Acta Physica Sinica

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Dynamic range of X-ray streak camera affected by space charge effect

Yuan Yong-Teng, Hao Yi-Dan, Zhao Zong-Qing, Hou Li-Fei, Miao Wen-Yong

Acta Physica Sinica. 2010, 59 (10): 6963 doi: 10.7498/aps.59.6963
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x ray streak camera is an important equipment for time resolved measurement in the field of inertial confinement fusion. Its dynamic range indicates the ability that effectively measuring the intensity of incidence x ray. The photoelectron pulse will be broaden in passing through the photocathode-to-mesh region because of space charge effect. This limits the dynamic range of the streak camera. This paper adopts a fluid model, making use of particle conservation, momentum conservation, and Poisson equations to deduce the widening of the electron pulse and derive the change in the electron density distribution. The results can be used to evaluate the dynamic range of the streak camera.

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Time-domain inverse scattering problem for two-dimensional frequency-dispersive lossy media

Liu Guang-Dong, Zhang Ye-Rong

Acta Physica Sinica. 2010, 59 (10): 6969 doi: 10.7498/aps.59.6969
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A time-domain inverse scattering method for reconstruction of dispersive dielectric properties of two-dimensional (2D) lossy media based on the Debye model by using functional analysis and variational methods is developed. Firstly, the approach formulates a cost functional to turn the inverse problem into a constrained minimization problem according to least squares criterion, then the resulting constrained minimization problem is transformed into an unconstrained minimization problem by using a penalty function technique, and then the closed Fréchet derivatives of the Lagrange function with respect to the properties are derived based on the calculus of variations. Finally, one can solve the resulting problem by using any gradient-based algorithm and the finite-difference time-domain (FDTD) method. Also, the first-order Tikhonov’s regularization is adopted to cope with noise and the ill-posedness of the problem. In numerical example, the presented algorithm is applied to a 2D breast model with the help of the Polak-Ribière-Polyak (PRP) conjugate gradient (CG) method, and the results demonstrate its feasibility.

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Hyper-spectral imaging system with harmonic diffraction element in medium and far infrared

Liu Ying, Sun Qiang, Lu Zhen-Wu, Qu Feng, Wu Hong-Sheng, Li Chun

Acta Physica Sinica. 2010, 59 (10): 6980 doi: 10.7498/aps.59.6980
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In order to obtain enough information about the target and make full use of medium- and long-wave infrared spectral data, this article describes a harmonic diffractive/refractive (HDE) optical imaging system. Taking advantage of its special dispersion capability, the application of HDE in the infrared dual-band provides hundreds of spectral images in infrared band, medium-wave infrared band of 3.7—4.8 μm and long-wave infrared band of 8—12 μm. The design results show that: at 18 lines/mm, the optical modulation transfer function is greater than 0.55 in medium-wave infrared band, at 13 lines/mm the optical modulation transfer is greater than 0.5 in long-wave infrared band, in the circle of 30 μm radius, the encircled energy is greater than 85% in medium-wave infrared band, in the circle of 38 μm radius, the encircle energy is great than 80% in long-wave infrared band, the spectral resolution is 0.039 μm at 4.25 μm and 0.072 μm at 8.5 μm respectively. So the optical modulation transfer function in infrared dual-band is close to the diffraction limit, and the encircled energy meets the energy requirement of one pixel of existing domestic detectors.

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Laser one-dimensional range profile

Li Yan-Hui, Wu Zhen-Sen, Gong Yan-Jun, Zhang Geng, Wang Ming-Jun

Acta Physica Sinica. 2010, 59 (10): 6988 doi: 10.7498/aps.59.6988
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Pulse laser one-dimensional range profile theory and simulation are investigated. Laser one-dimensional range profile simulation is studied based on pulse wave scattering theory and the radar equation, and the calculated formula of laser one-dimensional range profile is obtained. As examples, the range profile simulations are calculated for the sloped-plane, sphere, and cone. It is also analyzed that the influences of target shape, radial length and pulsewidth on the simulation results. This paper offers theory bases and simulation method for abstraction and identification target feature on the laser.

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The system of loading hidden information in random spectrum of Fourier domain and incremental compensation

Wang Xiao-Lei, Li Zhi-Lei, Zhai Hong-Chen, Wang Ming-Wei

Acta Physica Sinica. 2010, 59 (10): 6994 doi: 10.7498/aps.59.6994
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The system of loading hidden information in random spectrum of Fourier domain and incremental compensation, which is based on optical principle and can be used in optical image information hiding, is proposed in this paper. A typical method of loading hidden information to the system is also presented. The random spectrum of host image multiplied by random phase mask is obtained by Fourier transform, and the hidden information is embedded in the random spectrum. At the same time, the effects induced by the hidden information can be compensated for by the proposed system. When the carrier image embedded with hidden information is decrypted with incorrect key-random phase mask, the hidden information will spread in the Fourier frequency domain, thus it is impossible to retrieve the hidden information. In addition, even though the attackers know the presence of hidden information and even the hiding method, they still can not decrypt the hidden content without the key, and it is also difficult to removal the hidden information without destroying the carrier image. While in the decryption process, neither the original image nor the information related to the hidden code is necessary. The feasibility of proposed system is demonstrated by simulation experiment and the robustness to the Gauss noise as well as salt and pepper noise is also presented at the end of this paper.

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Dispersion management optimization of multi-wavelength all-optical regeneration based on self-phase modulation

Zhang Jing, Pan Wei, Yan Lian-Shan, Luo Bin

Acta Physica Sinica. 2010, 59 (10): 7002 doi: 10.7498/aps.59.7002
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In connection with the multi-wavelength all-optical regeneration system based on self-phase modulation in fibers, the effect of the average fiber dispersion for the quality factor Q improvement of regenerator is analyzed and a dispersion management optimization method is proposed. The stability of performance of the regenerator will degrade because of dispersion discrepancy between different wavelengths. By choosing the fiber length of dispersion compensating fiber and single mode fiber to make the dispersion curve of combination of two kinds of fiber approximately fitting with the dispersion curve corresponding to the best performance of each wavelength respectively, and keeping the compound dispersion curve in the better dispersion region, the stability of performance of the regenerator is effectively improved if the input signal power and offset of the filter are properly adjusted. The optimization of multi-wavelength dispersion management can be realized.

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Electromagnetically induced absorption and transparency in a closed lambda-shaped four-level system

Li Xiao-Li, Zhang Lian-Shui, Yang Bao-Zhu, Yang Li-Jun

Acta Physica Sinica. 2010, 59 (10): 7008 doi: 10.7498/aps.59.7008
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A quasi-lambda four-level system shows both electromagnetically induced absorption (EIA) and electromagnetically induced transparency (EIT). In addition to an optical coupling field and a probing field, there is a radio field which interacts with two excited state hyperfine levels of the quasi-lambda four-level system consisting of two excited state hyperfine levels and two ground state hyperfine levels. If a driving field which interacts with two ground state hyperfine levels is introduced, the quasi-lambda four-level system is modified to a closed-lambda four-level system. The behaviors of the driving field and radio field are studied in this paper and it is seen that the occurence of EIA or EIT and the whole probing properties are controlled by the Rabi frequencies of both driving field and radio field.

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Evolution of silicon surface microstructure induced by Nd:YAG nanosecond laser

Yuan Chun-Hua, Li Xiao-Hong, Tang Duo-Chang, Yang Hong-Dao, Li Guo-Qiang

Acta Physica Sinica. 2010, 59 (10): 7015 doi: 10.7498/aps.59.7015
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We investigate the evolution of surface microstructure created on single crystal silicon wafer by irradiation of cumulative Nd:YAG nanosecond laser pulses (wavelength 532 or 355 nm) in vacuum. The wavy structures are formed on silicon surface by 532 or 355 nm laser on early stage of laser pulse irradiation, and nearly concentric but slightly disordered semi-circular rings are formed under 355 nm laser pulse irradiation. With the number of laser pulses increasing, the structures gradually evolved into the concave-convex structures which are similar to the beads. And finally quasi-ordered arrays of conical spikes are formed. The growth of these microstructures depends on the capillary waves and self-organization of structures. We find that the cross-ring structures are caused by the superposition of some wavy structures created by capillary waves in the process of 355 nm laser pulses irradiation.

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Ne-like Ti X-ray laser driven by a single femtosecond laser

Zheng Bing-Song, Sun Yan-Qian, Chen Yu, Ma Jing-Long, Li Ying-Jun

Acta Physica Sinica. 2010, 59 (10): 7020 doi: 10.7498/aps.59.7020
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A physical scheme is presented for Ne-like Ti x-ray laser driven by a single laser pulse. According to the self-similarity method, we analyze the properties of Ne-like Ti slab plasma generated by irradiation of femtosecond laser with various front edges. Scaling laws for the temperature, scale length, and electron density are obtained. The characteristics of scaling laws for different input parameters are analyzed. Our results show that x-ray laser can be generated by a single femtosecond laser. The femtosecond laser with a gentle front edge is profitable to drive x-ray laser. Our results provide a new schemc for experiments using a single laser pulse to drive the x-ray laser.

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The flow field heat distribution of inorganic liquid laser under oblique pumping

Hu Tao, Wei Yong-Tao, Song Ying-Song, Zhang Yu-Ming, Li Mi, Ma Zai-Ru, Feng Guo-Ying

Acta Physica Sinica. 2010, 59 (10): 7027 doi: 10.7498/aps.59.7027
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The multi-segment liquid laser system connected in series and obliquely pumped by LD can have significantly improved laser beam quality and higher output power. A flow-heat-solid interaction model for calculating the temperature distribution in the sub-gain section is established, which is focused on the flow, heat transfer and coupling in sub-gain section. We performed the numerical simulation of transient flow-field-heat distribution by way of the finite element method. The method proposed precludes the influence of the inaccurate film coefficient on the calculation results, the film coefficient is no longer a prerequisite, but a result of the calculation. Our method provides a new effective way to assess and control the flow-field-heat distribution which is affected by the flow channel shape, flow rate, absorption coefficient and other factors. Numerical results show that the film coefficient is a function of spatial location. Flow and heat transfer effieciency decreases with increasing velocity. When the laser medium is flowing, the temperature distribution and temperature gradient distribution are similar and are complementary to the film coefficient distribution, the maximum temperature and temperature gradient appears in the sharp corner downstream the flow.

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Enhancement of contrast ratio in chirped pulse amplified laser system by cross-polarized wave generation

Liu Cheng, Wang Zhao-Hua, Li Wei-Chang, Liu Feng, Wei Zhi-Yi

Acta Physica Sinica. 2010, 59 (10): 7036 doi: 10.7498/aps.59.7036
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This paper reports our experimental research on the laser contrast ratio enhancement in the XL-Ⅲ (eXtreme Light Ⅲ) facility with the technology of cross-polarized wave (XPW) generation. Based on the theoretical analysis of the relerant principles, we introduced an XPW filter in the facility, which was upgraded with a double chirped pulse amplification (DCPA) scheme. Under optimized system design and alignment, we measured the conversion efficiency from fundamental wave to cross-polarized wave to be higher than 10%. The pre-pulses in nanosecond scale were deeply suppressed and the contrast ratio in picosecond scale was enhanced from 10^-5 to 10^-7. Our results show the XPW generation provides an effective technique to improve the contrast ratio of a Chirped-pulse amplification laser system, which is a key issue in ultrahigh intensity laser-matter researches.

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Propagation of femtosecond chirped Gaussian pulse in dense three-level Λ-type atomic medium

Wang Zhen-Dong, Liang Bian, Liu Zhong-Bo, Fan Xi-Jun

Acta Physica Sinica. 2010, 59 (10): 7041 doi: 10.7498/aps.59.7041
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We investigate propagation of femtosecond chirped Gaussian laser pulse in a dense three-level Λ-type atomic medium by using the numerical solution of the full Maxwell-Bloch equations without the slowly varying envelope and the rotating-wave approximations, and the solution is obtained by PC-FDTD method. It is shown that, variation of the sign and size of the chirp coefficient has considerable effect on pulse propagation property, and the effect is closely relative to size of the pulse area. When the area of chirped pulse is smaller than 4π, splitting doesn’t occur and the chirped pulse evolves gradually to an approximate normal Gaussian pulse (C=0), and this characteristic doesn’t vary with the chirp coefficient varying. However, variation of the chirp coefficient will changed the amplitude and group velocity of the pulse. For the positive chirp(C>0), amplitude and group velocity of the pulse decrease with chirp coefficient increasing, for the negative chirp(C<0), amplitude and group velocity of the pulse don’t monotonically increase or decrease with absolute value of C increasing. Both the chirped pulses with area equal to larger than 4π will split into sub-pulses of different numbers and shapes, the time and number of the pulse splitting will be determined by the sign and size of the chirp coefficient. But in the two cases, the pulse splitting patterns are much different, and the effects of the coefficient are also different. When the pulse area equals 4π, larger chirp coefficient will lead to increased sub-pulse number, but when the pulse area is larger than 4π, larger chirp coefficient will lead to decreased sub-pulse number. In addition, regardless of pulse area being larger or smaller, changing sign and size of the chirp coefficient always produces obvious effect on the atomic population.

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Bandwidth in qusai-phase-matched frequency doubling

Ren Ai-Hong, Liu Zheng-Ying, Zhang Rong-Zhu, Liu Jing-Lun, Sun Nian-Chun

Acta Physica Sinica. 2010, 59 (10): 7050 doi: 10.7498/aps.59.7050
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Based on the theory of quasi-phase-matched frequency doubling, the condition to generate the broadband second-harmonic is investigated. We analyze the conversion performances of the high efficiency broadband second-harmonic for type-0 (e+e→e) and type-Ⅰ(o+o→e) quasi-phase-matchad cases in periodically poled LiNbO₃ crystal and 7mol% periodically poled MgO:LiNbO₃ crystal. The results show that the central wavelengths of the fundamental wave and the bandwidth shift toward short waves in periodically poled MgO:LiNbO₃ crystal, and the wider bandwidth is obtained in the type-0 quasi-phase-matched case.

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Two-photon absorption coefficient spectra of indirect transitions in silicon

Cui Hao-Yang, Li Zhi-Feng, Ma Fa-Jun, Chen Xiao-Shuang, Lu Wei

Acta Physica Sinica. 2010, 59 (10): 7055 doi: 10.7498/aps.59.7055
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The two-photon absorption coefficient spectra of indirect transitions in silicon have been measured using a picosecond Nd:YAG pulsed laser pumped optical parametric generator, whose wavelength being tunable. By employing the pulsed laser with the photon energy less than the indirect energy gap of silicon, the photovoltaic response between two electrons of the silicon photovoltaic diode has been detected significantly. The peak intensity of the pulsed photovoltaic response shows a quadratic dependence on the incident intensity. This suggests a typical two photon absorption process. A relationship between the pulsed photovoltaic response and the incident intensity has been established with an equivalent RC circuit model to derive the two-photon absorption coefficient, and the spectra can also be obtained by turning the incident wavelengths. The results show that when the incident photon energy change from 0.689 eV to 0.912 eV, the two-photon absorption coefficient increase form 0.42 cm/GW to 1.17 cm/GW. The mechanism for the two-photon absorption coefficient increasing with the incident photon energy can be attributed to the electrons excited from valance band finding an increasing availability of conduction-band states as the photon energy increase from E_ig/2 to near E_ig. This photon frequency dependence of the two-photon absorption coefficient has been fairly interpreted by the Dinu model.

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Polarization-independent self-collimation bends and beam splitters in 3²,4,3,4 Archimedean photonic crystals

Zhong Qi, Han Kui, Shen Xiao-Peng, Tong Xing, Wu Qiong-Hua, Li Ming-Xue, Wu Yu-Xi

Acta Physica Sinica. 2010, 59 (10): 7060 doi: 10.7498/aps.59.7060
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By using equi-frequency contour analysis and finite-difference time-domain simulation, self-collimation for TE- and TM-polarizations are achieved at the same frequency in two dimensional 3²,4,3,4 Archimedean photonic crystals. The bends and beam splitters are realized by truncating an air block in the photonic crystals. It is observed that the line defect can produce a tunable one-to-two beam splitter by controlling the width of the air block. A bend and a 1 ∶1 beam splitter for the TE- and TM- polarization are designed respectively, both have high efficiency. This study proposes a new design method for optical devices based on photonic crystals.

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Wave localization in one-dimensional periodic-on-average disordered system composed of single-negative metamaterials

Liu Dong-Mei, Han Peng

Acta Physica Sinica. 2010, 59 (10): 7066 doi: 10.7498/aps.59.7066
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By using the transfer-matrix method,we study the Anderson localization behavior in one-dimensional periodic-on-average disordered system composed of two different single-negative(SNG) metamaterials. Non-dispersive and dipersive models have been studied respectively. It was found that the disorder has great effect on waves with frequency in the pass band of the corresponding periodic structure. However,inside the gap,the effect can be almost ignored. These features are different from those we ever found in the random single-negative system. The main reason of the difference should be the number of the interfaces between two kinds of single negative metamateirals,which should be the basic mechanism of the wave propagation in systems made of single negative metamaterials. In periodic-on-average disordered systems,the number of the interface is the same as that in periodic one. However,there is an obvious decrease in random systems,which will have a great effect on the ability of wave transport,leading to small localization length. In the case of a dispersive model,it has been proved that the randomness has no effect on the wave propagation with frequency at the center of the gap. Especially,this special point becomes a delocalization point when the ratio of effective optical thickness of two single negative materials equals one. The results facilitates further understanding of the wave transport mechanism in systems composed of metamaterials.

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Fabrication and luminescence characterization of two-dimensional GaAs-based photonic crystal nanocavities

Peng Yin-Sheng, Ye Xiao-Ling, Xu Bo, Niu Jie-Bin, Jia Rui, Wang Zhan-Guo, Liang Song, Yang Xiao-Hong

Acta Physica Sinica. 2010, 59 (10): 7073 doi: 10.7498/aps.59.7073
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This paper describes the design and fabrication process of a two-dimensional GaAs-based photonic crystal nanocavity with InAs quantum dots (QDs) emitters and analyzes the optical characteristics of cavity modes at room temperature. The micro-luminescence spectrum recorded from the nanocavities exhibits a narrow optical transition at the lowest order resonance wavelength of about 1137 nm with about 1 nm emission linewidth. In addition,the spectra of photonic crystal nanocavities processed under different etching conditions show that the verticality of air hole sidewall is an important factor determing the luminescence characteristics of photonic crystal nanocaivties. Finally,the variance of resonant modes is also discussed as a function of r/a ratio and will be used in techniques aimed at improving the probability of achieving spectral coupling of a single QD to a cavity mode.

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Reflectivity uncertainty analysis of planar mirror calibration in BSRF

Chen Bo-Lun, Yang Zheng-Hua, Cao Zhu-Rong, Dong Jian-Jun, Hou Li-Fei, Cui Yan-Li, Jiang Shao-En, Yi Rong-Qing, Li San-Wei, Liu Shen-Ye, Yang Jia-Min

Acta Physica Sinica. 2010, 59 (10): 7078 doi: 10.7498/aps.59.7078
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A key diagnostic for absolute radiation flux and radiation temperature in hohlraum experiments is the Dante soft x-ray spectrometer in which grazing incidence x-ray mirrors are used to diminish the high energy response of the filters. The reflectivities of planar mirrors made of different materials were calibrated in BSRF in 2009.Considering both the influence of the source such as the spectra resolution,harmonic and the attenuation of the source intensity and the influence of the coherence of two detectors responses,we give the corrected mirror reflectivities and the uncertainty, including the statistical uncertainty of the expermental data.

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A fiber decorated by colloidal photonic crystal

Liu Qing, Wang Ming, Guo Wen-Hua, Yan Hai-Tao, Yu Ping

Acta Physica Sinica. 2010, 59 (10): 7086 doi: 10.7498/aps.59.7086
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A method of fabricating fiber decorated by colloidal photonic crystal is devised. Three-dimensional nanostructure colloidal crystal on the end face of optical fiber was grown by isothermal heating evaporation induced self-assembly method. The optical fiber with colloidal crystals was connected to another lapped optical fiber by glass capillary,and the fiber decorated by colloidal photonic crystal was formed. The nanostructural morphology of the colloidal crystal was examined by SEM. The optical characteristics of the colloidal crystal was also analyzed. The spectral feature of the optical fiber colloidal crystal was measured by using optical sensing analyzer. It has been found that the optimal conditions for a good quality crystal are an evaporation temperature of 40 ℃ with a volume fraction of 0.5% and a deposition time of 12 hours.SEM reveals that the colloidal crystal on the end face of optical fiber has face-centered-cubic structure. Transmission measurement shows the existence of photonic band gap,and the stopgap is located at 1365 nm.

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Numerical and experimental study on coherent combining of double cladding multi-core photonic crystal fiber

Han Wei-Tao, Hou Lan-Tian, Geng Peng-Cheng

Acta Physica Sinica. 2010, 59 (10): 7091 doi: 10.7498/aps.59.7091
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The supermodel mode field characteristics of double cladding multi-core photonic crystal fiber were analyzed with coupled-mode theory. Through the phase adjustment of evanescent wave on 7 beams of light, one can realize the coherent combination, by which the laser brightness is greatly enhanced. We analyzed and measured the coherent power density of the light emitted from the double cladding multi-core photonic crystal fiber using coherent combination theory, and provide the theoretical and experimental basis for this multi-core photonic crystal fiber to achieve self-coherent synthesis.

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Properties of photon counting imaging system with Si thin films

Zhao Fei-Fei, Liu Yong-An, Hu Hui-Jun, Zhao Bao-Sheng

Acta Physica Sinica. 2010, 59 (10): 7096 doi: 10.7498/aps.59.7096
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The Si thin films on ceramic substrates,which were fabricated by electron beam evaporation,were applied as charge induction layers in photon counting imaging system with induction readout. The structures and micrograph of Si thin films were studied. The X-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FESEM) images indicate that the thin film has amorphous structure and is coarse due to the lattice boundary of ceramic substrate. The experimental setup was established and the detector resolution,counting rate,pulse height distribution curves etc., with different Si film thickness were compared. The results suggest that the film thickness influences on spatial resolution less than on the counting rate. Moreover,the properties of the system with Si and Ge thin films of the same resistance were compared,which shows that the properties such as distortion,counting rate and dark count rate are better with the Si films.

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Approaching 100 nJ pulse energy output from a mode-locked photonic crystal fiber laser

Song You-Jian, Hu Ming-Lie, Xie Chen, Chai Lu, Wang Qing-Yue

Acta Physica Sinica. 2010, 59 (10): 7105 doi: 10.7498/aps.59.7105
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Pulse energy directly output from a mode-locked fiber laser approaching one hundred nanojoule is demonstrated. The fiber laser is based on a σ-shaped cavity design. A segment of single polarization Yb-doped large mode area photonic crystal fiber acts as gain medium. A semiconductor saturable absorber mirror is used for self-starting mode-locking operation. The fiber laser works in an all normal dispersion mode-locking regime with no intracavity dispersion compensation introduced in the laser. A long multi-pass cavity is used to reduce the repetition rate of the fiber laser. Direct output pulse energy of 97 nJ with an average power of 1.08 W is achieved at a low repetition rate of 11.1 MHz. The pulse duration is 4.17 ps,which can be extracavity dechirped to 740 fs.

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Structural damage imaging based on time-reversal theory for focusing of Lamb waves

Zhang Hai-Yan, Sun Xiu-Li, Cao Ya-Ping, Chen Xian-Hua, Yu Jian-Bo

Acta Physica Sinica. 2010, 59 (10): 7111 doi: 10.7498/aps.59.7111
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This study presents a theoretical and experimental investigation of the application of the time-reversed concept to dispersive and multimode Lamb waves for health monitoring of plate-like structures. When a Lamb wave signal is excited in a plate-like structure with damage,the damage will serve as a passive wave source. With the transfer function,the focusing in the time-reversal field composed of distributed transducer network is analyzed by deducing the amplitude expression of the time reversal Lamb wave signals. The result demonstrates that time-reversal signal reaches the maximum amplitude when the observation point is located at the damage location. To validate the focusing effect of the time-reversal method,an efficient imaging method suitable for distributed actuator/sensor networks is adopted for locating and approximate sizing of structural damages. Experimental results combined with finite element simulation illustrate that the inspection energy can be focalized on the damage. It indicates that the time-reversal method is an effective way for identifying and locating damage for Lamb wave inspection.

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Two-dimensional numerical simulation of laser-ablation of aluminum material by nanosecond laser pulse

Zhang Peng-Bo, Qin Ying, Zhao Ji-Jun, Wen Bin

Acta Physica Sinica. 2010, 59 (10): 7120 doi: 10.7498/aps.59.7120
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To investigate the interaction between high-power pulsed laser and metal materials,we established a two-dimensional numerical model. The laser-induced two-dimensional temperature distribution was simulated using a finite difference method. From comparison of temperature evolution under different pulse time,spot sizes and energies,it can be seen that the rise of temperature in the initial period is faster than that in the later periods. Isothermal diagram shows that the temperature rising rate is fastest in the center of laser irradiating zone and that the ablation depth is in the range of 1—5 μm. As the laser pulse duration becomes longer,the ablation zone becomes narrower and deeper. As the laser spot diameter increases,the ablation zone becomes wider and shallower. The present numerical results indicate that: (1) the ablation shape and depth sensitively depend on the laser shape,pulse duration and power density, (2) with laser power density in the order of 10⁹ W/cm²,the ablation area is roughly of the orgc of the laser spot. These results are helpful for designing relevant laser parameters in experiments.

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Hamilton’s principle based on thermomass theory

Song Bai, Wu Jing, Guo Zeng-Yuan

Acta Physica Sinica. 2010, 59 (10): 7129 doi: 10.7498/aps.59.7129
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Based on thermomass theory, the Hamilton's principle as well as the Lagrangian equations governing the motion of thermomass were established by methods analogous to those of classical mechanics. With the kinetic energy of thermomass taken into consideration, the Hamiltons principle for thermomass is expected to be capable of dealing with non-Fourier phenomena. When the kinetic energy is small enough to be ignored, the principle gets back to Fourier transfer. The application of Lagrangian equations was illustrated by the approximate solution of a 1D transient heat conduction problem with heat source. The unification of thermal and mechanical theories was demonstrated from the perspective of analytical mechanics, the drawbacks of existing theory are discussed, a new way to the approximate solution of heat transfer problem was suggested, and in the meantime the concepts of thermomass and energy of thermomass were to some extent justified.

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A symmetric product of two optimal third-order force gradient symplectic algorithms

Li Rong, Wu Xin

Acta Physica Sinica. 2010, 59 (10): 7135 doi: 10.7498/aps.59.7135
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This paper provides two new fourth-order force gradient symplectic intrgrators,each of which is obtained from a symmetric product of two identied optimal third-order force gradient symplectic algorithms reported in the literature. They are both greatly superior to the fourth-order non-gradient symplectic method of Forest and Ruth in the accuracy of either energy on chaotic perturbed Kepler problems or the energy eigenvalues for one-dimensional Schrö,dinger equations. So are they to the known optimalfourth-order force gradient symplectic scheme.

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Electrical conduction mechanism in polar molecule dominated electrorheological fluid

Wang Xue-Zhao, Shen Rong, Lu Yang, Ji Ai-Ling, Sun Gang, Lu Kun-Quan, Cui Ping

Acta Physica Sinica. 2010, 59 (10): 7144 doi: 10.7498/aps.59.7144
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Polar molecule dominated electrorheological (ER) fluid is a new type of ER material with high shear stress. The alignment of polar molecules adsorbed on the dielectric particles in the direction of the high local field between the particles plays a decisive role in such new ER fluids. In measuring the current density of ER fluid composed of Ca—Ti—O particles, it was found that the conductive behavior of the fluid exhibits Poole-Frenkel character, which is one of the particular features for polar molecule dominated electrorheological fluids. By heating the Ca—Ti—O particles at 500 ℃ to remove the polar molecules adsorbed on the particles, however, the current density of ER fluid fabricated with pure Ca—Ti—O particles has linear dependence on the electric field approximately, same as in the traditional ER fluids.

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The theory of nonlinear interfacial-internal wave propagation in three-layer fluid systems

Wen Wen-Ying, Chen Xiao-Gang, Song Jin-Bao

Acta Physica Sinica. 2010, 59 (10): 7149 doi: 10.7498/aps.59.7149
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Based on the small steepness parameter assumption, the three-layer incompressible, inviscid and irrotational fluid system of arbitrary depth is discussed by using the perturbation method, and a unified theory of nonlinear interfacial-internal wave propagation and the approximate nonlinear evolution equations (NEEs) for interfacial-internal elevations are given on the basis of the rigid upper boundary and the flat impermeable bottom. At last we also discuss on NEEs arising from various limiting cases of fluid depth. It is also noted that the theories obtained from the present work include the theoretical results derived by Yoshimasa Matsuno (1993) as special cases.

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Growth and structure characterization of Cr⁴⁺ doped Ca₂GeO₄ laser crystal

Zhang Shan-Li, Zeng Fan-Ming, Wang Xin-Tong, Li Chun, Wang Cheng-Wei, Zhang Ying, Lin Hai, Qin Jie-Ming, Liu Jing-He

Acta Physica Sinica. 2010, 59 (10): 7214 doi: 10.7498/aps.59.7214
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A new kind of Cr⁴⁺ :Ca₂GeO₄ infrared tunable laser crystals were synthesized by flux growth method with CaCl₂ as solvent. The structure of Cr⁴⁺ :Ca₂GeO₄ was characterized by x ray diffraction, Raman spectroscopy (RS) and x ray photoelectron spectroscopy(XPS). The results showed that the obtained crystal was γ-Cr⁴⁺ :Ca₂GeO₄ single crystal with monoclinic structure belonging to olivine structure, and the lattice parameters are: a=5.3209 (1 =0.1 nm), b=6.6648 , c=11.2606 . The result that (GeO₄)^4- exists in the crystal was verified by RS measurement and its vibration was determined. We can see from the XPS measurement that Cr in the crystal is in the form of Cr⁴⁺ and no other valence states exist.

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Effects of In doping on crystal structure and thermoelectric properties of n-type skutterudites

Zhou Long, Li Han, Su Xian-Li, Tang Xin-Feng

Acta Physica Sinica. 2010, 59 (10): 7219 doi: 10.7498/aps.59.7219
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Skutterudite compounds In_xCo₄Sb₁₂(x=0.1—0.4) have been synthesized by a melt-quench-anneal-spark plasma sintering method. x-ray diffraction (XRD) and filed emission scanning electron microscopy (FESEM) results show that doping of In results in a nano structured InSb phase distributed in the grain boundaries when the content of In exceeds its filling fraction limit in the skutterudites. Furthermore, the content of InSb increases with increasing In content. Our research indicates that the existence of nanostructured secondary phase InSb increases the power factor, decreases the lattice thermal conductivity, and therefore remarkably improves the thermoelectric properties of the compounds. The highest thermoelectric figure of merit ZT=1.21 is achieved at 800 K in the In_0.35Co₄Sb₁₂ compound.

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Molecular dynamics simulation of temperature effects on CF⁺₃ etching of Si surface

Ning Jian-Ping, Lü Xiao-Dan, Zhao Cheng-Li, Qin You-Min, He Ping-Ni, Bogaerts A., Gou Fu-Jun

Acta Physica Sinica. 2010, 59 (10): 7225 doi: 10.7498/aps.59.7225
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Molecular dynamics method was employed to investigate the effects of the reaction layer formed near the surface region on CF⁺₃ etching of Si at different temperatures. The simulation results show that the coverages of F and C are sensitive to the surface temperature. With increasing temperature, the physical etching is enhanced, while the chemical etching is weakened. It is found that with increasing surface temperature, the etching rate of Si increases. As to the etching products, the yields of SiF and SiF₂ increase with temperature, whereas the yield of SiF₃ is not sensitive to the surface temperature. And the increase of the etching yield is mainly due to the increased desorption of SiF and SiF₂. The comparison shows that the reactive layer plays an important part in the subsequeat impacting, which enhances the etching rate of Si and weakens the chemical etching intensity.

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Synthesis and characterization of Sb₂Te₃ nanostructures

Zhang Fan, Zhu Hang-Tian, Luo Jun, Liang Jing-Kui, Rao Guang-Hui, Liu Quan-Lin

Acta Physica Sinica. 2010, 59 (10): 7232 doi: 10.7498/aps.59.7232
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Single-crystalline Sb₂Te₃ nanostructures, of which the bulk is one of the best thermoelectric materials at room temperature, are synthesized by chemical vapor deposition. The composition, crystal structure, and growth mechanism of the sample are investigated. According to our experimental results, Sb₂Te₃ normally grows into hexagonal nanoplates without using catalyst, but single-crystalline nanowires can be fabricated with Au nanoparticles as the catalyst. The growth mechanism of Sb₂Te₃ nanostructures is closely related to its anisotropic crystal structure. Sb₂Te₃ has a rhombohedral structure, which exhibits a layered anisotropy with the Te and Sb atom layers arranged along the c-axis. Moreover, there are two adjacent Te layers connected by van der Waals bonds. Therefore, Sb₂Te₃ prefers to grow into hexagonal plates in the ab-plane. When Au nanoparticles are used as the catalyst, the growth direction of the precipitated Sb₂Te₃ is restricted, leading to the formation of Sb₂Te₃ nanowires.

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Design and fabrication of multilayer antireflection coating for optoelectronic devices by plasma enhanced chemical vapor deposition

Yuan He, Sun Chang-Zheng, Xu Jian-Ming, Wu Qing, Xiong Bing, Luo Yi

Acta Physica Sinica. 2010, 59 (10): 7239 doi: 10.7498/aps.59.7239
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The design and fabrication of multilayer antireflection (AR) coating based on plasma enhanced chemical vapor deposition (PECVD) is studied for its applications in optoelectronic devices. Deposition conditions for obtaining SiO₂/SiN_x thin films with large refractive index difference is determined through systematic study of factors influencing the refractive index of deposited SiN_x. Four-layer SiO₂/SiN_x AR coating is designed to exhibit a reflectivity of less than 10^-4over 70 nm bandwidth. Reflectivity of the thin film structure at the center wavelength of 1550 nm remains less than 5×10^-4 when the thickness deviation of any single layer is within ±5 nm from the designed value. Based on the simulation results, SiO₂/SiN_x multilayer AR coating is deposited on the end facet of a Fabry-Perot laser. By analyzing the output spectra of the laser, the residual reflectivity of the AR coating is determined to be on the order of 10^-4 over the wavelength range of 1535—1565 nm.

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Influence of doping on the crystallization ability of mono-component materials

Peng Kun, Ming Chen, Ye Xiang-Xi, Zhang Wen-Xian, Zhuang Jun, Ning Xi-Jing

Acta Physica Sinica. 2010, 59 (10): 7245 doi: 10.7498/aps.59.7245
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Recently, we developed a condensing potential model to predict the ability for materials to form single crystals, and it showed that the ability of mono-component materials (Ni, Al, Cu, Ar, Mg) increases monotonically with the increasing condensing potentials. The present work applied the condensing potential model to binary-component materials. Via molecular dynamics simulations, we investigated the influence of 6 wt% Al doping on the crystallization ability of Ni crystal and found that the doping heavily decreased the crystallization ability. Then a condensing potential model for binary-component materials was developed and was shown as a promising tool to predict the crystallization ability of binary-component materials.

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Defect microstructures in polycrystalline pure copper induced by high-current pulsed electron beam——the vacancy defect clusters and surface micropores ^Hot!

Wang Xue-Tao, Guan Qing-Feng, Qiu Dong-Hua, Cheng Xiu-Wei, Li Yan, Peng Dong-Jin, Gu Qian-Qian

Acta Physica Sinica. 2010, 59 (10): 7252 doi: 10.7498/aps.59.7252
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In this paper, high-current pulsed electron beam (HCPEB) was used to irradiate the polycrystalline pure copper. The vacancy defect clusters of the irradiated surface layer have been investigated by using transmission electron microscopy. Very dense vacancy defect clusters involving square cells, vacancy dislocation loops and stacking fault tetrahedra were formed after HCPEB irradiation. It suggests that the very high stress and high strain rate induced by rapid heating and cooling due to HCPEB irradiation could cause the shifting of whole atomic planes synchronously, which is the probable mechanism of the formation of the vacancy defect clusters. Additionally, it was established by scanning electron microscopy investigations that dense, fine and dispersed micropores on the irradiated surface of pure copper can be successfully fabricated by using HCPEB irradiation. The dominating formation mechanism of surface micropores should be attributed to the formation of supersaturation vacancies within the near-surface introduced during HCPEB irradiation and vacancy migration along grain boundaries and (or) dislocations towards the irradiated surface. The present results indicate that HCPEB technique may become a new method for rapid synthesis of surface porous materials.

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Quasicontinuum simulation of crack propagation in nanocrystalline Ni

Shao Yu-Fei, Wang Shao-Qing

Acta Physica Sinica. 2010, 59 (10): 7258 doi: 10.7498/aps.59.7258
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The propagation process of crack in the nanocrystalline Ni is simulated via the quasicontinuum method. The results show that the stress near the crack tip could prompt the disassociation of grain boundaries, and the formation of stacking faults and deformation twins. Farther from the crack tip, fewer deformation twins can be found. There are more stacking faults than deformation twins in the grains, which approximately have the same distance to the crack tip. The effect on deformation twins from the variation of local stress and generalized planar fault energies is manifested by these results. The distribution of hydrostatic stress on atomic-level around the crack tip is also calculated. It is shown that nanovoids can be easily created in grain boundaries in front of the crack tip. There exists an intense tensile stress state in the grain boundary regions around these nanovoids. As a result of the stress accumulation, the crack propagates along the grain boundaries. Our simulated results qualitatively uncover the propagation process of crack in nanocrystalline Ni, which agrees well with the relevant experimental results.

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Heat conduction in one-dimensional Fibonacci chain with on-site potential

Xu Hui, Cui Mai-Ling, Ma Song-Shan

Acta Physica Sinica. 2010, 59 (10): 7266 doi: 10.7498/aps.59.7266
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By making use of the method of transfer matrix, we study the behaviors of heat conduction in one-dimensional Fibonacci chain under the influence of on-site potential (including transmission coefficient, Lyapunov coefficient and heat conduction). The results show that, with the on-site potential increasing while fixing the ratios of atom mass and force constant, the transmission coefficient of the low-frequency region decreases, and the corresponding Lyapunov coefficient increases, and the transmission spectrum moves to the higher frequency region. Meanwhile, with the increasing of on-site potential, the heat conductivity of the system decreases. When the on-site potential is large enough, the thermal conductivity of the system will tend to zero. In the curve of κ-ω², the thermal conductivity shows a slowly increasing trend in steps, and tends to a certain value in the high-frequency region.

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On the equilibrium conditions for a spherical-cap liquid drop on a solid surface——Also comments on “Thermodynamic mechanism for the condensation of liquid drops on the condense surface” etc.

Zhu Ru-Zeng, Yan Hong, Wang Xiao-Song

Acta Physica Sinica. 2010, 59 (10): 7271 doi: 10.7498/aps.59.7271
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For a liquid drop of first kind (with the size much bigger than the interface thickness), whether on or far away from a solid surface, it is proved that the classical Laplace equation is valid and the related arguments are clarified. The formula of additional pressure for the liquid drop of the first kind dependent on contact angle, given in Ref. 48 1823] is wrong, the comment of Ref. is correct.

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First-principles study on chemisorption of Cl on γ-TiAl(111) surface

Wu Xiao-Xia, Wang Qian-En, Wang Fu-He, Zhou Yun-Song

Acta Physica Sinica. 2010, 59 (10): 7278 doi: 10.7498/aps.59.7278
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The chemisorption of Cl atoms on the γ-TiAl(111) surface is investigated by density functional theory. The calculated results show that the more stable sites for Cl atoms adsorption are the surface face-centred cubic (fcc) sites and the surface hexagonal close-packed (hcp) sites. When the coverage of Cl is less than 1 monolayer (ML), Cl atoms prefer the adsorption site with more Ti atoms as its nearest neighbors on the surface layer. From the analysis of the electronic structures, it can be found that the bonds formed by Cl and metal atoms are mainly ionic and directional. When Cl and O atoms are co-adsorbed on γ-TiAl(111) surface, both of them prefer the fcc and hcp sites. As a result, there is a competition between them. Furthermore, the adsorption energy per oxygen atom is increased by the adsorption of Cl atoms, which indicates that interactions between oxgen and metal atoms are weakened by the adsorption of Cl atoms on γ-TiAl(111) surface. This may be one of the reasons why the oxidation resistance of γ-TiAl can be improved by chlorine treatment.

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First-principles study of optical and electronic properties of N-doped SnO₂

Yu Feng, Wang Pei-Ji, Zhang Chang-Wen

Acta Physica Sinica. 2010, 59 (10): 7285 doi: 10.7498/aps.59.7285
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Using first-principles full potential linearized augmented plane wave method (FP-LAPW), we present the isosurface of spin density, total density of states and optical properties of undoped SnO₂, substitutional N for O and substitutional N for Sn in SnO₂. The results show that the band gap in two kinds of N-doped SnO₂ is wider than that of SnO₂ eigenstate, and the imaginary part of the dielectric function makes a blue shift corresponding to the increasing band gaps. It points out the relationship between electronic structure and optical properties in theory.

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Phonon band structure and electron-phonon interactions in Ga and Sb nanowires: a first-principles study

Sun Wei-Feng, Li Mei-Cheng, Zhao Lian-Cheng

Acta Physica Sinica. 2010, 59 (10): 7291 doi: 10.7498/aps.59.7291
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We present first-principles calculations of the electronic and phonon band structure considering electron-phonon coupling in thin Ga and Sb nanowires. A full Brillouin zone analysis of the phonons is performed for the investigation of nanowire structural stability. The examined nanowires show instability while the wave vectors are away from the zone center. Compared with the usual Peierls distortion picture, the unstable transverse phonon modes induce a transition without electronic band-gap opening. Electron-phonon interaction yields orders-of-magnitude changes depending on the nanowire structure.

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Effect of molecular internuclear distance on non-sequential double ionization

Wei Ya-Na, Yang Shi-Ping

Acta Physica Sinica. 2010, 59 (10): 7298 doi: 10.7498/aps.59.7298
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Using the semiclassical rescattering model, we have studied the effect of molecular internuclear distance on non-sequential double ionization. In the process of our analysis, the non-sequential double ionization rate, two-electron ionization energy, two-electron momentum correlation and the combined potential of Coulomb field and laser field are calculated with the molecular internuclear distance changing. The results show that non-sequential double ionization rate and the double ionization events with the sum of the two electron momentums equal to zero increase with the molecular internuclear distance increasing when the molecular internuclear distance is within 1.0—6.0 a.u. When the molecular internuclear distance continues to increase (greater than 6.0 a.u.), non-sequential double ionization rate and the double ionization events with sum of two electron momentums equal to zero decrease.

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Crystal field energy-levels of Nd³⁺:Gd₃Sc₂Al₃O₁₂ and fitting

Xiao Jin, Zhang Qing-Li, Zhou Wen-Long, Tan Xiao-Liang, Liu Wen-Peng, Yin Shao-Tang, Jiang Hai-He, Xia Shang-Da, Guo Chang-Xin

Acta Physica Sinica. 2010, 59 (10): 7306 doi: 10.7498/aps.59.7306
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Nd³⁺ :GSAG, a laser crystal of 942 nm with good performance, was grown by Czochralski method successfully, and its transmission spectra at room temperature were studied. Sixty-eight crystal field splitting levels of Nd³⁺ with the maximum up to 29967 cm^-1 were identified, to which the Hamiltonian parameters of free-ion and crystal field were fitted, and the root-mean-square deviation of energy level fitting is 16.7 cm^-1, which indicated that the experimental and calculated energy levels are well consistent. The obtained Hamiltonian parameters can be used to calculate the wavefunctions of Nd³⁺ in GSAG, predict its energy level splitting, study the luminescent properties and so on.

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Cryogenic thermoelectric properties of BiTe-based alloys and cryo-energy power generation

Jiang Ming-Bo, Wu Zhi-Xiong, Zhou Min, Huang Rong-Jin, Li Lai-Feng

Acta Physica Sinica. 2010, 59 (10): 7314 doi: 10.7498/aps.59.7314
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The BiTe-based alloys were fabricated by mechanical alloying and cold-pressing sintering. Seebeck coefficient and electrical conductivity were measured at the temperature range of 80—300 K. Results showed that the thermoelectric properities of the materials were excellent during the experiments. With the thermoelectric conversion device made of BiTe-based alloys, a new cryo-energy utilization equipment were established. By applying liquid nitrogen in the experiments, the cryo-energy was released during evaporation of liquid nitrogen, and then, a study of electric properties of thermoelectric conversion devices was further deployed. The relationship of output voltage and output power versue current intensity was obtained from the experiments. The maximum output power in the experiments was up to 1.33 W,which verified the feasibility of cryo-energy power generation.

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Effect of spin polarization on the ground state of Kondo system

Li Huan, Guo Wei

Acta Physica Sinica. 2010, 59 (10): 7320 doi: 10.7498/aps.59.7320
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The effect of spin polarization on the ground state of Kondo type system is a fundamental issue in study of Anderson model. By using variational and diagonal methods we analysis the stability of Kondo singlet state in s-d model and Zhang-Rice singlet state in two-component model for high T_c superconductivity when Cu site spin polarization is considered.

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Effect of temperature gradient on space charge waveform in pulsed electroacoustic method

Chen Xi, Wang Xia, Wu Kai, Peng Zong-Ren, Cheng Yong-Hong

Acta Physica Sinica. 2010, 59 (10): 7327 doi: 10.7498/aps.59.7327
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Temperature rise of power equipment in service serionsly affect the lifetime of insulation, so many researchers have focused on space charge measurements at high temperature. But the changes of polymeric properties (e.g. sound impedance, Young’s modulus, density, velocity of sound wave, decay characteristic etc.) at high temperature make measurement of space charge profiles in polymer inaccurate. What is more, the changes of polymeric properties are more complex under temperature gradient. In this paper, based on the propagation characteristic of sound wave in pulsed electroacoustic method and temperature dependence of polyethylene properties, the effect of temperature gradient on space charge measurement is analyzed and the space charge waveform is recovered.

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High temperature annealing of enhancement-mode AlGaN/GaN high-electron-mobility transistors

Wang Chong, Quan Si, Ma Xiao-Hua, Hao Yue, Zhang Jin-Cheng, Mao Wei

Acta Physica Sinica. 2010, 59 (10): 7333 doi: 10.7498/aps.59.7333
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The high temperature annealing effect of DC characteristics of the different enhancement-mode AlGaN/GaN high-electron-mobility transistors (HEMTs) were investigated. The threshold voltage shifted from 0.12 V to 0.57 V and the gate leakage current was reduced one order after the recessed-gate enhancement-mode AlGaN/GaN HEMTs were annealed at 500 ℃ for 5 min in N₂ atmosphere. The threshold voltage shifted from 0.23 V to -0.69 V and the gate leakage current increased after the F-implantation enhancement-mode AlGaN/GaN HEMTs were annealed at 400 ℃ for 2 min in N₂ atmosphere. The height of Schottky barrier increased in annealing process that enhanced the depletion of gate to channel electrons, so that the threshold voltage shifted in the positive direction of x axis, the gate leakage current was reduced and the device can work at higher gate voltage. The depletion of F ions and the increased barrier height of F ions were weakened after annealing, so that the threshold voltage shifted in negative direction of x axis and the gate leakage current increased. The channel electron mobility of F-implantation enhancement-mode AlGaN/GaN HEMTs increased obviously after annealing process.

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Design and study of second-order Y-loop frequency selective surfaces

Gao Jin-Song, Wang Shan-Shan, Feng Xiao-Guo, Xu Nian-Xi, Zhao Jing-Li, Chen Hong

Acta Physica Sinica. 2010, 59 (10): 7338 doi: 10.7498/aps.59.7338
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The multiband properties of self-similar fractals can be used to design multiband single-layer frequency selective surfaces (FSS). Combined with Floquet periodic boundary conditions, the moments method is applied to characterize the second-order Y-loop fractal FSS frequency response to different valuses of iterative scaling factor F and lattice as the incidence varies, and then the estimated empirical constant is obtained. Experimental results show good correlation to the calculations, indicating that the resonant frequencies are mainly determined by the iteration factor and the initial unit size,while the lattice impacts the transmission coefficient and bandwidth apparently.

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Energy levels and magnetic moments of the quantum solitary wave in a one-dimensional ferromagnetic chain

Li De-Jun, Mi Xian-Wu, Deng Ke

Acta Physica Sinica. 2010, 59 (10): 7344 doi: 10.7498/aps.59.7344
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By using the Hartree approximation and the simplified method of quasidiscreteness multiple scales, we have studied quantum solitary wave solutions for a one-dimensional ferromagnetic chain with exchange interaction and classical magnetic moment interaction. In this chain there are both traveling and stationary quantum solilary waves. With the help of the obtained quantum solitary wave solution, the energy levels and magnetic moments of the quantum solitary wave have been investigated further. It is shown that the energy and magnetic moments of the quantum solitary wave are quantized. These novel results provide a possible way for understanding macroscopic quantum effects such as quantum steps of the hysteresis loop in magnetic materials.

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Orbital ordering driven spin dimer state in double-layered antiferromagnet K₃Cu₂O₇

Chen Dong-Meng, Liu Da-Yong

Acta Physica Sinica. 2010, 59 (10): 7350 doi: 10.7498/aps.59.7350
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Magnetic, orbital and lattice structures of K₃Cu₂F₇ are determined by cluster self-consistent field approach based on the spin-orbital-lattice Hamiltonian. Symmetry breaking and Jahn-Teller distortion of approximately isolated bilayer cause Cu²⁺ ions alternatively to occupy  z²-x²〉/ z²-y²〉 orbitals in each layer. This orbital ordering occupation leads to the dominant intrabilayer antiferromagnetic coupling, which favors spin dimerization, and the weak intralayer ferromagnetic coupling. Due to absence of spin frustration resulting from the intralayer orbital arrangement and the weak ferromagnetic coupling satisfing Goodenough-Kanamori-Anderson (GKA)rule, the ground state is a stable spin dimer state. The spin singlet-triplet excitation gap obtained by bond-operator mean field method is about 326 K, which is close to the experimental value of 400 K. The present theory is also applicable to explaining the formation of spin dimer state in Cs₃Cu₂Cl₄Br₃.

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Training effect in the ferromagnetic/antiferromagnetic bilayers

Xu Mian, Pan Jing, Shen Ying, Hu Jing-Guo

Acta Physica Sinica. 2010, 59 (10): 7357 doi: 10.7498/aps.59.7357
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Using Monte Carlo method to study the magnetic training effect in the ferromagnetic/antiferromagnetic bilayers, it was shown that the magnetic relaxation of the net magnetization induced by cold magnetic field which exists in the interface between ferromagnetic and antiferromagnetic bilayer can result in the training effect in the exchange bias and coercivity of the system. Further studies have shown that the doping in antiferromagnetic layer can modulate the training effect in the exchange bias, because the doping in antiferromagnetic layer can effectively change the magnetic relaxation process of the net magnetization induced by the cold field.

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Physical origin of transient Kerr peak induced by circularly polarized laser in ferromagnetic films

Chen Da-Xin, Chen Zhi-Feng, Xu Chu-Dong, Lai Tian-Shu

Acta Physica Sinica. 2010, 59 (10): 7362 doi: 10.7498/aps.59.7362
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The magnetization dynamics of in-plane anisotropic FePt and perpendicularly anisotropic GdFeCo films induced by circularly polarized laser excitation is investigated using femtosecond time-resolved pump-probe Kerr spectroscopy. It is found that a transient Kerr peak occurs near zero-time delay, respectively for each sample. The origin of the peaks is analyzed. It is pointed out that the transient Kerr peaks are not related to ferromagnetism and may originate from paramagnetic magnetization of free electrons in the samples, while the magnetic field that magnetizes the free electrons comes from inverse Faraday effect of the circularly polarized pump laser. The calculation results based on the paramagnetic magnetization model support such a viewpoint. Based on our points, the duration of magnetic pulses induced by inverse Faraday effect should be the same as that of the pump laser pulses.

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Design and thermodynamical analysis of a new refrigerator model driven by photovoltaic and thermoelectric power generation

Liu Yong-Sheng, Gu Min-An, Yang Jing-Jing, Shi Qi-Guang, Gao Tian, Yang Jin-Huan, Yang Zheng-Long

Acta Physica Sinica. 2010, 59 (10): 7368 doi: 10.7498/aps.59.7368
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According to solar cell’s temperature properties and thermoelectric power properties, a refrigerator model is newly designed, which is driven by solar photovoltaic and thermoelectric power generation. It includes solar cells, thermoelectric power modules, power control system, etc. Based on the load demand for electricity, a photovoltaic power generation system is designed. The operating efficiency and exergy efficiency of the model are analyzed by thermodynamic theory. We find that the COP (coefficient of performance) achieves 2.73 (COP is about 2 for general refrigerators) and exergy efficiency achieves 42.5%. By using the model, the emissions of carbon dioxide 1394.2 kg, sulfur dioxide 27.2 kg and nitrogen oxides 21.0 kg are reduced, which can provide an interesting direction to the applications of renewable energy.

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Calculation of positron wave function in the single crystal solid

Xiong Tao, Zhang Jie, Chen Xiang-Lei, Ye Bang-Jiao, Du Huai-Jiang, Weng Hui-Min

Acta Physica Sinica. 2010, 59 (10): 7374 doi: 10.7498/aps.59.7374
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In this paper, we first introduce two basic methods for calculating the positron wave function: the finite differential method and the plane wave method (PW). Then taking Si as an example, we calculate the positron wave function from the wave function, and get the positron density distribution in silicon. Then we obtain the bulk positron lifetime from the positron density. The calculation result agrees with our latest experimental result of 220 ps. At last, we discuss the respective advantages and disadvantages of the two methods.

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Influence of excitation frequency on the growth properties of nanocrystalline silicon films with high hydrogen dilution

Song Jie, Guo Yan-Qing, Wang Xiang, Ding Hong-Lin, Huang Rui

Acta Physica Sinica. 2010, 59 (10): 7378 doi: 10.7498/aps.59.7378
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Nanocrystalline silicon films were prepared from SiH₄ highly diluted with hydrogen by plasma enhanced chemical vapor deposition. The influence of excitation frequency on their growth properties was investigated. The cross-section transmisson electron microscopy images show that all the films grow with certain fastigiated structure in the crystalline region. However, the films deposited at 13.56 MHz undergo a transition from amorphous incubation layer to crystalline structure. In contrast, for the films deposited at a high excitation frequency (40.68 MHz), nanocrystalline silicon grains can directly grow on the amorphous substrates. Furthermore, the results of Raman spectra and Fourier transform infrared spectroscopy manifest that the nanocrystalline silicon films deposited at high excitation frequency (40.68 MHz) possess high crystalline fraction, low hydrogen content and small microstructure factor.

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Preparation of nano-particle carbonates emission materials

Wang Qi-Fu, Wang Xiao-Xia, Luo Ji-Run, Zhao Qing-Lan

Acta Physica Sinica. 2010, 59 (10): 7383 doi: 10.7498/aps.59.7383
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Oxide cathode has been widely used as electron emission source in vacuum electronic devices. Emission of an oxide cathode is dependent upon the ratio of the three kinds of ingredients and the microscopic shape of alkaline earth carbonates on the cathode surface. The synthesizing method plays a key role in dctermining the shape and ingredient of the carbonates. A gas-liquid synthetic method has been used to prepare the carbonate in this paper. The influences of temperature, concentration of constituents and whisk velocity were investigated. A nano-particle carbonate is synthesized by optimizing temperature and concentration.

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Magnetically correlated I-V nonlinearity and electrical transport property of the double-layered perovskite La_1.8Ca_1.2Mn₂O₇ compound

Deng Heng, Yang Chang-Ping, Huang Chang, Xu Ling-Fang

Acta Physica Sinica. 2010, 59 (10): 7390 doi: 10.7498/aps.59.7390
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The double-layered perovskite La_1.8Ca_1.2Mn₂O₇ceramic was synthesized by traditional solid-state reaction after heat treatment for two times at high temperature. Its structure, magnetic and electrical properties were characterized by x ray diffraction (XRD), scanning electron microscopy (SEM), HL5500PC and physical properties measurement system (PPMS). It has a double-layered Sr₃Ti₂O₇ tetragonal structure with lattice constants a, b=3.901 (1 =0.1 nm) and c=19.369 , and unit cell volume V=295.21 ³. The Curie temperature T_C is 177 K. The I-V characteristic shows a nonlinearity increasing with decreasing temperature at low temperatures below the magnetic critical point of T_C and the nonlinear coefficient α goes up to a maximum of 68.6 when the temperature goes down to the lowest of 14 K in this experiment. However, the nonlinearity disappears when temperature goes above the magnetic transition point of T_C. It indicates that a magnetically correlated Schottky barrier between grain boundaries is responsible for the I-V nonlinearity when temperature is below the Curie temperature. A maximum value of 0.18 eV was obtained for the magnetic Schottky barrier at 14 K after using a back to back pn junction model to describe such a potential barrier between grain boundaries.

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Impedance analysis of BaFe_0.4Sn_0.6O₃/BaBiO₃ composite negative temperature coefficient ceramics

Yuan Chang-Lai, Liu Xin-Yu, Yang Yun, Xu Ji-Wen, Gu Yan

Acta Physica Sinica. 2010, 59 (10): 7396 doi: 10.7498/aps.59.7396
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The BaFe_0.4Sn_0.6O₃/BaBiO₃ composite negative temperature coefficient (NTC) thermistor ceramics were prepared by conventional solid-state reaction method. The raw materials used are composed of conductive BaBiO₃ phase and high resistive BaFe_0.4Sn_0.6O₃ phase. The conductive mechanism of thermistor ceramics before and after the percolation threshold (containing 12 mol% of BaBiO₃), is investigated by impedance analysis. For compositions with 5 mol%—8 mol% of BaBiO₃, the contribution to the conductivity is mainly due to the grain boundary (R_b), grain (R_g), and grain shell (R_s) existing in the BaFe_0.4Sn_0.6O₃. In the range of 10 mol%—12 mol% of BaBiO₃, the grain (R_bg) and grain boundary resistance (R_bb) corresponding to the BaFe_0.4Sn_0.6O₃ melted with BaBiO₃ in composite ceramic, are also main factor governing the resistance magnitude, the values of which are lower than the other main sources like R_b, R_g, and R_s. For composition x=0.15, the values of R_bb and R_bg are higher than that of R_b, R_g and R_s. For BaBiO₃ contents around 20 mol%, the resistance is mainly determined by the values of R_bb and Rbg. In addition to the electrode-specimen interface, all of the components in composite ceramic show NTC feature. The NTC composite ceramics with different BaBiO₃ contents show nonideal Debye-like behavior, and the conduction mechanism of the composite ceramics is of the localizing type.

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A knotted polymer chain passing through a pore

Wen Xiao-Hui, Zhang Lin-Xi

Acta Physica Sinica. 2010, 59 (10): 7404 doi: 10.7498/aps.59.7404
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A knotted polymer chain passing through a pore is investigated by molecule dynamics method. In this paper, we take 3₁ knot as an example. It is found that, during the process of translocation, the size of the knot fluctuates until the knot is unknotted. In addition, the effect of the knot on the translocation velocity of the knotted chain is also discussed. For the given external force, the average translocation time τ satisfies the scaling relation:τ～N ^α, and the scaling exponent α increases with the external force f. For short knotted polymer chains, the average translocation time τ decreases when the external force f increases. However, for very long knotted polymer chains, the average translocation time τ increases when the external force f increases. In the meantime, the position of knot in a knotted polymer chain also affects the average translocation time τ strongly. The closer the knot approaches the first translocated monomer, the longer the average translocation time. This investigation can provide some insights into the translocation of knotted polymer chains (especially knotted DNA) through the nanopore, and help us understand the translocation behavior of biomacromolecules.

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Influence of annealing on the microstructure and electrochemical properties of B-doped nanocrystalline diamond films

Pan Jin-Ping, Hu Xiao-Jun, Lu Li-Ping, Yin Chi

Acta Physica Sinica. 2010, 59 (10): 7410 doi: 10.7498/aps.59.7410
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The annealing under different temperatures was performed on boron-doped nanocrystalline diamond films synthesized by hot filament chemical vapor deposition (HFCVD). The effects of annealing on the microstructure and electrochemical properties of films were systematically investigated. The results show that there are four peaks at 1157,1346,1470 and 1555 cm^-1 in Raman spectra of the unannealed sample. When the films were annealed at temperatures above 800 ℃, there are only two peaks of D and G band, indicating that the hydrogen in grain boundaries significantly decreased. The area-integrated intensity ratio of D band to G band (I_D/I_G) reaches minimum value, revealing that the cluster number or cluster size of sp² phase was reduced. The G peak position shifts to lower wave number, indicating an decrease in the ordering of graphitic component. The electrode exhibits the widest potential window and the highest oxygen evolution potential, and the quasi-reversible reaction occurs on the surface of the samples. The D peak is quite sharp and its intensity increases when the sample was annealed at 1000 ℃. The I_D/I_G value attains to the maximum value and the G peak position clearly shifts to higher value. The electrode exhibits the narrowest potential window and the lowest oxygen evolution potential, and the reversible electrochemical reaction occurs in the surface of the sample. The above results reveal that the cluster number or cluster size of sp² phase, the amounts of trans-polyacetylene related to hydrogen in the grain boundaries, the disordering of graphitic components and the boron diffusion in the nanocrystalline diamond films give contributions to the complex change in electrochemical properties of the films with the annealing temperature increasing.

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Denedritic growth in forced flow using the phase-field simulation

Zhu Chang-Sheng, Wang Jun-Wei, Wang Zhi-Ping, Feng Li

Acta Physica Sinica. 2010, 59 (10): 7417 doi: 10.7498/aps.59.7417
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The assymmetrical dendritic growth and the effect of flow velocity on the temperature distribution and laminar flow boundary layer of both facing-flow side and against-flow side has been investigated numerically based on the phase-field model which incorporates both fluid flow and thermal noise, as well as reasonably high efficiency 3DAADCR. The computed results indicate that, the forced flow causes the dissymmetry of the distribution of the temperature distribution and laminar flow boundary layer of both facing-flow side and against-flow side, leading to the different undercooling on either sides, as a result, the dendritic growth towards the flow and inclination relative to the dissipating heat direction appear. At the same time, the undercooling of facing-flow side is greater than that of against-flow side, which is helpful to accelerate dendritic growth rate and makes the sidebranching steady growth, accordingly, resulting in assymmetrical sidebranching growth. With the increase of flow velocity, the greater the inclination, and the more obvious the assymmetrical degree.

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Directional growth of monotectic alloy with and without shear flow

Wang Jian-Yuan, Chen Chang-Le, Zhai Wei, Jin Ke-Xin

Acta Physica Sinica. 2010, 59 (10): 7424 doi: 10.7498/aps.59.7424
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The directional growth process of para-dichlorobenzene and succinonitrile (DCB-SCN) monotectic alloy is realized under static condition and in presence of shear flow. The experimental results show that, with the increase of pulling rate, the DCB phase exhibits faceted growth while the monotectic structure undergoes a transition in which "separated liquid and solid phases-aligned fibrous composite structure-droplet dispersion in solid matrix" take place. When shear flow is applied, perturbation and fluctuation appear at each growing crystal plane. In the meantime, the fibrous spacing is larger compared with those under the same pulling rate without flow. However, the spacing and pulling rate also follow the relationship λV^0.5=C. In the formation process of droplet dispersion structure, shear flow enhances the nucleation rate of second liquid drops and hinder the growth and interaction of second liquid droplets at the solid-liquid interface, leading to the refinement of the final droplet dispersion structure.

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Effect of low diffusion coefficient on glass phase formation in Pd₇₇Cu₆Si₁₇ alloy

Wang Zhen-Zhong, Wang Nan, Yao Wen-Jing

Acta Physica Sinica. 2010, 59 (10): 7431 doi: 10.7498/aps.59.7431
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The microstructure evolution of laser rapidly solidified Pd₇₇Cu₆Si₁₇ alloy was investigated. The experimental results showed that with increasing growth velocity, a phase transition series of Pd₃Si dendrite+eutectic-ξ dendrite+eutectic-eutectic grain-regular eutectic-amorphous phase occurred. The critical velocity of amorphous transition was determined to be about 6 mm/s and the smallest lamellar spacing was 35 nm. Compared with those of Al-25 wt% Sm and Al-32.7 wt% Cu alloys, it was proposed that low diffusion coefficient is the main reason for the good glass formation ability of Pd₇₇Cu₆Si₁₇ alloy.

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Performance of SnO₂:F/SnO₂ composite film as front-electrode for CdTe solar cells

Zeng Guang-Gen, Li Bing, Zheng Jia-Gui, Wu Li-Li, Zhang Jing-Quan, Lei Zhi, Li Wei, Feng Liang-Huan

Acta Physica Sinica. 2010, 59 (10): 7437 doi: 10.7498/aps.59.7437
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Decreasing CdS thickness is one of the effective ways to improve the conversion efficiency of CdS/CdTe solar cells. In order to eliminate the adverse effects of the decrease in CdS thickness on the performances of the devices, it is necessary to introduce a buffer layer between CdS and front electrode layer. The un-doped SnO₂thin films, as a buffer layer, were deposited on SnO₂:F thin film by magnetic reactive sputtering. Then the composite film was annealed at 550 ℃ in N₂/O₂=4 ∶1 ambience for 30 minutes. The morphology, structure and optical properties of the composite film before and after annealing were studied by AFM, XRD, UV-Vis and the electrical properties were analyzed, respectively. As a result, the crystal lattice parameters of un-doped SnO₂ films matched those of the substrate, so the un-doped SnO₂ films, which had an obvious preferred orientation along (110) plan, had the same structure as the substrate materials. This implied that there was no lattice mismatch. After annealing, the surface topography and electricity uniformity were improved, higher than 80% transparency was obtained, and resistance increased to meet the requirements of the buffer layers. Finally, continuous and homogeneous SnO₂:F/ SnO₂ composite thin films have been obtained, which were very suitable for CdS/CdTe cells.

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Comparative study on fractal model and spherical model of fire smoke particles for light scattering

Zhang Qing, Deng Xiao-Jiu, Zhang Qi-Xing, Li Yao-Dong, Zhang Yong-Ming

Acta Physica Sinica. 2010, 59 (10): 7442 doi: 10.7498/aps.59.7442
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It is important to research light scattering from fire smoke particles by numerical calculation. Traditionally, spherical or spheroid models were used to approximate the shape of smoke particles for light scattering calculations. But actually, smoke particles have a similar fractal structure, which is different from spherical structure. Using the discrete-dipole approximation method, the light scattering Muller matrices were computed for the randomly oriented fractal aggregate, as well as the spherical particle with the same aggregate volume, and then their normalized Muller matrix elements were compared. The results indicate that the angular distributions of the normalized matrix elements F₁₁(θ)/F₁₁(0), F₂₂(θ)/F₁₁(θ) and F₃₄(θ)/F₁₁(θ) have significant differences between the fractal model and spherical model. We can discriminate spherical non-fire aerosols from smoke particles, using the difference of F₂₂(θ)/F₁₁(θ) between fractal model and spherical model.

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Model of the relationship between properties and phase composition of zirconia solid electrolyte

Hu Yong-Gang, Xiao Jian-Zhong, Xia Feng, Wu Xi-Wang, Yan Shuang-Zhi

Acta Physica Sinica. 2010, 59 (10): 7447 doi: 10.7498/aps.59.7447
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The relative content of each phase at room temperature and the ratio of transformable phase at high temperature of zirconia solid electrolyte are important to its thermal shock resistance and electrical conductivity. The match of thermal shock resistance and electrical conductivity plays an important role in measuring the lower oxygen activity in molten steel. A linear model between the thermal shock resistance and the phase composition at room temperature is proposed based on this concept, another evolved relationship between the pyroconductivity and the elevated temperature transformation is also proposed. These models provide theoretical reference for the preparation of the high precision oxygen sensor for measuring the lower partial pressure of oxygen in molten steel.

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Spatial configurations and X-ray absorption of Ti catalyzing on NaAlH₄ surfaces: Car-Parrinello molecular dynamics and density functional theory study

Zhou Jing-Jing, Chen Yun-Gui, Wu Chao-Ling, Xiao Yan, Gao Tao

Acta Physica Sinica. 2010, 59 (10): 7452 doi: 10.7498/aps.59.7452
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A theoretical study on the spatial configurations of the catalytic dehydrogenation of the pre- and post- Ti-doped NaAlH₄(001)2×2×1 supercell surface crystals was performed by using the Car-Parrinello molecular dynamics (CPMD) method at 333 K (60 ℃). It was be found that two of the Al—H bond lengths increased from approximately 1.64 to 1.74 and 1.93  respectively in the AlH₄ groups of the Ti-doped alloy. Compared with this change, the four Al—H bond lengths almost kept invariant in the AlH₄ group of un-doped alloy, which means that it was easier to dehydrogenate for the Ti-doped alloy than un-doped alloy. There was no bonding tendency between atom Ti and Al observed, which is probably because the temperature in the simulation process is not high enough. Based on the obtained surface crystal configuration, the Ti K-edge x ray absorption near-edge structure (XANES) spectra of the TiAl₃, TiH₂ crystals and Na₈Ti₈Al₁₆H₆₄(001) surface crystal have been calculated by using the full-potential linearized augmented plane wave method (FPLAPW). It was also found that the atom Ti may not only exist in the mixture of TiAl₃ and TiH₂ but also probably partially substitute for the Na atoms in NaAlH₄ surface crystal, by comparing the experimental XANES and edge x ray absorption fine structure (EXAFS) spectra.

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Base pairs composition, on-site energies of electrode and DNA-metal coupling effects on current-voltage characteristic of DNA molecule

Ma Song-Shan, Zhu Jia, Xu Hui, Guo Rui

Acta Physica Sinica. 2010, 59 (10): 7458 doi: 10.7498/aps.59.7458
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Based on a tight-binding approximation and transfer matrix method, we investigated the effects of the composition of nucleotide base pairs, on-site energies of the electrode and DNA-metal coupling strength on the current-voltage characteristic. The results indicate that the saturation current of DNA molecule which is composed of one single kind of nucleotide base pair is much higher than that composed of two kinds of nucleotide base pair. Meanwhile, the DNA molecule which is rich in G-C base pairs has higher electronic transport ability. When the bias is low, the on-site energies of the electrode have the effect of impeding charge injection. On the other hand, when the bias is high, the on-site energies of the electrode have the effect of enhancing charge injection. In addition, we can find that a stronger DNA-metal coupling does not always result in a larger saturation current. When t_dm=t_d, there is a resonance injection, which is optimized for electron transport. When t_dm departs from t_d, the resonance injection is reduced, which lead to the stronger of DNA-metal coupling at the range of t_dm>t_d and the lower of saturation current of DNA.

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Phantom study of the classification of liver fibrosis based on nuclear magnetic resonance elasto-graphy

Wang Hong-Zhi, Xu Ling-Feng, Yu Jie, Huang Qing-Ming, Wang Xiao-Yan, Lu Lun, Wang He, Huang Yong, Cheng Hong-Yan, Zhang Xue-Long, Li Geng-Ying

Acta Physica Sinica. 2010, 59 (10): 7463 doi: 10.7498/aps.59.7463
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Accurate detection of liver fibrosis stage and fibrosis procession is crucial for assessing prognosis and candidacy for treatment of patients with chronic hepatic disease. A significant need exists for developing a noninvasive technique for quantitative detection of liver fibrosis stage. Magnetic resonance elasto-graphy (MRE) is one of the most repidly advancing technologies for classifying the liver fibrosis. This study establishes a platform for liver fibrosis classification, and discusses some details in developing stimulator and displacement-phase imaging pulse. At last, the preliminary result and analysis of phantom experiment are given, which would form a basis for subsequent research on phantom MRE and its clinic application.

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Approximate solution of sea-air oscillator for El Ni?o-southern oscillation model

Mo Jia-Qi, Lin Yi-Hua, Lin Wan-Tao

Acta Physica Sinica. 2010, 59 (10): 6707 doi: 10.7498/aps.59.6707
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A class of time delayed coupled system of the El Niñ,o-southern oscillation (ENSO) model is considered. By using the homotopic mapping method, the approximate expansion of the solution for the ENSO model is obtained and the asymptotic behavior of solution of corresponding problem is studied.

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New infinite sequence exact solutions to the general lattice

Taogetusang

Acta Physica Sinica. 2010, 59 (10): 6712 doi: 10.7498/aps.59.6712
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To seek infinite sequence exact solutions to nonlinear difference-differential equations, a kind of auxiliary equation of hyperbolic function type is intruduced, and the Bä,cklund transformation of the solutions to the equation and the formula of nonlinear supperposition of solutions are presented. Based on these and combing auxiliary equation with function transformation, the general lattice equation is chosen as example for which the infinite sequence exact solutionsto the equation are obtained.

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Propagating solitons and chaotic behaviour of (2+1)-dimensional Korteweg-de Vries system

Wu Hong-Yu, Ma Song-Hua, Fang Jian-Ping

Acta Physica Sinica. 2010, 59 (10): 6719 doi: 10.7498/aps.59.6719
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With a projective equation and a linear variable separation method, new exact solutions of the (2+1)-dimensional Korteweg-de Vries system(KdV) is derived. Based on the derived solitary wave excitation, we obtain the propagating solitons and study the chaotic behaviours with a new chaotic system.

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Spreading of epidemics in complex networks with infective medium and spreading delay

Wang Ya-Qi, Jiang Guo-Ping

Acta Physica Sinica. 2010, 59 (10): 6725 doi: 10.7498/aps.59.6725
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In this paper, we propose a new susceptible-infected-susceptible (SIS) model with infective medium and spreading delay (MD-SIS) to study epidemic spreading in networks based on the mean-field theory. Theoretical analysis and simulation results show that the existence of infective medium and spreading delay can significantly enhance the risk of outbreak of epidemics and accelerate the epidemic spreading in the networks. For a given propagation rate, we found that the epidemic prevalence on the homogeneous network varies logarithmically with infection probability of infective medium and spreading delay respectively, and the epidemic prevalence on the scale-free network has a power-law relation with infection probability of infective medium, but a linear relation with spreading delay.

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Virus spreading on complex networks with imperfect immunization

Wang Ya-Qi, Jiang Guo-Ping

Acta Physica Sinica. 2010, 59 (10): 6734 doi: 10.7498/aps.59.6734
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[PDF 1091 KB] Download:(1812)

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The imperfect immunization includes immune failure and immune invalidity on complex networks. In this paper, based on mean-field theory, we propose a new susceptible-infected-removed model to study epidemic spreading in networks with both immune failure and immune invalidity. Theoretical analysis shows that the immune failure and immune invalidity can significantly reduce the epidemic threshold and enhance the epidemic prevalence in the networks. According to the relationships between epidemic threshold, immune density of nodes, immune success rate and immune invalid rate, some suggestions on how to effectively control the propagation of epidemics are presented. Numerical simulations have confirmed the theoretical results.

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Image encryption based on arithmetic coding with order-1 Markov model

Duan Li-Li, Liao Xiao-Feng, Xiang Tao

Acta Physica Sinica. 2010, 59 (10): 6744 doi: 10.7498/aps.59.6744
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Encryption based on compression can provide compression and encryption in a single step, in which redundancy is removed by compression and security is guaranteed by encryption. A novel secure arithmetic coding scheme based on order-1 Markov model is proposed in this paper, and it is applied to image encryption where images can be transmitted securely on the Internet and the proposed algorithm significantly improve the compression efficiency of coding. Experimental results and security analyses indicate that, the algorithm can not only resist existing attacks based on arithmetic coding, but also be immune to other cryptanalysis.

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Direct perturbation method applied to three-dimensional nonlinear Schr?dinger equation

Cheng Xue-Ping, Lin Ji, Han Ping

Acta Physica Sinica. 2010, 59 (10): 6752 doi: 10.7498/aps.59.6752
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[PDF 631 KB] Download:(908)

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By applying the direct perturbation method to the 3-dimensional nonlinear Schrö,dinger equation with perturbation, we obtain its asymptotical solutions, which contain not only the zero-order solutions, but also the first-order corrections. Through these solutions, the effect of perturbation on the soliton is analyzed as well.

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Analysis on fractional Oldroyd-B viscoelastic Poiseuille flow by numerical inversion of Laplace transforms

Wang Yu, Ouyang Jie, Yang Bin-Xin

Acta Physica Sinica. 2010, 59 (10): 6757 doi: 10.7498/aps.59.6757
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In this paper the unsteady Poiseuille flow of fractional Oldroyd-B viscoelastics fluid between two parallel plates is studied, which sheds light on the investigation on fractional differential equations. Stehfest algorithm for numerical inversion of Laplace transform is used for obtaining the numerical solutions, and its validity is verified by comparing the results with approximate analytic solutions. Then the laminar Poiseuille flow of fractional Oldroyd-B viscoelastic fluid is investigated by the Stehfest algorithm. Phenomena of velocity and stress overshootings are found, which are proved to be dependent on the order of fractional derivative. Simultaneously, compared with the integer constitutive equations, the fractional constitutive equations have wider scope of application. This conclusion was drawn based on the obvious fact that the integer constitutive equations are only special cases of the fractional constitutive equations.

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Approximate Lie symmetries and approximate invariants of the orbit differential equation for perturbed Kepler system

Lou Zhi-Mei

Acta Physica Sinica. 2010, 59 (10): 6764 doi: 10.7498/aps.59.6764
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We obtained the orbit differential equation of Kepler system when the θ is the independent variable. The Lie symmetries and invariants of the orbit differential equation for Kepler system , the exact Lie symmetries and exact invariants of the orbit differential equation for perturbed Kepler system are discussed firstly. Then we discuss the approximate Lie symmetries and approximate invariants of the orbit differential equation for perturbed Kepler system. Nine first order approximate Lie symmetries and six first order approximate invariants are obtained, one of them is a exact invariant in fact, and the other five of them are equivalent to the corresponding invariants of Kepler system multiplyied by the perturbation coefficient ε.

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Stability analysis of a relative rotation time-delay nonlinear dynamic system

Liu Hao-Ran, Zhu Zhan-Long, Shi Pei-Ming

Acta Physica Sinica. 2010, 59 (10): 6770 doi: 10.7498/aps.59.6770
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The dynamic equation of a relative rotation time-delay nonlinear dynamic system is established, which contains time-varying stiffness, nonlinear damping and harmonic excitation. The bifurcation equation of time-delay dynamic system is deduced by the method of multiple scales. The structure stability of the system is studied by singularity theory, the transfer concourse of primary resonance equation and topological structure of bifurcation function are obtained. The dynamic stability of the system is discussed by the Hopf bifurcation theory and the condition for the limit cycle occurrance is given. Moreover, it is indicated by numerical method that parameters of time delay affect the limit cycle amplitude.

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Simulation of vapor-liquid coexistence using dissipative particle dynamics

Wang Xiao-Liang, Chen Shuo

Acta Physica Sinica. 2010, 59 (10): 6778 doi: 10.7498/aps.59.6778
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Due to a purely repulsive conservative interaction adopted in the traditional dissipative particle dynamics, the vapor-liquid coexistence phenomena or fluid flows with free surfaces could not be simulated. In the present study a recently proposed combination of short-range repulsive and long-range attractive interaction for DPD was investigated to explore its ability of simulating vapor-liquid coexistence or fluid flows with free surfaces. With this modified interaction, steady vapor-liquid interface could be obtained in DPD simulation, and the stress distribution across the vapor-liquid interface region was also discussed, which were found in accordance with those obtained by multibody DPD. Furthermore, surface tension of vapor-liquid interface was studied, and it was verified that Laplace’s law is satisfied in our simulation. Surface tensions obtained by theoretical method and Laplace’s law, respectively, are in agreement with each other.

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Drag reduction in turbulent channel flow by spanwise oscillating Lorentz force

Mei Dong-Jie, Fan Bao-Chun, Huang Le-Ping, Dong Gang

Acta Physica Sinica. 2010, 59 (10): 6786 doi: 10.7498/aps.59.6786
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Direct numerical simulation (DNS) of a turbulent channel flow is carried out to investigate the effect and mechanism of using spanwise oscillating Lorentz force to reduce boundary layer friction.We discussed the influence of Lorentz force intensity St and oscillating frequency T⁺ on the drag reduction effect and turbulent burst events. The results suggest the varying tendencies with St or T⁺ of the frequency of the turbulent bursts events are opposite to the intensity of the turbulent bursts events,and there exists an optimal parameter to achieve the largest amount of drag reduction.The composite effect of St and T⁺ can be well described by the equivalent spanwise wall velocity W⁺.

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Abundant interaction solutions of the mKdV-sine-Gordon equation

Lü Da-Zhao, Cui Yan-Ying, Liu Chang-He, Zhang Yan

Acta Physica Sinica. 2010, 59 (10): 6793 doi: 10.7498/aps.59.6793
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In this paper, based on the forms and structures of Wronskian solutions of the mKdV-sine-Gordon equation, a Wronskian form expansion method is presented to find abundant interaction solutions of the mKdV-sine-Gordon equation. One characteristic of the method is that Wronskian entries don’t satisfy linear partial differential equations.

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Controlling entanglement sudden birth and sudden death of two-atom X-states in Tavis-Cummings model

Shan Chuan-Jia, Liu Ji-Bing, Chen Tao, Liu Tang-Kun, Huang Yan-Xia, Li Hong

Acta Physica Sinica. 2010, 59 (10): 6799 doi: 10.7498/aps.59.6799
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In this paper, we investigate the entanglement dynamics of two entangled two-level atoms with initial X state and dipole-dipole coupling intensity in Tavis-Cummings model. The interesting phenomena of entanglement sudden death as well as sudden birth appear during the evolution process. We analyze in detail the effect of purity of initially entangled state of two atoms, the dipole-dipole coupling intensity between two atoms, and the field in the Fock state on the apparition time of entanglement sudden death and entanglement sudden birth. Furthermore, the conditions for the conversion of entanglement sudden death and entanglement sudden birth can be generalized when the initial entangled state is not pure. The results show that the above system parameters affect the concurrence, entanglement sudden birth and sudden death remarkably, the dipole-dipole coupling intensity affects amplitudes of the concurrence oscillation and leads time interval of the ESD to decrease. With the increasing of the purity, the time of entanglement sudden death and entanglement sudden birth will decrease, it is also notable that invariant and stable entanglement, which can be controlled by different initial states of the atoms, occurs for particular initial X state.

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Properties of Wigner function of spin coherent states based on Schwinger Bose operator realization

Song Jun, Fan Hong-Yi

Acta Physica Sinica. 2010, 59 (10): 6806 doi: 10.7498/aps.59.6806
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Based on the Schwinger Bose operator realization of angular momentum, we introduce the entangled state representation as well as the Wigner operator in such representation and then derive the Wigner quasiprobability function of spin coherent states. The properties of corresponding Wigner function in the phase space are discussed by numerical calculation. The results indicate that the spin coherent states based on Schwinger Bose operator realization actually show entanglement properties.

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Dipole squeezing of atomic systems in dissipative environment

Pan Chang-Ning, Zhao Xue-Hui, Yang Di-Wu, Fang Mao-Fa

Acta Physica Sinica. 2010, 59 (10): 6814 doi: 10.7498/aps.59.6814
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[PDF 1086 KB] Download:(709)

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The atomic squeezing effect in the dissipative environment is investigated by means of the quantum theory of damping-density operator approach and numerical calculations. The effects on the atomic dipole squeezing effect produced by the atomic initial state and mean photon number of the thermal reservoir are discussed. The results show that the atomic dipole squeezing declines asymptotically to zero, and doesn’t disappear in finite time if the population rate in the excited state is higher than the ground state in the atomic initial state in the vacuum reservoir. However, the squeezing effect always disappears in the thermal reservoir, irrespective of the atomic initial state. With increase of mean photon of the thermal reservoir, the squeezing effect disappears faster.

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Exact solutions of the Schr?dinger equation for a ring-shaped noncentral potential

Zhang Min-Cang, Huangfu Guo-Qing

Acta Physica Sinica. 2010, 59 (10): 6819 doi: 10.7498/aps.59.6819
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A new ring-shaped noncentral potential is proposed and the exact complete solutions of the Schrö,dinger equation with this potential are presented by the Nikiforov-Uvarov method.The effect of the angle-dependent part on the radial solutions and some particular cases of this potential are also discussed.

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Recurrence spectra of Rydberg NO molecules in a strong magnetic field

Li Hong-Yun, Liu Wei, Lin Sheng-Lu

Acta Physica Sinica. 2010, 59 (10): 6824 doi: 10.7498/aps.59.6824
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Considering the influence of core rotation, we calculate the recurrence spectra of Rydberg NO molecules in the strong external magnetic field by using the molecular closed orbit theory and the multichannel quantum defect theory. The results indicate that the complicated recurrence spectra can be explained by the molecular closed orbit theory including the molecular core-scattering. Not only the elastic core-scattering effect arising from the intrachannel scattering, but also the inelastic core-scattering effect arising from the interchannel scattering is vital to the dynamical properties of the Rydberg molecule. Especially on the larger scaled action, the contribution of core-scattering is more crucial than that of the primary closed orbits and their repetition, and affects the dynamical properties of system to a large extent.

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Single-particle coherence and pairwise entanglement in a two-component Bose-Einstein condensate impacted by the periodic impulses

Yan Dong, Song Li-Jun

Acta Physica Sinica. 2010, 59 (10): 6832 doi: 10.7498/aps.59.6832
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The influence of the quantum chaos on the single-particle coherence and the pairwise entanglement is investigated in a two-component Bose-Einstein condensate impacted by periodic impulses. The results reveal that the single-particle coherence decays strongly when driven by chaos and keeps a lower degree of coherence. Simultaneously, there apears the maximal pairwise entanglement and it disappears after a short time. By using the properties of the single-particle coherence, we can measure directly the structure of the phase space in which the chaos exists, and this contributes to prevent the collapse of a Bose-Einstein condensate and control the chaotic behavior.

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Subspace quantum process tomography via nuclear magnetic resonance

Yao Xi-Wei, Zeng Bi-Rong, Liu Qin, Mu Xiao-Yang, Lin Xing-Cheng, Yang Chun, Pan Jian, Chen Zhong

Acta Physica Sinica. 2010, 59 (10): 6837 doi: 10.7498/aps.59.6837
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Experimental investigation of subspace quantum process tomography in three-spin system was implemented via nuclear magnetic resonance. A quantum process was characterized by measuring a complete set of input states and corresponding outputs. The method using ancillary qubit remarkably reduces the number of the initial input states. And the pulse sequences used in this paper have fewer J-coupling evolutions. The experiment time was shortened and quantum decoherence of the system was weakened efficiently.

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Corrections to Hawking radiation from the black hole surrounded by quintessence

Gong Tian-Xi, Wang Yong-Jiu

Acta Physica Sinica. 2010, 59 (10): 6842 doi: 10.7498/aps.59.6842
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In this paper, using the Hamilton-Jacobi method beyond semiclassical approximation in black hole physics which was developed by Banerjee and Majhi, we compute the temperature and entropy of the black hole surrounded by quintessence and obtain the corrected temperature and entropy. In the corrected entropy, the area law involves logarithmic area correction together with the standard inverse power of area term.

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Generalized Stenfan-Boltzmann law of the Dirac field of Barriola-Vilenkin black hole

Meng Qing-Miao, Li Zhong-Rang, Li Yu-Shan

Acta Physica Sinica. 2010, 59 (10): 6847 doi: 10.7498/aps.59.6847
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Using the thin film model of black hole, the thermal radiation laws of the Barriola-Vilenkin black hole are studied. We obtained the result that the thermal radiation of the black hole always satisfies the generalized Stenfan-Boltzmann law. The derived generalized Stenfan-Boltzmann coefficient is no longer a constant. When the cut-off distance and the thin film thickness are both fixed, it is a proportional coefficient related to the space-time metric near the event horizon and the average radial effusion velocity of the radiation particles in the thin film. The radiation energy flux of the Dirac field of the Barriola-Vilenkin black hole is proportional to the average radial effusion velocity of the radiation particles in the thin film, and inversely proportional to the square of the black hole mass.

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Synchronization between fractional-order chaotic system and chaotic system of integer orders

Zhou Ping, Kuang Fei

Acta Physica Sinica. 2010, 59 (10): 6851 doi: 10.7498/aps.59.6851
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Based on the idea of tracking control and the stability theory of linear fractional-order system, chaotic synchronization between fractional-order chaotic system and chaotic system of integer orders is proposed. A compensation controller and a feedback controller are given. Synchronization between the fractional-order Chen chaotic system and the Loren chaotic system of integer orders is used to illustrate the effectiveness of the proposed synchronization approach. Numerical and circuit simulations coincide with the theoretical analysis.

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Acquisition method of precise periodic signal and uniqueness of periodic solutions of Duffing oscillator system

Wang Kun, Guan Xin-Ping, Ding Xi-Feng, Qiao Jie-Min

Acta Physica Sinica. 2010, 59 (10): 6859 doi: 10.7498/aps.59.6859
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The acquisition method of precise periodic signal and uniqueness of periodic solutions of Duffing oscillator system is investigated. The necessary condition of uniqueness of periodic solutions of a kind of Duffing oscillator system is presented and the uniqueness of periodic solutions of some extensive nonlinear periodic system is simultaneously obtained by using qualitative analysis method .The acquisition method of precise periodic signal Duffing oscillator system is given under certain conditions.

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Synchronization of spatiotemporal chaos in large scale rich-club network

Lü Ling, Zou Jia-Rui, Yang Ming, Meng Le, Guo Li, Chai Yuan

Acta Physica Sinica. 2010, 59 (10): 6864 doi: 10.7498/aps.59.6864
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The Plankton spatiotemporal chaos system is taken as network node and constructed as a rich-club network through nonlinear coupling. The synchronization of spatiotemporal chaos for the above network is investigated. The general selection rule of nonlinear coupling function connecting nodes in the rich-club network is presented. Furthermore, the condition to realize the network synchronization is analyzed theoretically based on Lyapunov stability theory. Finally, the synchronization effect of spatiotemporal chaos for the rich-club network is checked through artificial simulation. The results show that complete synchronization can be realized for all rich nodes in the rich-club network and all nodes in every subnetwork constructed in star-shape.

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Mechanism analysis of the abnormal activities and polymorphism in subtropical high based on the objective fitting of space-basis function

Hong Mei, Zhang Ren, He Jin-Hai, Xue Feng, Ge Jing-Jing

Acta Physica Sinica. 2010, 59 (10): 6871 doi: 10.7498/aps.59.6871
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In order to analyze the dynamical mechanism of the abnormal activity of the subtropical high, the variables in the partial differential vortex equations based on the heat force and the whorl movement dissipation effect, are separated in space and time with Galerkin methods. Aiming at resolving the problem of the insufficiency and shortcoming of the conventional method in the choice of space-basis function, we set forth the research idea of using the expirical orthogonal function (EOF) and the genetic algorithm combined with inversion of the space-basis function from the actual sequence of data fields. After the EOF of the daily time series of the subtropical high potential fields, the first three major typical space fields whose cumulative variance contribution is more than 90 percent as the fitting object are chosen, and a group of trigonometric function is selected as the general space-basis function. And then, the dual-constraint function is formulated with the complete orthogonality between space-basis function and the least square of error of general space-basis function and EOF typical field. Then the genetic algorithm is introduced to carry out the curved surface fitting and coefficient optimization of the basis function, and through inversion, an objective and reasonable ordinary differential dynamical model of subtropical high is obtained. Furthermore, through the EOF and inversion of history sensible heat field data, an ordinary differential dynamical model of subtropical high which objectively takes into account of the distribution of thermal factors is set up. Finally, based on the above obtained nonlinear dynamical model, the complicated dynamic behaviors and mechanism of the subtropical high under the impact of heat force are analyzed and discussed, also some new opinions are obtained. For example, the east-west sensitive heat intensity and the configuration distribution and the east-west sensitive heat difference are important factors that lead to a complex configuration (such as the subtropical high double-ridges phenomenon) of the subtropical high flow field and potential field. The heliacal season radicalization heat and the east-west sensitive heat distribution of the East Asia are the important reasons that lead to the subtropical high mutations and the subtropical high flow abnormality, such as the subtropical high north leap and west extend.

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First-principles calculation of elastic and thermodynamic properties of copper nitride

Li Shi-Na, Liu Yong

Acta Physica Sinica. 2010, 59 (10): 6882 doi: 10.7498/aps.59.6882
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A first-principles full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory is applied to the study of the static equilibrium lattice structure as well as the elastic constants of the cubic anti-ReO₃ structural copper nitride(Cu₃N). The quasi-harmonic Debye model, in which the phononic effects are considered, is used to investigate the thermodynamic properties of Cu₃N. The pressure and temperature dependences of lattice constant, heat capacity and thermal expansion coefficient are successfully obtained . The bulk modulus and Debye temperature are also calculated at different pressures and temperatures.

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Network model with synchronously increasing nodes and edges based on Web 2.0

Xiong Fei, Liu Yun, Si Xia-Meng, Ding Fei

Acta Physica Sinica. 2010, 59 (10): 6889 doi: 10.7498/aps.59.6889
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We investigate the growing process and topological features of Web 2.0 networks. By analyzing the network’s degree distribution, average degree and time evolution of the node degree of an actual blog on portal website, we found these properties are different from those of the former scale-free network models. According to the growth characteristics of actual networks, we put forward a new type of network with synchronously increasing nodes and edges, including construction algorithms of randomly linking and connection between close neighbours. The simulation results show that the networks generated from our model have power-law degree distribution in case of absence of the preferential attachment process, and the clustering coefficient increases and the connectivity correlations are assortative.

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A novel quartz micro-structure based on shear stress detection and its gyroscopic effect

Xie Li-Qiang, Wu Xue-Zhong, Li Sheng-Yi, Wang Hao-Xu, Dong Pei-Tao

Acta Physica Sinica. 2010, 59 (10): 6896 doi: 10.7498/aps.59.6896
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In order to simplify sidewall electrode pattern of quartz gyroscope, a novel micro-structure used to sense Coriolis’ force based on shear stress detection is demonstrated. The approach of shear stress detection is analyzed and the structure of sidewall electrode is a single polarity electrode. A tapered beam with 15° taper designed as the sensing beam can increase its sensitivity. A prototype structure is fabricated by processing z-cut quartz by anisotropic wet etching technique. The prototype has a drive mode frequency of about 5.6 kHz, and the quality factor is over 5000 in atmosphere. The spectrum analysis of the structure’s output signal reveals the Coriolis force, which validates our new design scheme.

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Calculation of meniscus force during separation of microsurfaces

Liu Si-Si, Zhang Chao-Hui, Liu Jun-Ming

Acta Physica Sinica. 2010, 59 (10): 6902 doi: 10.7498/aps.59.6902
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The adhesive force between microsurfaces is very important to microelectric mechanical system (MEMS), being always a key factor that detemines the energy dissipation and even the life span. In MEMS, the meniscus force mainly depends on the meniscus shape formed between the contact surfaces. This paper analyzes the meniscus shape changes during the seperation of two microsurfaces. Different meniscus shapes were obtained as a result of different hydrophilic/hydrophobic properties, initial liquid heights and separate distances and so on. The fracture height, the meniscus force value and their change rules in different initial conditions are obtained by numerical simulation, which provides a basis of the MEMS performance analysis and life span calculation.

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Photoacoustic signal saturation characteristics of concentrated gases

Yuan Chang-Ying, Yan Zheng-Xin, Meng Gui, Li Zhi-Hui, Shang Li-Ping

Acta Physica Sinica. 2010, 59 (10): 6908 doi: 10.7498/aps.59.6908
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The photoacoustic (PA) spectrum of methane in the concentration range of 5%—100% has been experimentally investigated by coustant direct current drive coupling mechanical chopper technology. The results indicated that abnormal signal saturation occurred at high gas concentrations. The main reasons and its correlated factors of the photoacoustic signal has been quantitatively analyzed based on signal absorption and photoacoustic principles. It is found that the change in coupling coefficient of sound source and optical cavity modes caused by the intensity of incident light absorbed by gas sample is the major reason, and a criterion was put forward for signal saturation depth estimation.

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Gas concentration and temperature reconstruction by genetic simulated annealing algorithm based on multi-wavelengths diode laser absorption spectroscopy

Li Ning, Weng Chun-Sheng

Acta Physica Sinica. 2010, 59 (10): 6914 doi: 10.7498/aps.59.6914
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Gas concentration and temperature distribution reconstruction is realized based on tunable diode laser absorption spectroscopy. A measurement system using wavelength multiplexing technology with four absorption transitions is designed to reduce the number of projections and enrich the gas absorption measurement data. According to the nonlinear system established, a hybrid algorithm based on genetic algorithm and simulated annealing algorithm is introduced to obtain the global optimization and improve the search efficiency. A model for H₂O concentration and temperature distribution in combustion is assumed, and numerical simulation is utilized to reconstruct the images with the transitions within 1.3—1.5 μm range. Both concentration and temperature distribution reconstruction results are in agreement with the model. The influence of random errors in projections on reconstruction is also analyzed. The increased error in projection would lead to larger mean square error of temperature reconstruction results, but little affect the concentration reconstruction results.

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Nanofocusing by phase delayed plasmonic nanostructures illuminated with a linearly polarized light ^Hot!

Song Wen-Tao, Lin Feng, Fang Zhe-Yu, Zhu Xing

Acta Physica Sinica. 2010, 59 (10): 6921 doi: 10.7498/aps.59.6921
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We report the near-field nanofocusing through two types of plasmonic nanostructures consisting of annular grooves and annular slit, respectively. The radius of one half of each circle is designed to be bigger than the other half by half wavelength of the surface plasmon polaritons. By illuminating the structures with linearly polarized light, one single tight focal spot was detected by the scanning near-field optical microscope. Compared with the method of using radially polarized light, this method does not need to keep the center of the illuminating light right on the center of the structure, hence is much easier to use. Furthermore, theoretical simulations based on the finite-difference time-domain method testified the experimental results.

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Design and fabrication of hard X-ray phase grating

Liu Xin, Lei Yao-Hu, Zhao Zhi-Gang, Guo Jin-Chuan, Niu Han-Ben

Acta Physica Sinica. 2010, 59 (10): 6927 doi: 10.7498/aps.59.6927
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The x-ray phase grating made on silicon wafer was designed under considerations of the parameters of the phase contrast imaging system, the spatial coherence characteristics of x-ray source and its diffraction efficiency for x-ray of 40—100 keV, which is usually used for phase contrast imaging in laboratories and hospitals. The phase grating with diameter of 5 inch , pitch of 5.6 μm, wall width of 2.8 μm and depth of 40—70 μm depending on the energy of x-ray photon, was fabricated using the technique of photo-assisted electrochemical etching developed in our lab. Two special methods, namely, the enhancement of the voltage applied to the silicon wafer and modification of the current density defined by Lehmann formula, have been used to reduce the lateral etching. A reproducible technique has been developed for fabrication of precise and large x-ray phase grating on silicon wafer.

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Possible probe on the momentum dependent interaction in the equation of state of nuclear matter

Liu Jian-Ye, Guo Wen-Jun

Acta Physica Sinica. 2010, 59 (10): 6933 doi: 10.7498/aps.59.6933
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The effects of momentum dependent interaction on the kinetic energy spectrum of the neutron-proton ratior_b(E_k)in the equation of state of nuclear matter was investigated.We found that the kinetic energy spectrum of the neutron-proton ratio r_b(E_k) depends sensitively on the momentum dependent interaction and weakly on the in-medium nucleon-nucleon cross section and symmetry potential so that the r_b(E_k) is a sensitive physical probe for extracting the information of momentum dependent interaction in the heavy ion collisions. At the same time, the comparing investigate between r_b(E_k) for the neutron-rich collision system and the same mass stable collision system gives a important judgment for extracting the information of momentum dependent interaction in the heavy ion collisions.

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Spectroscopic studies of molecular ions and their dissociation dynamics by the threshold photoelectron-photoion coincidence

Tang Xiao-Feng, Niu Ming-Li, Zhou Xiao-Guo, Liu Shi-Lin

Acta Physica Sinica. 2010, 59 (10): 6940 doi: 10.7498/aps.59.6940
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In a recently built threshold photoelectron-photoion coincidence spectrometer, the photoelectrons and photoions were velocity-focused simultaneously to effectively improve the collection efficiency and the energy resolution. With this spectrometer we measured the threshold photoelectron spectra (TPES) and the mass-selected threshold photoelectron-photoion coincidence mass spectra (TPEPICO-MS) of NO molecules, as well as Xe/Ar/Ne rare gas mixtures. The ionization potential of NO was accurately determined, and the vibrationally resolved TPES spectra of the X¹Σ⁺, c³Π and B¹Π states of NO⁺ were obtained. Subsequently, the dissociation dynamics of the c³Π state of NO⁺ were studied by measuring the TPEPICO-MS and fitting the time-of-flight profile of the N⁺ fragment. The overall kinetic energy released from dissociation was determined to be 0.717 eV.

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Nano-resolution imaging of filopodia in HeLa cells ^Hot!

Chen Dan-Ni, Liu Lei, Yu Bin, Niu Han-Ben

Acta Physica Sinica. 2010, 59 (10): 6948 doi: 10.7498/aps.59.6948
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Nano-resolution imaging based on single molecule localization is simulated with Matlab. A sample consisted of several lines of molecules are simulated imaged. The results demonstrate that two lines of molecules separated by 20 nm can be resolved. Effect of pixel size on the localization accuracy is also discussed here. Nano-resolution imaging is realized on an IX71 inverted fluorescent microscope with the resolution (FWHM) of 48 nm. Nano-resolution images of filopodias are reconstructed, in which filopodias with diameter of 75 nm are resolved.

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Structure and properties of Zr_nPd clusters by density-functional theory

Jin Rong, Chen Xiao-Hong

Acta Physica Sinica. 2010, 59 (10): 6955 doi: 10.7498/aps.59.6955
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The geometries, stabilities and electronic properties of Zr_nPd (n=1—13) clusters have been systematically investigated by using density functional theory B3LYP/LANL2DZ Method. The optimized geometries of the Zr_nPd clusters have been considered, and the growth patterns of the Zr_nPd clusters have been discussed. The results show that the isomers with Pd atom on the surface of Zr_nPd cluster are more stable. On the basis of the optimized geometries, various energetic properties including the average binding energies, the second-order difference of energies, the gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), have been calculated for the most stable isomers of Zr_nPd clusters. The investigation shows that the Zr_nPd (n=7, 12) clusters have high stability and the Zr_nPd clusters are more stable in chemical stability than the respective Zr_nCo and Zr_nFe clusters. Magnetic clusters with higher magnetic moment can be acquired by doping Pd atom to Zr_n (n>5) clusters. Mulliken population analysis shows that there is a weak charge transfer from Zr atoms to Pd atom for Zr_nPd clusters.

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Prediction of transport properties of O₂-CO₂ mixtures based on the inversion method

Wang Xiao-Po, Song Bo, Wu Jiang-Tao, Liu Zhi-Gang

Acta Physica Sinica. 2010, 59 (10): 7158 doi: 10.7498/aps.59.7158
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A new potential energy surface of O₂-CO₂ mixtures was obtained by means of inversion method. According to the kinetic theory of gas,the transport properties of O₂-CO₂ mixtures,including viscosity coefficient,thermal diffusion coefficient and thermal diffusion factor, were caluclated in the temperature range between 273.15 K and 3273.15 K at zero-density.

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Electrostatic oscillation and coupling resonance in double trap of unbalanced magnetron sputtering

Mu Zong-Xin, Mu Xiao-Dong, Jia Li, Wang Chun, Dong Chuang

Acta Physica Sinica. 2010, 59 (10): 7164 doi: 10.7498/aps.59.7164
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The coupling resonance is induced by the plasma electrostatic oscillation in the magnetic trap consisting of the cross-field at the surface of the unbalanced magnetron sputtering target and the potential well composed of the magnetron sputtering target and the opposite bias substrate in parallel. Langmuir probe was used to study the plasma properties and power spectra density (PSD) of the floating potential signals. Under typical discharge conditions, the eigenfrequencies in both traps were respectively in the range of 30—50 kHz or 10—20 kHz, and the electron temperatures in both traps calculated with the acoustic standing wave mode conformed with the experimental results.

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Plasma convergence time of radiation hohlraum with single-end drive on SG-III prototype laser facility

Cao Zhu-Rong, Li San-Wei, Jiang Shao-En, Ding Yong-Kun, Liu Shen-Ye, Yang Jia-Min, Zhang Hai-Ying, Yang Zheng-Hua, Li Hang, Yi Rong-Qing, He Xiao-An

Acta Physica Sinica. 2010, 59 (10): 7170 doi: 10.7498/aps.59.7170
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Plasma convergence time of half-hohlraum target with single-end drive by 8 bundled lasers are researched on SG-III prototype laser facility. Four radiation sources were established by changing the structure of target bottom. The relation between plasma radial convergence time obtained by x-ray framing camera and radiation temperature from soft x-ray spectrometer have been investigated. The results showed that plasma radial convergence time is directly proportional to radiation temperatures on different structures of target bottom, which lengthens as radiation temperature increases.

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Runaway electrons behaviors during ion cycolotron range of frequency and lower hybrid wave plasmas in the HT-7 Tokamak

Lu Hong-Wei, Hu Li-Qun, Zhou Rui-Jie, Xu Ping, Zhong Guo-Qiang, Lin Shi-Yao, Wang Shao-Feng

Acta Physica Sinica. 2010, 59 (10): 7175 doi: 10.7498/aps.59.7175
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HT-7 Tokamak is equipped with a lower hybrid wave (LHW) system and an ion cyclotron range of frequency (ICRF) system. ICRF can accelerate ions effectively, while LHW can accelerate electrons effectively. The generation of runaway electrons during the LHW and ICRF plasmas, as well as the time evolution of electron temperature during the ICRF and LHW plasmas was investigated in this paper. The runaway critical energy for runaway electrons was also calculated according to the experimental data. It was observed that the combination of ICRF and LHW can produce a higher heating efficiency and a better coupling between ICRF and plasmas if the power of LHW exceeds a critical value. Therefore, the generation of runaway electrons and fusion neutrons are affected by ICRF.

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On the effect of magnetic field gradient on the discharge characteristics of Hall thrusters

E Peng, Duan Ping, Jiang Bin-Hao, Liu Hui, Wei Li-Qiu, Xu Dian-Guo

Acta Physica Sinica. 2010, 59 (10): 7182 doi: 10.7498/aps.59.7182
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An experiment was performed to investigate how the magnetic field gradient in strong field zone affects the discharge processes of Hall thrusters, such as the ionization and acceleration of propellants, for further research on optimal design theory of magnetic field in discharge channels of Hall thrusters. The results show that magnetic field strength has little effect on the ionization of propellants within the designed range of magnetic field gradient, but has significant influence on the acceleration of ions.With the increase of magnetic field gradient, the ion-beam energy distribution tends to be concentrated, and the thrust efficiency tends to rise. Finally, further increase of magnetic field gradient may lead to a series of physical problems,among whith such as the finite Larmor radius effect, the changes in the law of electronic conduction mechanism, and the magnetic field gradient drift are analyzed.

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Impact of injecting positions on penetration and deposition of supersonic molecular beam on Tokamak

Jiao Yi-Ming, Yao Liang-Hua, Feng Bei-Bin, Chen Cheng-Yuan, Zhou Yan, Shi Zhong-Bing, Dong Jia-Qi, Duan Xu-Ru

Acta Physica Sinica. 2010, 59 (10): 7191 doi: 10.7498/aps.59.7191
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Fuelling and particle control are important topics for ITER physics. Because of the low efficiency of gas puffing and the high cost of pellet injection, other methods were explored in the last decades. A new method for plasma gas fueling, the pulsed supersonic molecular beam injection (SMBI) was successfully developed at Southwestern Institute of Physics in China and applied on HL-1M and HL-2A devices in recent years. SMBI possesses a great advantage over conventional gas puffing, mainly due to the higher instantaneous fueling intensity and speed, smaller spread of velocity and angular distribution of the particles than the latter. In this paper, we report the experiment results of the SMB injected from LFS and HFS in HL-2A device, the effect of  Δ B on SMB penetration is considered. During SMB injection in Tokamak, there is a rapid movement of the ablation beam substance towards the outward major radius R direction. The favorable injection from the high field side in order to promote deeper fuel penetration can be obtained. The motion has been attributed to a vertical curvature and  Δ B drift current induced inside the ionized ablated SMB particles by the 1/R toroidal field variation. The uncompensated vertical drift current inside the weakly diamagnetic ablation particles will cause charge separation at the plasma edge. The resulting electrostatic field induces the  E×B  drift to the large R side of the torus.

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Numerical simulation of femtosecond laser heating of metal films using electron thermal emission

Chen An-Min, Gao Xun, Jiang Yuan-Fei, Ding Da-Jun, Liu Hang, Jin Ming-Xing

Acta Physica Sinica. 2010, 59 (10): 7198 doi: 10.7498/aps.59.7198
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The whole process of the electron thermal emission by ultrafast pulsed laser is studied in the paper. When an ultra-short laser pulse interaction with the target film, first of all, the incident laser excites free electrons within the absorption depth, next, electron energy is transferred to nearby lattice through the heat transfer systems of the free electron and lattice, and by the thermal coupling between the electron and the lattice, the energy is delivered to the internal material. Therefore, in a short period of ps and shorter, the energy coupling of the electron and lattice can not be established. So that the electron temperature is much higher than the lattice temperature, the electron thermal emission becomes apparent. The characteristics of thermionic emission of the films during ultrashort pulse laser ablation are investigated using two-temperature model coupled with the Richardson-Dushman equation. It is found that electron thermal emission can significantly change the development of electron and lattice temperatures, meanwhile, the film thickness and laser fluence directly affect electron thermal emission.

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Preionization of buffer chamber in ATON Hall thruster

Liu Hui, Wu Bo-Ying, E Peng, Duan Ping

Acta Physica Sinica. 2010, 59 (10): 7203 doi: 10.7498/aps.59.7203
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ATON is a new type of Hall thruster proposed in the 1990s, while the buffer chamber is a new structure used in it. In this paper, the main functions of buffer chamber are analyzed, and the method by adopting additional electric source is proposed to increase the preionization rate. Then the particle in cell method is used to simulate the plasma behavior in it. The numerical results show that additional electric power source can increase preionization rate effectively.

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Application of wavelet transform in the dynamic frequency spectrum analysis of magnetohydrodynamics oscillations on HT-7 Tokamak

Ma Tian-Peng, Hu Li-Qun, Chen Kai-Yun

Acta Physica Sinica. 2010, 59 (10): 7209 doi: 10.7498/aps.59.7209
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Gaussian complex wavelet transform was used in the dynamic frequency spectrum analysis of HT-7 MHD (magneto-hydrodynamic) oscillations. It is shown that this method can provide good temporal resolution and spatial resolution, which is suitable to analyze the dynamic frequency spectrum of MHD oscillations. Typical discharges with sawtooth and MHD instabilities are analyzed with this method. The results show that the oscillation frequency is associated with the plasma pressure gradient.

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Compression properties of rare gases in region of ionization

Zheng Jun, Gu Yun-Jun, Chen Qi-Feng, Chen Zhi-Yun

Acta Physica Sinica. 2010, 59 (10): 7472 doi: 10.7498/aps.59.7472
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The equations of state and ionization degrees of helium, neon, argon, krypton, and xenon in the region of ionization have been presented based on the Saha equation with the Debye-Hückel correction. The calculated results were compared with the experimental data and other calculations and the reliability of this model has been validated. The compressibility and the regularity of ionization were discussed by the calculated isotherms and shock compression curves of the rare gases. The results indicate that xenon has better compression resistance among the gases cousidered.

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New GMF+RAIN model based on rain rate and application in typhoon wind retrieval

Zhang Liang, Huang Si-Xun, Zhong Jian, Du Hua-Dong

Acta Physica Sinica. 2010, 59 (10): 7478 doi: 10.7498/aps.59.7478
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This paper firstly selects three typhoon cases (SHANSHAN, YAGI, XANGSANE) which occurred in 2006, and analyzes the distribution characteristic of the normalized radar cross-section (NRCS, σ^o), which were received by QuikSCAT scatterometer in the case of rain effect. Secondly, in order to account for the effects of rain to σ^o, we follow the theory of atmospheric radiation transfer and introduce two different types of rain radiation transfer models (called SY model and AMSR model, respectively), then combine these two models with NSCAT2 GMF to produce an improved GMF suitable for the case of rain effect (called GMF+RAIN). Lastly, based on this GMF+RAIN, we use the ambiguity removal method which integrates 2DVAR (two-dimensional variational assimilation) with MSS (multiple solution scheme) to retrieve the YAGI and XANGSANE typhoon wind fields which had different intensity. The new approach which combines GMF+RAIN with 2DVAR+MSS improves the result, which further verifies the effectiveness of GMF+RAIN. This new approach also makes the scatterometer data more effective and valuable for application in the research of typhoon.

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Long-range correlation and group-occurrence of return intervals of extreme events

Wang Qi-Guang, Hou Wei, Zheng Zhi-Hai, Feng Ai-Xia, Deng Bei-Sheng

Acta Physica Sinica. 2010, 59 (10): 7491 doi: 10.7498/aps.59.7491
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This paper studies the long range correlation of the return intervals of extreme events using the method of percent threshold. In view of return intervals of the extreme events, the long range-correlations of return intervals are studied by simulated time series when the extreme events happened. It is found that the constructed extreme event time series also have the characteristics of long-range correlation if the original time series have one. Meanwhile, the scaling exponents of the two time series are very close, it is very different from the return intervals of stochastic series. The probability density function of time series with long-range correlation has significant difference from the stochastic time series. It was found that there is a group-occurrence phenomenon in the return time series with long-range correlation, so a so-called group occurrence index is defined and computed, the stability of the index is also studied. The results show that the reason of the group occurrence of extreme events series is attributed to the long-range correlation of time series.

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Distribution of most probable temperature of daily average temperature records in China and the slowing down of warming trend

Qian Zhong-Hua, Feng Guo-Lin, Gong Zhi-Qiang

Acta Physica Sinica. 2010, 59 (10): 7498 doi: 10.7498/aps.59.7498
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Most probable temperature (MPT) is defined according to the skewed function by using daily average temperature records of the National Meteorological Information Center from 1961 to 2008 in China, it can represent every stations background temperature explicitly. MPT interannual variations show that MPT in summer was relativelly low-temperature-major before the mid-1990s and from then on was warming with fluctuation, but since 2005 the trend slowed down, and that MPT in winter was relatively low-temperature-major in 1961—1986, and from 1987 to the beginning of the 21st century was warming up obviously, but since 2000 the warming trend slowed down. The warming amplitude in winter was stronger than that in summer and the time of beginning of warming in winter was earlier than that in summer by about 5—10 years. Studying three climate states of MPT changes of 1961—1990, 1971—2000 and 1981—2008, we found that in summer MPT got warmer obviously in the third climate state, while in winter in the second state. MPT warming trend was slowing down in the third state. Its worthy of note that in Sichuan, Guangdong and Guangxi MPT even began to decline in the last few years. Whether it means climatic transformation or not needs further research.

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A parallel immune genetic algorithm in adaptive resource allocation for cognitive radio network

Zhou Jie, Zu Yun-Xiao

Acta Physica Sinica. 2010, 59 (10): 7508 doi: 10.7498/aps.59.7508
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A parallel immune genetic algorithm for adaptive modulation and cognitive radio spectrum assignment was developed, and simulations are conducted to compare the parallel immune genetic algorithm method with simple genetic algorithm and non-adaptive modulation algorithm. The simulation results show that the algorithm has strong global searching capability and fast convergence speed, and it is efficient and superior to the simple genetic algorithm and non-adaptive modulation algorithm in case of limited total transmitting power and presence of notable bit error rate, while the computation complexity is reduced significantly.

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Optical variability periodicity analysis of BL Lac object S5 0716+714 based on bispectrum estimation

Tang Jie, Zhang Xiong

Acta Physica Sinica. 2010, 59 (10): 7516 doi: 10.7498/aps.59.7516
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Large and rapid variability is one of the defining properties of BL Lac objects. Variability in BL Lac objects has always served as a powerful and important tool for inquring into the physics of these unusual objects. From an extensive seach in the literature we have collected a total of data points of effective observations of BL Lac object S5 0716+714 in V, R and I bands from 1994 to 2008. Then these data are processed on 30 days baseline by autoregressive bispectrum model. In order to eliminate noise interference to extract useful information in the background of Gaussian noise, we propose a method of signal analysis and processing,which analyzes the additive Gaussion noise signal based on autoregressive bispectrum model. Bispectrum is not sensitive to Gaussian noise, it not only suppresses the Gaussion noise in the signal and greatly improves the signal to noise ratio, but also can identify the periodical variations of BL Lac objects. Our results show that the long term periods of variation are 3.33 years and 3.47 years. The conclusion is consistent with 3.3 years period which was found by Raiteri et al. The brightness peak was observed in 2007, so we expect the next burst in 2011—2012.

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Modeling of infrared characteristics of deep space target

Sun Cheng-Ming, Yuan Yan, Zhang Xiu-Bao

Acta Physica Sinica. 2010, 59 (10): 7523 doi: 10.7498/aps.59.7523
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An accurate modeling method is proposed for the infrared characteristics of space target. Fully considering the heat conduction among the surfaces and the effect of inner heat source, the heat balance equation is presented for space target in the background radiation environment, and on the basis of structural and material properties of the target, the temperature distribution of target surface is calculated by node network method. According to the optical radiation and scattering theory, the mathematical model on infrared characteristics of space target is established and the general calculation method for infrared characteristics of space target is derived. Finally, the temperature field and irradiation distribution of ZY-1 and FY-3 satellite are computed using the given parameters. The computation results illustrate the validity of the theoretical analysis.