance is deduced in this work, which provides a theoretical guidance for experimental research.

Coulomb oscillations effect in dual gate controlled silicon nanowire Hot!

Zhang Xian-Gao, Fang Zhong-Hui, Chen Kun-Ji, Qian Xin-Ye, Liu Guang-Yuan, Xu Jun, Huang Xin-Fan, He Fei
Acta Physica Sinica. 2011, 60 (2): 027304 doi: 10.7498/aps.60.027304
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The tunable single electron effect and Coulomb oscillations were observed in Si nanowire transistors. By measuring the channel current as function of applied back-gate and side-gate voltage, the tunable single electron effect and Coulomb oscillations are investigated. From the differential conductance characteristics, the Coulomb diamonds are clearly observed due to the gate voltage-induced quantum dots formation in the Si nanowire.

Gate tunneling current predicting model of strained Si for scaled metal-oxide semiconductor field effect transistor

Wu Tie-Feng, Zhang He-Ming, Wang Guan-Yu, Hu Hui-Yong
Acta Physica Sinica. 2011, 60 (2): 027305 doi: 10.7498/aps.60.027305
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For scaled metal-oxide semiconductor field effect transistor (MOSFET) devices, normal operation is seriously affected by the static gate tunneling leakage current due to the ultra-thin gate oxide of MOSFET, and the novel MOSFET devices based on strained Si are similar to bulk Si devices in the effects. To illustrate the impact of gate leakage current on performance of novel strained Si device, a theoretical gate tunneling current predicting model by integral approach following the analysis of quasi-two-dimensional surface potential is presented in this study. On the basis of theoretical model, performance of MOSFET device was quantitatively studied in detail using ISE simulator, including different gate voltages and gate oxide thickness. The experiments show that simulation results agree well with theoretical analysis, and the theory and experimental data will contribute to future VLSI circuit design.

Electrical transport and photo-induced properties in Fe3O4 film

Luo Bing-Cheng, Chen Chang-Le, Xie Lian
Acta Physica Sinica. 2011, 60 (2): 027306 doi: 10.7498/aps.60.027306
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Highly oriented Fe3O4 film was fabricated on Si (111) substrate by pulsed laser deposition. The resistivity-temperature curve shows that the Verwey transition point is about 122 K, and the electrical transport mechanism agrees with Mott varial-range hopping model and the small polaron model for temperatures below TV and above TV, repectively. The laser irradiation results in the decrease of the resistivity of the film in the whole temperature range were measured, which is attributed to the intersite transitions of Fe 3d t2g electrons.

Theoretical research on the electronic structure and transport properties of nitrogen doping chiral carbon nanotubes

Wei Yan, Hu Hui-Fang, Wang Zhi-Yong, Cheng Cai-Ping, Chen Nan-Ting, Xie Neng
Acta Physica Sinica. 2011, 60 (2): 027307 doi: 10.7498/aps.60.027307
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Using density functional theory and nonequilibrium Greens function, the electronic structure and transport properties of chiral (6, 3) single-walled carbon nanotubes substituted by nitrogen atoms were investigated. The results show that the configurations and the concentration of the doped atoms have complicated effects on the transport properties of the chiral single-walled carbon nanotubes. The electronic structures of the carbon nanotubes are changed obviously. The transportation properties are degraded by the doping of nitrogen atoms and change significantly with the positions of impurity atoms in the structure. The currents-voltage curve shows nonlinear variation. Under certain conditions the metallic single-walled carbon nanotubes may be converted into semiconductors.

Effects of additional permanent magnet on the levitation force of single domain GdBCO bulk superconductor

Ma Jun, Yang Wan-Min, Li Guo-Zheng, Cheng Xiao-Fang, Guo Xiao-Dan
Acta Physica Sinica. 2011, 60 (2): 027401 doi: 10.7498/aps.60.027401
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Effects of additional permanent magnet on the levitation force of a single domain GdBCO bulk superconductor have been investigated with a cylindrical permanent magnet in their coaxial configuration under zero field cooled state at liquid nitrogen temperature. The magnetic polarity N of cylindrical permanent magnet is pointed to the GdBCO bulk superconductor, and the two additional permanent magnet of rectangular parallelepiped shape are fixed on two sides of the GdBCO bulk superconductor in different arrangments. It was found that the levitation force can be improved to about 61.5 N, which is more than 2 times higher than that (29.8 N) of the system without the additional permanent magnet, when the magnetic polarity N of two additional permanent magnets points to the GdBCO bulk superconductor in horizontal direction. The levitation force is reduced to 19.6N, which is about 65.8% of the levitation force 29.8N of the system without the additional permanent magnets, when the magnetic polarity N of two additional permanent magnet are antiparallel to the magnetic polarity N of the cylindrical permanent magnet. The results indicate that the levitation force of high temperature bulk superconductors can be effectively improved by introducing additional permanent magnet based on reasonably designing the system configuration, which is very important during the practical design and applications of superconducting magnetic levitation systems.

Structure and magnetic properties of Pr2Fe14(C, B)/α-(Fe, Co)-type nanocomposite ribbons

Li An-Hua, Lai Bin, Wang Hui-Jie, Zhu Ming-Gang, Li Wei
Acta Physica Sinica. 2011, 60 (2): 027501 doi: 10.7498/aps.60.027501
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The phase evolution, microstructure and magnetic properties of PrxFe82-x-yTiyCo10B4C4 (x=9—10.5; y=0, 2) melt-spun ribbons have been investigated. All ribbons are mainly comprised of the 2 ∶14 ∶1, 2 ∶17 and α-(Fe, Co) phases. For the group of Ti-free ribbons (y=0), the coercivity increases with increasing x while the remanence decreases with increasing x. When 2 at.%Ti is substituted for Fe in the Ti-free ribbons, the magnetic properties are remarkably enhanced. The coercivity and squareness of demagnetization curve of the Ti-substitution ribbons are substantially improved without a sacrifice of remanence (except for x=9), the remanence even obviously increases at x=10.5. The optimal magnetic properties of Br=9.6 kGs (1 Gs=10-4T), iHc =10.2 kOe (1 Oe=79.5775 A/m), (BH)max=17.4 MGOe have been obtained in Ti-substituted Pr10.5Fe69.5Ti2Co10B4C4 group. The volume fraction of the 2 ∶14 ∶1 phase increases with increasing x, which leads to an increase of coercivity. Ti-substitution suppresses the grain growth of α-(Fe, Co) phase during annealing process, which makes the volume ratio of magnetically hard phase and soft phase and grain size tend to have optimal values, and the intergranular exchange coupling substantially enhances.

Origin of ferromagnetic properties in Ni doped ZnO by the first principles study

Xiao Zhen-Lin, Shi Li-Bin
Acta Physica Sinica. 2011, 60 (2): 027502 doi: 10.7498/aps.60.027502
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Theoretical calculation based on density functional theory (DFT) and local density approximation (LDA) has been carried out to study the magnetic properties of Ni doped ZnO. The results show that ferromagnetism (FM) coupling between Ni atoms is more stable for 8 geometrically distinct configurations. The results from density of states show that O 2p hybridizes with Ni 3d, which results in electronic states spin polarization at the Fermi energy. Moreover, the effect of oxygen vacancy on FM properties of Ni doped ZnO has also been investigated. It was found that FM coupling is enhanced in the presence of oxygen vacancy, which is strong enough to lead to electron-mediated ferromagnetism at room temperature. In addition, the origin of the FM state in Ni doped ZnO has also been discussed by analyzing the coupling of Ni 3d levels. We also analyzed the strain effect on FM properties of Ni doped ZnO.

Effect of microstructure on the ferroelectric properties of Eu-doped Bi4Ti3O12 ferroelectric thin film

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Acta Physica Sinica. 2011, 60 (2): 027701 doi: 10.7498/aps.60.027701
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Eu-doped bismuth titanate Bi3.15Eu0.85Ti3O12 (BET) ferroelectric thin film was prepared on the Pt/Ti/Si(111) substrates by metal-organic decomposition (MOD) at different annealing temperatures of 600℃, 650℃ and 700℃. The structure and ferroelectric properties of BET thin film were analyzed. The nanoscale domain switching was investigated by scanning probe microscopy (SPM) via direct observation. When the polarizing voltage increases to +6V, the ferroelectric c-domain suffers 180° domain switching. The ferroelectric r-domain can not be reversed due to its highly tetragonal structure even if the polarized voltage value increases to +12V. The ferroelectric properties of the BET thin films are dependent on the polarization of ferroelectric c-domain. With the increasing annealing temperature, the area of c-domain becomes larger, and the remnant polarization (2Pr) values of BET films increase. The value of 2Pr reaches 84μC/cm for BET thin film annealed at the temperature of 700℃.

Deduction and verification of electromagnetic parameter of arbitrary polyhedron cloaks

Gu Chao, Qu Shao-Bo, Pei Zhi-Bin, Xu Zhuo, Liu Jia, Gu Wei
Acta Physica Sinica. 2011, 60 (2): 027801 doi: 10.7498/aps.60.027801
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On the basic of the coordinate transformation theory, we deduce the condition for irregular polyhedron cloaks and obtain tensor expressions of electromagnetic parameters. Using tensor expressions of electromagnetic parameters, we verify the effect of 4-sided polyhedron cloak and 14-sided polyhedron cloak through full-wave simulations. The results confirm the validity of tensor expressions of electromagnetic parameters we derived. The present work may serve as a basis for the design of three-dimensional baroque cloak.

Optical and electrical properties of CuS nanoparticles in terahertz frequency

Yang Yu-Ping, Feng Shuai, Feng Hui, Pan Xue-Cong, Wang Yi-Quan, Wang Wen-Zhong
Acta Physica Sinica. 2011, 60 (2): 027802 doi: 10.7498/aps.60.027802
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The spectral response of the mixture composed of CuS nanoparticles and polyethylene powder was measured by the terahertz time-domain spectroscopy (THz-TDS). The low-frequency optical properties of pure CuS nanoparticles, including absorption coefficient, complex dielectric constants as well as conductivity, were calculated by the effective medium theory. The Lorentz theory of dielectric response and the Drude-Smith model of conductivity provide good fits on the measured dielectric function as well as conductivity, respectively. In addition, some terahertz optical properties, such as the frequency of the lattice vibration and the time constant for the carrier scattering, are also obtained by the fitting. Our investigation could help to reveal the material properties in the terahertz range and to find out the promising physical effect for special application.

Upconversion luminescence properties of Y2SiO5: Er3+ ,Yb3+ ,Tm3+ synthesized by co-precipitation method

Guo Lin-Na, Wang Yu-Hua
Acta Physica Sinica. 2011, 60 (2): 027803 doi: 10.7498/aps.60.027803
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A series of up-conversion luminescence materials of Y1.98-2xYb2xEr0.02SiO5(0.00≤x≤0.15) and Y1.736Yb0.24Er0.02Tm0.004SiO5 were synthesized by co-precipitation method.The absorption spectra from 400 to 1600 nm of Y1.98-2xYb2x Er0.02SiO5 (x=0.00,0.08) were compared, and the up-conversion emission spectra of all samples were investigated when excited by 976 nm opo laser. The decay curves of Er3+4S3/2(4F9/2)→ 4I15/2,Tm3+1G43H6,as well as the relationship between the blue up-conversion emission intensity and pumping power were measured,consequently, the possible up-conversion luminescence mechanisms of Er3+,Tm3+ in Y2SiO5 were discussed. The results show that X2-type monoclinic Ln3+(Ln3+=Er3+,Yb3+,Tm3+) co-doped Y2SiO5 phosphors have been synthesised under relatively low temperature of 1250 ℃, and the absorption intensity and bandwidth are remarkably increased by Yb3+ sensitizing around 976 nm. Up-conversion emission spectra has been analyzed and the results suggest that both the green and red lights increase first and then decrease with the increase of the Yb3+ doping concentration. However,the concentration quenching of the red light emission is higher, due to the forward (ETU3) and back (ETU4) energy transfer between Yb3+ and Er3+ ions; the blue emission occurs mainly through phonon-assisted energy transfer between Yb3+ and Tm3+ ions, which is a three photon absorption process.

A Gires-Tournois mirror for dispersion compensation in the Ti-sapphire laser system

Ma Qun, Zhang Yue-Guang, Shen Wei-Dong, Luo Zhen-Yue, Zhang Qing, Zhang Shu-Na, Ye Peng, Yuan Wen-Jia, Liu Xu, Wei Zhi-Yi
Acta Physica Sinica. 2011, 60 (2): 027804 doi: 10.7498/aps.60.027804
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A Gires-Tournois(GT) mirror with a group delay dispersion (GDD) of -60 fs2 in one reflection was designed according to the requirement of dispersion compensation in the Ti-sapphire femtosecond laser system. It was manufactured by ion assisted deposition combined with the optical monitoring in transmission. The reflectance of the mirror was measured by a spectrophometer working in the range from 650 nm to 950 nm with a resolution of 1 nm. The results were consistent with the design. Furthermore, a home-made white light interferometry system was employed to test the reflection GDD and the result also agreed well with the design. The experimental GDD oscillation was less than ± 20 fs2. The GT mirror was applied in the Ti-sapphire femtosecond laser system and a good clamping result was obtained. Finally a 29 fs ultra-short pulse was acquired.

Silicon surface microstructures created by 1064 nm Nd∶YAG nanosecond laser

Yang Hong-Dao, Li Xiao-Hong, Li Guo-Qiang, Yuan Chun-Hua, Tang Duo-Chang, Xu Qin, Qiu Rong, Wang Jun-Bo
Acta Physica Sinica. 2011, 60 (2): 027901 doi: 10.7498/aps.60.027901
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We investigated the evolution of surface microstructures created on single crystal silicon wafers by the cumulative Nd ∶YAG nanosecond laser pulses (wavelength 1064 nm ) in different atmospheres (N2, air and vacuum). Micropore structure and the fracture lines are formed after irradiation of a few laser pulses,compared with ripple structures created by laser pulses of wavelengths of 532 and 355 nm. The fracture line structure is different for (111) and (100) silicon. The fracture lines have 60°and 120° intersections for (111) silicon. For (100)-oriented silicon wafers, two sets of fracture lines intersect at 90° to form a grid that divides the surface into rectangular blocks with side length of from 15 to 20 μm. We think that phase explosions are responsible for the growth of micropore structure. The fracture lines are mainly due to thermal stress. Finally, We studied the formation of microstructures under different atmospheres, and the results show that it is closely related to the etching and growth rate.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Epitaxial growth of Ge0.975Sn0.025alloy films on Si(001) substrates by molecular beam epitaxy Hot!

Su Shao-Jian, Wang Wei, Zhang Guang-Ze, Hu Wei-Xuan, Bai An-Qi, Xue Chun-Lai, Zuo Yu-Hua, Cheng Bu-Wen, Wang Qi-Ming
Acta Physica Sinica. 2011, 60 (2): 028101 doi: 10.7498/aps.60.028101
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Ge0.975Sn0.025 alloy films have been grown on Si(001) substrates by molecular beam epitaxy with high-quality Ge films as buffer layers.The alloys have high crystalline quality without Sn surface segregation, determined by double crystal X-ray diffraction and Rutherford backscattering spectra measurement. In addition, the Ge0.975Sn0.025 alloy has rather good thermal stability at 500 ℃, which makes it possible to be used in Si-based optoelectronic devices.

Direct measurement of group delay of optical elements

Deng Yu-Qiang, Sun Qing, Yu Jing
Acta Physica Sinica. 2011, 60 (2): 028102 doi: 10.7498/aps.60.028102
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A technique for direct measurement of group delay of optical elements is introduced. With the joint time-frequency analysis of white-light spectral interferogram, group delay can be directly extracted from the ridge of wavelet-transform. The technique is accurate and simple. The measurement results of group delay and group delay dispersion of a piece of fused silica was demonstrated. The results agree well with those from theoretical calculation, and the noise is greatly reduced. This technique is suitable for various application of white-light interferometer.

Thermal transport in L-shaped graphene nano-junctions

Bao Zhi-Gang, Chen Yuan-Ping, Ouyang Tao, Yang Kai-Ke, Zhong Jian-Xin
Acta Physica Sinica. 2011, 60 (2): 028103 doi: 10.7498/aps.60.028103
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By using nonequilibrium Green’s function method, the thermal transport properties of L-shaped graphene nano-junctions consisting of a semi-infinite armchair-edged nanoribbon and a semi-infinite zigzag-edged nanoribbon were studied. It is shown that the thermal conductance of the L-shaped graphene nano-junctions depends on the included angles and the widths of the graphene nanoribbons. As the angle of L-shaped graphene nano-junctions increases from 30° to 90° and further to 150°, the thermal conductance obviously increases. For the right-angle L-shape graphene nano-junction, the thermal conductance undergoes a transition with the increasing of the widths of the armchair nanoribbons. The thermal conductance decreases at low temperature region and increases at high temperature region. Meanwhile the thermal conductance of L-shape graphene nano-junction with included angle 150° decreases by increasing the widths of zigzag-edged nanoribbons in both low and high temperature regions. These thermal transport phenomena can be reasonably explained by analyzing the phonon transmission coefficient. We illustrate the mechanisms of thermal transport for different L-shaped graphene nano-junctions. The results provide significant physical models and theoretical basis for designing the thermal devices based on the graphene nano-junctions.

Effect of Al(OH)3 sol concentration on characteristics of microarc oxidation coatings of titanium alloy

Yu Song-Nan, Wu Han-Hua, Chen Gen-Yu, Yuan Xin, Li Yue
Acta Physica Sinica. 2011, 60 (2): 028104 doi: 10.7498/aps.60.028104
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The effect of Al(OH)3 sol on the growth characteristics, microstructure, phase structure and electrochromic properties of the coating fabricated on titanium alloy substrates were investigated by means of changing the Al(OH)3 sol concentration. The results show that the rate of growth of coating thickness gradually increased from slow to fast with the increasing concentration of Al(OH)3 sol and the roughness and size of micropore on the coating surface gradually increased, while its pore density was reduced. The coating was composed of anatase TiO2 when the volume fraction C≤10%. The rutile TiO2 began to emerge at C>10%, and its relative content gradually increased with the increase of the Al(OH)3 sol concentration. When C=40%, the obtained coating was composed of rutile TiO2. The cyclic voltammetry tests in pH 2.0 HCl solution showed that the color of the sample fabricated at C≤20% did not change significantly, with the increase of the Al(OH)3 sol concentration, the color change of the sample became clear. When C=40%, the obtained sample showed good stability and reversibility between blue coloration and bleaching cycles in pH 2.0 HCl solution.

Composition and crystal structure of N doped TiO2 film deposited with different O2 flow rates

Ding Wan-Yu, Wang Hua-Lin, Ju Dong-Ying, Chai Wei-Ping
Acta Physica Sinica. 2011, 60 (2): 028105 doi: 10.7498/aps.60.028105
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N doped TiO2 films were deposited in direct current pulsed magnetron sputtering system at room temperature. We have studied the influence of O2 flow rate on the crystal structure of deposited films by using stylus profilometer, X-ray photoelectron spectroscope, X-ray diffractometer, and ultraviolet-visible spectrophotometer. The results indicate that the growth behavior and crystal structure of N doped TiO2 film is dominated by the O2 flow rate. It was found that the chemical stiochiometry is close to TiO1.68±0.06N0.11±0.01 for all film samples, in which the N mainly exists in substitutional doped state. When O2 flow rate is 2 sccm (1 sccm=1 mL/min), N doped TiO2 film has amorphous structure with high growth rate, which contains both anatase phase and rutile phase crystal nucleuses. In this case, the film displays the mix-phase of anatase and rutile and the band gap is 2.86eV after annealing treatment. The film growth rate decreases with increasing O2 flow rate. After annealing treatment, the band gap of N doped TiO2 films decreases with increasing O2 flow rate. While N doped TiO2 film is anatase phase when O2 flow rate is 12sccm. In this case, the band gap is 3.2eV after annealing treatment. It should be noticed that no TiN phase appears for all samples before and after annealing treatment.

Influence of the high-repetition-pulsed laser beam size on the damage characteristics of absorbing glass

Han Jing-Hua, Feng Guo-Ying, Yang Li-Ming, Zhang Qiu-Hui, Fu Yu-Qing, Niu Rui-Hua, Zhu Qi-Hua, Xie Xu-Dong, Zhou Shou-Huan
Acta Physica Sinica. 2011, 60 (2): 028106 doi: 10.7498/aps.60.028106
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The influence of the beam size of pulsed laser on damage morphology of absorbing glass, as well as the mechanism of the damage produced by high-repetition-pulsed laser (kHz magnitude), is investigated. We show that the damage morphology changes greatly with the decrease of the beam size under the condition that the energy of each individual pulse,the number of the pulses incident on the glass and the repetition frequency are kept invariant. The damage is induced by melting of the glass material due to dispersed energy of the incident laser with large beam size. With decreased beam size of laser, the material will break resulting from the melting and evaporating of glass induced by the densing and increasingly deposited laser energy in glass material. When the beam size is further reduced, too intensive laser will penetrate the dielectric material on the surface of glass. As a result, the laser induced plasma shock wave occurs. In addition, the super-heated liquid at the center where the laser beam interacts with glass will be produced as a consequence of the tremendous deposited laser energy. When the threshold of phase explosion is reached, the mixture of the evaporated, melted and original solid materials will blast outwards. Consequently, characteristic morphology made up of three regions covered with solid granules of original glass material and the re-crystallized material of the evaporated and melted glass will form around the damage crater.

A first principles study of the lattice dynamics property of LiFePO4

Xin Xiao-Gui, Chen Xiang, Zhou Jing-Jing, Shi Si-Qi
Acta Physica Sinica. 2011, 60 (2): 028201 doi: 10.7498/aps.60.028201
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Lattice dynamical properties of LiFePO4 were studied using first principles density functional theory taking into account the on-site Coulomb interaction within the GGA+U scheme. The Born effective charge tensors, phonon frequencies at the Brillouin zone center and phonon dispersion curves were calculated and analyzed. The Born effective charge tensors exhibit anisotropy, which gives an indirect evidence for the one-dimensional Li migration tunnel along the [010]direction in LiFePO4, which has been proposed by other theoretical calculations and experimental observations. The calculated phonon frequencies at the Г point of the Brillouin zone agree well with the available experimental results.

Base resistance in Si unijunction transistor irradiated by 60Co γ-radiation

Zhao Hong-Fei, Du Lei, He Liang, Bao Jun-Lin
Acta Physica Sinica. 2011, 60 (2): 028501 doi: 10.7498/aps.60.028501
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The change of base resistance in Si-UJT under irradiation of 60Co γ-ray is provided. Through multipoint measurement and real-time monitoring, it was shown that the base resistance decreased immediately and then increased slowly. Compared with domestic and foreign related research results, this proves that the displacement effect is the main effect of base resistance in Si-UJT irradiated by 60Co γ-ray, but it lags behind the ionization effect from microanalysis of the interaction between γ-ray and Si material. This is very important for the radiation hardened research.

Total dose characteristics of single poly EEPROM and SONOS EEPROM on SOI

Xiao Zhi-Qiang, Li Lei-Lei, Zhang Bo, Xu Jing, Chen Zheng-Cai
Acta Physica Sinica. 2011, 60 (2): 028502 doi: 10.7498/aps.60.028502
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Devices of single poly electrically ersable programmable read only memory (EEPROM) and silicon-oxide-nitride-oxide-silicon (SONOS) EEPROM on silicon on insulator (SOI) are fabricated on self-built 0.8 μm SOI process. And through a set of experiments on EEPROMs of these configurations and comparisons, SOI SONOS EEPROM is successfully developed with good and stable total dose radiation hardened characteristics. These provide stronger proofs to choose EEPROM in radiation hardened circuits.

Effect of spectrum-control in dual-wavelength light-emitting diode by doped GaN interval layer

Zhang Yun-Yan, Fan Guang-Han, Zhang Yong, Zheng Shu-Wen
Acta Physica Sinica. 2011, 60 (2): 028503 doi: 10.7498/aps.60.028503
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A two-dimensional simulation of electrical and optical characteristics of dual-wavelength LED (light-emitting diode) with doped GaN interval layer is conducted with software.It shows that by the use of doped GaN interval layer, we can solve the luminescence intensity disparity of the two kinds of quantum wells in dual-wavelength LED. And through control of the thickness of the interval layer, we can adjust the relative luminescence intensity of the two kinds of quantum wells. Therefore, the effect of spectrum-control in dual-wavelength LED is due to the blocking effect of holes or electrons by doped GaN interval layer.

Digital simulation for coherent X-ray diffractive imaging

Zhou Guang-Zhao, Tong Ya-Jun, Chen Can, Ren Yu-Qi, Wang Yu-Dan, Xiao Ti-Qiao
Acta Physica Sinica. 2011, 60 (2): 028701 doi: 10.7498/aps.60.028701
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Phase retrieval is one of the most important steps for coherent X-ray diffractive imaging (CXDI), Which uses the oversampled far-field diffraction pattern for phase retrieval iterative algorithm in order to achieve the lost phase information. Here we used a small nonperiodic 2D digital image as the object for studying the effect of the oversampling ratio and obtained the optimum oversampling ratio of 3—7 when the iteration times was 1000. We also added random noise to the diffraction pattern to examine the applicability of this approach to real data. We found the reconstruction failed when the signal to noise ratio is less than 10. As the reconstruction process may fail when the twin image or stochastic shift appears in the reconstructed image simultaneously, we explained why these phenomena come into being, and found methods to overcome the difficulty effectively.

Theoretical study on the rotation of particles driven by Gaussian beam

Du Yun-Gang, Han Yi-Ping, Han Guo-Xia, Li Ji-Jun
Acta Physica Sinica. 2011, 60 (2): 028702 doi: 10.7498/aps.60.028702
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Based on the fact that the polarized beam is composed of L-photon and D-photon, the expressions of the radiation trapping forces and torques of spherical particle exerted by polarized Gaussian beam are obtained in the framework of the generalized Lorenz-Mie theory. The reasons of the two different rotations of particles driven by circularly polarized Gaussian beam are analyzed and explained in combination with the quantum properties of photon. Then numerical simulations are performed for the two kinds of torques acted on the particles by polarized Gaussian beam, and the effects on the torques and optically driven rotations of the radius, relative refractive index, absorbing coefficient of the particle and waist radius of the beam are discussed.

Field emission of carbon nanotube under atmospheric pressure

Qian Li, Wang Yu-Quan, Liu Liang, Fan Shou-Shan
Acta Physica Sinica. 2011, 60 (2): 028801 doi: 10.7498/aps.60.028801
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Field emission of carbon nanotube in different gases (for example, Air, He, Ne) under atmospheric pressure has been studied. The distance between anode and cathode was 100—200 nm. Detailed comparison has been made to characterize the field emission currents and fluctuations in various gases with different anode-cathode distances.

In situ growth and characterization of Cu2ZnSnS4 thin films by reactive magnetron co-sputtering for solar cells

Zhang Kun, Liu Fang-Yang, Lai Yan-Qing, Li Yi, Yan Chang, Zhang Zhi-An, Li Jie, Liu Ye-Xiang
Acta Physica Sinica. 2011, 60 (2): 028802 doi: 10.7498/aps.60.028802
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Cu2ZnSnS4 (CZTS) thin films have been first in situ grown by reactive magnetron co-sputtering and its characterizations has been carried out by energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), scan electron microscope(SEM), optical transmittance and electronic measurement. It was observed that the grown film shows homogeneous, compact surface morphology, and consists of large columnar grains throughout the thickness. The atom ratio Cu/(Zn+Sn) is about 1, while Zn/Sn is larger than 1 and decreases with the increase of substrate temperature. XRD analysis indicates that the grown film exhibits strong preferential orientation along (112) plane and the structural properties depend on growth temperature and Cu/(Zn+Sn) ratio. The in situ grown CZTS film has an optical absorption coefficient higher than 104 cm-1, and the optical band gap becomes narrow with the increase of substrate temperature and achieves (1.51±0.01)eV at 500℃. The conduction type of the CZTS films is p-type and the value of carrier concentration is comparable with values of device quality CIGS.

Effect of distribution of weight on the efficiency of weighted networks

Tian Liu, Di Zeng-Ru, Yao Hong
Acta Physica Sinica. 2011, 60 (2): 028901 doi: 10.7498/aps.60.028901
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Weighted networks can give more detailed description of interaction between agents of corresponding systems. Link weight also provides another way to improve the properties and functions of networks. Based on the concept of network efficiency in binary networks, in this paper, the efficiency of weighted networks with similarity or dissimilarity weight is defined. The effect of weight distribution on the network efficiency are investigated. From the initial regular network with homogeneous link weights, a method is introduced to randomize the weight distribution over the links. The results demonstrate that the random redistribution of link weight can improve the network efficiency. Moreover, exponential distribution of link weight shows more significant improvement compared with the other common distributions, such as uniform, Poisson, Gauss, and power law distributions. Meanwhile, it is also found that the total weight of the corresponding minimum spanning tree is reduced with the randomization of link weight. That means the cost of transportation is decreased with the increase of link weight heterogeneity. All these results can help us get deeper understanding about the effect of link weight on the property and function of networks.

GENERAL

Causal algebra and its applications to physics

Huang Yong-Chang, He Bin, Huang Chang-Yu, Yang Shi-Lin, Song Jia-Min
Acta Physica Sinica. 2011, 60 (2): 020201 doi: 10.7498/aps.60.020201
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A causal algebra and its application to high energy physics is proposed. Firstly on the basis of quantitative causal principle, we propose both a causal algebra and a causal decomposition algebra. Using the causal decomposition algebra, the associative law and the identity are deduced, and it is inferred that the causal decomposition algebra naturally contains the structures of group. Furthermore, the applications of the new algebraic systems are given in high energy physics. We find that the reactions of particles of high energy belonging neither to the group nor to the ring, and the causal algebra and the causal decomposition algebra are rigorous tools exactly describing real reactions of particle physics. A general unified expression (with multiplicative or additive property) of different quantities of interactions between different particles is obtained. Using the representation of the causal algebra and supersymmetric R number, the supersymmetric PR=(-1 )R invariance of multiplying property in the reactions of containing supersymmetric particles is obtained. Furthermore, a symmetric relation between any components of electronic spin is obtained, with the help of which one can simplify the calculation of interactions of many electrons. The reciprocal eliminable condition to define general inverse elements is used, which may renew the definition of the group and make the number of axioms of group reduced to three by eliminating a superabundant definition.

The variational iteration solution method for a classof nonlinear disturbed evolution equations

Mo Jia-Qi
Acta Physica Sinica. 2011, 60 (2): 020202 doi: 10.7498/aps.60.020202
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Using the generalized variational iteration method, a class of nonlinear disturbed evolution equations are studied. Firstly, a functional is introduced, then its variational is computed, and the iteration expansion is finally constructed. The approximate and exact analytic solutions to the problem are obtained.

Quantum turbo product codes

Xiao Hai-Lin, Ouyang Shan, Xie Wu
Acta Physica Sinica. 2011, 60 (2): 020301 doi: 10.7498/aps.60.020301
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Quantum communication is a growing interdisciplinary field which combines classical communications and quantum mechanics. Quantum error correction coding is one of the key techniques in quantum communication. Nearly all of the classical error correction coding schemes have been transplanted to the domain of quantum communication, and the quantum counterparts of classical error correction coding techniques have been found. Based on the classical turbo product codes (TPCs) which is one of the most outstanding schemes in classical coding region, a new structure of the CSS-type quantum convolutional codes (QCC) as stabilizer sub-code of the quantum turbo product codes (QTPC) is presented. Firstly, CSS-type QCC stabilizer generator is constructed with the help of group theory and the basic principle of stabilizer coders, and the corresponding networks are described. Secondly, the interleaved coded matrix of the QTPC is obtained by quantum permutation SWAP gate definition. Finally, the corresponding relation between the quantum trace distance of QTPC decoding and the distance of classical TPCs decoding is obtained, and the scheme of QTPCs coding and decoding is completed. The coding and decoding of QTPCs have a highly regular structure and a simple design idea, and the networks are easy to realize.

Relations of classical-quantum correspondencein Dicke model

Song Li-Jun, Yan Dong, Gai Yong-Jie, Wang Yu-Bo
Acta Physica Sinica. 2011, 60 (2): 020302 doi: 10.7498/aps.60.020302
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Dicke model displays quantum chaotic dynamic properties in the non-rotating wave approximation. On the basis of properties of the classical phase space of Dicke model, we employ the one-to-many notion, namely, evolution from one point on the classical phase space to two initial coherent states. Then we obtain a good quantum phase space, which corresponds to the classical one, by using the method of averaging the statistical entangled values of two initial states in the evolution. The numerical computation shows that classical chaos can promote the origination of bipartite entanglement, and simultaneously, the average entanglement can be regarded as the signature of quantum chaos. A good classica-quantum correspondence can be obtained by using the average entanglement.

Adiabatic tunneling of Bose-Einstein condensatein double-well potential

Huang Fang, Li Hai-Bin
Acta Physica Sinica. 2011, 60 (2): 020303 doi: 10.7498/aps.60.020303
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We studied the adiabatic tunneling of Bose-Einstein condensates (BEC) in double-well potential with circle adiabatic variation of energy level spacing. We found that the adiabatic theorem is violated during the evolution of BEC, when the initial state is chosen such that all condensate atoms are in the shallow well and the interaction between atoms is strong enough. Furthermore, we found that the condensates can return to the initial state or not, depending on the evolution periods. In addition, we also found the evolution is dependent on the choice of initial state, which indicates an asymmetric character. With the help of the graph of energy levels and the phase diagram, we explained the results obtained.

Influence of isotope substitution of sodium molecule on the integral cross sections of rotational excitation in low-temperature collisions of He-Na2

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Acta Physica Sinica. 2011, 60 (2): 020304 doi: 10.7498/aps.60.020304
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Multiple ellipsoid model is applied to the 4He,10He-18Na2,23Na2, and 37Na2collision systems, and integral cross-sections for rotational excitation and the total collision cross-sections at the incident energy of 50,100 and 200 meV are calculated. By analyzing the differences of these integral cross-sections, the change rules of the integral cross sections with the increase of rotational angular quantum number of Na2 molecule, as well as with the change of the reduced mass of symmetric isotopic substituted system are obtained. Based on the calculation, influence on the cross-sections exerted by the variations in the reduced mass of systems and in the relative incoming energy of incident atom is discussed. Moreover, at the relative incident energy of 100 meV, the contributions of different regions of the potential to integral cross-sections of rotational excitation for10He-18Na2,23Na2 and 37Na2 collision systems are investigated.

The conversion between subluminal and superluminal lightpropagation phenomena in an inverted Y-typefour-level quantum system

Meng Dong-Dong, Liu Xiao-Dong, Zhang Sen-Lin
Acta Physica Sinica. 2011, 60 (2): 020305 doi: 10.7498/aps.60.020305
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We have studied the light propagation properties in an inverted Y-type four-level quantum system coupled with probe, couple and driving fields. Using the numerical simulation method, we investigate the absorption properties of the probe light field when the Rabi frequency and detuning of the driving field are changed. From the three-dimensional graphics, we find the variations of the probe group velocity at the electromagnetically induced transparency windows. Farthermore, we theoretically obtain the conversion among subluminal, vacuum and superluminal light propagation by adjusting the Rabi frequency and detuning of the external driving field properly.

The single solitary wave with double peaks of the coupled KdV equation and its stability

Shi Yu-Ren, Zhang Juan, Yang Hong-Juan, Duan Wen-Shan
Acta Physica Sinica. 2011, 60 (2): 020401 doi: 10.7498/aps.60.020401
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We obtained six classes of exact solutions for the coupled KdV equation by the extended hyperbola function expansion Method.One of the solutions is a solitary wave solution, which has two peaks.This solution is reduced to the kink or bell-like soliton solution of the coupled KdV equation under different limitations. We also investigated the stability of the single solitary wave solution with double peaks numerically.The results indicate that the solution is stable when the amplitude of the disturbance, which has long wave length, and is very small.

The single solitary wave with double kinks of the combined KdV equation and its stability

Shi Yu-Ren, Zhang Juan, Yang Hong-Juan, Duan Wen-Shan
Acta Physica Sinica. 2011, 60 (2): 020402 doi: 10.7498/aps.60.020402
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Based on the ideas of the hyperbola function expansion method, we obtained some analytical solutions of the combined KdV-mKdV (cKdV) equations by introducing new expansion functions.One of the single soliton solutions has the kink-antikink structure, and this solution reduces to the kink-like solution and the bell-like solution under different limitations. Theoretical analysis shows that the cKdV equation has both propagated-type and non-propagated-type solitary wave solutions. We also investigated the stability of the single solitary wave solution with double kinks numerically. The results indicate that the solution may be stable or unstable, depending on different sets of parameters.

Interaction of force and coupled system and stochastic energetic resonance

Lin Min, Zhang Mei-Li
Acta Physica Sinica. 2011, 60 (2): 020501 doi: 10.7498/aps.60.020501
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The process of work done on the system by the external force is equivalent to the process of change in system state. The thermodynamic relations of coupled bistable system based on single stochastic trajectories are established by using microcosmic dynamics and macroscopic thermodynamic methods, according to the stochastic dynamics described by Langevin equation. The transmission and conversion relations of energy are quantitatively characterized via interaction of force and work of coupled system, which reveals the coupled system exhibiting stochastic energetic resonance phenomenon. Through analyzing relationship between work done and energy, the physical nature of produced stochastic resonance is further revealed.

Circuit design of tabu learning neuron models and their dynamic behavior

Chen Jun, Li Chun-Guang
Acta Physica Sinica. 2011, 60 (2): 020502 doi: 10.7498/aps.60.020502
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The circuit design and implementation of neuron models have attracted much attention in recent years due to its importance in both theoretical studies and applications. In this paper, we designed electronic circuits for the recently proposed tabu learning chaotic neuron model, including the circuit design of single tabu learning neuron, a two-neuron system with linear proximity function, as well as a two-neuron system with quadratic proximity function. We used the electronic workbench (EWB) software to perform simulations of the designed circuits. We also studied the nonlinear behavior, especially the Hopf bifurcation and chaos, of the designed circuits. The consistency between the nonlinear behavior in the designed circuits and that in the numerical simulations demonstrates the correctness of the circuits design.

Mechanism of high frequency resonance of parameter-adjusted bistable system

Leng Yong-Gang
Acta Physica Sinica. 2011, 60 (2): 020503 doi: 10.7498/aps.60.020503
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For clarifying the response of a bistable system to a high-frequency signal, the mechanism of high-frequency resonance with parameter-adjusted bistable system is investigated. It was shown that the method of twice sampling frequency transformation does not change the bistable system structure to realize resonance at the low frequency corresponding to the high frequency, and that the method of tuning bistable system parameters can directly realize resonance at the high frequency through adjusting the system parameters to change the system structure. The reason for the realization of high-frequency stochastic resonance of tuning system parameters is that adjusting the two parameters of the bistable system simultaneously leads to no limiting value for Kramers rate, and hence the limitation of stochastic resonance frequency within small frequency range is broken through.

Chaos for a class of complex epidemiological models

Di Gen-Hu, Xu Yong, Xu Wei, Gu Ren-Cai
Acta Physica Sinica. 2011, 60 (2): 020504 doi: 10.7498/aps.60.020504
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We study the well-known SIR (susceptible, infected, recoverd) model with nonlinear complex incidence rates. Firstly,a series of coordinate transformations are carried out to change the equations as the amenable Hamiltonian systems. Secondly the Melnikov's method is used to establish the conditions of existence of chaotic motion and find the analytically critical values of homoclinic bifurcation. Good agreement can be found between numerical results and analytical results.

Complexity analysis of chaotic sequence based on the intensive statistical complexity algorithm

Sun Ke-Hui, He Shao-Bo, Sheng Li-Yuan
Acta Physica Sinica. 2011, 60 (2): 020505 doi: 10.7498/aps.60.020505
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To analyze the complexity of the chaotic sequences, based on the intensive statistical complexity algorithm, the complexities of the discrete TD-ERCS and continuous simplified Lorenz chaotic systems were investigated respectively, and the complexities of the chaotic sequences with different system parameters were calculated. The complexities of pseudo-random sequences of the continuous chaotic systems disordered by m-series and chaotic pseudo-random sequences were analyzed. The results indicate that the intensive statistical complexity algorithm is an effective method for analyzing the complexity of the chaotic sequences, and the complexity of the discrete chaotic systems is larger than that of the continuous ones. However, after disordering by m-series or chaotic pseudo-random sequences, the complexities of the pseudo-random sequences can be increased significantly. This study provides a theoretical basis for the applications of chaotic sequences in the field of secure communication and information encryption.

Fast-scale instability and dynamic parameter resonance of power factor correction Boost converter

Cheng Wei-Bin, Kang Si-Min, Wang Yue-Long, Tang Nan, Guo Ying-Na, Huo Ai-Qing
Acta Physica Sinica. 2011, 60 (2): 020506 doi: 10.7498/aps.60.020506
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Based on the multiplication of dynamic eigenvalue coefficient and its dynamic stabilizing capability, fast-scale instability and its asymmetry in power factor correction (PFC) Boost converter with continuous peak current control mode are investigated. To realize higher power factor and less harmonic distortion, a kind of compensation strategy is proposed to make the input current a sinusoidal wave, and it is optimized with parameter resonance. The formulas are deduced,and the overall optimization is carried out. The results of digital simulation shows that the overall compensating strategy has the most powerful dynamic ability to ensure the quick stabilization during every stroboscopic period, and the fast-scale instability is controlled, and the approximate unit power factor and the best compensating effects are obtained finally, resulting in the increase of the conversion efficiency of PFC Boost converter.

Construction of grid multi-scroll chaotic attractors and its circuit implementation with polynomial and step function

Chen Shi-Bi, Zeng Yi-Cheng, Xu Mao-Lin, Chen Jia-Sheng
Acta Physica Sinica. 2011, 60 (2): 020507 doi: 10.7498/aps.60.020507
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A constructing approach to generating N×M-scroll attractors with polynomial and step function is reported. In Chuas circuit, only two or three scrolls can be generated by traditional polynomial function. On this basis, the multi-scroll of x direction in phase space is obtained by polynomial shift. And then the saddle-focus equilibrium points with index-2 in phase space are extended by combining both polynomial and step function, which makes it possible to extend the multi-scroll in y direction. Then the grid multi-scroll chaotic attractors are generated. The main feature of this constructing approach is generating grid multi-scroll chaotic attractors by combining both smooth curves and non-smooth curves for the first time. And the arbitrary planar grid multi-scroll chaotic attractors array can be generated by adjusting the values of natural numbers N and M. The effectiveness of this method has been verified by theoretical analysis, numerical simulation and circuit simulation.

Multivariate chaotic time series phase space reconstruction based on extending dimension by conditional entropy

Zhang Chun-Tao, Ma Qian-Li, Peng Hong, Jiang You-Yi
Acta Physica Sinica. 2011, 60 (2): 020508 doi: 10.7498/aps.60.020508
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For multivariate chaotic time series, a method of conditional entropy extending dimension(CEED) in the reconstructed phase space is proposed. First, the delay time of any variable time series is selected by mutual information method, and then the embedding dimension of phase space is extended by the conditional entropy. This method can ensure the independence of reconstructed coordinates from low space to high space and eliminate the redundancy of phase space, because the largest condition entropy is choosen. The effective input vector for the prediction of multivariate time series is given. Simulations of the Lorenz system and Henon system show that the neural network predictions of multivariate time series are much better than the prediction of univariate and existing multivariate. Therefore, CEED is effective for multivariate chaotic systems.

Optimum parameters setting in symbolic dynamics of heart rate variability analysis

Song Ai-Ling, Huang Xiao-Lin, Si Jun-Feng, Ning Xin-Bao
Acta Physica Sinica. 2011, 60 (2): 020509 doi: 10.7498/aps.60.020509
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The Shannon entropy Hk in symbolic dynamics analysis of time series has less data demand and can be complemented easily, and therefore is applied to heart rate variability (HRV) analysis. However, the criterion has not been established as to the parameter α, which is used during the transformation into symbols. Like all other physiological signals, great differences between individuals as well as nonstationarity are usual in HRV. Therefore, to achieve a robust and consistent analysis, the parameter α should be considered together with the mean and standard error of the series. In this paper, the integrative effects on Hk of the three parameters were studied firstly in simulation time series, and it was suggested that under certain conditions, the clusters of Hk approach a convergent upper boundary named Hk-up, which reflects the intrinsic dynamics of the time series. Then, in the heart beat interval series analysis of 15 subjects, the abilities of Hk-up to alleviate the impacts brought by both difference between individuals and nonstationarity were testified.

A novel unified equalization and demodulation of chaoticdirect sequence spread spectrum signal based on state estimation

Xu Xin-Zhi, Guo Jing-Bo
Acta Physica Sinica. 2011, 60 (2): 020510 doi: 10.7498/aps.60.020510
Full Text: [PDF 968 KB] Download:(950)
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A novel unified algorithm based on state estimation was proposed for equalization and demodulation of chaotic direct sequence spread spectrum (CD3S) signal through a non-ideal channel. The algorithm uses the state equations of the channel and the CD3S signal, as well as the reciprocal relationship between equalization and demodulation. Multiple extended kalman filters (EKF) were used for equalizing the channel while demodulating the binary message simultaneously by implementing them in reciprocal interaction. This algorithm could not only overcome the impact brought about by non-ideal channel, such as multipath interference and channel noise, but also demodulate the binary message from CD3S signal. This unified approach utilizes the information more adequately and has better real-time performance than independent approaches. Simulation results demonstrated that the proposed algorithm has a fast convergence rate, and is resistant to the multipath effect without knowledge of channel characteristic and the noise, so the efficient and reliable transmission of the CD3S signal through the non-idea channel is realized.

Abrupt change of synchronization of ring coupled Duffing oscillator

Wu Yong-Feng, Zhang Shi-Ping, Sun Jin-Wei, Peter Rolfe
Acta Physica Sinica. 2011, 60 (2): 020511 doi: 10.7498/aps.60.020511
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The ring coupled Duffing oscillator was investigated, a phenomenon was observed when analyzing the synchronization evolution between coupled oscillators, which shows that if all oscillators are driven by the same periodic driving force,the motion trajectory between weakly coupled oscillators will generate two abrupt changes from synchronization to non-synchronization and then to synchronization in the phase transition of period-doubling bifurcation, chaotic state and large-scale periodic state. Any synchronous abrupt change can be used to rapidly identify system phase transition, and thus a weak periodic signal detection method was proposed based on the phase transition of period-doubling bifurcation and chaotic state.

Synchronization of uncertain chaotic systems based on neural network and sliding mode control

Li Hua-Qing, Liao Xiao-Feng, Huang Hong-Yu
Acta Physica Sinica. 2011, 60 (2): 020512 doi: 10.7498/aps.60.020512
Full Text: [PDF 626 KB] Download:(1134)
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The synchronization between two unknown chaotic systems is achieved by designing a controller based on the sliding mode control technique and radial basis function neural network. The controller design method is independent of the system mathematical model, but only depends on the output of the system state. Moreover, it is robust to parameter uncertainties and the outside interference. Finally, synchronization between unknown Lorenz systems and between unknown Lorenz system and Chen system are achieved using the proposed method. The response time is very short and the synchronization performance is good.

Approximate entropy based meso-spray transfer analysis of Al-alloy pulsed metal inert-gas welding under self-adapting control

Zhang Wei-Chao, Yang Li-Jun, Lü Xiao-Qing
Acta Physica Sinica. 2011, 60 (2): 020601 doi: 10.7498/aps.60.020601
Full Text: [PDF 1053 KB] Download:(998)
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The meso-spray transfer of Al-alloys metal inert-gas (MIG) welding has the advantages of well-adjusting of the length of arc and beautiful appearance of weld due to the characters of droplet transfer. In this study, the self-adapting control which is brought to meet the arc of meso-spray transfer is accessed by analyzing the approximate entropy (ApEn) of the arc voltage on the aspect of non-linear dynamics. Under self-adapting control, the change of ApEn value with the varing metal transfer mode is discussed, which is due to the change of the parameter of process. Under spray transfer, two kinds of ApEn values of the self-adapting control and common pulsed control are compared, and we find that the self-adapting control is fit for meso-spray transfer. The results show that the smaller the value of approximate entropy is, the better the effect of the self-adapting control is.

A nuclear micro-battery based on silicon PIN diode

Qiao Da-Yong, Chen Xue-Jiao, Ren Yong, Zang Bo, Yuan Wei-Zheng
Acta Physica Sinica. 2011, 60 (2): 020701 doi: 10.7498/aps.60.020701
Full Text: [PDF 1222 KB] Download:(1034)
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Due to the use of heavily doped N type silicon substrate, the nuclear micro-battery based on silicon PN diode suffers from the small minority carrier life-time and small depletion region width, and can not achieve high energy transfer efficiency. A nuclear micro-battery utilizing silicon PIN diode as the energy transfer structure was demonstrated with achieves higher electrical power output. Theoretical model was built to predict the power output performance of this kind of micro-nuclear battery and structure optimization was performed in terms of the stopping range of beta particles, the depletion region width, the minority carrier life-time and the body resistance. Prototypes of PIN energy transfer structure were fabricated and were illuminated by using beta radioisotopes 63Ni,147Pm and alpha radioisotope 241Am as the radiation sources, and proved to be effective to improve the energy transfer performance.

Effect of asymmetrical micro electrode surface topography on alternating current electroosmosis flow rate

Jiang Hong-Yuan, Li Shan-Shan, Hou Zhen-Xiu, Ren Yu-Kun, Sun Yong-Jun
Acta Physica Sinica. 2011, 60 (2): 020702 doi: 10.7498/aps.60.020702
Full Text: [PDF 1013 KB] Download:(871)
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AC Electroosmosis(ACEO) induced by electric field is the basic approach for non-mechanical microfluid pumping. Traditional ACEO theory is based on electric double layer (EDL) theory, and gives electric-flow field coupling equations for ACEO flo w rate. But there is a big deviation between the calculation data and experimental velocities. In this paper, electrode surface topography is included to solve ACEO flow rate. Withelectrode surfaceroughness as the characteristic parameter, equivalent EDL model is set up to modify the classical EDL model. The relationship between flow rate and electrode surface roughness is studied. Experiment results agree with the simulation very well, proving the feasibility ofequivalent EDL model.

Preparation and photoluminescence study of patterned substrate quantum wires

Wang Xiu-Ping, Yang Xiao-Hong, Han Qin, Ju Yan-Ling, Du Yun, Zhu Bin, Wang Jie, Ni Hai-Qiao, He Ji-Fang, Wang Guo-Wei, Niu Zhi-Chuan
Acta Physica Sinica. 2011, 60 (2): 020703 doi: 10.7498/aps.60.020703
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GaAs/AlGaAs quantum wires grown by molecular beam epitaxy on a V-groove patterned substrate was described. The cross section of scan electron microscopy (SEM) image shows that crescent-type quantum wire were formed at the V groove bottom, which is a triangle of about 60nm in width and 14nm in height. Two peaks at 793.7nm and 799.5nm of photoluminescence spectrum at 87K verified the existence of quantum wires. Theoretical calculation gives 8meV blue shift, which is proved to be casued by lateral confinement compared with quantum well of the same width.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Renormalization of two neutral mixing-loop chain propagators in standard model and its e+e-→μ+μ- cross section

Chen Xue-Wen, Fang Zhen-Yun, Zhang Jia-Wei, Zhong Tao, Tu Wei-Xing
Acta Physica Sinica. 2011, 60 (2): 021101 doi: 10.7498/aps.60.021101
Full Text: [PDF 1074 KB] Download:(838)
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Adopting the electroweak standard model, We analyzd the framework forms of photon γ and neutral gauge boson Z0 mixing-loop chain propagators and the relevant renormalization. Based on this, We obtained the analytic results of renormalized γ and Z0 mixing-loop chain propagators composed of different physical loops that participate in electroweak interactions. In addition, We applied our result to an important type of lepton interaction in high energy physics: e+e-→μ+μ-, then obtained the analytic result of cross section via renormalized γ and Z0 mixing-loop chain propagators. Furthermore, we compared the result with a series of experimental results, and found that the result of this paper is in good agreement with the experimental results. This study would offer certain academic reference to the theoretical study and application of common complex propagators.

Composite electromagnetic scattering from two adjacent finite length cylinders

Wang Yun-Hua, Zhang Yan-Min, Guo Li-Xin
Acta Physica Sinica. 2011, 60 (2): 021102 doi: 10.7498/aps.60.021102
Full Text: [PDF 862 KB] Download:(804)
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Based on the equivalence principle and the reciprocity theorem, the composite electromagnetic scattering from two adjacent finite length cylinders is considered and a solution that accounts for multiple scattering up to second-order is deduced. Numerical results obtained by our formulas are compared with the results obtained by the method of moments. Meanwhile, the dependence of the composite scattered field on the parameters, such as the distance between the cylinders, the length of the cylinders, polarization state and so on, is discussed.

Reliability of multi-state and multi-subsystem below stress-strength interference

Zhang Yong-Jin, Song Wei-Cai
Acta Physica Sinica. 2011, 60 (2): 021201 doi: 10.7498/aps.60.021201
Full Text: [PDF 675 KB] Download:(875)
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Based on multivariate random analysis and statistical physics, the reliability model of a system with stress-strength interference and initial failure is developed, the system has multi-state and dependent multi-subsystem. According to the definition of conditionally ordered order statistics, the probability density function of random strength vector is studied. Considering the coherence of subsystem items, the system reliability evaluation for different structures is given, and the reliability of any coherent structure is represented as a linear combination of the reliabilities of (ni+1)-out-of-n system(1≤in). Finally, an example is given to demonstrate the effectiveness of the model, where the stress-strength variable has a bivariate Pareto distribution.
NUCLEAR PHYSICS

Adaptive source biasing sampling for time-dependent radiation transport problems

Li Gang, Deng Li, Li Shu, Mo Ze-Yao
Acta Physica Sinica. 2011, 60 (2): 022401 doi: 10.7498/aps.60.022401
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Monte Carlo method is used to simulate the radiation transport problems which have characteristics of high temperature, high pressure, multi-media and large deformation of the grid. Due to the nonuniform particle distribution and great difference in the sizes of the grid, it makes the statistical errors of the grid fluxes fluctuate wildly. The error accumulation after many time steps may even influence the truth of the calculated results. So the global source biasing technique is developed. The importance function used here for source biasing sampling is based on the grid fluxes and errors of the previous time step. This is much faster than the traditional methods for solving the adjoint equation. The numerical tests showed that the neutron flux errors in the important grids are obviously reduced by using global source biasing which adaptively assigns the number of particles in each grid.

ATOMIC AND MOLECULAR PHYSICS

Electronic structure and optical properties of Al-doped SnO2

Yu Feng, Wang Pei-Ji, Zhang Chang-Wen
Acta Physica Sinica. 2011, 60 (2): 023101 doi: 10.7498/aps.60.023101
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Based on the full-potential linearized augmented plane-wave method (FP-LAPW), we investigated the electronic structures and the optical properties, including dielectric function, absorption spectra, refraction and extinction of Sn1-xAlxO2 (x=0, 0.0625, 0.125, 0.1875, 0.25) via substituting for Sn with Al in SnO2 supercell. Calculated results show that the introduced Al could induce the band gap widening, and this can be attributed to the increased folded states, which lead to the contraction of the valence band and less Sn 5s states at the bottom of the conduction band. With the increasing of Al concentration, the band gap becomes wider, and the intensity of the first main peaks decreases. All of the optical spectra contain the imaginary part of dielectric function, the absorption spectrum, the refraction, and the extinction show blue shift corresponding to the increasing of the band gaps. Finally, it is expected that our results may inspire the future experimental research.

First principles study on the interaction of Aun(n=2, 3, 4) clusters with ethanol molecules

Yu Yong-Jiang, Yang Chuan-Lu, An Yi-Peng, Wang Hua-Yang
Acta Physica Sinica. 2011, 60 (2): 023102 doi: 10.7498/aps.60.023102
Full Text: [PDF 731 KB] Download:(871)
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The mechanism of the adsorption between Au n (n=2,3,4) clusters and ethanol molecules is investigated with the density functional theory. It is found that Au n (n=2,3,4) clusters can adsorb several ethanol molecules to form the Aun-(C2H6O)1-ncompounds. There are many adsorbing conformations when the ethanol molecules are adsorbed by the Au4 cluster. The adsorbing sequence and the corresponding stable configurations are confirmed through the analysis of the adsorption energies and the Mulliken electrical displacement. When the last ethanol molecule is adsorbed,the bonding style changes from the Au—O bond to the Au—H bond. The constructions of the Aun clusters and the ethanol molecule are less changed in the adsorbing process. And the interaction between Aun clusters and ethanol molecules is weak interaction.

Full vibrational energy spectra and dissociation energies for some electronic states of diatomic alkali-metal molecules

Tian Yin, Feng Hao, Sun Wei-Guo
Acta Physica Sinica. 2011, 60 (2): 023301 doi: 10.7498/aps.60.023301
Full Text: [PDF 824 KB] Download:(881)
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It is difficult to obtain the accurate high-lying vibrational energies for most of the diatomic electronic states on modern experiments or theoretical computations based on quantum mechanics. Based on the new analytical formula for dissociation energy and algebraic method (AM) generated by Sun et al., the second order perturbation theory are used to study the full vibritional energies{EAMυ} and dissociation energies of the Li2-33Σ+g,Li2-13Δg,Li2-23Πg,Na2-B1Πu and K2-41Σ+g electronic states. The obtained results not only agree well with the experimental data for the low-lying vibrational energies, but also give all high-lying vibrational energies which are still difficult to obtain by experiment at present. These results supply necessary data for the studies which need high-lying vibrational energies and dissociation energies of diatomic alkali-metal molecule.

Momentum transfer cross sections of low-energy electron scattering from H2 molecule with the polarization potential using the distributed spherical Gaussian model

Wang Xiao-Lian, Feng Hao, Sun Wei-Guo, Fan Qun-Chao, Wang Bin, Zeng Yang-Yang
Acta Physica Sinica. 2011, 60 (2): 023401 doi: 10.7498/aps.60.023401
Full Text: [PDF 798 KB] Download:(853)
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Based on the distributed spherical Gaussian (DSG) polarization potential model, the momentum transfer cross sections (MTCSs) of low-energy electron scattering from H2 molecule are studied with the body frame vibrational close coupling (BFVCC) method and vibrational scattering potentials. The vibrational scattering potentials include the static, exchange, and correlation-polarization contributions calculated based on ab initio method. By including the contributions of 18 Morse vibrational wave functions, 5 partial waves, and 16 molecular symmetries, We obtained well converging MTCSs of ν=0→ν'=0, 1, 2, 3 transition excitations. The comparisons show that DSG polarization potential is a good approximation in the study of low energy electron scattering.

Probing the distorted wave effects in (e, 2e) reaction for the outer valence orbitals of ferrocene

Liu Kun, Ning Chuan-Gang, Shi Le-Lei, Miao Yu-Run, Deng Jing-Kang
Acta Physica Sinica. 2011, 60 (2): 023402 doi: 10.7498/aps.60.023402
Full Text: [PDF 734 KB] Download:(967)
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The binding energy spectrum and electron momentum spectra of outer valence orbitals of ferrocene have been obtained by using our high efficiency electron momentum spectrometer at two different impact energies of 600 eV and 1500 eV. The theoretical momentum profiles of outer valence orbitals of ferrocene for the eclipsed and staggered conformations have been calculated by non-relativistic and scalar relativistic density functional methods. It was found that the outer valence orbitals in the eclipsed conformation are in one-to-one correspondence with the ones in the staggered conformation, and there is little difference between theoretical momentum profiles of them. In addition, it was found that relativistic effects have little influence on the momentum distributions of outer valence orbital of ferrocene. Strong distorted wave effect in the low momentum region related to the outer valence orbitals were observed, Which is due to that those orbitals are mainly composed of Fe 3d atomic orbital.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Electrical properties and impedance analysis of Bi0.5Ba0.5FeO3 ceramic

Yuan Chang-Lai, Liu Xin-Yu, Huang Jing-Yue, Zhou Chang-Rong, Xu Ji-Wen
Acta Physica Sinica. 2011, 60 (2): 025201 doi: 10.7498/aps.60.025201
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Ba0.5Bi0.5FeO3 ceramic was fabricated by conventional solid-state reaction method. The microstructures and electrical properties were characterized by X-ray diffraction, scanning electron microscopy, direct current (DC) resistance-temperature measurement and alternative current (AC) impedance analysis. According to the analysis, Ba0.5Bi0.5FeO3 ceramic is a cubic perovskite-type compound, and its grain size is about 1.0 μm. In the measured temperature range of 16—280 ℃, Ba0.5Bi0.5FeO3 ceramic shows obvious negative temperature coefficient thermistor characteristic, and the thermistor constant and activation energy of the ceramic are 6490 K and 0.558 eV, respectively. The temperature dependence of dielectric constant reveals that below 280 ℃ no phase transition occurs. The AC impedance characteristic in the ceramic can appropriately be modeled in terms of an equivalent electrical circuit comprising of a series combination of three parallel RQ components in connection with the grain, grain shell and grain boundary effects. The fitting results are in good agreement with the experimental data. The components of grain, grain shell and grain boundary, showing NTC characteristic, have the order of resistive contribution of Rg>Rs>Rgb. In the temperature range 25—115 ℃, the significant mismatch between the peaks of parameters Z″(ω) (imaginary part of impedance) and M″(ω) (imaginary part of electric modulus) suggests a development of persistent localized conduction in Ba0.5Bi0.5FeO3 ceramic.

Direct measurement technique for shock wave velocity under super high pressure

Wang Feng, Peng Xiao-Shi, Liu Shen-Ye, Li Yong-Sheng, Jiang Xiao-Hua, Ding Yong-Kun
Acta Physica Sinica. 2011, 60 (2): 025202 doi: 10.7498/aps.60.025202
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With the ionization mechanism for the transparent material under the super high pressure, the basic measurement method of shock wave has been analyzed. With the Drude-free electron model, the change in reflectivity of shock wave front under different pressures has been analyzed. The reflectivity of shock wave front for different probe lasers has been compared in theory. And it was found that the reflectivity of shock wave front for 660 nm of probe laser is higher than that for 532 nm. The effect of the detector was found to be caused by the X-ray ionization of the transparent material after analyzing the reflectivity data in space-time scale. From the experiment data, it is found that the beginning of "blank" effect coincides with the start point of laser pulse. The shock wave is later than the "blank" effect under the square laser pulse. In the experiment, the reflectivity of shock wave front is about 40% when the shock velocity is 35 km/s. The theoretical decreasing curve of shock velocity in the sapphire window is confirmed by the experiment data. The formula to calculate the shock wave velocity in the transparent material was deduced and verified.

Optical emission spectra of Si plasma induced by femtosecond laser pulse

Gao Xun, Song Xiao-Wei, Guo Kai-Min, Tao Hai-Yan, Lin Jing-Quan
Acta Physica Sinica. 2011, 60 (2): 025203 doi: 10.7498/aps.60.025203
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The time- and space-resolved optical emission spectra (OES) of Si plasma produced by femtosecond laser pulse with center wavelength of 800 nm and pulse width of 100 fs in air were investigated. The results show that the OES mainly consist of continuous spectrum at the early stage of plasma expansion (within the first 50 ns), then the continuous spectrum weakens gradually while the line spectrum becomes dominating. The existence time of ion spectra is shorter than that of atomic spectra in the process of plume expansion. The wavelength red-shift, which has a second order exponential decay with delay time, has been found by the time-resolved emission spectroscopy. Finally, the spatiotemporal evolution of OES intensity are presented.

Effect of electron temperature anisotropy on BN dielectric wall sheath characteristics in Hall thrusters

Yu Da-Ren, Qing Shao-Wei, Wang Xiao-Gang, Ding Yong-Jie, Duan Ping
Acta Physica Sinica. 2011, 60 (2): 025204 doi: 10.7498/aps.60.025204
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The effect of electron temperature anisotropy on BN dielectric wall sheath characteristics in Hall thruster plasma is studied by using a one-dimensional fluid sheath model with the help of emitted electron velocity distribution and multi-species mixed ion effects. Analytic results show that, in comparison with that of a pure univalent xenon plasma, the sheath potential drop and the critical secondary electron emission coefficient are decreased in mixed valence xenon plasmas, while the primary electron flux at the wall is increased. The electron temperature anisotropy in Hall thrusters thus significantly enhances the electron energy emission coefficient, and further reduces the sheath potential drop while intensifies the electron-wall interaction. Numerical results also indicate that the electron temperature anisotropy influences the potential distribution of space charge saturated sheath remarkably.

Numerical simulation of microwave power absorption of large-scale surface-wave plasma source

Lan Chao-Hui, Hu Xi-Wei, Liu Ming-Hai
Acta Physica Sinica. 2011, 60 (2): 025205 doi: 10.7498/aps.60.025205
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A full-size three-dimensional model of large-scale rectangular surface-wave plasma (SWP) source was built, the power deposition problems of SWP source based on collision mechanism were investigated through numerical simulations. The microwave reflectivity curves varying with plasma parameters were obtained, and the influence of different antenna arrays on power deposition is analyzed. The results show that the power deposition of uniformly discharged SWP source mainly depends on plasma property, and too big or too small plasma density is unfavorable to the energy absorption. In the range of working gas pressure, SWP source can achieve effective power deposition only through collision mechanism, and the absorption rate of microwave can reach more than 80%, which agrees with the existing experimental result. The results also show that compact and intensive surface wave is more favorable to the absorption of microwave.

Numerical simulation of reaction-diffusion process of air plasma with a plasma source in open atmospheric environment

Yin Zeng-Qian, Zhao Pan-Pan, Dong Li-Fang, Fang Tong-Zhen
Acta Physica Sinica. 2011, 60 (2): 025206 doi: 10.7498/aps.60.025206
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A one-dimensional model is used to investigate the reaction-diffusion process of air plasma with a plasma source by numerical simulation in low pressure open atmospheric environment. The spatial evolutions of main charged species’ densities in the chemical reaction, drift and diffusion processes are obtained for a given plasma flow. The results of numerical simulation are combined with an approximate analytical formula to estimate the necessary plasma flow for electron density when a stable state is formed, with which the necessary power of the plasma source also can be estimated.

Characterization on the temperature of radio frequency argon capacitive discharge mode transition at atmospheric pressure

Guo Qing-Chao, Zhang Jia-Liang, Liu Li-Ying, Wang De-Zhen
Acta Physica Sinica. 2011, 60 (2): 025207 doi: 10.7498/aps.60.025207
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The mode transition and coexistence were investigated in atmospheric pressure argon radio frequency capacitive discharge. By use of a program compiled by the authors for the nitrogen's second positive band simulation, comparison between the experimental and simulated spectra of band (0, 1) and (1, 2) was used to determine the rotational and vibrational temperatures of N2. The trends of vibrational and rotational temperatures with discharge power were studied to observe the temperature jump corresponding to the discharge mode transition. Utilizing a well-known software named Lifbase, the simulated spectra of OH (A—X)(0, 0) was calculated to obtain the rotational temperature of OH by comparing with the experimental OH (A—X)(0, 0) band. The calculated rotational temperature of OH is well consistent with the result of nitrogen's second positive band, which shows that the neutral species are at thermal equilibrium in the space of discharge. According to the current-voltage characteristic, the temperature jump corresponding to the discharge mode transition was confirmed in accordance with the photograph of discharge.

Laser time fiducial for precise physical experiment in Shenguang-Ⅲ prototype facility

Lin Hong-Huan, Jiang Dong-Bin, Wang Jian-Jun, Li Ming-Zhong, Zhang Rui, Deng Ying, Xu Dang-Peng, Dang Zhao
Acta Physica Sinica. 2011, 60 (2): 025208 doi: 10.7498/aps.60.025208
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Using comb laser pulses synchronized with the main pulse output by large laser facility as time fiducial to scale the reaction process between high power laser pulse and target is very important for the realization of precise measurement and simulation in the intense field experiment. We demonstrate a fiber multiharmonic time fiducial laser pulse generation system using optic-electric modulation and optical pulse stacking. A unit optical pulse with a width of 150 ps generated by modulation was stacked in a fiber stacker to form a 1053 nm comb pulse. The pulse was then amplified and frequency-converted to generate green (527 nm) and UV (351 nm) fiducials. The system can stably provide Shenguang-Ⅲ prototype facility with multi-frequency laser time fiducials which is essential for the precise physical experiment. In addition, the system is highly adaptive since it can generate fiducial signals with variable pulse intervals and amplitudes flexibly according to the requirements of different physical experiments.

X-ray radiation power optimization in 1MA to 4MA wire-array implosions

Wang Zhen, Li Zheng-Hong, Xu Rong-Kun, Yang Jian-Lun, Ding Ning, Xu Ze-Ping, Guo Cun, Ning Cheng, Ning Jia-Min, Jiang Shi-Lun, Zhang Fa-Qiang, Xia Guang-Xin, Li Lin-Bo, Ye Fan, Qin Yi, Xue Fei-Biao, C
Acta Physica Sinica. 2011, 60 (2): 025209 doi: 10.7498/aps.60.025209
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Tungsten wire array implosions driven by 1 MA to 4 MA current were experimentally investigated. X-ray radiation power was improved through load parameters optimization,electrode structure improvement and well control of initial array conditions. The maximum powers of 5.3±1.0 TW and 5.6±1.1 TW, the highest at the 3 MA to 4 MA current level up to now, were measured in the single array and the double array implosions, respectively.

Effect of temperature gradient on the non-equilibrium rate of flux emitted by plane gold wall

Meng Guang-Wei, Li Jing-Hong, Pei Wen-Bing, Li Shuang-Gui, Zhang Wei-Yan
Acta Physica Sinica. 2011, 60 (2): 025210 doi: 10.7498/aps.60.025210
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In the theoretical and experimental research of radiation transport in inertial confinement fusion (ICF), the radiation spectrum in the foam cylinder can be changed by the surrounding high-Z wall. In this paper, we simulated and studied the property of flux emitted by the high-Z wall using 1-D plane model. Our work shows that the gradient of electron temperature is the reason why spectrum of flux emitted by the high-Z wall deviates from equillibrium. In order to quantitatively study the property of flux emitted by the high-Z wall, we define the non-equilibrium rate and deduced its estimating formula in the temperature scale of ICF experiment.

Radio frequency identification anti-collision test based on Markov chain model

Hou Zhou-Guo, He Yi-Gang, Li Bing
Acta Physica Sinica. 2011, 60 (2): 025211 doi: 10.7498/aps.60.025211
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The anti-collision theory of adaptive Q algorithm and radio frequency identification(RFID) communication timing sequence were analyzed. Then a Markov chain model for simulating multi-tag identification process was established based on the following three definitions. The definitions are identifying efficiency, identifying speed and data state(Q, n), where n is the total remanent tag number, and Q is the slot count. The identifying efficiency and speed were obtained from the model using Monte Carlo statistical method. A software-defined radio program was built to simulate the collision of RFID which could quantify the identifying efficiency and speed effectively. The consistency of model simulation result and test data proves the validity of the model and test method.

Analysis of high-resolution X-ray imaging of an inertial-confinement-fusion target by using a Fresnel zone plate

Wang Xiao-Fang, Wang Jing-Yu
Acta Physica Sinica. 2011, 60 (2): 025212 doi: 10.7498/aps.60.025212
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Aiming at 1μm high resolution in imaging an inertial confinement fusion (ICF) target, a method is developed for analyzing the direct imaging by a Fresnel zone plate (FZP), and numerical calculations are carried out to study the FZP imaging characteristics in thekeV X-ray range. For the Ti K α line (photon energy 4.51keV, wavelength 0.275nm), the FZP parameters are suggested, for which the technical requirement of fabricating the outmost zone is relatively low. The influence of the target size on the imaging is studied for the first time. It is shown that the FZP has a large effective field of view and the image quality can be guaranteed even for a target of several millimeters. The influence of the spectral bandwidth of a polychromatic incident light on the imaging is also studied. Monochromatic imaging can be obtained due to the achromatic property of the FZP. However, if the bandwidth is larger than a certain limit, the image contrast will be degraded. These results indicate the feasibility of applying an FZP in high-resolution X-ray imaging of an ICF ignition target and put forward the requirements as well.

Numerical study on Hall thruster magnetic configuration and its optimization

Deng Li-Yun, Lan Hong-Mei, Liu Yue
Acta Physica Sinica. 2011, 60 (2): 025213 doi: 10.7498/aps.60.025213
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Based on Maxwell's equations, under axis-symmetric assumption, a mathematical model of the magnetic field of a Hall thruster is established. A finite difference method is used for discretizing the model. An iterative method for numerically solving the model is given. The numerical results are obtained. From analysis of the results, the effect of the current in the magnetic field coils on the magnetic configuration of a Hall thruster is investigated. Through adjusting the current, the ideal magnetic configurations are found. It was shown that, for ideal magnetic configuration, the magnetic mirror ratio in the inner channel is between 3 and 3.5, and the magnetic mirror ratio in the outer channel is between 0.4 and 0.9. With the increasing of the current in the magnetic field coils, the magnetic field at the exit of the channel increases, but the magnetic mirror ratio cannot be increased. The magnetic field in the inner channel hardly changes with change of the currents in the magnetic field coils.

Numerical simulation on the effect of shielding gas on the plasma cutting arc

Zhou Qian-Hong, Guo Wen-Kang, Li Hui
Acta Physica Sinica. 2011, 60 (2): 025214 doi: 10.7498/aps.60.025214
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By comparing two diffierent torch geometries, it was found that the shielding flow has no significant effect on plasma velocity and temperature,except in the shock wave region. The shielding flow decreases the shock wave, and increases the arc voltage due to cooling. In the impinging geometry, shielding flow will crash the plasma jet after the nozzle exit and slightly increase the pressure in the torch. It was also shown that the component of shielding gas has no significant effect on plasma cuttingarc. The mole fraction of oxygen decreases very slowly along the axis and is still more than 90% at 10 mm downstream the nozzle exit.

Defect mode properties of two-dimensional unmagnetized plasma photonic crystals with line-defect under transverse magnetic mode

Zhang Hai-Feng, Liu Shao-Bin, Kong Xiang-Kun
Acta Physica Sinica. 2011, 60 (2): 025215 doi: 10.7498/aps.60.025215
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The piecewise linear current density recursive convolution finite-difference time-domain method of plasma is used to study the defect mode properties of transverse magnetic wave propagation in the two-dimensional unmagnetized plasma photonic crystals with a line-defect layer. In frequency domain, the transmission coefficients of electromagnetic differential Gaussian pulses are computed, and the effect of lattice constant, dielectric column radius, periodic constant, parameters of plasma and parameters of line-defect layer on defect mode properties of two-dimensional unmagnetized plasma photonic crystals are analyzed. The results illustrate that the frequency of defect mode cannot be tuned by changing periodic constant, position of the defect layer and plasma collision frequency, but be tuned by changing relative permittivity and radius of dielectric column in the defect layer, and central distance between defect layer and dielectric layer with the width of prohibit band gaps fixed. Furthermore, the defect mode and the width of prohibit band gaps can also be tuned by changing lattice constant, dielectric column radius and plasma frequency.

Characteristics of dielectric barrier discharge with different dielectric layer structures

Dong Li-Fang, Yang Yu-Jie, Liu Wei-Yuan, Yue Han, Wang Shuai, Liu Zhong-Wei, Chen Qiang
Acta Physica Sinica. 2011, 60 (2): 025216 doi: 10.7498/aps.60.025216
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A dielectric barrier discharge device with two glass dielectric layers, one of which is covered with an indium tin oxide (ITO) conductive layer, was designed. Its discharge characteristics was studied and compared with that in dielectric barrier discharge devices with two glass dielectric layers and single glass layer. The charge transport in two dimensions, zero dimension, and three dimensions were realized by the above three devices respectively. Single steady filament is obtained in the two devices with two glass layers. Different from the single filament obtained in the device with two glass dielectric layers without ITO conductive layer, the single filament obtained by using the device of two glass dielectric layers with ITO conductive layer in one side was "T" shapes, its halo was twice as much as that of the former, its current was greater, and the phenomenon of discharge interval changing alternatively between long and short was more evident. Moreover, the discharge intensity also varied alternatively between strong and weak. The analysis indicated that the differences of the wall charge transport and secondary electron emission between different dielectric structures lead to different discharge characteristics.

Numerical simulation of outgassing in the breakdown on dielectric surface irradiated by high power microwave

Cai Li-Bing, Wang Jian-Guo
Acta Physica Sinica. 2011, 60 (2): 025217 doi: 10.7498/aps.60.025217
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A simple outgassing model for dielectric surface breakdown due to the high power microwave (HPM) irradiation was establised. By using the PIC (particle-in-cell)-MCC(Monto Carlo collisions) method, the numerical simulation program of the dielectrics surface breakdown was developed, and the simulation of breakdown for different outgassing speeds was performed. The temporal evolution of the electron number and delay time of the process of breakdown in the case of different outgassing speeds were obtained. The numerical results show that when the speed of outgassing is small, the breakdown does not occur for an HPM pulse of a given duration, because the formation of the gas layer on the dielectric surface is slow. When the speed of outgassing is greater than a certain value, the breakdown occurs and the breakdown delay time shortens with the gas desorption rate increasing in a certain range. Finally, the numerical simulation results were compared with the experimental results of the direct current dielectric surface breakdown, and the trends of their development agree very well.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

A non-linear similarity method for season division in China

Sun Shu-Peng, Zhang Lu, Hou Wei, Feng Guo-Lin
Acta Physica Sinica. 2011, 60 (2): 029201 doi: 10.7498/aps.60.029201
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Using the daily observational data of temperature, pressure, relative humidity and precipitation in 752 stations of China from 1961 to 2008, three methods of division of season, i.e. Zhang’s method, non-linear similarity method and Fisher optimal dissection method are applied to different meteorological elements fields of China. Results indicate that division of season through multi-variables methods is more reasonable than single variable ones, especially in non-linear similarity method and Fisher optimal dissection method. When considering the seasonal climate transition between successive seasons, the results are in good accordance with actual observations. As a result we recommend the non-linear similarity method as a better way of season division.

Biot-Savart law and the formation mechanism of Somali low-level jet

Feng Shi-De, Feng Tao
Acta Physica Sinica. 2011, 60 (2): 029202 doi: 10.7498/aps.60.029202
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Firstly, we investigate the impact of cross-equatorial Somali low-level jet on the atmospheric circulation in the east of Tibet Plateau using lattice Boltzmann model simulation. Secondly, we study the relationship between thermal conditions on the bottom boundary and the formation of Somali jet based on Biot-Savart law using the data from National Centres for Environmental Prediction (NCEP). As the radiation from the Sun gradually moves from the southern meridian, the temperature on the ground surface of Somali Peninsular and Arabic Peninsular gradually increases. During the same period the surface temperature of the Northern Indian Ocean increases much slower. It is shown that this increase in the temperature difference between the land and sea is inductive to the formation and development of Rayleigh-Benard convection and leads to the increasing relative vorticity strength between positive and negative vertical vortices over the land and sea. According to Biot-Savart law, the increase in vorticity strength will induce correspondingly a large horizontal velocity. The pair of positive and negative vorticity fields over the two Peninsulars and the sea surface is effective in forming and maintaining this current. This mechanism is referred to as "Somali suction pump". It draws air continually from the Southern hemisphere and releases it at the coastal area of Somali.

Comparison of applications of different filter methods for de-noising detrended fluctuation analysis

He Wen-Ping, Wu Qiong, Cheng Hai-Ying, Zhang Wen
Acta Physica Sinica. 2011, 60 (2): 029203 doi: 10.7498/aps.60.029203
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We studied the effects of continuous noises and random spikes on detrended fluctuation analysis, and found that the noises lead to the appearance of crossovers in the double logarithm curves when the linear fitting scale was less than a characteristic scale s×. To solve this problem, we use three kinds of filter methods, multi-stage Vondrak filter, N-point weighted moving average filter and fast Fourier filter, to filter high frequency from the analyzed time series. The results indicate that the evolution trend and intensity of high frequency series by multi-stage Vondrak filter is almost identical to those of real noises. Further investigation showed that multi-stage Vondrak filter can eliminate the phenomenon of crossover, and the DFA results of lowpass filtering time series are less dependent on the threshold of the filter periods. To some extent, N-points weighted moving average filter can partly eliminate the effect of noises on DFA, but can not completely eliminate the phenomenon of crossover caused by noises. Fast Fourier filter can almost totally eliminate the effect of noises on DFA when the period of filter adopts an appropriate value, but the filtering results have a stronger dependence on the period of filter, so it is difficult to select the period of filter in practical application. Therefore, comparatively speaking, multi-stage Vondrak filter is an effective measure to alleviate the effects of noises on the DFA results.

Dynamic optimal multi-indexes configuration for estimating the prediction errors of dynamical climate model in North China

Yang Jie, Wang Qi-Guang, Zhi Rong, Feng Guo-Lin
Acta Physica Sinica. 2011, 60 (2): 029204 doi: 10.7498/aps.60.029204
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Based on the idea of using the historical-analogue information to revise the prediction errors of National Climate Centre numerical business model, for North China, based on analysis data of the CMAP from 1983 to 2009, 40 pieces of climate indices from NOAA, 27 years of the season prediction model results from 1983 to 2009 and 74 pieces of circulation characteristics materials provided by Weather Diagnostic Forecasting Room of National Climate Center, using the method of combining data analysis and numerical simulation of diagnostic tests, taking the advantage of the prediction error of the key information of similar model from the historical data, by identifying key factors, optimizing allocation of the different factors of different forecasting years, we established specific multi-factor dynamic optimal portfolios to revise prediction errors in different periods of the power-statistical model in North China, and constructed early environmental factors similar to field multiple objective criteria, to develop new technology of revising prediction errors from the power-statistical model based on dynamic optimal combination of multi-factor, and improved the prediction effect in the summer precipitation in North China and the forecasting skills. Results of independent sample return of 2005—2009 shows that, the score of similarity revised method has improved significantly compared with the score of systematic revised method. The method has a good prospect for summer precipitation forecast in North China, and is going to be put into operation.

Diffraction theory analysis and numerical simulation of non-modulation two-sided pyramid wavefront sensor

Wang Jian-Xin, Bai Fu-Zhong, Ning Yu, Huang Lin-Hai, Jiang Wen-Han
Acta Physica Sinica. 2011, 60 (2): 029501 doi: 10.7498/aps.60.029501
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Two-sided pyramid wavefront sensor (TSPWFS) is a kind of wavefront sensor with high spatial resolution and light energy utilization. To deeply study the principle of wavefront reconstruction of this wavefront sensor using wave optics theory, this paper deduces the diffraction theory of non-modulation TSPWFS and gives the analytic solution of linear reconstruction matrix for wavefront reconstruction. With numerical simulation the optimal distance between adjacent pupil image centers was determined. Also, wavefront reconstruction and closed-loop correction of static aberrations by using non-modulation TSPWFS as a wavefront sensor were simulated. The results show that non-modulation TSPWFS has three main advantages. i.e., it does not require measuring the response matrix in real optical setup, and can correct the optical systemic aberration, and can achieve stable closed-loop correction result. Additionally, non-modulation TSPWFS can be applied to a real adaptive optics system to detect wavefront.

A simulation experiment system for X-ray pulsar based navigation

Hu Hui-Jun, Zhao Bao-Sheng, Sheng Li-Zhi, Yan Qiu-Rong
Acta Physica Sinica. 2011, 60 (2): 029701 doi: 10.7498/aps.60.029701
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A simulation experiment system for X-ray pulsar based navigation is setup in order to study the key technologies of X-ray pulsar navigation. The system consists of X-ray pulsar source generator, super sensitive X-ray photon counting detector, charge sensitive amplifier, shaping amplifier, time measurement, X-ray pulse profile reconstruction and pulse time of arrival (TOA) measurement. The system can simulate the X-ray pulsar source with different intensities, period and pulse profile. The TOA of individual X-ray photon is recorded, the pulse profile is reconstructed with these data. And by comparing the measured pulse profile with the standard pulse profile of the X-ray pulsar source generator, the pulse TOA is calculated. The construction and the principle of the simulation experiment system are introduced and experiment results are presented.
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