Acta Physica Sinica

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Multi-scale modeling of radiation damage in FeCr alloy

He Xin-Fu, Yang Wen, Fan Sheng

Acta Physica Sinica. 2009, 58 (12): 8657 doi: 10.7498/aps.58.8657
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Since irradiation experiments of ferritic/martensitic （F/M） FeCr alloys show that F/M steels undergo much less swelling than austenitic steels during neutron or charged particle irradiation，in addition, it is well-known that high chromium content of F/M alloys provide good resistance against corrosion, they are considered as one of the most attractive candidate materials for future nuclear facilities, such as Fusion Reactor, ADS and generation Ⅳ reactors. Although irradiation experiments can not be replaced by modeling, a purely experimental approach to understanding the effects of irradiation is also not practicable, so in recent years substantial progress has been made in the field of multi-scale modeling of radiation damage in F/M FeCr alloys. The present paper is a review of methods used and results achieved within the last couple of years, and some suggestions are put forward for the further improvements.

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An improved shift operator finite-difference time-domain method based on digital signal processing technique for general dispersive medium

Zhang Yu-Qiang, Ge De-Biao

Acta Physica Sinica. 2009, 58 (12): 8243 doi: 10.7498/aps.58.8243
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An improved shift operator finite-difference time-domain （SO-FDTD） method for general dispersive medium based on the implementation of infinite impulse response filter in digital signal processing technique is presented. Compared with the commonly used SO-FDTD, the storage variables in the improved SO-FDTD are reduced by 33% and computational efficiency is also increased. Finally, the generality and the feasibility of the presented scheme are validated by calculations of scattering by first order and second order dispersive objects.

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Super-resolution characteristics of time-reversed electromagnetic wave

Ge Guang-Ding, Wang Bing-Zhong, Huang Hai-Yan, Zheng Gang

Acta Physica Sinica. 2009, 58 (12): 8249 doi: 10.7498/aps.58.8249
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Time-reversed electromagnetic wave has the property of super-resolution in some special far-field circumstances. A model with the property of super-resolution was constructed and simulated by time-reversal technique. By analyzing the simulation results, we can find the main reason for realization of property of super-resolution. The research provides support for the design of compact multi-antenna wireless communication system.

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Interactions of electromagnetic wave and Langmuir wave in an inhomogeneous plasma

Zhou Lei, Tang Chang-Jian

Acta Physica Sinica. 2009, 58 (12): 8254 doi: 10.7498/aps.58.8254
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The linear conversion and interactions of Langmuir and electromagnetic waves in an inhomogeneous plasma has been demonstrated by numerical and theoretical methods adequately. The dispersion relation of electromagnetic wave in an inhomogeneous plasma has been deduced. The physical processes of conversion of incident electromagnetic or Langmuir wave in an inhomogeneous plasma and the relationship of the spread vector with the coordinates have been researched, and the mechanism of interactions between the electromagnetic and Langmuir waves have been discussed. The results are of significance for the generation of electromagnetic radiation from density gradient-driven plasma.

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Divergent characteristic of the second order moment of nonparaxial vector beams ^Hot!

Deng Xiao-Jiu, Wang Guo-An, Liu Cai-Xia, Lai Chuan-Wei

Acta Physica Sinica. 2009, 58 (12): 8260 doi: 10.7498/aps.58.8260
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Based on the accurate expression of light intensity of nonparaxial vector beams at the transverse plane and the vectorial second order moment theory of light beam propagation，by applying rigorous vectorial diffraction theory of the angular spectrum representation，the nonparaxial propagation of any vectorial diffraction beam has been systemically investigated，the integral expressions of beam width，transversal divergence angle have been presented，and the divergent characteristic of the second order moment of nonparaxial vector beams has been demonstrated. The definitions of beam width，transversal divergence angle of non-paraxial vector beams and some related problems have been discussed.

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Pulse-front-distortion in large-aperture short-pulse laser systems

Zuo Yan-Lei, Zeng Xiao-Ming, Huang Xiao-Jun, Zhao Lei, Wang Xiao, Zhou Kai-Nan, Zhang Ying, Huang Zheng

Acta Physica Sinica. 2009, 58 (12): 8264 doi: 10.7498/aps.58.8264
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The principles of pulse-front distortions production and its possible sources in a large-aperture short-pulse laser system are described. By using Fourier optics, a theoretical model based on single-pass compression is set up for the study of the pulse-front distortion. For the first time the effects of the pulse-front distortion on the spatial and temporal properties of the output pulse from the compressor is investigated. With the model we analyze all kinds of distortion sources, including the AOPDF, the lens and the wedges by numerical simulation for a large-aperture short-pulse system. The result shows that the pulse width in the near field broadens remarkably and the pulse-front shape of the output pulse differs from that of the input pulse except in the central part in the cross section whose area is determined by the bandwidth of the system.

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Coherent transmission of terahertz wave through randomly packed subwavelength-sized aluminium particles

Chen Hua, Wang Li

Acta Physica Sinica. 2009, 58 (12): 8271 doi: 10.7498/aps.58.8271
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We experimentally discovered that the efficient coupling of surface plasmon wave to free-space radiation beyond the interaction zone via random metallic particles. In the experiments of terahertz wave transmission through an ensemble of randomly packed aluminium particles with sub-wavelength sizes, we observed a strong dependence of the transmission on the lateral boundary conditions. Our results showed that the processes of terahertz wave propagating in the disk-shaped samples and reemitting to the free space were resulted from surface modes excitation, which is critically affected by lateral sizes of the particle ensembles.

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Modulation of feedback strength to enhance the security of chaos optical communication system

Guo Dong-Ming, Yang Ling-Zhen, Wang An-Bang, Zhang Xiu-Juan, Wang Yun-Cai

Acta Physica Sinica. 2009, 58 (12): 8275 doi: 10.7498/aps.58.8275
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There is a high tolerance on parameters mismatch between transmitter and receiver in the chaos communication system based on injection locking synchronization，so to a certain extent，the information security has been reduced. We propose the synchronous modulation of feedback strength to improve the system security. The change of signal extraction quality after modulation is studied numerically，and the effects of modulation rate detuning and modulation delay time on signal extraction are analyzed too. The research results indicate that the synchronization of the original system is destroyed and the bit error rate increases by two orders of magnitude when the transmitter feedback strength is modulated. The information can not be recovered unless the receiver uses the same modulation. Furthermore，the results also show that high quality information could be obtained when rate detuning and delay time are in the range of ±5 MHz and ±0.1 times the modulation cycles, respectively. All of these prove that modulating the feedback strength can enhance the security of chaos communication efficiently.

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Wigner functions of multiple-photon excited coherent states

Lan Hai-Jiang, Pang Hua-Feng, Wei Lian-Fu

Acta Physica Sinica. 2009, 58 (12): 8281 doi: 10.7498/aps.58.8281
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Wigner functions in phase space are reconstructed for the excited coherent states，which are generated by applying the inverse of k-Boson operators repeatedly to the coherent states. The non-classicality of these states is discussed by calculating their Wigner functions in Fock-state space. Numerical results show that these excited coherent states always reveal non-classical characteristics，no matter whether the excited number k is even or odd，and also the corresponding non-classicality is more obvious with the number k increasing.

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Analysis of the beam characteristics and the propagation model of spectral combining systems for Yb-doped fiber lasers

Pan Lei-Lei, Zhang Bin, Yin Su-Qin, Zhang Yan

Acta Physica Sinica. 2009, 58 (12): 8289 doi: 10.7498/aps.58.8289
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The propagation model for the spectral combining systems including Yb-doped fiber laser arrays，transform lens，grating and output coupler has been built up. By taking into considerotion the grating angle dispersion，the fabrication errors of groove angle and the diffraction efficiency of the grating，the formula for the phase change of the Gaussian beam unparallelly oblique incidence on the grating and the analytical expression for the intensity distribution of the combining beam have been derived by using the ray tracing method，the diffraction integral method，the principle of incoherent superposition of laser beams and the intensity second-order moments method. Consequently，the effects of the angle dispersion，the diffraction efficiency and the fabrication errors of groove angle of the grating on the beam characteristics of the spectral combining system have been analyzed for the case of Gaussian beam unparallelly oblique incidence on the grating. The results show that the beam quality of the combined beam remains almost the same as that of a single fiber laser. The effect of the angle dispersion of the grating on the beam quality of combined beam can be neglected. The beam quality of combined beam degrades with the increasing of the fabrication errors of groove angle of the grating. For the case of the large fabrication errors of groove angle of the grating，the effect of the diffraction efficiency of the grating on the beam characteristics of the combined beam should be considered.

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Experimental research on phase detection and correction of two fiber amplifier based on active segmented mirrors

Yang Ruo-Fu, Yang Ping, Shen Feng

Acta Physica Sinica. 2009, 58 (12): 8297 doi: 10.7498/aps.58.8297
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The measurement of piston noise is a critical issue in coherent combining of fiber lasers. This paper presents a strip extracting algorithm, which get the amplitude of phase noise in fiber amplifier. By this algorithm, phase noise of fiber amplifier working in 10^-3 W level is measured and real-time controlled by high-speed digital processing circuit and active segment mirrors. Experimental results indicate, that after closing the loop, fringe contrast improves from 0.09 to 0.25, intensity value of piston noise decreases from 1053.4 nm down to 116.7 nm; the calibration precision and bandwidth of the system achieve 1/10λ and ～50　Hz, respectively.

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Scattering of a beam with orbital angular momentum by a single sphere

Lü Hong, Ke Xi-Zheng

Acta Physica Sinica. 2009, 58 (12): 8302 doi: 10.7498/aps.58.8302
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The propagation properties and scattering characteristic of a beam with orbital angular momentum transmission were researched by using the generalized Lorenz-Mie theory. Based on the research on the scattering of the Gaussian beam from single sphere，the intensity distributions of LGB beam at different propagation distance is analyzed. Without considering the relation between scattering and phase shift，the beam coefficients is obtained by the solution of scattering cross section，and the LGB is expanded in terms of the vector spherical harmonics as fundamental Gaussian beam. The scattering of the beam with orbital angular momentum from single sphere located on the propagation axis is studied. The influence of scattering intensity and angular distribution on scattering characteristic for different beam width is discussed by numerical simulation，and compared with those for the plane wave. The results show that when the beam waist radius is very small，the beam waist radius has serious influence on the decay rate. When the beam waist radius is relatively large，the influence is similar to that of plane wave.

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Self-consistent field description of whispering-gallery mode in circular cavity

Qiu Shan-Liang, Li Yong-Ping

Acta Physica Sinica. 2009, 58 (12): 8309 doi: 10.7498/aps.58.8309
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On the base of introduction of circular cavity eigenfield and its reflection coefficient，the self-consistent field description of whispering-gallery mode （WGM） in circular cavity is discussed. Accroding to the self-consistency，the same eigenvalue equation as the one directly deduced from the Helmholtz equation determining WGM is obtained. Also based on the wave-ray correspondence of circular cavity eigenfield，the self-consistent ray description of WGM is discussed. The results of resonance wavenumbers and the Q-factors of WGMs deduced from the intuitive self-consistent picture of eigenray beam are well coincident with the ones obtained by directly solving the eigenvalue equation.

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Dynamics of relaxation oscillation caused by stimulated Brillouin scattering in optical fiber and its suppression

Yin Jing-Chan, Xiao Xiao-Sheng, Yang Chang-Xi

Acta Physica Sinica. 2009, 58 (12): 8316 doi: 10.7498/aps.58.8316
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In order to further study the dynamics of relaxation oscillation during stimulated Brillouin scattering （SBS） and to avoid optical damage caused by SBS under high power lasers in applications such as fiber amplifier and fiber phase conjugate mirror，etc.，the dynamics of relaxation oscillation during SBS in fibers are studied on the basis of the SBS coupled amplitude equations using numerical simulations of finite difference methods. Meanwhile，we propose a method to suppress the relaxation oscillation. For different rise time of SBS pump pulse，the temporal and spatial variation of intensities of pump and Stokes waves is plotted as three-dimensional figures. The corresponding experiments have been conducted and the experimental results agree well with the theoretical results. From the experiments and numerical calculations it can be concluded that，by increasing the rise time of SBS pump pulse the relaxation oscillation can be suppressed effectively and the optical damage caused by SBS can be avoided consequently.

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Effects of gain saturation in terahertz radiation based on difference frequency generation

Huang Nan, Li Xue-Feng, Liu Hong-Jun, Xia Cai-Peng

Acta Physica Sinica. 2009, 58 (12): 8326 doi: 10.7498/aps.58.8326
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Numerical studies of terahertz （THz） radiation based on difference frequency generation in GaSe crystal are reported. When the gain saturation is achieved at a wavelength of 227.5 μm，which corresponds to a crystal length of 26.3 mm，the peak output power for THz radiation reaches 945 W. As a result of crystal absorption，the gain saturation region of THz radiation is the unstable output region，which is in front of the stable output region; and the stability of THz radiation is determined by the stability of pump. The peak output power for THz radiation reaches 735 W at the wavelength of 227.5 μm and at the corresponding crystal length of 37.9 mm in stable region.

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Analytical solution in the Ince-Gaussian form of the beam propagating in the strong nonlocal media

Zhang Xia-Ping, Liu You-Wen

Acta Physica Sinica. 2009, 58 (12): 8332 doi: 10.7498/aps.58.8332
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Based on the Snyder-Mitchell model that describes the paraxial beam propagating in strongly nonlocal nonlinear media and by constituting the trial solution with modulating the Gaussian beam by Ince polynomials in elliptic coordinate，the close forms of Ince-Gaussian beams have been accessed. Depending on the power of the beam，the Ince-Gaussian beams can be either a soliton state when the input power is equal to the critical power or a breather state. The Ince-Gaussian beams constitute the exact and continuous transition modes between Hermite-Gaussian beams and Laguerre-Gaussian beams. The profiles of the breather at different propagating distance are numerically obtained and the transitions of a few Ince solitons are given.

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Effect of rotating cavities on the group velocities of the coupled-resonater optical waveguides

Zhang Jian-Xin, Qu Dao-Kuan, Feng Shuai, Wang Yi-Quan, Wang Chuan-Kui

Acta Physica Sinica. 2009, 58 (12): 8339 doi: 10.7498/aps.58.8339
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In this article，the influence of cavity rotation on the group velocities of the coupled-resonator optical waveguides，which consists of the two-dimensional square-lattice photonic crystal，is studied theoretically by the multiple-scattering method and the finite-difference time-domain method. Simulation results show that the original single propagation mode becomes two modes when the cavities within the waveguide are rotated alternately，and the group velocities of the modes is reduced greatly. When the rotated angle of the selected cavities is 45°，the group velocities of the propagating modes can be reduced by one order of magnitude. Compared with that of the coupled-resonator optical waveguide without rotation of selected cavities，the two velocities get their minimum value，which are 0.0016c and 0.0009c respectively. The difference between them is determined by the symmetry of the propagating modes.

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Octagonal photonic crystal fiber of birefringence

Yang Qian-Qian, Hou Lan-Tian

Acta Physica Sinica. 2009, 58 (12): 8345 doi: 10.7498/aps.58.8345
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In this paper we propose a novel octagonal birefringent photonic crystal fiber，which shows birefringence when the size of several holes near the core is enlarged. The modal field，dispersion，confinement loss，birefringence of the fiber fundamental mode and the influence on birefringence of some parameters are simulated by multipole method. The dispersion，confinement loss，birefringence of the hexagonal photonic crystal fiber having the same parameters were also computed. By comparision，we conclude that the octagonal photonic crystal fiber have larger birefringence，smaller confinement loss and shorter wavelength of zero dispersion than the hexagonal photonic crystal fiber with the same parameters.

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Mechanical anti-aliasing acoustic low-pass filtering fiber-optic hydrophones with side cavities

Wang Ze-Feng, Hu Yong-Ming, Meng Zhou, Luo Hong, Ni Ming

Acta Physica Sinica. 2009, 58 (12): 8352 doi: 10.7498/aps.58.8352
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A novel mechanical anti-aliasing fiber-optic hydrophone with an acoustic low-pass filter of side cavities has been reported，to the best of our knowledge，for the first time. The low frequency lumped parameters model and the effective acoustic circuit of the hydrophone is constructed based on the theories of electro-acoustic analogy，and the acoustic performance is predicted by the circuit analysis methods. Theoretical results show that the hydrophone has three resonant frequencies and one inverse resonant frequency induced by the side cavities，and the hydrophone has good high frequency attenuation properties. A hydrophone with side cavities，designed and fabricated by us，is tested in a standing-wave tube filled with water. The measured frequency response curve，on the whole，has identical form as that predicted by theory, over the test frequency range of 50 to 7000 Hz. To be speaific，the low frequency responses are in good accordance，and the acoustic sensitivity is about -140 dB re 1 rad/μPa. The high frequency responses have obvious difference，which is mainly induced by the operation limitation of the low frequency model. It is expected that this new type of fiber-optic hydrophone will work as an important class of sensors used to eliminate the aliasing in the future fiber-optic sonar systems.

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Flexural vibration property of periodic pipe system conveying fluid based on Timoshenko beam equation

Shen Hui-Jie, Wen Ji-Hong, Yu Dian-Long, Wen Xi-Sen

Acta Physica Sinica. 2009, 58 (12): 8357 doi: 10.7498/aps.58.8357
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Fluid and structure interaction induced vibration in pipe system conveying fluid occurs in many fields, and the flexural vibration control is very important. The idea of phononic crystals is introduced into the design of pipe system conveying fluid. Basing on Timoshenko beam equation, and using the transfer matrix method, we study the band gap properties of the vibration and its transmission properties. The effect of the material damping ratio and spring support stiffness on the band gap is analyzed. The existence of band gaps in the periodic pipe system conveying fluid lends new insight into vibration control of pipes.

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Sound field separation technique based on single surface measurement using pressure-velocity transducers

Zhang Yong-Bin, Xu Liang, Bi Chuan-Xing, Chen Xin-Zhao

Acta Physica Sinica. 2009, 58 (12): 8364 doi: 10.7498/aps.58.8364
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The sound field separation technique based on single surface measurement is investigated in this paper. A modified separation formula based on the spatial Fourier transform is presented to overcome the inherent singularity of the current single surface separation technique. However due to the wraparound error associated with fast Fourier transform （FFT）, the accuracy of separation technique based on FFT is not satisfactory and a novel separation method based on the statistically optimized nearfield acoustic holography is proposed to improve the separation. The simulations as well as experiments carried out with the p-u intensity probe produced by Microflown demonstrate the validity of the proposed modified formula and the effectiveness of the new separation method.

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Laser induced bubble characteristics with experimental and numerical methods

Wang Yu-Hong, Wang Jiang-An, Ren Xi-Chuang

Acta Physica Sinica. 2009, 58 (12): 8372 doi: 10.7498/aps.58.8372
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According to the characteristics that a laser induced bubble is filled with mostly water vapor and a little noncondensable gas, a specific Rayleigh-Plesset equation which was used to determine the position of the dynamic bubble wall and other concerned conditions were used. Mass diffusion between the bubble and the gases dissolved in surrounding water, compression of water, condensation and evaporation at the bubble wall, heat conduction, sound radiation, viscosity of water and surface tension were considered. A laser induced bubble producing, photographing and pressure measuring system was set up. Numerical and experimental method was used; the relative error of pressure inside bubble was under 10%. The relations were showed among the absorbed laser puergy, the pressure and the temperature in the bubble and the bubble radius.

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Cyclic shift keying spread spectrum underwater acoustic communication

He Cheng-Bing, Huang Jian-Guo, Han Jing, Zhang Qun-Fei

Acta Physica Sinica. 2009, 58 (12): 8379 doi: 10.7498/aps.58.8379
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Aimed at solving the problem of low data rate of direct sequence spread spectrum underwater acoustic communication and that of complexity of the receivers of M-ary spread spectrum underwater acoustic communication, cyclic shift keying spread spectrum underwater acoustic communication is proposed based on the good characteristic of spread sequences. At the transmitter, base waveform is cyclically shifted according to the input information. At the receiver, only one correlator is used to estimate the time delay and decode. Multi-code spread spectrum based on cyclic shift is presented. Lake experiments at both middle and long range were conducted for the proposed methods. Single and two code cyclic shift keying underwater acoustic communication were realized in the range of 15 km and the bandwidth of 2 kHz. The data rate was 438 bit/s with bit error ratio around 10^-2—10^-5. The result demonstrated the bandwidth efficiency and low complexity of the proposed methods and the applicability for long range underwater acoustic communication and multi-user underwater acoustic communication network.

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Augmenting the mixing of size-type binary granular systems in a rotating horizontal drum

Zhao Yong-Zhi, Zhang Xian-Qi, Liu Yan-Lei, Zheng Jin-Yang

Acta Physica Sinica. 2009, 58 (12): 8386 doi: 10.7498/aps.58.8386
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Cross shaped baffles are set in the horizontal drum to augment mixing of the size-type binary particles, and the discrete element method was employed to study the mixing of the size-type binary granular systems in the rotating horizontal drums with different sized cross shaped baffles. The influences of the baffle and the size of the baffle on the mixing were discussed. The mechanisms of the augmenting of mixing of the baffles were discussed in this paper. The simulation results show that the convection, the diffusion and the segregation controlled the mixing and demixing of the binary granular systems in the rotating horizontal drum without baffle. When the baffle was set in the drum, only the convection and the diffusion operated, and the segregation of the binary particles were suppressed, because the cross shaped baffles can break the free-surface flow in the drum and the segregation of the binary particles in the free-surface flow can not occur, and the mixing can be enhanced. An optimum size of the baffle exists for the augmenting mixing of the size-type binary granular systems in the drum with baffles. The oversized and undersized baffles are unfavorable for the mixing of binary particles in the drum.

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Enhancing compressive strength of electrorheological fluid by patterning the electrode

Zhang Min-Liang, Tian Yu, Jiang Ji-Le, Meng Yong-Gang, Wen Shi-Zhu

Acta Physica Sinica. 2009, 58 (12): 8394 doi: 10.7498/aps.58.8394
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Slip at the interface of solidified electrorheological （ER） fluid and electrodes is harmful for ER applications. Compression tests using four kinds of electrodes, namely the smooth, hole array patterned by laser pulse, nylon net covered, and acid etched column patterned electrodes, have been done, respectively. Results show that laser patterned and nylon net covered electrodes significantly enhanced the compressive stress of the ER fluid. The enhancement is ascribed to the increase of local electric field near electrodes after patterning, which increased the interfacial strength between ER fluid and electrodes, and effectively suppressed the slip of solidified ER fluid from electrode. The tests of current density during compression and the finite element analysis of the electric field distribution of patterned electrodes supported this slip suppression effect. The results raised a fundamental question of what is the real strength of ER fluids, since the slip of highly solidified ER fluid are usually not considered during various tests. This investigation also shows that patterning electrodes is a good way to improve mechanical performances of ER fluids.

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Influence of bubble content on laser-induced cavitation bubble oscillation in glycerol-water mixture

Zhao Rui, Xu Rong-Qing, Liang Zhong-Cheng, Lu Jian, Ni Xiao-Wu

Acta Physica Sinica. 2009, 58 (12): 8400 doi: 10.7498/aps.58.8400
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The effect of viscosity and bubble content on cavitation bubble oscillation is investigated by the fiber-optical sensor based on the beam deflection in combination with theoretical analysis. The maximum bubble radius at each oscillating cycle in different viscous fluid is determined by experiment. It is observed that the maximum bubble radius at each oscillating cycle does not decrease but increases. A reasonable explanation based on experimental results and numerical calculation is given to this anomaly. The results indicate that both the bubble content and the viscosity have obvious influence on the bubble oscillation and it does increase during the bubble oscillating cycle.

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Three-dimensional cavitation simulation using lattice Boltzmann method

Zhang Xin-Ming, Zhou Chao-Ying, Islam Shams, Liu Jia-Qi

Acta Physica Sinica. 2009, 58 (12): 8406 doi: 10.7498/aps.58.8406
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The cavitation is a complex phenomenon which is microcosmic, transient, stochastic and multiphased. The extreme condition and related cavitation effects which the collapsed cavities generate will affect the liquid-vapor system greatly. In this article, we accurately simulate heterogeneous cavitation in liquid system with single component multiphase lattice Boltzmann model and successfully reproduce the complete cavitation process of a bubble: inception, growth and collapse. The relationship between the radius of bubble seed and cavitation for a specified tension has been investigated by lattice Boltzmann method simulations. The simulations show excellent agreement with energy considerations based on interface formation and bubble expansion.

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Bottom quark pair production in γγ collision

Huang Jin-Shu, Luo Peng-Hui, Lu Gong-Ru

Acta Physica Sinica. 2009, 58 (12): 8166 doi: 10.7498/aps.58.8166
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We study the Yukawa corrections to the γγ→b cross section in the topcolor assisted technicolor models at the photon-photon colliders. We find that, for the favorable parameters, the relative corrections from pseudo-Goldstone bosons give out a 3.17%—5.90% decrement of the cross section from the tree level when /{s/}²=500 GeV, the total relative corrections are significantly larger than the corresponding corrections in the standard model, the general two Higgs doublet model and the minimal supersymmetric standard model. So the observation of the correction to the γγ→b process at the International Linear Colliders is certainly the clue to the standard model and new physics.

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Electromagnetic mode analysis on the cold characteristics of photonic-band-gap resonant cavity loaded in gyrotron

Liu Chang, Luo Yao-Tian, Tang Chang-Jian, Liu Pu-Kun

Acta Physica Sinica. 2009, 58 (12): 8174 doi: 10.7498/aps.58.8174
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The traditional cylindrical resonant cavity loaded in gyrotron is substituted by the photonic-band-gap resonant cavity （PBGC） which is constructed by triangular arrays of metal posts, and the TE operating modes in PBGC are analyzed and calculated. Under the consideration of the cavity structure features, a research method for the mode theory on PBGC is provided. The single-mode operation in the cavity is found, and the distribution characteristics of the azimuthally inhomogeneous electromagnetic modes are reported. The research results show that the resonant frequency in the cavity can be excited without the limitation of transverse dimension. The study provides a physical theoretical fundamental of which reveals the possibility of changing the operating status of gyrotron essentially. This possibility will play an important role in the following aspects: enhancing the power capacity of cavity, carrying out the beam-wave interaction between high order electromagnetic single-mode and high electronics cyclotron harmonic wave efficiently, and reducing the gyrotron operating magnetic field.

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Breakdown parameter in hybrid method

Lan Xu-Dong

Acta Physica Sinica. 2009, 58 (12): 8415 doi: 10.7498/aps.58.8415
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The multiscale flow is a hot topic recently. The hybrid method by coupling different methods is the main approach to investigate multiscale flows.The two processes involved in hybrid method are determining interface position and transferring information through the interface. The paper discusses the existing breakdown parameters and proposes a unified form of the breakdwon parameter.

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Plasma screening effect on the differential cross sections of collision ionization of H by He²⁺

Ding Ding, He Bin, Liu Ling, Zhang Cheng-Hua, Wang Jian-Guo

Acta Physica Sinica. 2009, 58 (12): 8419 doi: 10.7498/aps.58.8419
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A classical trajectory Monte Carlo method is used to investigate the collision ionization of H by He²⁺ in Debye plasma, and the total and differential cross sections are obtained for collision energies of 5—400 keV/u in a large plasma parameter range. The interaction between charged particles is described by the Debye-Hückel model. Plasma screening changes the ionization energy and classical microcanonical distribution of bound electrons and the interaction between electron and the projectile, which result in the modification of ionization cross sections. It is found that both the total and differential cross sections increase with the increasing of screening interaction, and especially for energies below 10 keV/u, the cross sections are one to two magnitudes larger than those in the unscreened case. The emitted electron moves to the higher energy range, and the binary-encounter ionization mechanism becomes more important and a new hump appears due to the screening effect. Our unscreened cross section is in a good agreement with the experimental measurement for collision energies beyond 70 keV/u.

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Velocity gradient in Kelvin-Helmholtz instability for supersonic fluid

Wang Li-Feng, Teng Ai-Ping, Ye Wen-Hua, Fan Zheng-Feng, Tao Ye-Sheng, Lin Chuan-Dong, Li Ying-Jun

Acta Physica Sinica. 2009, 58 (12): 8426 doi: 10.7498/aps.58.8426
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Two-dimensional numerical calculations using weighted essentially non-oscillatory schemes （WENO） scheme were performed to study velocity gradient in the Kelvin-Helmholtz （KH） instability for supersonic fluid. It is found that the velocity gradient has a stabilization effect on the KH instability for supersonic fluid, and the linear growth rate empirical formula with velocity gradient stabilization effect is deduced. The empirical formula with velocity gradient stabilization effect agrees well will the simulation results. The sharp density contour is obtained, which indicates that the WENO finite difference scheme has good capturing ability in interface deformation. The evolution of KH vortex is influenced by the velocity gradient. When the density gradient is fixed, it is found that the larger the velocity gradient the smaller the transverse scale of the KH vortex.

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Sheath structure of a hot-cathode in plasma

Wang Dao-Yong, Ma Jin-Xiu, Li Yi-Ren, Zhang Wen-Gui

Acta Physica Sinica. 2009, 58 (12): 8432 doi: 10.7498/aps.58.8432
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The plasma sheath in the presence of virtual-cathode structure near a hot cathode was studied by combining the theory of thermionic emission and plasma fluid equations. Using Sagdeev potential method, the sheath solution and generalized Bohm criterion were discussed. It is shown that, different from usual Bohm sheath, the critical ion Mach number at the sheath-presheath edge is not an independent constant but depends on sheath potential drop as well as other parameters, owing to the fact that there exists large quantity of thermionic electrons near the hot cathode which has a significant influence on the whole sheath structure. The critical Mach number first increases and then decreases with the potential drop （from sheath-presheath edge to the virtual cathode）, and monotonically increases with the temperature of the hot cathode. In the plane geometry, there exists an appreciable quantity of residual thermionic electrons which traverse the virtual cathode and sheath and enter into bulk plasma.

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Investigation of scaling laws for radiation temperature with shock wave velocity in Al

Jiang Shao-En, Li San-Wei

Acta Physica Sinica. 2009, 58 (12): 8440 doi: 10.7498/aps.58.8440
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The scaling laws of the radiation temperature with shock wave velocity in Al were simulated and investigated with one-dimensional radiation hydrodynamic program Hyades. The simulation results indicated that the formula T_r=0.0126D^0.63 could be valid for the radiation temperature generated by the shaped pulse of lasers such as PS22 and PS26 profile on Nova facilities and Shenguang Ⅲ Prototype （SGⅢ Prot）, but was not suited for the radiation temperature by laser pulse with the Gaussian and trapezoid profiles, for which the scaling should be given by the modified formula，which well agrees with similarity solution. Additionally, the minimum thickness sustaining stable shock wave velocity driven by the radiation temperature with the shaped profile on SGⅢ Prot was also obtained by using the Hyades code. Finally, The experiments of shock wave driven radiation were made on Shenguang Ⅱ laser facilities. The radiation temperature T_r calculated from the modified scaling relation well agreed with the T_r measured by the soft X-ray spectrometer. The experimental results also showed the reliability of the modified formula.

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Experimental study of large power lower hybrid current drive on HT-7 tokamak

Xu Qiang, Gao Xiang, Shan Jia-Fang, Hu Li-Qun, Zhao Jun-Yu

Acta Physica Sinica. 2009, 58 (12): 8448 doi: 10.7498/aps.58.8448
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Large power current drive of lower hybrid wave （LHW） was performed （P_LHW 100—800 kW at 2.45 GHz） recently in the HT-7 tokamak. The lower hybrid current drive （LHCD） efficiency is studied for different injected powers and for different densities. Improved particle confinement is observed by application of LHCD as characterized by an increase of central line average electron density and decrease of D_α emission. The particle confinement time τ_p increased about 1.5 times compared with ohm discharge. The dependence of energy confinement time τ_E on plasma density and LHW power is experimentally studied in detail.

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Generation of plasma current under arbitrary strong direct current electric field

Weng Su-Ming, Sheng Zheng-Ming, Zhang Jie

Acta Physica Sinica. 2009, 58 (12): 8454 doi: 10.7498/aps.58.8454
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The generation of plasma current and the evolution of electron distribution under arbitrarily strong direct current electric fields have been studied by Fokker-Planck simulation. It is found that the behaviors of plasma are different under different fields: in the weak field, Spitzer’s law is suitable for describing the relationship between plasma current and electric field, and the response time to generate current is approximately equal to the relaxation time to reduce current after switching off the electric field; in the moderate field, the electron distribution is well represented by the sum of a stationary and drifting Maxwellian, and the relaxation time is much longer than the response time. According to the detailed knowledge of electron distributions, a set of hydrodynamic-like equations, similar to Spitzer’s but without the weak-field limit, is given for calculating the current. It is more suitable for application in hybrid particle-in-cell simulations.

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Spatial distributions of the intensity of luminescence and the vibrational temperature of single micro-discharge channel in air dielectric barrier discharge

Dong Li-Fang, Yang Li, Li Yong-Hui, Zhang Yan-Zhao, Yue Han

Acta Physica Sinica. 2009, 58 (12): 8461 doi: 10.7498/aps.58.8461
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A stable micro-discharge channel（filament）in air discharge is obtained by discharge cleaning method in a dielectric barrier discharge system with two water electrodes. The distributions of intensity of luminescence and the vibrational temperature of a single micro-discharge filament are measured from instantaneous anode to instantaneous cathode. It is found that the emission intensity of discharge filament presents a distribution like a goblet with base locating at instantaneous cathode in each half period of the applied voltage. The vibrational temperature reaches the maximum at the middle of gap of the two parallel electrodes and is the minimum at the instantaneous anode.

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Soliton-like homotopic approximate analytic solution for a class of disturbed nonlinear evolution equation

Shi Lan-Fang, Mo Jia-Qi

Acta Physica Sinica. 2009, 58 (12): 8123 doi: 10.7498/aps.58.8123
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The approximate solution for a class of disturbed nonlinear evolution equation is considered taking a simple and valid technique. We first introduce approximate solution of a corresponding typical differential equation. And then the approximate solution for a original disturbed nonlinear evolution equation is obtained using the homotopic mapping method.

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Nonergodicity of Brownian motion in a periodic potential

Lu Hong, Qin Li, Bao Jing-Dong

Acta Physica Sinica. 2009, 58 (12): 8127 doi: 10.7498/aps.58.8127
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Nonergodicity in Brownian dynamics can be divided into two classes by adding a periodic potential in a force-free ballistic diffusive system. Class-Ⅰ is the system in which the Laplace transform of the damping kernel is equal to zero at low frequency. When the temperature is much higher than the barrier height, the kinetic part of the mean energy depends on the initial distribution of the velocity; with the temperature decreasing, the ergodicity is recovered. Thinking the stable velocity variance of class-Ⅰ as an internal noise to drive a force-free Brownian particle, the Laplace transform of the damping kernel is infinite at zero frequency. It is found that the diffusion coefficient approaches vanishing with the temperature increasing, which exhibits the characteristic of classical locality. The asymptotic mean-square coordinates of the class-Ⅱ depends on its initial coordinates and the ergodicity cannot be ensured through introducing a potential.

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Chaotic control of permanent magnet synchronous motor based on washout filter technique

Li Chun-Lai

Acta Physica Sinica. 2009, 58 (12): 8134 doi: 10.7498/aps.58.8134
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A chaos control method is presented in the paper for the permanent magnet synchronous motor （PMSM）, which uses the current of the PMSM as its feedback based on washout filter technique. Only the parameter of the filter is needed and no parameter of the original system will be affected by using the controller. Simulation result presents the simplicity, effectiveness and robustness of the method.

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Scheme for doubling the number of wings in hyperchaotic attractors

Hu Guo-Si

Acta Physica Sinica. 2009, 58 (12): 8139 doi: 10.7498/aps.58.8139
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The construction methods for designing multi-wing attractors are rarely mentioned little. With the application of coordinate translation, mirror mapping and hysteresis switching to an existing five-dimensional hyperchaotic system, we can double the number of wings and a four-wing attractor is realized. If similar operations have been applied to the system n-1 times, a 2ⁿ-wing attractor can be constructed. A simple circuit implementation was designed for doubling the number of wings in attractors. On the basis of preserving the hyperchaotic property of resulting system, the complexity of attractor is enhanced and it is more suitable for use in secure encryption communication.

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Analysis of chaos and circuit implementation of a permanent magnet synchronous motor

Xue Wei, Guo Yan-Ling, Chen Zeng-Qiang

Acta Physica Sinica. 2009, 58 (12): 8146 doi: 10.7498/aps.58.8146
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The permanent magnet synchronous motor, which is a nonlinear dynamic system, can exhibit a variety of chaotic or limit cycle phenomenon under some choices of system parameters and external inputs, and its chaotic characteristics are more prominent. Based on the mathematical model of a permanent magnet synchronous motor, its nonlinear characteristics are analysed with respect to the bifurcation diagram, Lyapunov exponent map and the nature of its equilibrium point in this paper, and the results in well demonstrated by numerical simulations. Finally, an analog electronic circuit is designed to implement the mathematical model of a permanent magnet synchronous motor, and the experimental results of the system well agreed with the simulation results.

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Three-dimensional four-wing generalized augmented Lü system

Qiao Xiao-Hua, Bao Bo-Cheng

Acta Physica Sinica. 2009, 58 (12): 8152 doi: 10.7498/aps.58.8152
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The augmented Lü system is a three-dimensional chaotic system, which can generate a false 4-wing attractor with only two control parameters. By using the method of anti-control chaos, a new three-dimensional chaotic system, named as generalized augmented Lü system, is proposed by the introducing a simple linear state controller into the augmented Lü system. The new system implements a real 4-wing attractor with compound structure and contains two mirrored symmetrical sub-system. By either of theoretical analyses, numerical simulations and circuit experiments, the existence of 4-wing chaotic attractor evolved from the generalized augmented Lü system is verified. It is also elaborated that the generalized augmented Lü system having more abundant dynamical behaviors than the augmented Lü system.

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Multiscale base-scale entropy analysis of heart rate variability

Huang Xiao-Lin, Cui Sheng-Zhong, Ning Xin-Bao, Bian Chun-Hua

Acta Physica Sinica. 2009, 58 (12): 8160 doi: 10.7498/aps.58.8160
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Multiscale base-scale entropy （MBE） is used to analyze heart beat interval series of both congestive heart failure （CHF） sufferers and the healthy people. The results indicate that, in contrast to the higher base-scale entropy（BE） value in short time scale, the data of CHF sufferers have actually lower BE value compared with those of the healthy people in long time scale. This supports the view that CHF patients’ heart beats are more random in short time scale due to impaired cardiac dynamic system, but are not versatile enough in long time scale to adapt to external impacts. More importantly, we found that δ, a parameter in MBE analysis, can be used to distinguish effectively the CHF patients from the healthy, which is proved in analysis of a database containing 72 healthy people and 44 CHF sufferers.

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Numerical solution of the three-dimensional time-dependent Schr?dinger equation and its application

Zeng Si-Liang, Zou Shi-Yang, Wang Jian-Guo, Yan Jun

Acta Physica Sinica. 2009, 58 (12): 8180 doi: 10.7498/aps.58.8180
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We present an accurate and effective pseudospectral method for solving the three-dimensional time-dependent Schrdinger equation involving the Coulomb potential. In this method, the Hamiltonian is evaluated by exploiting the two representations of the wave function. One is a grid representation, in which the angular dependence of the wave function is expanded in a two-dimensional Gauss-Legendre-Fourier grid in the coordinate space of polar and azimuthal angles. The radial coordinate is discretized using a discrete variable representation constructed from the Coulomb wave function （CWDVR）. The other is a spectral representation, in which the wave function is expanded in a set of square integrable functions chosen as the eigenfunctions of a zero-order Hamiltonian. The time of propagation of the wave function is calculated using the well-known second-order split-operator method implemented through the transform between the grid and spectral representations. Calculations on the photo-absorption strength of hydrogen atom are presented to demonstrate the accuracy of present method in low energy limit by the time-dependent wave-packet propagation method. As another example, the present method is applied to multiphoton ionization of H atom. For a wide range of field parameters, ionization rates calculated using the present method are in excellent agreement with those from other accurate numerical calculations. The new algorithm will be found more efficient than the close coupled wave packet method using CWDVR and/or methods based on evenly spaced grids.

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Molecule structure and analytical potential energy function for the ground state of MgB₂

Ruan Wen, Hu Qiang-Lin, Xie An-Dong, Yu Xiao-Guang, Luo Wen-Lang, Zhu Zheng-He

Acta Physica Sinica. 2009, 58 (12): 8188 doi: 10.7498/aps.58.8188
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Ab initio methods and density functional theory B3LYP with QCISD/6-311++G** basis set have been used to calculate the equilibrium geometries and vibrational properties of the possible structures and electronic states of MgB₂ molecule. The present computational results predict that the ground electronic state is the triplet state ³B₁ of C_2v （B—Mg—B） with equilibrium geometry R_e=2.2977，α_BMgB=41.5521° and the energy of the ground state ³B₁ is -248.9645 a.u.. Similarly, the harmonic frequency has been calculated. Then, the analytic potential energy function of MgB₂ molecule is derived by many-body expansion theory for the first time. The contours of the potential energy surface are constructed, which clearly reproduce the character of the accurate equilibrium structure and dissociation energy for MgB₂ molecule. Furthermore, the molecular static reaction pathway is investigated based on this potential energy function.

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Zheng Yu-Jun, Zhang Zhao-Yu, Zhang Xi-Zhong

Acta Physica Sinica. 2009, 58 (12): 8194 doi: 10.7498/aps.58.8194
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In this paper, we study the similarity of high-order cumulants of single molecule kinetics based on the generating function approach developed recently. The high-order cumulants have their differences for the different models compared with single molecule kinetics although the generating functions of the models are of the maximum similarity.

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Focusing characteristic of chromium atoms under elliptical standing wave

Zhang Wen-Tao, Zhu Bao-Hua, Xiong Xian-Ming

Acta Physica Sinica. 2009, 58 (12): 8199 doi: 10.7498/aps.58.8199
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Direct-write atom lithography is a new technique in which resonant light is used to pattern an atomic beam and the nanostructures are formed when the atoms are deposited on the substrate. The characteristics of chromium atoms deposit on a substrateare are discussed. We simulated and analysed the characteristics of nanostructure under different laser power and on different y-plane. At the same time, the characteristics of nanostructure are analysed with respect to the effects of atomic beam divergence, the resulting full width at half maximum and contrast are shown under respective conditions.

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Investigation of atom-optical properties of laser focused Cr atomic deposition

Lu Xiang-Dong, Li Tong-Bao, Ma Yan, Wang Li-Dong

Acta Physica Sinica. 2009, 58 (12): 8205 doi: 10.7498/aps.58.8205
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Gating structure of one dimensional Cr layer is experimentally obtained through the technology of laser focused atomic deposition. The periodicity of grating is （212.8±0.2） nm measured by atomic force microscope, which is just equal to half of the wavelength of laser standing-wave field. Then, based on the semiclassical model and numerical calculation of the Adams-Bashforth-Moulton algorithm, both Cr atom motion trajectories are simulated and the atom-optical properties are analyzed at the same experimental conditions. The results show that the analytical results agree well with the experimental results.

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Propagation property of ultra-short laser pulses in multi-level quantum system

Lu Jian-Qing, Zhang Xiang-Yun, Zhang Shi-An, Jia Tian-Qing, Sun Zhen-Rong, Wang Zu-Geng

Acta Physica Sinica. 2009, 58 (12): 8212 doi: 10.7498/aps.58.8212
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The propagation property of an ultrashort pulse in multi-level quantum system has been investigated with numerical method. A strong absorption is observed and its degree depends on the characteristic time of quantum system. For rather weak laser field, the self-induced transparency can still be observed with proper pulse area of the input ultrashort laser. When the ultrashort laser pulse becomes stronger, it will be split, and its basic split unit （i.e. the minimum area of a stably propagating laser pulse） A₀ is not the same as that of two-level quantum system, which depends on the number of the excited states and their dipoles. Furthermore, after a rather long propagating distance, there only remains a shorter but more intense sub-pulse with an area of A₀.

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Theoretical study on molecular reaction dynamics of the SiH₂ system

Feng Xing, Zhu Zheng-He, Liu Xiao-Ya, Yang Xiang-Dong, Huang Wei

Acta Physica Sinica. 2009, 58 (12): 8217 doi: 10.7498/aps.58.8217
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The atomic and molecular reaction dynamics for Si（¹D_g）+H₂（0，0）and H（²S_g）+SiH（0,0） have been studied on the potential energy function SiH₂（X¹A₁） by Monte-Carlo quasi-classical trajectory approach.It is shown that the reaction Si（¹D_g）+H₂（0，0）has no threshold energy，and the principal product of this reaction is SiH₂（X¹A₁）.However, the reaction H（²S_g）+SiH （0,0） gives a great number of products of the interchange reaction of H（²S_g）+SiH （0,0）→Si（¹D_g）+H₂（0，0），and it has also no energy threshold.

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Density functional study of CO₂ adsorption on Pu(100) surface

Meng Da-Qiao, Luo Wen-Hua, Li Gan, Chen Hu-Chi

Acta Physica Sinica. 2009, 58 (12): 8224 doi: 10.7498/aps.58.8224
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The adsorption of CO₂ on Pu（100） surface has been studied with periodic slab model by revised Perdew-Burke-Ernzerh approximation within the framework of density functional theory. The optimized results of adsorption energies and geometrical structures show that the H-C4O4-type adsorption is optimum adsorption mode with adsorption energy of 1.48 eV. The atomic population and density of states analysis indicate that the interaction between Pu atom and CO₂ molecule results mainly from strong electron transfer and weak overlap-hybridization between molecular orbital 2π_μ of CO₂ molecule and Pu5f, Pu6d and Pu7s orbitals of surface Pu atom. The calculated activation barrier and adsorption energy CO₂→CO+O dissociative reaction are 0.66 and 2.65 eV, respectively, which indicates the dissociative adsorption of CO₂ on Pu（100） surface is favorable under the certain heat activation condition. The comparison of O₂，H₂，CO and CO₂ adsorption on Pu（100） surface indicates the adsorption strength follows the ordering: O₂，CO，CO₂，H₂ and O₂，CO₂，CO，H₂ at lower and higher temperature, respectively.

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Dependence of sensitivity of atom interferometer gravimeters on the Raman laser pulse sequences ^Hot!

Ren Li-Chun, Zhou Lin, Li Run-Bing, Liu Min, Wang Jin, Zhan Ming-Sheng

Acta Physica Sinica. 2009, 58 (12): 8230 doi: 10.7498/aps.58.8230
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We investigate the dependence of the sensitivity of atom interferometer gravimeter on the Raman laser pulse sequence. The sensitivity of atom gravimeter can be adjusted by changing the pulse duration. Under the standard pulse configuration condition, the atom interferometer with four pulses is insensitive to the gravity if only gravity and its first order gradient are taken into account. The three-pulse Raman atom interferometer gravimeter displays best sensitivity. Atom interferometers with more than four Raman pulses show poorer sensitivity.

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Density functional theory study of the interaction of H₂ with rhodium clusters

Ge Gui-Xian, Cao Hai-Bin, Jing Qun, Luo You-Hua

Acta Physica Sinica. 2009, 58 (12): 8236 doi: 10.7498/aps.58.8236
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The adsorption for H atoms on the Rh_n cluster has been systematically investigated by density functional theory. The result indicates that the lowest energy structures of Rh_nH₂ are generated with H atoms being adsorbed on the lowest energy structure of Rh_n clusters, and the lowest energy structures of Rh_n clusters are not changed by adsorbing H atoms. The total magnetic moment is affected by average bond distance. The chemisorption of H atoms on Rh_n clusters belongs to dissociative adsorption. When H₂ is absorbed on the Rh_n clusters, the stability and chemical action of corresponding clusters are dramatically increased. The second order difference indicates 4 is magic number in Rh_nH₂ and Rh_n clusters. Among various possible adsorption sites, bridge site is energetically preferred for n≤5. The hollow site adsorption appears for n≥6.

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Synthesis and electric, magnetic properties of single crystalline and twin-crystalline Co-doped ZnO thin films

Lu Zhong-Lin, Zou Wen-Qin, Xu Ming-Xiang, Zhang Feng-Ming

Acta Physica Sinica. 2009, 58 (12): 8467 doi: 10.7498/aps.58.8467
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c-oriented Co-doped ZnO （Zn_0.96Co_0.04O） thin films have been grown on the a-plane and c-plane sapphire substrates using molecular-beam epitaxy, respectively. In contrast to single crystalline Zn_0.96Co_0.04O film grown on a-plane sapphire, the film grown on c-plane sapphire were found to be twin-crystalline; some domains have a 30° rotation to reduce the large mismatch. The presence of these rotation domains in the twin-crystalline ZnO thin film causes much more carrier scattering at the boundaries, leading to much lower mobility and smaller mean free path of the mobile carriers, as compared with those of the single crystalline one. X-ray absorption fine structure studies revealed that most Co ions were in divalent state and actually substituted into ZnO lattice without formation of any detectable secondary phase. As compared with just a small saturation moment in the single crystalline Zn_0.96Co_0.04O thin film, the much stronger ferromagnetism in the twin-crystalline one indicates that the ferromagnetic origin should be highly correlated with structural defects in the twin-crystalline film. The possible magnetic mechanisms were discussed.

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Using conductive atomic force microscope on carbon nanotube networks

Zhao Hua-Bo, Li Zhen, Li Rui, Zhang Zhao-Hui, Zhang Yan, Liu Yu, Li Yan

Acta Physica Sinica. 2009, 58 (12): 8473 doi: 10.7498/aps.58.8473
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Conductive atom force microscopy observations have been performed on carbon nanotube networks. The results indicate that within an imaging range of several tens of micrometers the resistance of a carbon nanotube is much smaller than the contact resistance between two crossed carbon nanotubes and so the potential difference hardly appears along a carbon nanotube if the carbon nanotube network is electrically biased. Besides, if several semiconducting carbon nanotubes wind into a bundle, they tend to appear like metallic carbon nanotubes.

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Pore structure determination of mesoporous SiO₂ thin films by slow positron annihilation spectroscopy ^Hot!

Wang Qiao-Zhan, Yu Run-Sheng, Qin Xiu-Bo, Li Yu-Xiao, Wang Bao-Yi, Jia Quan-Jie

Acta Physica Sinica. 2009, 58 (12): 8478 doi: 10.7498/aps.58.8478
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Mesoporous silica thin films with different pore shapes were prepared by evaporation induced self-assembly method. The synchrotron radiation x-ray reflectivity and slow positron annihilation techniques were used to characterize the pore structures. The results indicated that with increase of the spin-coating speed, the pore structure transformed from 3-D cubic to 2-D hexagonal, the average porosity also decreased. The correlation of the film structures and positron annihilation parameters was songht for with FT-IR spectroscopy and isotropic inorganic pore contraction model.

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Band structure of phononic crystal constructed by Fibonacci super-cell on square lattice

Hao Guo-Jun, Fu Xiu-Jun, Hou Zhi-Lin

Acta Physica Sinica. 2009, 58 (12): 8484 doi: 10.7498/aps.58.8484
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Using the plane-wave expansion method, we study the band structure of a phononic crystal with water rods embedded in mercury to form a super-cell according to the two-dimensional Fibonacci array. It is found that each band splits into three sub-bands with the change of quasilattice constants and there exist intermediate states, which reflect the peculiar properties of quasiperiodic systems.

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Electrical properties of the deformed carbon nanotube field-effect transistors

Liu Hong, Yin Hai-Jian, Xia Shu-Ning

Acta Physica Sinica. 2009, 58 (12): 8489 doi: 10.7498/aps.58.8489
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On the basis of the tight-binding theory, we derive the band structure formula of the deformed carbon nanotube. The results show that the band gap varies with increasing deformation, which shows that the deformation can change the nature of the conductivity of carbon between the metal-type and semiconductor-type. Especially for zigzag nanotubes，there are three different rules goveoning this translation, which is dependent on the remainder of n divided by 3. Furthermore, by using Natori theory on the field-effect transistor we study the current-voltage characteristics of deformed carbon nanotube field-effect transistors. For strain deformation, the conductivity of zigzag nanotube presents different characteristics with the remainder of n by 3. For armchair nanotubes, the conductivity does not change with the strain parameter. However, for torsion deformation, the conductivity rapidly increases, specially for the armchair tube. It has many obviously different conductivity behaviors between zigzag tubes and armchair tubes. At some special torsion angles, the conductivity of zigzag tube and armchair tube has obvious changes, which reveals the translation between metal-type and semiconductor-type conductivities.

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Structure and optical properties of Ni-doped ZnO films

Lan Wei, Tang Guo-Mei, Cao Wen-Lei, Liu Xue-Qin, Wang Yin-Yue

Acta Physica Sinica. 2009, 58 (12): 8501 doi: 10.7498/aps.58.8501
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ZnO:Ni films with different doping concentrations （0—7at.%） have been deposited by radio frequency magnetron sputtering. The results of x-ray diffraction, including θ-2θ mode and rocking curve mode, indicate that the film doped with 5at.% Ni shows an excellent preferred growth along c-axis orientation. The （002） diffraction peak shifts to a larger angle, which implies that Ni atoms are incorporated into the ZnO lattice. For ZnO:Ni films with good transparency in the visible range, the optical band gap evaluated by the fitting method decreases linearly from 3.272 to 3.253 eV with increasing Ni concentration. Undoped ZnO film exhibits a green emission peak and Ni-doped ZnO films mainly emit a blue photoluminescence centred at 430 nm, we believe that they might be ascribed to crystal defects of oxygen vacancies and interstitial zinc, respectively.

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Morphology and defect of a-GaN grown by metal orgamic chemical vapor deposition

Cui Ying-Chao, Xie Zi-Li, Zhao Hong, Mei Qin, Li Yi, Liu Bin, Song Li-Hong, Zhang Rong, Zheng You-Dou

Acta Physica Sinica. 2009, 58 (12): 8506 doi: 10.7498/aps.58.8506
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On the substrate of r-sapphires a-GaN films grown by metal orgamic chemical vapor deposition was etched in molten KOH-NaOH for 1.0,1.5 and 2.0 min. Scanning electron microscope, atomic force microscope, X-ray diffraction and cathodoluminescence was used to study its morphology and defect. We find that etching for 1.5 min at the temperature of 400 ℃ is appropriate for a-GaN on sapphires substrate. Different from c-GaN which show hexagonal pits, a-GaN shows parallelogram strips. In the direction of c axis it is easier to be etched. That is because the polarity of a-GaN films is anisotropic which leads to different absorption capacities of OH ions in different directions. We also find hexagonal protuberance on the surface which is associated with threading dislocations.

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Y elastic constants of polycrystalline materials with hexagonal system structure

Lin Zheng, Liu Min

Acta Physica Sinica. 2009, 58 (12): 8511 doi: 10.7498/aps.58.8511
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In this paper, the physical parameters Y elastic constants mewly proposed in our previous paper are applied to polycrystalline materials with hexagonal structure to deduce Y elastic constants thereof and to compare with the x-ray elastic constants of polycrystalline materials of hexagonal structure through calculation of examples. Though the expressions of mechanical elastic constants of polycrystalline materials deduced from the application of Y elastic constants are different from the conclusions of Kneer, the calculaled results for concrete materials are in full compliance.

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Energy dissipation mechanism of phononic friction

Ding Ling-Yun, Gong Zhong-Liang, Huang Ping

Acta Physica Sinica. 2009, 58 (12): 8522 doi: 10.7498/aps.58.8522
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Focusing on the interfacial friction, the energy accumulation and dissipation mechanisms are analyzed in the present paper. Based on the lattice thermokinetics theory, the potential difference of interfacial atom during the jumping process is calculated, then the formula of interfacial temperature rise is deduced successfully. The analysis indicates that the interfacial temperature depends on the contact status and material properties of the friction system, and the interfacial interactive potential is an important factor. In the initial stage of slipping process, as the interfacial atoms are in the non-equilibrium thermal state, new phonon are excited to enable the friction energy dissipation, which finally makes the non-thermal equilibrium transit to equilibrium state. Based on the quantum mechanics and the thermodynamics, the energy dissipation mechanism of interfacial friction is studied. The results show that the elastic potential energy stored during the sticking process dissipates more quickly with higher vibration frequency, and the dissipation time is much shorter than the slip time in one cycle.

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Numerical simulation of space charge packet behavior in low-density polyethylene under direct current voltage

Xia Jun-Feng, Zhang Ye-Wen, Zheng Fei-Hu, Lei Qing-Quan

Acta Physica Sinica. 2009, 58 (12): 8529 doi: 10.7498/aps.58.8529
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Packet-like space charge behavior is a kind of special transport behavior of space charge in polyethylene. It has been demonstrated that many factors, such as the intensity of applied field, temperature and material have great influence on the formation and migration of space charge packets. This would cause much difficulty in understaning the general mechanism of the phenomenon. In this paper, on the basis of analysis of charge injection and migration, the interaction between the charge and charge trap and the influence of electric field on charge trap level, a model is proposed to simulate the packet-like space charge behavior. We suppose thar there exists a negative differential relationship for the charge velocity against the electric field when the electric ficld exceeds a threshold value. By considering the negative differential relationship, we simulated various kinds of packet-like charge behaviors and the results of numerical simulation show a good agreement with the experimental results issued by different research groups.

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Effect of the non-nearest-neighbor hopping on the electronic structure of armchair graphene nanoribbons

Jin Zi-Fei, Tong Guo-Ping, Jiang Yong-Jin

Acta Physica Sinica. 2009, 58 (12): 8537 doi: 10.7498/aps.58.8537
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Based on the tight-binding model, the non-nearest-neighbor hopping terms of electrons are taken into account and the energy spectra of the armchair graphene nanoribbons （AGRNs） are given analytically. The changes of the energy band and the gap with the non-nearest-neighbor terms are discussed. The results show that the next-nearest-neighbor term can increase the gap and the third-nearest-neighbor term can narrow the gap. The competition relationship between the edge relaxation and the non-neighbor term is compared. When the width n is odd, the van Hove singularity from graphene sheets leads to the dispersion-less band. When the width of AGRNs goes to infinity, the spectrum of AGRNs tends to that of graphene sheets.

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Mechanical and electronic properties of TiO₂ nanotubes

Lin Feng, Li Zuan-Yi, Wang Shan-Ying

Acta Physica Sinica. 2009, 58 (12): 8544 doi: 10.7498/aps.58.8544
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The structure, stability, Youngs modulus and electronic band structures of lepidocrocite-type and anatase-type TiO₂ nanotubes were investigated using density functional theory calculation. It was found that the anatase-type nanotubes were energetically more favorable than lepidocrocite-type nanotubes when the diameter of nanotube is small, whereas the lepidocrocite-type nanotubes were energetically more favorable when the diameter of nanotube was large. Youngs modulus of TiO₂ nanotubes is calculated. The results obtained show that all TiO₂ nanotubes have relatively good mechanical properties, and lepidocrocite nanotubes are stronger than anatase nanotubes. Interestingly, it was found that the electronic band structures of TiO₂ nanotubes are influenced by the tubular chirality. Lepidocrocite （0, n） and anatase （n, 0） nanotubes are of indirect band gap type, whereas lepidocroctie （n, 0） and anatase （0, n） nanotubes have direct band gaps.

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Negatively charged exciton on the quantum ring

Wu Hong

Acta Physica Sinica. 2009, 58 (12): 8549 doi: 10.7498/aps.58.8549
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In this paper, the energy-optical spectra and their Aharonov-Bohm oscillation of the negatively charged exciton are studied. A negatively charged exciton is composed of three charge particles, electrons and hole, the number of basic wave functions （basic vectors） which compose the state wave functions are large, so the numerical computing work is quite tedious. So far, many authors usually separate the spatial wave function into motion of mass centre and relative motion parts to save the numerical computing time. There is considerable discrepancy in the results of this method. It only suits the case when the external magnetic field is very weak. Considering the conservation of angular momentum, in case that there is no external electric field, we classity the whole set of basic vectors according to the values of their total orbital angular momentum. Then starting from Hamiltonian directly, we propose an alternative computing method to find the eigen values and eigen functions of the system. Our method can save more than 90% of computer time. There is no so called diamagnetic shift in our results. Our results fit well with the experimental data. The effects of the radii of the quantum ring, the value of dielectric constant and the effective mass of hole on the energy-optics spectra are systematically discussed.

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Characteristics of photoconductivity oscillation in semi-insulating GaAs photoconductive semiconductor switches

Shi Wei, Xue Hong, Ma Xiang-Rong

Acta Physica Sinica. 2009, 58 (12): 8554 doi: 10.7498/aps.58.8554
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The 4 mm gap and 5 ns pulse width semi-insulating GaAs photoconductive switches were triggered by 532 nm laser pulse with gradual increase of bias voltage from 500 V in steps of 50 V until the emergence of nonlinear electrical pulse. The expermental results showed that the linear and nonlinear electrical pulse waveforms had smaller amplitude and varying degrees of oscillation reduction after going through a main pulse. Then the microscopic state and transport process of carriers （hot-electron） in the switch material were studied in detail using the quantum theory. It was found that in the DC bias electric field, when the relaxation time of the hot-electrons in the electron-electron and electron-phonon interaction process is longer than the carrier life, the photoconductivity oscillation can be caused by the change of mobility in the process of optoelectronic transport, which is the main cause for the output electrical pulse to show oscillations.

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Electronic noise of diluted magnetic semiconductor (Ga,Mn)As around Curie point

Yang Wei, Ji Yang, Luo Hai-Hui, Ruan Xue-Zhong, Wang Wei-Zhu, Zhao Jian-Hua

Acta Physica Sinica. 2009, 58 (12): 8560 doi: 10.7498/aps.58.8560
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We have studied the spontaneous fluctuation noise spectrum of （Ga,Mn）As in frequency domian from 1 kHz to 250 kHz. We found that the electronic noise can be reduced by a magnetic field and its magnitude increases with increasing temperature of the （Ga,Mn）As sample. The electrical noise spectra at different frequencies have different temperature dependence and their amplitude changes at the phase transition temperature, suggesting that the phase transition process of （Ga,Mn）As is subtly different from normal magnetic materials. Our results may help understanding the origin of magnetism in （Ga,Mn）As.

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High mobility polymer thin-film transistors

Liu Yu-Rong, Wang Zhi-Xin, Yu Jia-Le, Xu Hai-Hong

Acta Physica Sinica. 2009, 58 (12): 8566 doi: 10.7498/aps.58.8566
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Polymer-based thin film transistors （PTFTs） were successfully fabricated on silicon substrates which was used as gate electrode, thermal silicon dioxide was used as gate insulators and poly（3-hexylthiophene） as semiconducting active layers for the transistors. The fabrication and measurement of the devices were all performed in the clean air. The PTFTs with a surface-modified gate insulator show better electric characteristics with the field-effect mobility of 0.02 cm²/（Vs） and the on/off ratio higher than 10⁵.

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Influence of groove in metallic subwavelength slit on transmission properties

Zheng Xian-Hua, Wang Ying-Qi, Zhang Yan

Acta Physica Sinica. 2009, 58 (12): 8571 doi: 10.7498/aps.58.8571
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The influence of the structure and position of groove in a two-dimensional metallic subwavelength slit on transmission properties has been studied with the finite-difference time-domain method. The whole structure of slit with perpendicular groove could be regard as a LC oscillation circuit. The capacitance and inductance of this oscillation circuit will be altered when the structure of groove varies，so that the resonant transmission peaks shift. And the drive source of circuit changes when the position of groove moves along the slit, as a result the distribution of electromagnetic filed in the structure is changed also. So the resonant transmission peaks are split. In this paper， the change of resonant transmission peaks as each parameter of the groove changes is analyzed with the principle of LC resonance.

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Electronic transport properties of the multilayer structure double spin-filter tunnel junction

Jin Lian, Zhu Lin, Li Ling, Xie Zheng-Wei

Acta Physica Sinica. 2009, 58 (12): 8577 doi: 10.7498/aps.58.8577
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Based on the transfer matrix method and the quantum coherent transport theory of Mireles and Kirczenow, the effects of the Rashba spin-orbit coupling and the spin-filter on the electronic transport properties in the NM/FS1/I/FS2/NM（NM represents the nonmagnetic metal layer, I represents the nonmagnetic insulator layer, and FS represents the magnetic semiconductor layer）double spin-filter tunnel junction are investigated. The influence of thickness of insulator layer and magnetic semiconductor layer on the tunnel magnetoresistance （TMR） and conductance are studied for different Rashba spin-orbit coupling strength and the different angle θ between the two magnetic moments of the left and right magnetic semiconductor layer. The results indicate that: in the presence of the spin-filter effect and the Rashba spin-orbit coupling interaction in the magnetic semiconductor layer, large TMR can be obtained in this double spin-filter junction. With the strength of Rashba spin-orbit coupling increasing, the tunnel magnetoresistance and conductance exhibit rapidly oscillating behavior and the oscillation period decreases gradually.

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A physical-model of small-signal InP-based double heterojunction bipolar transistors and its parameter extraction technique

Ge Ji, Jin Zhi, Su Yong-Bo, Cheng Wei, Liu Xin-Yu, Wu De-Xin

Acta Physica Sinica. 2009, 58 (12): 8584 doi: 10.7498/aps.58.8584
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The influence on the base-collector junction capacitance C_bc of the energy band structure of the InP heterojunction bipolar transistors is researched. A physical model of small-signal InP double heterojunction bipolar transistor （DHBT） is developed, which takes into account the base-emitter and collector-emitter metalisations by using two additional capacitances C_mb and C_mc. The resistance of the model is divided into the intrinsic resistance, the extrinsic resistance and the parasitic resistance. Meanwhile, a physically meaningful small-signal parameter extraction procedure for the model is presented, in which all the equivalent circuit elements are extracted without reference to numerical optimization. An experimental validation is carried out, and excellent results are obtained over a wide range of bias points, which demonstrates good modeling accuracy.

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Current phase relation in the superconducting tunnel junction

Wu Yi-Hua, Wang Zhen-Yan, Shen Rui

Acta Physica Sinica. 2009, 58 (12): 8591 doi: 10.7498/aps.58.8591
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The dc Josephson current in the equal spin pairing superconducting tunnel junction is calculated in this paper. It is shown that the current phase relation is I∝sin 4φ when the orbital pairing symmetries of the two superconductors fall into the irreducible representations A and ²E of the magnetic point group D₄, respectively.

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Two-step thermoelastic martensitic transformation and stress-strain characteristic of Ni_53.2Mn_22.6Ga_24.2 single crystal

Cui Yu-Ting, You Su-Qin, Wu Liang, Ma Yong, Chen Jing-Lan, Pan Fu-Sheng, Wu Guang-Heng

Acta Physica Sinica. 2009, 58 (12): 8596 doi: 10.7498/aps.58.8596
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Physical properties of the two-step complete thermoelastic Ni_53.2Mn_22.6Ga_24.2 single crystal are investigated by various measuring methods, especially, the stress-strain characteristic at different temperatures is studied. The results show that at low deformation temperatures the pressing stress along the ［001］ direction of the parent phase would induce a two-step martensitic transformation, and the alloy exhibits pseudoelastic characteristics. But at relatively high temperatures, the alloy exhibits complete superelastic characteristics, and only one-step martensitic transformation is observed. Furthermore, the dependence of critical stress on the deformation temperature for the martensitic transformation and intermartensitic transformation is calculated by the thermodynamic theory, and the result is consistent with that of two-step martensitic transformation obtained by experiment.

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Structure and properties of the ferromagnetic shape-memory alloy Co₅₀Ni₂₀Ga_30-xSi_x

Dai Xue-Fang, Sun Chen-Guang, Qu Jing-Ping, Li Yang-Xian, Zhu Wei, Chen Jing-Lan, Wu Guang-Heng

Acta Physica Sinica. 2009, 58 (12): 8602 doi: 10.7498/aps.58.8602
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The structure，martensitic transformation and magnetism have been studied in the CoNiGa alloys after certain Ga substrated by Si. From the experimental results，we found that the alloy can form pure body-centered cubic structure accompanied by good thermal martensitic transformation when the atom ratio of Si lies in the range 0—10%. It can be concluded from further analysis that it is not only the radius of the doped atom but also the radius ratio of the doped atom and the host atom that affect the stability of the austenite. At the same time，it can be found that the Curie temperature and the saturated magnetization decrease with increasing Si. But the anisotropy of the martensite increases with the increasing Si，which is of significance for obtaining large magnetically-induced-strain.

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Electric field-controlled permeability and impedance in a heterotypic composite of ferroelectrics/magnet with high permeability

Gao Jian-Sen, Zhang Ning

Acta Physica Sinica. 2009, 58 (12): 8607 doi: 10.7498/aps.58.8607
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Using the product effect of electrostrain and piezopermeability, a novel and heterotypic composite of magnet/ferroelectrics has been developed and its electromagnetic coupling has been investigated. Under a constant electric field of 5 kV/cm, about 40% electric-field-induced changes of inductance and impedance have been observed over a wide range of frequency for the composites. The electric-field dependent inductance and impedance show a joint behavior of ferromagnetic and ferroelectric relaxation. Analysis shows that all the behaviors observed can be ascribed to the electric field-controlled variation of the internal stress in the composite.

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Synthesis of silicon oxide nanocluster and C-Si-O nanospheres morphology and photoluminscence Fourier transform infrared spectroscopy study

Zheng Li-Ren, Huang Bai-Biao, Wei Ji-Yong

Acta Physica Sinica. 2009, 58 (12): 8612 doi: 10.7498/aps.58.8612
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Silicon oxide nanocluster and C-Si-O nanospheres are fabricated by the chemical vapor deposition method at 1100℃，in flowing N₂/H₂ atmosphere using the ferrcene and the silicon oil （201） as the raw material and the catalyzer, respcetively. The silicon oxide nanowires are uniform with diameter of 5—40 nm and length up to hundreds of nanometer. The diameter of the C-Si-O solid-nanospheres is 100—300 nm. SEM，TEM，EDS，FTIR and PL were used to characterize the microstructure，composition and optical propertics of the nanocluster and the C-Si-O nanospheres. Energy dispersive X-ray spectrum analysis reveals that the C-Si-O nanospheres consist of C，Si and O elements in an atomic ratio of approximately 1.13∶1∶2.35. The nanoclusters show IR absorption peaks at 474，802 and 1100 cm^-1. The PL peak of the nanoclusters is at 440 nm. It is very curious that the PL of the C-Si-O solid-nanospheres possesses the red，green and blue——trichromic luminescent peeks.

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Excitation processes of up-conversion green emission for Er³⁺ and Yb³⁺ codoped tellurite glass

Dong Li-Qiang, Huang Shi-Hua, Wen Hong-Yu, Yang Yan-Min, Wang Da-Wei, Duan Xiao-Xia

Acta Physica Sinica. 2009, 58 (12): 8617 doi: 10.7498/aps.58.8617
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This paper analyzed the build-up characteristics of Er³⁺ ⁴S_3/2 and the relationships between Er³⁺ ⁴S_3/2，⁴I_11/2 and Yb³⁺ ²F_5/2 according to the energy structure for green up-conversion emission and relative transition rating function model for Er³⁺-Yb³⁺ codoped tellurite glass. Through fitting the build-up and decay curves by the model the relative parameters for rating equation model were determined，and the relative value between energy transfer and excited state absorption when population of ⁴S_3/2 energy tend to be stable was calculated，also the dynamic processes in green up-conversion emission of Er³⁺-Yb³⁺ codoped tellurite glass were analyzed.

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Terahertz transmission properties of transparent conducting molybdenum-doped ZnO films

Wu Chen-Guo, Shen Jie, Li Dong, Ma Guo-Hong

Acta Physica Sinica. 2009, 58 (12): 8623 doi: 10.7498/aps.58.8623
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With direct current reactive magnetron sputtering method，transparent conducting molybdenum-doped ZnO （ZMO） thin films with different carrier concentration on glass substrate were fabricated by monitoring oxygen partial pressure. The dielectric responses of the ZMO films are characterized with terahertz time-domain spectroscopy. Frequency dependent conductivity，power absorption，and refractive index are obtained，and the experimental results can be well reproduced with classic Drude model. Our results reveal that，by adjusting the carrier concentration of ZMO film，the conducting ZMO film can serve as broadband antireflection coatings for substrates and optics in terahertz frequency range.

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High efficiency phosphorescence light-emitting diodes with conjugated polymer host

Niu Qiao-Li, Zhang Yong, Fan Guang-Han

Acta Physica Sinica. 2009, 58 (12): 8630 doi: 10.7498/aps.58.8630
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Polymer hosted phosphorescent light-emitting diodes （PLEDs） were attractive because of their high efficiency light-emission and easy fabrication technology using solution process. For green phosphorescence PLEDs，non-conjugated polymer，such as poly （N-vinylcarbazole）（PVK），were often used as host；while conjugated polymer have been proved to quench phosphorescence emission because of their low-lying triplet energy level. In this article，high efficiency phosphorescent green-emission was obtained with conjugated polymer of poly （9，9-dioctylfluorene）（PFO） as host using the device structure of ITO/poly （ehtlenedioxythiophene）: poly （styrene sulfonic acid）（PEDOT: PSS）（50 nm）/PVK （40 nm）/emissive layer （EML）（80 nm）/Ba （4 nm）/Al （150 nm）. The EML were PFO doped with different concentration of fac-tris （2-phenylpyridine） iridium （Ⅲ）（Ir（ppy）₃） in weight. The PLED with 2 wt% Ir（ppy）₃ demonstrated the maximum luminous efficiency of 24.8 cd/A at current density of 4.65 mA/cm² and power efficiency of 11 lm/w with the peak emission at 520 nm. The luminance reached 35054 cd/m² at the current density of 265 mA/cm². According to analyzsis，the hole transport layer PVK can play important role in obtaining highly efficient green light emissing，whose electrons blocking effect resulted in the interfacial emissing center, and then the interfacial PVK enhanced green emission through energy transfer due to its high triplet enery level.

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Emission properties of impregnated cathode with nanoparticle films

Liu Yan-Wen, Tian Hong, Han Yong, Zhu Hong, Li Yu-Tao, Xu Zhen-Ying, Meng Ming-Feng, Yi Hong-Xia, Lu Yu-Xin, Zhang Hong-Lai, Liu Pu-Kun

Acta Physica Sinica. 2009, 58 (12): 8635 doi: 10.7498/aps.58.8635
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The Ir nano particle thin film was grown by dcrect current magnetron sputtering at room temperature. Microstructure of thin films grown at different sputtering pressures were measured by scanning electron microscopy. The results show that the particle size of the films depends on the deposition rate in the nucleation stage of Ir films and the deposition rate can be well controlled by sputtering pressure. A new kind of cathodes are fabricated from 25% porous tungsten impregnated with 6∶1∶2-type barium calcium aluminate and coated with the nano particulate Ir thin film. The coating processes produces a film thickness of 200—500 nm and the cathodes are fired in hydrogen atmosphere for ten minutes at 1200℃ to further improve the coating microstructure. The cathodes have been studied with thermal electron microscope by which the electron-optical picture of a thermal emission cathode could be obtained. Time of flight mass spectrometer （ToFMS） has been used in a study of evaporation from impregnated cathodes. The chemical composition of evaporation of various impregnated cathodes have been measured by ToFMS. The variation of ion current of evaporants from S-type cathode and M-type cathode （coated with iridium） and n-type cathode （coated with iridium nano-particle thin film） with temperature and time have been studied and discussed. Emission current characteristics have been measured as a function of voltage and temperature.

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Revision of quantum efficiency formula for negative electron affinity photocathodes

Du Xiao-Qing, Chang Ben-Kang

Acta Physica Sinica. 2009, 58 (12): 8643 doi: 10.7498/aps.58.8643
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Quantum efficiency （QE） is one of the most important characteristics of photoemission performance of negative electron affinity （NEA） photocathodes. The quantum efficiency formulas for NEA photocathodes show the influences of photocathode parameters on photoemission performance and also provide theoretical guidance for optimum design of photocathodes. The photoemission process in bulk and surface of NEA photocathodes is firstly analyzed. Surface electron escape probability and attenuation length are respectively revised considering the effects of incident photon energy，surface band bending region and surface barrier on photoemission. The quantum efficiency formulas for NEA photocathodes are established by integration method. The theoretically estimated QE curve is consistent with the experimental one，which validates the practicability of the revised QE formula. This work can provide theoretical references for research of NEA photocathodes.

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Three-dimensional numerial simulation of single event upset effects in static random access memory

Zhang Ke-Ying, Guo Hong-Xia, Luo Yin-Hong, He Bao-Ping, Yao Zhi-Bin, Zhang Feng-Qi, Wang Yuan-Ming

Acta Physica Sinica. 2009, 58 (12): 8651 doi: 10.7498/aps.58.8651
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Three-Dimensional model of static random access memory （SRAM） six-transistor cell is generated by three dimensional process simulator FLOOPS, and device simulator DESSIS is used to simulate the single-event upset effect in SRAM. Single-event upset and charge collecting maps are calculated directly from 3-D simulations. Single event upset maps and cross-section curves obtained from numerial simulation show excellent agreement with broad beam cross section curves and micro-beam upset images for 2 kbit hardened SRAM. It indicates that the three-dimensional model could be used to research the single event upsets in SRAM.