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Experimental simulation of quantum entanglement distribution over a high-loss channel
Yin Juan, Yong Hai-Lin, Wu Yu-Ping, Peng Cheng-Zhi
Acta Physica Sinica, 2011, 60 (6): 060307
High-dimensional entanglement for long distance quantum communication
Yin Juan, Qian Yong, Li Xiao-Qiang, Bao Xiao-Hui, Peng Cheng-Zhi, Yang Tao, Pan Ge-Sheng
Acta Physica Sinica, 2011, 60 (6): 060308
Effect of exponential-doping structure on quantum yield of transmission-mode GaAs photocathodes
Zhang Yi-Jun, Niu Jun, Zhao Jing, Zou Ji-Jun, Chang Ben-Kang
Acta Physica Sinica, 2011, 60 (6): 067301
Acta Physica Sinica  
  Acta Physica Sinica--2011, 60 (6)   Published: 15 June 2011
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ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

A novel dual-band evolved split ring magnetic resonance metamaterial

Tang Ming-Chun, Xiao Shao-Qiu, Deng Tian-Wei, Wang Duo, Bai Yan-Ying, Jin Da-Peng, Wang Bing-Zhong
Acta Physica Sinica. 2011, 60 (6): 064101 doi: 10.7498/aps.60.064101
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A novel dual-band evolved magnetic metamaterial operating at X-band is proposed in the paper, which is compounded by evolved split ring resonators based on the principle of magnetic resonance. The dual frequencies can be easily adjusted due to its excellent performance of weak mutual coupling between the outer ring and the inner ring. Our work provides the helpful research ideas and design methods for multiple-band and wideband metamaterials.

Fast linear transformer high power pulse generator

Xiang Fei, Tan Jie, Luo Min, Wang Gan-Ping, Kang Qiang
Acta Physica Sinica. 2011, 60 (6): 064102 doi: 10.7498/aps.60.064102
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The realization technique of fast linear transformer driver on the compact modularized high power pulse generator was expounded. The influence on Modular amount and the output quality of fast linear transformer driver (FLTD) was analyzed. The limitation on FLTD primary inductance was reduced by optioned feeding structure. The waveform distortion was weakened by designed back swing coil. Through engineering experiments, electron beam closed 0.8MeV with repetition frequency of 25 Hz and top time of ~80 ns were obtained. So this paper gave a new idea for research on the modularization compact high power pulse generator with higher repetition rate.

808nm vertical-cavity surface-emitting laser with large aperture

Hao Yong-Qin, Feng Yuan, Wang Fei, Yan Chang-Ling, Zhao Ying-Jie, Wang Xiao-Hua, Wang Yu-Xia, Jiang Hui-Lin, Gao Xin, Bo Bao-Xue
Acta Physica Sinica. 2011, 60 (6): 064201 doi: 10.7498/aps.60.064201
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For the carriers-crowded effect in vertical-cavity surface-emitting laser (VCSEL), the injected current passes mainly through the edge of the circular active region, which results in nonuniformity of the output power density and annular facula with a poor central intensity, especially in large aperture VCSEL. How to restrain carriers-crowded effect becomes a technique problem to develop electrically pumped high power large aperture VCSEL. High power 808 nm VCSEL is demonstrated by introducing a novel structure. And an output power of 0.3 W is achieved at 1 A at room temperature under continuous wave operation.

Sensitivity analysis of hybrid fiber Fabry-Pérot refractive-index sensor

Gong Yuan, Guo Yu, Rao Yun-Jiang, Zhao Tian, Wu Yu, Ran Zeng-Ling
Acta Physica Sinica. 2011, 60 (6): 064202 doi: 10.7498/aps.60.064202
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Theoretical expressions for analyzing the refractive-index sensitivity of the hybrid optical fiber Fabry-Pérot sensor is developed. Influence of the experimental parameters on the measurement sensitivity is discussed. Hybrid optical fiber Fabry-Pérot sensor is fabricated by chemically etching a graded-index multimode fiber (GI-MMF), fusion splicing it into a single mode fiber, and cleaving the GI-MMF. The fringe contrast exceeds 30 dB and the corresponding measurement sensitivity of refractive index is about 45 dB per refraction index unit. Experimental results are in good agreement with the theoretical ones. It is indicated by the numerical simulations that the performance of this kind of sensor can be further improved.

External quantum efficiency of microcavity planar emitting devices

Ma Feng-Ying, Su Jian-Po, Guo Mao-Tian, Chi Quan, Chen Ming, Yu Zhen-Fang
Acta Physica Sinica. 2011, 60 (6): 064203 doi: 10.7498/aps.60.064203
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The calculation models of the external quantum efficiency for the planar surface emitting devices are presented with considering their spatial distribution of radiance/luminance and relative spectral power distribution. These models can be applied to all kinds of planar surface emitting devices including OLEDs, VCSEL, MOLED, MCLED and planar THz emitting devices. Two planar emitting devices with and without cavity are fabricated with the structure of Glass /DBR /ITO /NPB /Alq ∶C545T /Alq /LiF /Al and Glass /ITO /NPB /Alq ∶C545T /Alq /LiF /Al. The external quantum efficiencies are calculated at different current densities using the corresponding model. The external quantum efficiency of the cavity device is close to 1.5% at a current density of 14 A/m2 and brightness of 100 cd/m2, and reaches 2% around 0.14 A/m2 and 2.2 cd/m2.

Theoretical research of Fernald forward integration method for aerosol backscatter coefficient inversion of airborne atmosphere detecting lidar

Liu Hou-Tong, Chen Liang-Fu, Su Lin
Acta Physica Sinica. 2011, 60 (6): 064204 doi: 10.7498/aps.60.064204
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Preliminary inversion results show that the Fernald forward integration method (FFIM) can be used to calculate aerosol backscatter coefficient from airborne atmosphere detecting lidar. But the corresponding theoretical explanations have not been found in relevant papers. In this paper,We use the simulated data based on the ground-based atmosphere detecting radar in Hefei lidar data on February 27, 2008, to quantitatively analyze the above inversion results obtained by the FFIM . Results show that there are three main reasons that the FFIM can be used to calculate aerosol backscatter coefficient when the altitude of lidar calibration points is about 10km. First, the inversion error cannot be infinite and negative results will not appear because the difference batween the denominator items in the Fernald forward integration equation is always greater than zero. Second, inversion error is no more than 0.006 when calibration error is 100%, which is 0.6 percent of the denominator value. Third, Molecule backscatter coefficient is dominant in the calibration item of the Fernald forward integration equation. Big fluctuation range of aerosol backscatter coefficient in the calibration points has little influence on the calibration item value. In general, the atmosphere structure that has a small density in the upper layer but a big density in the lowerlayer, and a high calibration position are two basic reasons for which the FFIM can be applied to the aerosol backscatter coefficient inversion through using airborne atmosphere detecting lidar data.

Nonlinear Faraday rotation in electromagnetically induce transparency medium

She Yan-Chao, Zhang Wei-Xi, Wang Deng-Long
Acta Physica Sinica. 2011, 60 (6): 064205 doi: 10.7498/aps.60.064205
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By using multiple-scale methods, we study analytically the propagation properties of the weak linear polarization probe optical field in a cold lifetime-broadened five-level V type atomic system via electromagnetically induced transparency. It is shown that with the strength of the coupling field increasing, the absorption of the probe optical field decreases rapidly and the group velocity of the probe optical field increases quickly under the consideration of linear effect. However, the velocity is several orders of magnitude slower than the light speed in vacuum. Meanwhile, we find that for the same magnetic field the nonlinear Faraday rotation direction is opposite to linear Faraday rotation, and its rotation angle grows bigger than that of linear Faraday rotation. These results mean that the Faraday rotation of the electromagnetically induced transparency medium can be controlled by the nonlinear effect.

Generation of 27 GHz flat broadband chaotic laser with semiconductor laser loop

Feng Ye, Yang Yi-Biao, Wang An-Bang, Wang Yun-Cai
Acta Physica Sinica. 2011, 60 (6): 064206 doi: 10.7498/aps.60.064206
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Generation of flat broadband chaotic signal is demonstrated experimentally with a semiconductor laser loop, which consists of three laser diodes mainly. The output of each laser diode is injected into its neighbor diode as a loop. The injection light strength is controlled with erbium-dropped optical fiber amplifier or attenuator which is inserted between the diodes, and the detuning is adjusted by changing the temperature of the laser diode. Limited by the bandwidth of the laser diode, the bandwidth of the flat broadband chaotic signal is broader than 27 GHz or even more, and the fluctuation of the spectrum cure is less than 5 dB.

Influence of turbulence on the Rayleigh range of partially coherent cosh-Gaussian beams

Ji Xiao-Ling
Acta Physica Sinica. 2011, 60 (6): 064207 doi: 10.7498/aps.60.064207
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The analytical expressions for the Rayleigh range of partially coherent cosh-Gaussian beams both in free space and in atmospheric turbulence are derived. The influence of turbulence on the Rayleigh range of partially coherent cosh-Gaussian beams is studied. It is shown that the Rayleigh range of partially coherent cosh-Gaussian beams depends on the strength of turbulence and the beam parameters. The Rayleigh range decreases due to turbulence. The stronger the turbulence, the shorter the Rayleigh range is. In free space, the Rayleigh range increases with the increase of beam coherence parameter α , beam parameter β and Gaussian waist width w 0, and the decrease of wave length λ. However, the Rayleigh range is less sensitive to turbulence with α , β and w 0 decreasing and λ increasing. Furthermore, the influence of turbulence can be ignored when α , β and w 0 are small enough and λ is large enough.

Mode locked multi-core photonic crystal fiber laser

Fang Xiao-Hui, Hu Ming-Lie, Song You-Jian, Xie Chen, Chai Lu, Wang Qing-Yue
Acta Physica Sinica. 2011, 60 (6): 064208 doi: 10.7498/aps.60.064208
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A mode locked fiber laser based on Yb-doped large mode area photonic crystal fiber operating in the all-normal dispersion regime is experimentally studied. The eighteen cores of the gain fiber are arranged in array-type geometry with an equivalent mode diameter of about 52 μm. A sigma laser cavity is used without using any elements for dispersion compensation. Reliable self-starting mode-locking is achieved using a fast semiconductor saturable absorber mirror. The laser directly produces 4.92 ps chirped pulses at a 44.68 MHz repetition rate for an average power of 3.3 W corresponding to a pulse energy of 74 nJ. The pulses are compressed to 780 fs with a grating pair outside the cavity.

Effect of light polarization on thermal light correlated imaging

Zhang Er-Feng, Dai Hong-Yi
Acta Physica Sinica. 2011, 60 (6): 064209 doi: 10.7498/aps.60.064209
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Based on the effect of the polarization state of polarized light and the degree of polarization on the second-order correlation function, the influence of light polarization on visibility and signal-to-noise ratio (SNR) is investigated by use of the statistical optics theory. It is shown that only the polarization degree has effect on thermal light correlated imaging. The visibility of correlated imaging is a quadratic function of the polarization degree. An increase in the polarization degree leads to an increase in the SNR of conventional correlated imaging, but the SNR obtained by substracting the background and using the second-order coherent degree is independent of polarization degree.

Feasibility study of nonlinear optical loop mirror in the cascaded stimwlated Brillouin scatteving-based slow light system

Zheng Di, Pan Wei
Acta Physica Sinica. 2011, 60 (6): 064210 doi: 10.7498/aps.60.064210
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Based on the pulse compression characteristics in the nonlinear optical loop mirror (NOLM), the effect of NOLM on a cascad stimulated Brillouin scattering based slow light system is analyzed. In this paper, a ring structure is adopted to simulate the cascad system, so the complexity of system is reduced effectively, and the delay characteristics for various numbers of cycles and pump powers are studied. Analysis shows that the NOLM can effectively suppress the pulse-broadening in the cascaded slow light system, pump power determines the tendency and the final steady-state value of the broadening factor, and the broadening factor trends to the steady-state value after 4 cycles. Furthermore, zero-broadening can be obtained by optimizing the pump power; the delay time is continuously adjustable and without any limit in theory through changing the pump power and the number of cycles; through augmenting the pump power, the multiple-cascad-induced chirp can be reduced.

Enhanced stimulated Raman scattering of weak-gain mode C—H stretching vibration of benzene

Jiang Yong-Heng, Sun Cheng-Lin, Li Zhan-Long, Cao An-Yang, Li Zuo-Wei
Acta Physica Sinica. 2011, 60 (6): 064211 doi: 10.7498/aps.60.064211
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In the paper we report on the enhanced stimulated Raman scattering of the weak-gain mode of benzene. The stimulated Raman scattering of C—H stretching vibration of benzene is observed in liquid core optical fiber by mixing toluene. The result is explained by (toluene-benzene)+ and (toluene-toluene)+ dimmer of plasma

Design of high-index broken-ring-based all-solid photonic bandgap fibers

Li Yan-Feng, Hu Xiao-Kun, Wang Ai-Min
Acta Physica Sinica. 2011, 60 (6): 064212 doi: 10.7498/aps.60.064212
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The design of all-solid photonic bandgap fibers based on a high-index broken ring is investigated, where the background material is silica and the broken ring consists of several individual high-index rods. Density of states maps and Bloch mode field distributions obtained by plane wave expansion method show that a high-order bandgap in such fibers can be engineered and broadened. The principle is that both the azimuthal and the radial orders of the LP modes of the high-index rods in the cladding can be controlled by the broken ring. It is demonstrated that the highest azimuthal order of the group of less affected LP modes is determined by the rod number and the bandgap width is largely affected by the rod size. The high-order bandgap can be used to design all-solid photonic bandgap fiber with broad transmission ranges of 488 nm and 944 nm for a center wavelength of 800 nm and 1550 nm, respectively, and the transmission window features the typical normal-zero-anomalous dispersion profile.

Midinfrared As2 S3 chalcogenide glass broadband normal dispersion photonic crystal fiber with high birefringence and high nonlinearity

Wang Xiao-Yan, Li Shu-Guang, Liu Shuo, Zhang Lei, Yin Guo-Bing, Feng Rong-Pu
Acta Physica Sinica. 2011, 60 (6): 064213 doi: 10.7498/aps.60.064213
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A kind of midinfrared As2S3 chalcogenide glass photonic crystal fiber is proposed in this paper. The characteristics of this fiber are studied by multipole method, including high birefringence, chromatic dispersion, and high nonlinearity. Through numerical simulation, it is found that at midinfrared wavelength λ = 3.625 μm, the birefringence of this fiber reaches up to 0.098 and nonlinear parameters are 1.69 m-1 ·W-1 and 0.78 m-1 ·W-1 for x-polarized mode and y-polarized mode, respectively. In addition, the fiber keeps normal dispersion in a wavelength range from 3 to 7 μm . In conclusion, the band of transmitted wavelength extends into a midinfrared wavelength range of 3—10 μm, and high birefringence and high nonlinearity in this photonic crystal fiber are perfectly combined. The results are significant for the further development of new photonic devices.

Solitons of nonlinear Schrödinger equation withvariable-coefficients and interaction

Qian Cun, Wang Liang-Liang, Zhang Jie-Fang
Acta Physica Sinica. 2011, 60 (6): 064214 doi: 10.7498/aps.60.064214
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Search for exact solutions to the generalized nonlinear Schrödinger equation is one of the essential directions in studies of the nonlinear dynamics in optical soliton and Bose-Einstein condensates. Stable soliton modes are of great significance for the experimental realization and potential application. In this paper, based on the introduction of a similarity transformation, the variable-coefficient nonlinear Schrödinger equation is transformed into the nonlinear Schrödinger equation, and then the single soliton solution, two-soliton solution and soliton solution in continuous-wave background for the variable coefficient nonlinear Schrödinger equation are obtained by using the known solutions. Meanwhile, their image analysis and relative discussion are given by selecting the different parameters in detail.

New complexity metric of chaotic pseudorandom sequences using fuzzy relationship entropy

Chen Xiao-Jun, Li Zan, Bai Bao-Ming, Cai Jue-Ping
Acta Physica Sinica. 2011, 60 (6): 064215 doi: 10.7498/aps.60.064215
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A new complexity metric to evaluate the unpredictability of the chaotic pseudorandom sequences based on the fuzzy relationship entropy (F-REn) is proposed in the view of maximal randomness of the sequences with arbitrary length. On this condition,two basic properties of F-REn are proved. Simulations and analysis results show that, the proposed F-REn works effectively to discern the changing complexities of the chaotic pseudorandom sequences, and compared with complexity metric based on the approximate entropy(ApEn) and symbolic dynamics approach , F-REn works have obvious advantages in the applicability of symbolic space, the sensitivity of vector dimension and the robustness of resolution parameter.

M-dimensional space-time error correction code theory for switch node based on omnidirectionalradiation of electromagnetic wave

Xie Ying-Hai, Yang Wei, Xu Chang-Long
Acta Physica Sinica. 2011, 60 (6): 064216 doi: 10.7498/aps.60.064216
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In wireless communication field, the omnidirectional radiation of electromagnetic wave in free space is always considered as a big shortcoming, nevertheless, it can be used to improve the performace of wireless communication system in network entironment. Here, we consider that M nodes use a switch node to exchang their information in a wireless network. Differert from the conventional method, the switch node will take the joint coding method for the M independent information, then transmit the same codeword to all M nodes simultaneously through the omnidirectional radiation. For the novel network code, the mathematical definition of the M -dimension space-time error correction code is proposed, and some theorems about its performance are proved to lay a foundation to construct good codebooks. The redundancy of time and space domain is added to the novel codebook at the same time, and the efficiency of the transmit power is improved, so we can design high-rate codebook with good error detection and correction capability. Moreover, the complexity of its decoding algorithm can be reduced, owing to the distributed data processing. Here, we emphasize that contrary to one’s intuition, our proposed codebook reveals that it is in general not correct to take the rate of codebook which has the error detection and correction capability to be less than 1.

Equal intensity polarization-independent beam splitter based on photonic crystal self-collimation ring resonator

Tong Xing, Han Kui, Shen Xiao-Peng, Wu Qiong-Hua, Zhou Fei, Ge Yang, Hu Xiao-Juan
Acta Physica Sinica. 2011, 60 (6): 064217 doi: 10.7498/aps.60.064217
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By the equi-frequency contour analysis and the finite-difference time-domain simulation, it is observed that the distance of one lop in a photonic crystal self-collimation ring resonator can cause different periodic outputs of the ring resonator for TE and TM polarizations. Equal intensity polarization-independent beam splitter can be achieved by choosing a suitable propagation distance. It expands the range of application of beam splitter and will play a great role in integrated optical circuits.

Robust localization and identification method of moving sound sources based on worst-case performance optimization

Shi Jie, Yang De-Sen, Shi Sheng-Guo
Acta Physica Sinica. 2011, 60 (6): 064301 doi: 10.7498/aps.60.064301
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Based on the passive synthetic aperture principle, a new robust high-resolution focused array signal processing method of moving sound source localization and identification is proposed in this paper. By means of the integrated optimization, this method generates the coordinates of a virtual array and the data matrix through the vector maximum likelihood focused algorithm, then utilizes the sparse virtual array focused algorithm based on the worst-case performance optimization to obtain the robust high-resolution localization and recognition effects. The theory and the simulation analysis show that this method is applicable to the complex experimental situations such as non-uniform motion and tipsy array, and the focused spatial spectrum indicates the greater dynamic range, the sharper focused peak, and the stronger ability to suppress the fluctuations of the background noise. The higher robustness and better results of this proposed method are verified in the lake experiment. Under the same experimental condition, the dynamic range of high-resolution MVDR focused algorithm is only 3.5dB, however, it can reach 50 dB by the proposed method.

Surface capillary wave and the eighth mode sectorial oscillation of acoustically levitated drop

Yan Zhen-Lin, Xie Wen-Jun, Shen Chang-Le, Wei Bing-Bo
Acta Physica Sinica. 2011, 60 (6): 064302 doi: 10.7498/aps.60.064302
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The suspension of liquid drops provides a preferable boundary condition for investigating various free surface phenomena. Here we report the observation of concentric capillary wave formed on the surface of drastically flattened water drops levitated in ultrasound. The measured wavelength of capillary wave accords well with that from the classic dispersion relation equation. The eighth mode sectorial oscillation of acoustically levitated drop is excited by the active modulation of sound pressure. It is found that these phenomena are due to parametric excitation. The capillary wave is induced when the parametric instability arises and ultrasound pressure exceeds a threshold pressure. The sectorial oscillations take place when the equatorial radius varies at twice the natural sectorial frequency of the levitated drop. The frequency of the eighth mode sectorial oscillation decreases with the increase of equatorial radius and can be well described by modifying the Rayleigh equation. Further analysis reveals the parametric excitation mechanism for this kind of oscillations.

Theoretical and experimental study of femtosecond pulse laser heating on thin metal film

Ma Wei-Gang, Wang Hai-Dong, Zhang Xing, Wang Wei
Acta Physica Sinica. 2011, 60 (6): 064401 doi: 10.7498/aps.60.064401
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Ultrashort pulse laser heating is not only capable of resolving and observing the ultrafast interaction of energy carriers, i.e. electrons, phonons, but also widely applied to material processing, i.e., laser ablation. However, the previous theories, i.e., two-temperature model, parabolic one-step model, can be applied only to some limited segments. In this paper, according to the two-temperature model and Fourier’s law, a general theoretical model is presented for the description of the entire heat relaxation process after the thin metal film deposited on the substrate has been heated by the ultrashort pulse laser. Moreover, the heat conduction process is also experimentally studied by using the rear-pump front-probe transient thermoreflectance technique on Au/glass and Au/SiC at 300 K, and the theoretical prediction accords well with the experimental result, which illustrates the validity of the present theoretical model. Based on the good agreement between theoretical predictions and experimental data, the electron-phonon coupling factor of the thin gold film and thermal boundary conductance of the Au/glass and Au/SiC interfaces are extracted and the measured results are in good agrement with the previous reported values. The electron-phonon coupling factor is close to that of the bulk material and does not exhibit size effect. The thermal boundary conductance is greater than the prediction of diffuse mismatch model, and the reasons responsible for the discrepancies are electrons participating in the interfacial heat conduction, interfacial atom diffusion and inelastic scattering.

Discrete variational calculation of Hénon-Heiles equation in the Birkhoffian sense

Liu Shi-Xing, Liu Chang, Guo Yong-Xin
Acta Physica Sinica. 2011, 60 (6): 064501 doi: 10.7498/aps.60.064501
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The Hénon-Heiles equation that is nonlinear nonintegrable Hamilton system is studied by using the method of discrete variational valculation in the Birkhoffian sense. And the result from the method is compared with the result obtained by using symplectic algorithm and Runge-Kutta method, indicating that the method presented in this paper is reasonable and feasible in computing the dynamical action of the nonlinear nonintegrable Hamilton system in the Birkhoffian sense.

Magnetization mechanism of magnetized water

Ding Zhen-Rui, Zhao Ya-Jun, Chen Feng-Ling, Chen Jin-Zhong, Duan Shu-Xing
Acta Physica Sinica. 2011, 60 (6): 064701 doi: 10.7498/aps.60.064701
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The physical properties of three different kinds of water under the action of an electromagnetic field and stirring are studied. The result shows that the surface tension coefficient, the viscosity and the density of water significantly change with magnetic induction intensity and magnetization time. This experimental law has also been reported in many other papers, but has not yet been explained. In the present paper, according to the molecular structure of water and characteristics of hydrogen bond, we further study the mechanism of magnetized water with the theories of thermology, electromagnetism and structural chemistry, and also investigate more extreme phenomena about surface tension coefficient, viscosity and density of magnetized water. It is found that the breaking of a large number of hydrogen bonds is due to the fact ther electrons states are affected by magnetic field or perturbation, and thus the interaction between electrons is influenced when the water solution is magnetized in a field of 200 mT above. As the formation conditions of hydrogen bond are easily satisfied, the breaking and the forming of the hydrogen bond of the liquid water coexiste at a certain temperature, and their occurence probabilities are alternated in magnitude in the magnetization process, resulting in more extreme phenomena. The change extent of physical quantity with random fluctuation depends on the strong or weak extent of the breaking and the forming of hydrogen bond.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Range and annealing behavior of Er ions implanted in SiC

Qin Xi-Feng, Liang Yi, Wang Feng-Xiang, Li Shuang, Fu Gang, Ji Yan-Ju
Acta Physica Sinica. 2011, 60 (6): 066101 doi: 10.7498/aps.60.066101
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Er ions with an energy range of 300—500 keV are implanted in 6H-SiC crystal samples separately. The values of mean projected range Rp and range straggling ΔRp of Er ions with a dose of 5×1015 cm-2 implanted in 6H-SiC crystal are measured by Rutherford backscattering technique. The measured data are compared with TRIM code prediction. It is seen that the experimental Rp values are in good agreement with theoretical values, but for ΔRp values there are bigger differences between the experimental data and the theoretical values. Research shows that the higher the implanting energy, the heavier the damage is. Perfect recrystallization of 6H-SiC is achieved by annealing at 1400 ℃, however it is accompanied by the segregation of Er ions to the surface.

Dispersing performance of KTP(011) crystal

Zhao Jia, Cui Ming-Qi, Zhao Yi-Dong, Zhou Ke-Jin, Zheng Lei, Zhu Jie, Sun Li-Juan, Chen Kai, Ma Chen-Yan
Acta Physica Sinica. 2011, 60 (6): 066102 doi: 10.7498/aps.60.066102
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According to the requirements for the performance of analyzers in soft x-ray regime of synchrotron radiation, the qualities of various crystals often used in soft x-ray range are investigated. We find that crystals KTP (KTiOPO4)(011) crystal is an ideal one among large d-spacing crystals. We propose an experimental method to measure diffraction efficiencies of crystals with synchrotron radiation source. In particular, we find that the diffraction efficiency is closely related to the source emittance. The lattice constant and diffraction efficiencies of KTP(011)crystal are also presented in this paper.

Nanowelding of contact between carbon nanotubesand gold electrodes

Zuo Xue-Yun, Li Zhong-Qiu, Wang Wei, Meng Li-Jun, Zhang Kai-Wang, Zhong Jian-Xin
Acta Physica Sinica. 2011, 60 (6): 066103 doi: 10.7498/aps.60.066103
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We report on the results of molecular dynamics simulations of nanowelding at high temperature between the gold electrodes and single-walled carbon nanotubes (SWNTs). We find that SWNTs with gold nanoclusters absorbed on their tips can build an excellent welding contact with gold electrodes. First, gold clusters are placed on open tips of SWNTs and are annealed at 1100 K. Gold atoms enter into the SWNTs and a shell-like helical structure inside the SWNTs and an amorphous structure outside of the SWNTs. Furthermore, the SWNTs absorbed with gold cluster are then placed on surfaces of gold electrodes. After annealing at high temperature, gold atoms absorbed in the SWNTs are redistributed on the surface of the gold electrodes and form excellent welding contact with the electrodes. The best annealing temperature for welding is about 800 K.

Generalized planar fault energy of body-centered cubic Ta andits application to plastic deformation of mode Ⅱ crack tip

Mei Ji-Fa, Li Jun-Wan, Ni Yu-Shan, Wang Hua-Tao
Acta Physica Sinica. 2011, 60 (6): 066104 doi: 10.7498/aps.60.066104
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The generalized planar fault energy, including the generalized stacking fault (GSF) and the generalized twinning fault energy (GTF) of body-centered cubic metal Ta are investigated based on the embedded atom potential. The GSF of Ta, much different from that of fcc metal, reveals that no evident energy minimum is observed in the energy curve. This implies that only full dislocations are possibly emitted in the {112} slip plane. From the GTF it is predicted that the minimum thickness of a metastable twin is as large as four layers and the five-layer twin is more stable. The incipient twin Ta tends to grow thicker once it is created. To confirm the significance of the GSF and GTF in revealing incipient plasticity, quasicontinuum method is used to simulate the mode Ⅱ crack of single Ta crystal. The results show that deformation twin and full dislocation along <111> direction in {112} plane are two co-existing mechanisms of crack tip plastic deformation. The initial four-layer twin quickly extends into five-layer and more-layer twins with further loading. A full dislocation is emitted into the front of the crack tip in {112} plane. These two plastic deformation mechanisms are well explained by the GTF and the GSF respectively.

Effect of annealing on microstructure and mechanical propertiesof AlTiN multilayer coatings

Luo Qing-Hong, Lou Yan-Zhi, Zhao Zhen-Ye, Yang Hui-Sheng
Acta Physica Sinica. 2011, 60 (6): 066201 doi: 10.7498/aps.60.066201
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The AlTiN composition multilayer coatings with a periodic change in nitrogen content are deposited on high speed steel (W18Cr4V) substrates with a medium-frequency reactive magnetron sputtering system and TiAl targets and by alternately changing nitrogen flux during deposition. These of coatings are annealed separately at temperatures of 600, 700 and 800 ℃ in vacuum for 5 hours. Their microstructures are studied by x-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy, while their mechanical behaviors and adhesion properties are investigated using nano-indenter, scratch test, and friction and wear instrument. The results show that the AlTiN composition multilayer coatings obtained by alternately changing nitrogen flux during deposition possess stable and good mechanical properties. After 800 ℃ vacuum annealing, the interface of AlTiN multilayer coating is still very clear. Annealing increases crystallization degree and grain size of AlTiN multilayer coating, but the crystallization degree of high nitrogen content layer is still higher than that of low nitrogen content layer. After vacuum annealing, the hardness of AlTiN multilayer coating reduceds. The hardness of AlTiN multilayer coating after 800 ℃ annealing is larger than after 600 ℃ annealing, but as the annealing temperature increases, wear resistance and anti-spalling performance of AlTiN multilayer coatings decrease dramatically.

Simulation of bubble growth process in pool boilingusing lattice Boltzmann method

Zeng Jian-Bang, Li Long-Jian, Liao Quan, Jiang Fang-Ming
Acta Physica Sinica. 2011, 60 (6): 066401 doi: 10.7498/aps.60.066401
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In this paper, a new single-component lattice Boltzmann model, which is based on exact difference method and extended with an energy transfer equation to model heat transfer, is proposed to describe liquid-vapor phase transition process. The wettability of the heated wall is modeled by an interaction force between solid wall and fluid. This new model is validated through the simulation of water phase transition process. It is found that the simulation results are in good agreement with the experimental data. The surface tension of water, which is obtained from simulation results at different temperatures, is closed to experimental data. These results are in agree ment with those obtained from Laplace law. In order to demonstrate the availability of this model for dealing with phase transition and two-phase problems, the bubble growth process on a heated surface is simulated in pool boiling. It is found that the bubble departure diameter is proportional to g-0.5 and the release frequency scales with g0.75, where g is the gravitational acceleration. These results are in good agreement with those obtained from the empirical relationship and reference results. Finally, simulation results show no relationship between the bubble departure diameter and the static contact angle, but the bubble release frequency increases exponentially with the latter.

Analysis of heterogeneous nucleation on rough surfacesbased on Wenzel model

Zheng Hao-Yong, Wang Meng, Wang Xiu-Xing, Huang Wei-Dong
Acta Physica Sinica. 2011, 60 (6): 066402 doi: 10.7498/aps.60.066402
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Heterogeneous nucleation plays an important part in the solidification process. In order to describe the effects of the substrate surface on the heterogeneous nucleation, an idealized planar interface between the nucleus and the substrate is assumed in the consideration of the classical nucleation theory, but this may lead to the deviation of the experimental results from the theoretical predictions, since there is no idealized planar surface on any actual substrate. The heterogeneous nucleation procedure of solid phase on rough substrate surface is investigated, and the effect of the roughness factor of the substrate on nucleation energy is analyzed based on the Wenzel wetting model. The results show that when the intrinsic contact angle between the substrate and the nucleus in the base phase is less than 90°, higher roughness of the substrate surface makes it easier to induce heterogeneous nucleation; when intrinsic contact angle is greater than 90°, higher roughness would restrict the nucleation on the substrate surface. Meanwhile, attaching and wetting drift embryos on the substrate play an important part in the formation of effective nucleus on the substrate, while the change of interfacial free energy in the wetting process of the embryos on the rough substrate surface has an important effect on heterogeneous nucleation behaviors.

Effect of far field flow on the stability of thespherical crystal in undercooled melt

Cao Bin, Lin Xin, Huang Wei-Dong
Acta Physica Sinica. 2011, 60 (6): 066403 doi: 10.7498/aps.60.066403
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A model is developed to investigate the effects of far field flow on the solidification of a spherical particle from the melt, under the influence of thermal and solute flow. The stability of the spherical interface is studied and the growth rate of the interface perturbation is calculated. The perturbation to the maximum growth rate becomes larger when the spherical radius increases. The downwind side of the interface is more unstable than the upwind side. The effect of far field flow reduces the critical radius of the spherical crystal.

Shock-induced phase transformation in nanocrystalline iron

Ma Wen, Zhu Wen-Jun, Zhang Ya-Lin, Jing Fu-Qian
Acta Physica Sinica. 2011, 60 (6): 066404 doi: 10.7498/aps.60.066404
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The shock-induced phase transformation of nanocrystalline iron with different grain sizes is investigated by using molecular dynamic simulations. The critical shock stress for shock-induced phase transformation (from body-cubic centered α phase into hexagonal-close packed ε phase) of nanocrystalline irons is about 15 GPa. Under shock compression, the nanocrystalline irons first experience elastic deformation, then plastic deformation purely caused by grain boundaries, after that phase transformation nucleated mostly at the grain boundaries, and finally nucleation areas expanding into the entire samples. These processes can be reflected by the stress profile and the particle velocity profile, and also be distinguished by local atomic structures analyses in the corresponding areas. The microstructures of the shocked samples consist of grain boundary and hexagonal-closed packed new phase with the face-cubic centered atoms as the twin boundary. The grain size obviously influences the deformation of grain boundary and the microstructure after shock compression, and turns to change the profiles of stress or velocity. The mechanism is primarily analyzed.

Theoretical calculation of molar heat capacity at constant pressureof nanoparticle and nanocrystalline

Chen Hui-Min, Liu En-Long
Acta Physica Sinica. 2011, 60 (6): 066501 doi: 10.7498/aps.60.066501
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In this paper the theoretical calculation methods for CP(T) (molar heat capacity at constant pressure) values of nanoparticle and nanocrystalline are investigated. Theoretical formulas for calculating CP(T), Debye temperature and volume expansion coefficient of nanoparticle using melting point of nanoparticle are set up and the calculated values of CP(T) for copper nanoparticle are fairly consistent with the experimental ones. A relationship between Debye temperature and density of nanocrystalline is proposed, and Debye temperature can decrease with the reduction of nanocrystalline density. The calculated values of CP(T) of copper nanocrystalline are also quite consistent with the experimental ones. The bulk modulus of elasticity of nanocrystalline will drop off with the decrease of grain size of nanocrystalline, which should be taken into account when the CP(T) of nanocrystalline is calculated. The calculation methods proposed in this paper are feasible.

Molecular dynamics simulation of thermal conductivity for the TiO2/ZnO nano-film interface

Yang Ping, Wu Yong-Sheng, Xu Hai-Feng, Xu Xian-Xin, Zhang Li-Qiang, Li Pei
Acta Physica Sinica. 2011, 60 (6): 066601 doi: 10.7498/aps.60.066601
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In the paper, the equilibrium molecular dynamics and Buckingham potential function are used to investigate the thermal conductivity of TiO2/ZnO nano-film interface along to [0001](z-axis). The effects of the equilibrium temperature, the thickness and the cross section of the nano-film interface on the thermal conductivity of TiO2/ZnO are investigated by optimizing the cut-off radius(rc)and the time step for initial condition of molecular dynamics. The results indicate that the thermal conductivity of TiO2/ZnO nano-film interface decreases with temperature increasing from 300 K to 600 K, and increases with film thickness increasing from 1.8 to 5 nm. Finally, the relationship between the thermal conductivity and the thickness of TiO2/ZnO nano-film interface is discussed.

Liquid-like structure and self-diffusion channels on Al surfaces

Tang Fu-Ling, Chen Gong-Bao, Xie Yong, Lu Wen-Jiang
Acta Physica Sinica. 2011, 60 (6): 066801 doi: 10.7498/aps.60.066801
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Molecular dynamics simulation with embedded atom method potentials is performed to study the atomic structure and self-diffusion on three aluminum surfaces: (001), (110) and (111). Using mean-square displacement, structure ordering parameter, radial-distribution function and z-direction density, we find that their atoms on the first layer present obvious self-diffusion then change into liquid-like structure under melting points: Al(110) at 700±10 K, Al(001) at 860±10 K, and Al(111) at 930±10 K. In the liquid-like structure, self-diffusions always take place on the first layer of the original surface along the direction parallel rather than vertical to the surface: some of the diffusions occur on the outermost layer and more diffusions occur outside the original surface. The main diffusion channels of the three surfaces are different: along [001] on Al(110), [110] and [110] on Al(001), and [110], [101] and [011] on Al(111). No inter-layer diffusion takes place in liquid-like structure, which is different from in the liquid structure of melted surface.

Electronic structure and optical property of Boron adsorption on wurtzite ZnO(0001) surface

Zhang Yu-Fei, Guo Zhi-You, Cao Dong-Xing
Acta Physica Sinica. 2011, 60 (6): 066802 doi: 10.7498/aps.60.066802
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The geometrical structure of clean ZnO(0001) surface and B/ZnO(0001) adsorption system are optimized by using the ultra-soft pseudopotential method of total-energy plane wave based on the density functional theory. Adsorption energy, band structure, density of states and optical properties are calculated and discussed in detail. The results reveal that the T4 site is the most stable adsorption site of ZnO(0001) surface. After a B atom is adsorbed on T4 site, the surface band gap narrows down and the surface state changes a lot, the n-type conduction characteristic is weakened. As for the optical properties, we can find that the absorbing ability of ZnO(0001) surface to ultraviolet light is obviously enhanced after the B atom has been adsorbed on the T4 site of ZnO(0001) surface.

Influence of pressure on structure and properties of Si-doped glow discharge polymer film

Zhang Ying, He Zhi-Bing, Yan Jian-Cheng, Li Ping, Tang Yong-Jian
Acta Physica Sinica. 2011, 60 (6): 066803 doi: 10.7498/aps.60.066803
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The Si-doped glow discharge polymer (Si-GDP) films are deposited by glow discharge polymerization technology at different pressures. The structure and the composition of eath Si-doped glow discharge polymer film are characterized by the Fourier transform infrared spectroscopy and x-ray photoelectron. Using ultraviolet/visible spectroscopy, the optical band gap is analyzed. The results show that the Si element exists mainly in the form of Si—C, Si—H, Si—O, Si—CH3. The relative content of Si—C decreases and then increases with the increase of pressure. It can be found that the ratio between C—C and C C decreases with the increase of pressure. As the pressure increases, the optical band-gap decreases and then increases.

Surface modification and the friction coefficient of tetrahedral amorphous carbon films bombarded by energetic N ion

Han Liang, Chen Xian, Yang Li, Wang Yan-Wu, Wang Xiao-Yan, Zhao Yu-Qing
Acta Physica Sinica. 2011, 60 (6): 066804 doi: 10.7498/aps.60.066804
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The ta-C films with more than 80% sp3 fraction were deposited by FCVA technique, and then were bombarded by energetic N ion. The composition and structure of the ta-C films prior to and after the bombardment of energetic N ion is analyzed by x-ray photoelectron spectroscopy. The surface morphology is investigated by Atomic force microscopy .The result shows that the N concentration in the films slightly increase from 10% to 12% when N ion bombardment energy increases from 1000 eV to 2200 eV. The bombardment of energetic N ion induces the conversion of sp3 bond to sp2 bond. The CN bonds can be formed in the films after energetic N ion bombardment. Energetic N ion bombardment is implanted superficially. The RMS of the films decreases from 0.2 to 0.18 nm after the bombardment, and then increases again to 0.33 nm with the increment of the N ion energy. The friction test indicates that the minimum of friction coefficient is about 0.09 nm before ta-C film was bombarded by energetic N ion. The friction coefficient increased to about 0.16 nm after the bombardment of N ions. But the friction coefficient does not depend on the N ion energy.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Electronic structures cobalt group pnictides: BaT2P2 and BaT2As2 (T=Co, Rh, Ir)

Qian Yu-Min, Xu Gang
Acta Physica Sinica. 2011, 60 (6): 067101 doi: 10.7498/aps.60.067101
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We study the electronic structure of cobalt pnictides: BaT2P2 and BaT2As2 (T=Co, Rh, Ir) by the density functional theory within generalized gradient approximation, and find that the ferromagnetisms in BaCo2As2 and BaCo2P2 are due mostly to the high density of states (Van-Hove singularity) at Fermi level, which induce Stoner ferromagnetism. In these compounds, from Co-3d to Rh-4d, then to Ir-5d, the d-d bonding and the d-p bonding in the TX4(X=P, As) layers are strengthened. As a result, the antibonding d-d states are pushed away from the Fermi level, and the ferromagnetisms are suppressed in Rh and Ir compounds. The evolutions and the detailed electronic structures of these compounds are studied and compared, and spin orbital coupling interaction is negligible.

Theoretical study on electronic structure and properties of solid carbon dioxide

Qu Nian-Rui, Gao Fa-Ming
Acta Physica Sinica. 2011, 60 (6): 067102 doi: 10.7498/aps.60.067102
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We systematically investigate the equilibrium energy, the density of states, and the elastic property of solid CO2 by the plane wave pseudo-potential method in the generalized gradient approximation and local density approximation based on the density function theory. The calculated lattice parameters of α-quartz are consistent with other calculation values. The equilibrium energy calculation indicates that β-cristobalite structure is more stable under the ambient condition, which is consistent with the results reported in other reffrences.The computation results of elastic constants show that they are elastically stable in structure exception for stishovite and cubic-pyrite. The hardness values for these structures are evaluated according to the intrinsic hardness calculation theory of covalent crystal based on the Mulliken overlap population. The results indicate that none of these phases are of superhard material. Furthermore, we clarify the stereochemical effect of the lone-pair electrons on the hardness of the solid CO2.

Electronic structure of CuAlS2 doped with Mg and Zn

Wan Wen-Jian, Yao Ruo-He, Geng Kui-Wei
Acta Physica Sinica. 2011, 60 (6): 067103 doi: 10.7498/aps.60.067103
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Electronic structure of chalcopyrite-type CuAlS2 is analyzed from the band structure and the density of states. Compared with bulk CuAlS2, the effect of doping with Mg and Zn are investigated from the crystal structure, band structure, density of states and electron density difference. The results reveal that Mg and Zn substituting Al both increase the lattice constants and cell volume, yield acceptor states on the top of valence band, providing p-type conductance. CuAlS2 ∶Zn has a slightly larger ionization energy than CuAlS2 ∶Mg, while the former has lower total energy and its crystal structure is more stable.

Preparation and thermoelectric properties of β-Zn4Sb3/Zn1-δAlδO

Zhou Li-Mei, Li Wei, Jiang Jun, Chen Jian-Min, Li Yong, Xu Gao-Jie
Acta Physica Sinica. 2011, 60 (6): 067201 doi: 10.7498/aps.60.067201
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Single-phased β-Zn4Sb3 and β-Zn4Sb3/ Zn1-δAlδO composites with different amounts of Zn1-δAlδO (AZO) are prepared by the combination of vacuum melting and spark plasma sintering (SPS). Thermoelectric properties of the materials are investigated in a temperature range from 300 K to 673 K. As a result, the electrical conductivity of each sample increases while the Seebeck coefficient and the thermal conductivity decrease with the increase of AZO. The maximum ZT value of the composite reaches 1.16 at 673 K when the amount of AZO is 0.2 wt%, which is higher than that for the single-phased β-Zn4Sb3 (1.03).

Effect of exponential-doping structure on quantum yield of transmission-mode GaAs photocathodes Hot!

Zhang Yi-Jun, Niu Jun, Zhao Jing, Zou Ji-Jun, Chang Ben-Kang
Acta Physica Sinica. 2011, 60 (6): 067301 doi: 10.7498/aps.60.067301
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The quantum yield formulas for exponential-doping and uniform-doping transmission-mode GaAs photocathodes are modified by adding a shortwave constraint factor to the photoelectron generation function in a one-dimensional continuity equation. Based on the modified transmission-mode quantum yield formulas, the experimental exponential-doping and uniform-doping transmission-mode quantum yield curves are respectively fitted, and the fitted curves are consistent well with the experimental curves. In addition, the fitted cathode performance parameters indicate that as compared with the uniform-doping photocathode, the exponential-doping photocathode can obtain a higher cathode performance because of the built-in electric field. The exponential-doping structure can effectively increase the quantum yield of transmission-mode photocathode.

Aging in the electrical properties of nanostructured vanadium oxide thin film exposed to air

Luo Zhen-Fei, Wu Zhi-Ming, Xu Xiang-Dong, Wang Tao, Jiang Ya-Dong
Acta Physica Sinica. 2011, 60 (6): 067302 doi: 10.7498/aps.60.067302
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Radio frequency magnetron sputtering method is used to grow nanostructured VOx thin film on silicon nitride layer. X-ray diffraction and atomic force microscope are used to characterize the crystal structure and surface morphology, respectively. The variations of square resistance and thermal hysteresis loop are studied when the film is exposed to air for a long period of time, and the effects of these variations on the performance of device are analyzed. X-ray photoelectron spectrometer and Fourier transform infrared spectroscopy are employed to investigate the differences in composition and molecular structure between the fresh and aged films. The results indicate that the increase of square resistance is due to the oxidation of vanadium ions with low oxidation states. The reason to cause the change of thermal hysteresis loop is that the molecular structure of nanostructured VOx thin film is affected by the adsorbed atoms and functional groups.

Rectifying behavior and photovoltaic effect in La0.88 Te0.12 MnO3/Si heterostructure

Chen Peng, Jin Ke-Xin, Chen Chang-Le, Tan Xing-Yi
Acta Physica Sinica. 2011, 60 (6): 067303 doi: 10.7498/aps.60.067303
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The photovoltaic effect and the good rectifying behavior are observed in La0.88Te0.12MnO3(LTMO)/Si heterostructure fabricated by a pulsed laser deposition method. The photovoltage increases quickly to a maximum value at about 394 μs and then decreases gradually. The maximum photovoltage is about 13.7 mV at T = 80 K. The maximum photovoltage decreases with temperature increasing, which is attributed to the stronger thermal fluctuation. A nonlinear decrease of the maximum photovoltage in the photovoltages-temperature curve is observed, which is mainly caused by the change in the band structure of the LTMO layer due to the metal-insulator transition.

Effects of hydrogen flux on aluminum doped zinc thin films by pulsed magnetron sputtering

Li Lin-Na, Chen Xin-Liang, Wang Fei, Sun Jian, Zhang De-Kun, Geng Xin-Hua, Zhao Ying
Acta Physica Sinica. 2011, 60 (6): 067304 doi: 10.7498/aps.60.067304
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Aluminum doped zinc oxide (AZO) thin films are prepared by pulsed magnetron sputtering in pure argon gas. In order to improve the properties of AZO thin films, we add hydrogen gas into vacuum during sputtering. High purity ceramic ZnO ∶Al2O3 target and hydrogen gas at various flow rates are used as source materials. The microstructure, the surface information, the optical and electrical properties of AZO/H film are investigated. The crystallization, the Hall mobility and the transmission between 400 nm and 1100 nm are enhanced by increasing H2 flow rate, and resistivity is decreased, the lowest resistivities of these films are all 4.435×10-4 Ω·cm, and AZO thin films with 5.664×10-4 Ω·cm are achieved. In this experiment, it is observed that Raman peak is related to defects due to O-vacancies (579 cm-1) in the AZO/H thin films grown at different H2 flow rates. With the increase of hydrogen flow rate, the intensity of Raman peak at 579 cm-1 decreases. Finally, AZO and AZO/H thin films are etched in 0.5% dilute hydrochloric acid. Compared with AZO thin films, AZO/H thin films can be relatively easy to achieve the light trapping structure with crater-type morphology.

Effects of cross-section shape on fast electron beams excited plasmons in the surface of nanowire pairs

Wang Lei, Cai Wei, Tan Xin-Hui, Xiang Yin-Xiao, Zhang Xin-Zheng, Xu Jing-Jun
Acta Physica Sinica. 2011, 60 (6): 067305 doi: 10.7498/aps.60.067305
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In this paper,we investigate the gap plasmon excitation by swift electron beams in nanowire pairs, in particular, with different cross-section shapes (including circular, wedge and irregular shape). For all these nanowire pairs, our results show that fast electron beams can efficiently excite low-order monopole-monopole gap plasmons, which possess long propagation distance and well spatial localization. Furthermore, in contrast to high-order plasmons, the excited gap plasmons do not depend highly on cross-section shape of nanowire pairs through comparing the merit parameters in these three kinds of waveguides. Besides, the excited gap mode will be more confined in nanowire pairs with wedge cross-section. Our study will be helpful for the experiments of gap plasmon generation using electron microscope.

Bandgap energy tuning and photoelectrical properties of self-assembly quantum well structure in organic-inorganic hybrid perovskites

Zheng Ying-Ying, Deng Hai-Tao, Wan Jing, Li Chao-Rong
Acta Physica Sinica. 2011, 60 (6): 067306 doi: 10.7498/aps.60.067306
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Organic-inorganic hybrid perovskite materials have excellent performance in optical, electrical and magnetic properties. The energy-band structure of the hybrid materials can be tuned at the molecular level. In this paper, thin films of hybrid perovskite (C6H13NH3)2(CH3NH3)n-1PbnI3n+1 (n=1, 2, 3, n is the number of two-dimensional inorganic-sheet) have been successfully prepared by a simple spin-coating method. The effects of the inorganic-sheet number (n) on the crystal structure, bandgap energy, exciton binding energy, photoluminescent emission and photocondunctive performance of the hybrid materials have been investigated systematically. With the increasing of inorganic-sheet number, the exciton absorption peak shows an obvious red shift, the bandgap becomes narrow, and the exciton binding energy decreases. Further, the exciton is separated into holes and electrons easily due to the expansion of the exciton Bohr radius and, moreover, the carrier mobilities are increased due to the increasing of inorganic-layer thickness. Consequently, the photocondunctivity of the films is greatly enhanced.

Simulation of optical performance of red top emitting organic light emitting devices based on phase-shift on reflection theory

Li Hui-Ying, Duan Yu
Acta Physica Sinica. 2011, 60 (6): 067307 doi: 10.7498/aps.60.067307
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In this paper, we study the phase shift of the reflection from a semitransparent electrode of a top-emitting organic light-emitting device (TOLED) which is able to adjust spectrum of TOLED. Based on the micro-cavity theory and the transfer matrix theory, a model is set up to simulate the red TOLED. The simulation results show that the modulation of the device is not only limited to organic layer thickness, but also related to the reflection phase shift. The phase shift of the reflection of top electrode is adjusted through changing the thickness of organic layer capped on the top electrode, thus the TOLED optical performance can be changed. This result provides a useful method of improving the performance of the device.

Effect of High-permeability FeCuNbSiB on magnetoelectric property of magnetostrictive/piezoelectric composite

Chen Lei, Li Ping, Wen Yu-Mei, Wang Dong
Acta Physica Sinica. 2011, 60 (6): 067501 doi: 10.7498/aps.60.067501
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A brand-new magnetostrictive/piezoelectric laminated composite is presented using the giant magnetostrictive Terfenol-D, piezoelectric PZT and high-permeability FeCuNbSiB. Since the high-permeability FeCuNbSiB changes the effective magnetic field in the Terfenol-D and the deformed FeCuNbSiB applies a stress to the Terfenol-D in an external magnetic field, thus the saturation magnetostrictive coefficient of Terfenol-D is enhanced, resulting in a higher magnetoelectric voltage output for the composite. Based on the equivalent magnetic charge theory, the effect of the FeCuNbSiB on the effective magnetic field in the Terfenol-D is analyzed, and the magnetostrictive coefficient of Terfenol-D and the theoretical formula of low-frequency magnetoelectric voltage coefficient are derived based on the nonlinear constitutive model of magnetostrictive material and the equivalent circuit method. The analytical results accord with the experiments qualitatively, and the magnetoelectric voltage of the composite is 1.3 times as high as that of the Terfenol-D/PZT-8H (MP) composite. The experimental results indicate that the thickness of FeCuNbSiB has a great influence on magnetoelectric property. The magnetoelectric voltage coefficient increases nearly linearly with the increase of the thickness of FeCuNbSIB until 180μm.

Effects of thickness for Al doped ZnO thin films on their microstructure and magnetic properties

Qi Yun-Kai, Gu Jian-Jun, Liu Li-Hu, Zhang Hai-Feng, Xu Qin, Sun Hui-Yuan
Acta Physica Sinica. 2011, 60 (6): 067502 doi: 10.7498/aps.60.067502
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Al doped ZnO films of different thickness have been prepared on glass substrates by dc magnetron sputtering, these films were annealed in different atmosphere . The crystal structures were analyzed by x-ray diffraction (XRD), and the magnetic properties were measured by a Physical Properties Measurement System (PPMS) with the magnetic field paralleled to the films plane. The results indicate that with increase of the thickness, the crystallinity of the thin films gets better and the crystallites of the Al doped ZnO thin films increase gradually, whereas the internal stresses decreased. The results show the films annealed in air shows obvious room temperature ferromagnetism. With the increase of the film thickness the saturation magnetization is enhanced, and the coercivity is weakened.

Effect of compressive stress on the magnetization and magnetostriction of Fe0.81 Ga0.19 alloy

Zhang Hui, Zeng De-Chang, Liu Zhong-Wu
Acta Physica Sinica. 2011, 60 (6): 067503 doi: 10.7498/aps.60.067503
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The magnetomechanical effect and the magnetostriction in the <100>-oriented single crystal of Fe0.81Ga0.19 alloy have been investigated on the basis of Stoner-Wohlfarth model. The results have shown that in the demagnetized state the degeneracy of the resultant anisotropy in the alloy from the original cubic magnetocrystalline anisotropy into the biaxial anisotropy occurs under a critical stress. This leads to an increase in the fractional occupancy of 90° domain which causes an increase the bulk magnetostriction.

Theory and calculation of magnetoelectric effect in longitudinally polarized and magnetized laminate materials

Bao Bing-Hao, Luo Ying
Acta Physica Sinica. 2011, 60 (6): 067504 doi: 10.7498/aps.60.067504
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Based on constituent equations of longitudinally polarized piezoelectric materials and magnetized magnetostrictive materials, and equation of motion of the magnetoelectric element, the expression to calculate the open circuit voltage of the piezoelectric material is presented. In view of the characteristics of high impedance for the piezoelectric materials, and considering the capacitance of the lead cable to transfer signal, as well as the capacitance and the internal resistance of the measuring instrument, a formula to calculate the actual magnetoelectric voltage is derived by using an equivalent circuit. Taking different materials parameters, we calculate the effect of parameter variation on magnetoelectric voltage. The results show that the influence of material parameters, cable capacitance and the input capacitance and resistance of the measuring instrument on the output voltage must be taken into account. Non-uniformly biased field will yield forces on the two ends of the magnetostrictive materials and the research result shows that the constant force produced by gradient bias magnetic field will generate stabilized voltage, which is unable to be measured by the oscilloscope.

Preparation and electromagnetic wave absorption of flower-like ZnO-CoFe2 O4 nanotube bundles composites

Fu Wu-You, Cao Jing, Li Yi-Xing, Yang Hai-Bin
Acta Physica Sinica. 2011, 60 (6): 067505 doi: 10.7498/aps.60.067505
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Flower-like ZnO-CoFe2O4 nanotube bundle composites are prepared via two-step crystal growth process in water solution at 90 ℃, the wall thicknesses of the ZnO nanotubes are all about 60 nm, inner diameters of the tubes are all about 350 nm, ZnO nanotubes have been coated with CoFe2O4 nanoparticles, and the sizes of CoFe2O4 nanoparticles are below 40 nm. The thickness of CoFe2O4 coating layer increases with the increase of the content of CoFe2O4 in ZnO-CoFe2O4 composites. By using Flower-like ZnO,flower-like ZnO-CoFe2O4 nanotube bundles and CoFe2O4 nanoparticles as absorbents, and phenolic resin as the binder, their electromagnetic wave absorption properties are investigated, and the results show that the microwave wave absorbing performance is evidently improved compared with that of ZnO nanotube bundles and CoFe2O4 particles. When the content of ZnO is 60%, the maximum reflection loss is 28.3 dB.

Magnetoelectric coupling in NiFe2 O4-BiFeO3 composite films

Gu Jian-Jun, Liu Li-Hu, Qi Yun-Kai, Xu Qin, Zhang Hui-Min, Sun Hui-Yuan
Acta Physica Sinica. 2011, 60 (6): 067701 doi: 10.7498/aps.60.067701
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Multiferroic xNFO-(1-x)BFO (x =0.00 0.10, 0.15, 0.20, 0.25) composite films are prepared through self-assembling growth on Au/Ti/SiO2/Si substrates by chemical solution deposition (CSD). X-ray diffraction analysis shows that the perovskite BiFeO3 and the spinel structured NiFe2O4 phases are formed and separated. The leakage current density (J) in the film decreases and the remnant polarizations (M r) increases with the introduction of NFO. The value of J in 0.25NFO—0.75BFO film is found to be nearly two orders of magnitude lower than that in the BFO film, and the M r and the saturation magnetization ( M s) reach maxima, i.e. 2.3μC/cm2 and 70.2 kA·m-1, respectively. Therefore, from the calculation for magnetic moment of NFO we can conjecture that magnetoelectric coupling exists in the composite films.

Preparation and long-afterglow luminescence research of Sr0.6Ba0.2Ca0.2Al2O4 ∶Eu, Dy

Xie Wei, Wang Yin-Hai, Hu Yi-Hua, Zhang Jun, Zou Chang-Wei, Li Da, Shao Le-Xi
Acta Physica Sinica. 2011, 60 (6): 067801 doi: 10.7498/aps.60.067801
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The Ca and Ba co-doped long afterglow phosphors Sr0.6Ba0.2Ca0.2Al2O4 ∶Eu2+0.01, Dy3+0.02 and only Ba doped phosphors Sr0.6Ba0.4Al2O4 ∶Eu2+0.01, Dy3+0.02 are synthesized by a high temperature solid-state reaction method. The phase structures of the phosphors are characterized by x-ray diffraction, showing that the crystal structures of samples are hexagonal. Photoluminescence spectra show that Eu2+ ion acts as the only luminescence center in sample,and Sr0.6Ba0.2Ca0.2Al2O4 ∶Eu2+, Dy3+ display higher luminescent intensities due to the higher concentration of Eu2+ ions in the host crystal lattice. The decay characteristics of phosphors show that Sr0.6Ba0.2Ca0.2Al2O4 ∶Eu2+, Dy3+exhibit higher intensities in the initial afterglow process and longer afterglow time. The measurement of thermoluminescence reveals that the concentrations and depth of traps can be increased by Ca and Ba co-doping in Sr0.6Ba0.4Al2O4 ∶Eu2+, Dy3+ phosphor.

Electronic structure and photoluminescence properties of Ca2GeO4 ∶Eu3+ in ultraviolet and vacuum ultraviolet region

Qin Qing-Song, Yu Ming-Hui, Zhou Hong-Liang, Zhou Mei-Jiao, Xiang Xiao-Tian, Li Xiao-Di, Zeng Jun-Xi, Zhang Jia-Chi
Acta Physica Sinica. 2011, 60 (6): 067802 doi: 10.7498/aps.60.067802
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Red emitting Ca2GeO4 ∶Eu3+ phosphors are synthesized by solid state method. The ultraviolet and vacuum ultraviolet excited photoluminescence properties are investigated in detail. The phenomenon of reduction of Eu3+ ions in air and the color switches are discovered and explained. The Ca2GeO4 ∶Eu3+ presents intense excitation intensities at 163—230, 301 and 466 nm, showing the potential applications in plasma display panels and light emitting diodes. The excitation spectra are studied to identify the photoluminescence mechanism of Ca2GeO4 ∶Eu3+ . First principles calculation within the local density approximation of the density functional theory is used to calculate the electronic structure and the linear optical properties of Ca2GeO4.

Positron annihilation spectroscopy study on the Fe3O4 nanoparticle

Xu Hong-Xia, Hao Ying-Ping, Han Rong-Dian, Weng Hui-Min, Du Huai-Jiang, Ye Bang-Jiao
Acta Physica Sinica. 2011, 60 (6): 067803 doi: 10.7498/aps.60.067803
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The positron annihilation lifetime spectroscopy(PALS), coincidence doppler broadening spectroscopy(CDBS) and x-ray diffraction(XRD) are measured in the Fe3O4 . The aim is to ascertain how pressure and annealing temperature influence the properties of Fe3O4 nanoparticles, such as the change of phase, electronic structure, defect and distribution of electronic momenta. The results indicate that the defect concentration of Fe3O4 nanoparticles increases with the increase of pressure, but the phase and defect type do not change. The phase type, and the guantity and type of defect change significantly as the annealing temperature varies. The phase transition of the Fe3O4 wafer pressed in atmosphere occurs when the annealing temperature is between 350 ℃ and 500 ℃. The grain size of Fe3O4 increases with the increase of the annealing temperature, which leads to the decrease in boundary defect and parameter S but it is contrary to the ratio curve.

Microscopic theoretical investigation on propagation and breakdown depth of ultrashort-pulse laser in dielectrics

Li Dong-Hai, Chen Fa-Liang
Acta Physica Sinica. 2011, 60 (6): 067804 doi: 10.7498/aps.60.067804
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Based on the Fokker-Planck equation along with laser propagation equation, a theoretical model that describes the ultrashort-pulse laser propagation characteristics and breakdown in dielectrics is established. Using this model, the conduction band electron densities and the electric field intensities at different positions in a dielectric material at different time are calculated. The variations of reflection, transmittance and energy deposition rate with input laser energy density are discussed. With the threshold conduction band electron density criterion, the breakdown depth in the material under varying laser energy density is calculated, which is found to increase first with laser energy density, and then to decline after reaching a maximum value. Effect of the spatial distribution of laser energy deposition on breakdown depth is analyzed. Meanwhile, the maximum value of breakdown depth is found to decrease as the laser pulse duration becomes shorter.

Solid state dispersions of MoO3 into porous γ-Al2 O3

Kang Ting-Xia, Bi Ao-Xiang, Zhu Jun
Acta Physica Sinica. 2011, 60 (6): 067805 doi: 10.7498/aps.60.067805
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A series of the MoO3/γ-Al2O3 samples is prepared by mechanically mixing MoO3 with γ-Al2O3 powder. The solid state dispersion of the MoO3 in to the porous γ-Al2O3 is studied by SEM, XRD, XPS, TG/DTA, and positron annihilation spectroscopy. The positron annihilation lifetime spectra of the MoO3/γ-Al2O3 are measured as a function of the mass ratio of MoO3, heating temperature, heating time and in a way that the MoO3 is loaded gradually, separately. The experimental results show the process of the thermal dispersion of the MoO3 into the γ-Al2O3 support. It is shown that the MoO3 disperses into the outer surface first, and then into the secondary pores and the micro pores. The gradual Loading can make MoO3 effectively dispersed into γ-Al2O3. Grinding can also affecte the thermal dispersion process.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

The n-type conduction and microstructural properties of phosphorus ion implanted nanocrystalline diamond films

Hu Xiao-Jun, Hu Heng, Chen Xiao-Hu, Xu Bei
Acta Physica Sinica. 2011, 60 (6): 068101 doi: 10.7498/aps.60.068101
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Phosphorus ions are implanted into nanocrystalline diamond (NCD) films followed by being annealed at different temperatures. The results show that the samples exhibit good n-type conductivity when annealing temperature is increased to 800 ℃ and above. Raman spectroscopy and electron paramagnetic resonance measurements display that the sample with a larger quantity of diamond phase with better lattice perfection has a lower resistivity. It is indicated that nano-sized diamond grains make contributions to the n-type conductivity in the films. After 1000 ℃ annealing, the amorphous carbon grain boundaries become more ordered, which leads the dangling carbon bonds to decrease and the resistivity of the film to increases. It is revealed that the amorphous carbon grain boundaries supply a conduction path to the n-type phosphorus ion implanted nanocrystalline diamond grains.

Structural and optical properties of a-Si ∶H/SiO2 multiple quantum wells

Ma Xiao-Feng, Wang Yi-Zhe, Zhou Cheng-Yue
Acta Physica Sinica. 2011, 60 (6): 068102 doi: 10.7498/aps.60.068102
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a-Si ∶H/SiO2 multiple quantum wells (QWs) are fabricated by plasma enhanced chemical vapor deposition (PECVD) and subsequent different thermal annealing. Among them the annealed sample under 1100 ℃ in vacuum can be transferred into nc-Si:H/SiO2 QWs, and the size of formed nc-Si:H is controllable and it matches the thickness of a-Si ∶H sublayer. The optical absorptivity of a-Si ∶H/SiO2 QWs is compared with that of a-Si ∶H under the same fabrication condition, the former is higher evidently in the UV/Visible spectrum with the absorption edge blue-shifted, which shows that a-Si ∶H/SiO2 QWs has an obvious quantum confinement effect. So it is feasible to use a-Si ∶H/SiO2 QWs to enhance the efficiency of silicon solar cells. In addition, the formation of nc-Si:H/SiO2 QWs with controllable size built the basis for new-type nanocrystalline silicon solar cells.

Effect of interface kinetics on the interface morphology of a spherical crystal in the undercooled melt

Chen Ming-Wen, Ni Feng, Wang Yan-Lin, Wang Zi-Dong, Xie Jian-Xin
Acta Physica Sinica. 2011, 60 (6): 068103 doi: 10.7498/aps.60.068103
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The change of the interface kinetic coefficient with the interface temperature under the non-equilibrium solidification condition is considered in the growth model of a spherical crystal. The first-order approximation solutions of temperature and interface for the spherical crystal growth in the undercooled melt are obtained by the asymptotic analysis method. The effects of the nonlinear interface kinetic undercooling on the interface morphology and the growth velocity of the spherical crystal in the undercooled melt are studied. The results show that as the interface kinetic coefficient increases, the growth velocity of the spherical crystal increases; as the interface kinetic coefficient decreases, the growth velocity of the spherical crystal decreases. Compared with the situation of neglecting interface kinetics, the nonlinear interface kinetics during crystal growth significantly decreases the growth velocity of the spherical crystal.

A physical model to express grain boundaries in grain growth simulation by phase-field method

Zhang Xian-Gang, Zong Ya-Ping, Wang Ming-Tao, Wu Yan
Acta Physica Sinica. 2011, 60 (6): 068201 doi: 10.7498/aps.60.068201
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Grain boundary model in phase-field simulation during microstructure evolution in solid states is discussed based on the way to express grain boundary and its physical background. The effects of different values of simulation parameters on feature of grain boundary in the phase field model are investigated systematically and a new conception of grain boundary range is suggested based on the simulation results of recrystallization of AZ31 magnesium alloy. The gradient range of the order parameter expresses the boundary range, whose physical meaning is found to be the range of grain boundary energy distribution across the boundary. The range is also corresponding to the segregation range of alloying elements around the boundary. It is shown that the gradient parameter determines the boundary range but the grain boundary energy is determined by both the gradient parameter and the coupling parameter. The effect of the boundary range value on microstructure feature is examined by simulating the recrystallization of the alloy. The simulation results are consistent well with reported experimental measurements when the boundary range has a value of 1.18 μm. Grain growth phase-field simulation in industrial space and time scale is realized for the first time using the new model developed by introducing the new conception of the grain boundary range.

Nano-LiNiO2 as cathode material for lithium ion battery synthesized by molten salt method

Bai Ying, Wang Bei, Zhang Wei-Feng
Acta Physica Sinica. 2011, 60 (6): 068202 doi: 10.7498/aps.60.068202
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Molten salt method is applied to synthesis stoichiometric nano-LiNiO2 in rather low temperature and short time. Our results indicate that in the process of preheating the better-crystallized LiNiO2 powder with better electrochemical performances can be produced. The final samples before and after preheating exhibit the initial discharge capacities of 151 and 148 mAh ·g-1 respectively. After 100 cycles, they decay to only 55 and 118 mAh ·g-1, with capacity retentions being 36.4% and 79.7% respectively. The lowered cation disordering is thought to be favorable for the diffusion of lithium ions, by which the enhanced electrochemial properties can be explained.

Regularization method to retrieve synthetic aperture radar sea surface wind

Jiang Zhu-Hui, Huang Si-Xun, He Ran, Zhou Chen-Teng
Acta Physica Sinica. 2011, 60 (6): 068401 doi: 10.7498/aps.60.068401
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Due to the fact that the error exists in the priori wind direction for the problem of synthetic aperture radar data sea surface wind field retrieval, the regularization method is used to retrieve the wind field, while the L-curve method is adopted to select the optimal regularization parameter. Simulation experiments show that the retrieval accuracy of the regularization method is better than that of the variational method. Further researches in different true wind direction situations indicate that when the real wind direction is in the vicinity of 45 ° or 135 °, the wind speed retrieval accuracy is higher, when the real wind direction is in the vicinity of 0 ° or 90 °, the wind direction retrieval accuracy is higher, this phenomenon may be related to the derivative of backscatter cross section with respect to the wind direction in geophysical model function.

Beam-wave interaction and simulation program for sheet beam klystron

Zhang Xiao-Feng, Ruan Cun-Jun, Luo Ji-Run, Ruan Wang, Zhao Ding
Acta Physica Sinica. 2011, 60 (6): 068402 doi: 10.7498/aps.60.068402
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In this paper, a 2.5-dimensional macro-particle model is proposed for a nonaxisymmetrical and large width-height ratio sheet beam klystron (SBK) and a corresponding beam-wave interaction program is developed. An X-band 100-MW SBK is simulated for testing the computing capability of the program. The results are in good agreement with those from 3D PIC software, and the computation time can greatly be reduced, which is useful for the initial design and the optimization of the SBK beam-wave interaction structure.

Optimization of slow wave structures of space traveling wave tube based on collectability of spent beam

Yi Hong-Xia, Xiao Liu, Liu Pu-Kun, Hao Bao-Liang, Li Fei, Li Guo-Chao
Acta Physica Sinica. 2011, 60 (6): 068403 doi: 10.7498/aps.60.068403
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A design method to enhance the efficiency of traveling wave tube is explored. The stair-step energy distribution of spent beam which is beneficial for the development of high collector efficiency depressed collector is obtained via the optimization of slow wave structures without degrading the basic electronic efficiency. A goal function expressed in the form of maximum collector efficiency of spent beam is designed to evaluate the collectability of spent beam. The optimization of slow wave structure based on collectability enhances the overall efficiency in the operation frequency band, and improves the small signal gain, but does not degrade nonlinear characteristic greatly compared with the simply optimization of slow wave structure based on electronic efficiency.

Theoretical investigation on electron transport properties of singlewall carbon nanotube with oxygen molecular absorption

Zhao Pei, Zheng Ji-Ming, Chen You-Wei, Guo Ping, Ren Zhao-Yu
Acta Physica Sinica. 2011, 60 (6): 068501 doi: 10.7498/aps.60.068501
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Electron transport properties of (4,4) single wall carbon nanotube as well as the nanotube with oxygen molecule absorption, are investigated by using first principles analysis. The results show that electron current through the nanotube with oxygen molecule absorption system increases linearly under low bias ranging from 0 to 1.1 V, while the bias is larger than 1.1 V, the current through this system increases slowly. It is also shown that absorbed oxygen molecule brings two kinds of influence on the properties of electron transport: first, the oxygen molecular absorbed states afford new channels to electron transport and enhance the transmission. Second, the oxygen molecular absorbed states spoil the nanotube’s symmetry and enhance the electron scattering, so reduce the transmission.

Deep levels of HgCdTe diodes on Si substrates

Zhang Shan, Hu Xiao-Ning
Acta Physica Sinica. 2011, 60 (6): 068502 doi: 10.7498/aps.60.068502
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The deep levels of the mid-wave infrared HgxCd1-xTe diodes(x=0.31), which are fabricated on Si substrates, are studied using the current-voltage-temperature (IVT) relationship. Firstly, the I-1/(kBT) relationship is fitted when the reverse current is dominated by generation-recombination process, and the deep level Eg/4 is calculated at the reverse bias 0.01 V. Secondly, the deep levels at different reverse biases are investigated. The origins of these deep levels correspond well to the reverse current mechanisms. Finally, the deep levels of different area diodes are calculated and compared. It is confirmed that the deep level is not related to diode area. This result is well corresponding to the theory, and indicates that the experimental method is correct.

Electron transport property in wurtzite GaN at high electric field with Monte Carlo simulation

Guo Bao-Zeng, Zhang Suo-Liang, Liu Xin
Acta Physica Sinica. 2011, 60 (6): 068701 doi: 10.7498/aps.60.068701
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We present the results of the electron transport property in wurtize GaN using an ensemble full band Monte Carlo simulation. The data of wurtzite GaN band structure calculated with the first-principles total-energy pseudopotential method is used in the simulations. The impact ionization scattering rate is calculated based on Cartier’s method. The average electron drift velocity and the average electron energy each as a function of electric field are computed. The electron impact ionization coefficient is calculated as a function of applied electric field. The analysis of the impact ionization coefficient shows that when the applied electric field is greater than 1 MV/cm, the obvious impact ionization events occur. The analysis of the quantum yield shows that when the electron energy is greater than 7 eV, the quantum yield increases rapidly with electron energy increasing. We study the occupancy of the electrons in the eight conduction bands at the applied electric field ranging from 0 to 4 MV / cm. For the case of the low applied electric field all of the electrons are located in the 1st conduction band. With the increase of the applied electric field, some of the electrons move to high index conduction bands. For the whole range of the applied electric field, most of the electrons are located in the 1st conduction band and 2nd conduction band, a small number of the electrons are located in the 3rd, 4th and 5th conduction band, and very few electrons are located in the 7th and 8th conduction band.

Theorical model of enhanced low dose rate sensitivity observed in p-type metal-oxide-semiconductor field-effect transistor

Gao Bo, Yu Xue-Feng, Ren Di-Yuan, Cui Jiang-Wei, Lan Bo, Li Ming, Wang Yi-Yuan
Acta Physica Sinica. 2011, 60 (6): 068702 doi: 10.7498/aps.60.068702
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In this paper, the ionizing damage effects and the annealing behaviors of an import producti, p-type metal-oxide-semiconductor field-effect transistor (PMOSFET), an unhardened 4007 circuit under different doses are investigated. We measure the sub-threshold I-V characteristic curves of PMOSFET under different bias doses. The dependence of the drift of threshold voltage on total dose is discussed. We also observe the relationship between the parameter and the annealing time. The experiment results show that the PMOSFET of this kind can enhance low dose rate sensitivity (ELDRS) effect. The interface-trap formation by H+ transmission in the SiO2 is explained.We believe that the interface trap is a primary reason to induce ELDRS effect of PMOSFET. We also discuss the physical model of enhancing low dose rate sensitivity effect of PMOSFET.

a-Si ∶H/a-Si ∶H/μc-Si ∶H triple junction solar cells

Zheng Xin-Xia, Zhang Xiao-Dan, Yang Su-Su, Wang Guang-Hong, Xu Sheng-Zhi, Wei Chang-Chun, Sun Jian, Geng Xin-Hua, Xiong Shao-Zhen, Zhao Ying
Acta Physica Sinica. 2011, 60 (6): 068801 doi: 10.7498/aps.60.068801
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Low-cost triple junction solar cells, which much attention has been paid to by industry, are studied in this paper. Based on the amorphous silicon/amorphous silicon tandem solar cells realized in industry using completely single chamber deposition technique, amorphous silicon/amorphous silicon/microcrystalline silicon triple junction solar cell with 9.52% conversion efficiency is fabricated by changing deposition conditions for microcrystalline bottom solar cell and n-p junction in a single chamber developed on our own.

Approximate solution of homotopic mapping for nonlinear vibration problem of transmission line

Wu Qin-Kuan
Acta Physica Sinica. 2011, 60 (6): 068802 doi: 10.7498/aps.60.068802
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A class of dynamical model for the nonlinear vibration of a transmission line is studied. Using the homotopy mapping method, the approximate solution with an arbitrary degree of accuracy is obtained.

Chaos quantum clonal algorithm for spectrum allocation of cognitive wireless network

Chai Zheng-Yi, Liu Fang, Zhu Si-Feng
Acta Physica Sinica. 2011, 60 (6): 068803 doi: 10.7498/aps.60.068803
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Efficient spectrum allocation of cognitive wireless network is the key technology to dynamic spectrum access. Taking into account the needs of secondary users for the spectrum and the fairness allocation of the spectrum, mathematical model of spectrum allocation is given, and then it is converted into a constrained optimization problem with the goal of maximizing network profits. A chaos quantum clonal optimization algorithm is proposed to solve the problem, and then the convergence of the algorithm with probability 1 is proved. Finally, the simulation experiments are done to test the algorithm. The results show that compared with the color-sensitive graph coloring algorithm, the spectrum allocation based on genetic algorithm, and the spectrum allocation based on quantum-inspired genetic algorithm, the algorithm has good performances. It can achieve the maximization of network profits.

A traffic flow lattice model with the consideration of driver anticipation effect and its numerical simulation

Sun Di-Hua, Tian Chuan
Acta Physica Sinica. 2011, 60 (6): 068901 doi: 10.7498/aps.60.068901
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With the consideration of the effect of driver anticipation behavior on traffic flow, a new one-dimensional lattice model is proposed. The linear stability condition of the presented model is obtained by employing the linear stability theory. The density wave near the critical stable point is investigated analytically with the nonlinear analysis method. The results show that the occurrence of traffic jamming transitions can be described by the kink-antikink solution of the modified Korteweg-de Vries (mKdV) equation. The good agreement between the simulation results and the analytical results shows that the stability of traffic flow can be enhanced when the effect of driver anticipation behavior is considered.

Analysis on the topological properties of the linkage complex network between crude oil future price and spot price

Gao Xiang-Yun, An Hai-Zhong, Liu Hong-Hong, Ding Ying-Hui
Acta Physica Sinica. 2011, 60 (6): 068902 doi: 10.7498/aps.60.068902
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This paper analyzes the linkage between crude oil future price and spot price based on complex network theory. The linkage between oil future price and Daqing (China) crude oil spot price from November 25, 2002 to September 24, 2010 is transformed into symbolic sequences consisted of three characters {Y, O, N} through the process of coarse graining. The nodes of the complex network are 5-symbol strings in the number of 177 in the form of data window linked in the network’s topology by sliding sequence. The complexity of the linkage is verified through analyzing the topological properties of point of strength, strength distribution, weighted clustering coefficient, average shortest paths, betweenness centrality and subgroup in the complex network. The results indicate that the point of strength value of the former 32 nodes is larger, cumulative strength distribution is 73.27%, and most fluctuation models’ linkages have the character with the same direction. However, it does not show a good correlation between weighted clustering coefficient and point of strength. There are some small cluster groups appearing in the network. These small cluster groups constitute two camps whose cores are YYYYY node and NNNNN node. The results also show that average shortest paths length is 6.969 and 11.3% of nodes occupying 1/4 of centrality function, and there are not many subgroups with close linkage, which verifies the complex characteristics of the linkage fluctuation in the network topology. This paper finds the power law, clustering and periodicity between two kinds of prices in the long run, which is of great significance in grasping the crude oil market, predicting oil price volatility reasonable, formulating price and avoiding risk.

GENERAL

Mei symmetry leading to Mei conserved quantity of generalized Hamiltonian system

Jiang Wen-An, Luo Shao-Kai
Acta Physica Sinica. 2011, 60 (6): 060201 doi: 10.7498/aps.60.060201
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For a generalized Hamiltonian system, Mei conserved quantity derived by using Mei symmetry is studied. First, the definition,the criterion and the determining equations of Mei symmetry of generalized Hamiltonian system are given under infinitesimal transformations of group. Second, the conditions and the forms for existence of Mei conserved quantity are directly obtained by using the Mei symmetry of the system. Then, the theorem for existence of Mei conserved quantity of generalized Hamiltonian system with additional terms is given. Finally, a new three-dimensional generalized Hamiltonian system and the plane motion of the three vortices of three-body problem are studied by using the method presented in the paper.

Epidemic immunization on scale-free networks with traffic flow

Wang Ya-Qi, Jiang Guo-Ping
Acta Physica Sinica. 2011, 60 (6): 060202 doi: 10.7498/aps.60.060202
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In this paper, considering the influence of network traffic flow on the spreading behaviors of epidemics and according to the mean-field theory, we investigate the epidemic immunization strategies in scale-free networks, and propose an improved acquaintance immunization mechanism. Theoretical analysis shows that considering the influence of traffic flow, the random immunization can hardly reduce the spreading velocity of epidemics if the density of vaccinated nodes is small. However, the targeted immunization can sharply depress the epidemic spreading even only a tiny fraction of nodes are vaccinated, and the effects of immunizing the most highly connected nodes and vaccinating the nodes with the largest betweenness are almost the same. We also find that if the network global information is unknown, compared with the classical acquaintance immunization strategy, the strategy proposed in this paper can be used to obtain good immune effect. Numerical simulations confirm the theoretical results.

Folded soliton with periodic vibration for a nonlinear coupled Schrödinger system

Li Bang-Qing, Ma Yu-Lan, Wang Cong, Xu Mei-Ping, Li Yang
Acta Physica Sinica. 2011, 60 (6): 060203 doi: 10.7498/aps.60.060203
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Introducing symmetrical expansion and nonlinear transformation, the (G'/G)-expansion method is extended to investigate a nonlinear coupled Schrödinger system. Some exact solutions with variable separation are constructed for the system. The solutions involve two arbitrary functions of independent variables. By setting properly the arbitrary functions in the solutions, two types of folded solitons with periodic vibration are observed.

Influence of decoherence of entanglement on deterministic remote state preparation

Guo Zhen, Yan Lian-Shan, Pan Wei, Luo Bin, Xu Ming-Feng
Acta Physica Sinica. 2011, 60 (6): 060301 doi: 10.7498/aps.60.060301
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We investigate the influence of decoherence of entanglement on the deterministic remote state preparation. Firstly, the determinability and the depletion of entanglement bits and classical bits are obtained. Then two kinds of decoherent channels (depolarizing and dephasing) are analyzed. For the depolarizing channel, the fidelity is related only to the depolarization and the latitude of target quantum bits on the Bloch sphere, but is independent of longitude. For the dephasing channel, the fidelity is not affected by the quantum channel and only related to the latitude of target quantum bits.

A new quantum teleportation protocal

He Rui, Bing He
Acta Physica Sinica. 2011, 60 (6): 060302 doi: 10.7498/aps.60.060302
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A new quantum teleportation protocol is addressed in this article. By performing the joint measurement of number-phase on a pair of independent two-mode squeezed vacuum states (1- 2 and 3- 4 systems), whose squeezed parameters are the same, the entangled states of the other two bodies (1- 4 systems) as the entangled resource are prepared. Thus the quantum teleportation is successfully realized.

Protocol for deterministic entanglement concentration of three pairs of partially entangled particles

Zhang Wen-Zhao, Li Wen-Dong, Shi Peng, Gu Yong-Jian
Acta Physica Sinica. 2011, 60 (6): 060303 doi: 10.7498/aps.60.060303
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According to the Nielsens theorem and the basic idea of entanglement concentration, we improve and extend the deterministic entanglement concentration protocol that extracts one pair of maximally entangled particles out of two pairs of non-maximally entangled particles, thus establishing a deterministic entanglement concentration protocol that extracts two pairs of maximally entangled particles out of three pairs of non-maximally entangled particles in the way of the classical communication and local operation and the specific positive operator-valued measure. This is helpful for establishing a deterministic entanglement concentration protocol that extracts k pairs of maximally entangled particles out of n pairs of non-maximally entangled particles.

Gap solitons of a superfluid fermion gas in optical lattices

Yang Shu-Rong, Cai Hong-Qiang, Qi Wei, Xue Ju-Kui
Acta Physica Sinica. 2011, 60 (6): 060304 doi: 10.7498/aps.60.060304
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Based on the hydrodynamic model, gap soliton of a superfluid fermion gas in optical lattices was discussed. By using the variational method, the condition for existing gap soliton is obtained. It is found that, when the system crosses from Bose-Eingtein condensation side to the BCS side, the condition for existing gap soliton and the structure of gap soliton are very different.

Scheme for generating maximally two-mode entangled state in an S=1 antiferromagnetic Bose-Einstein condensation

Xu Yan, Fan Wei, Chen Bing, Li Zhao-Xin
Acta Physica Sinica. 2011, 60 (6): 060305 doi: 10.7498/aps.60.060305
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We propose a scheme to generate maximally two-mode entangled state in a spinor-1 anti-ferromagnetic Bose-Einstein condensation. We reduce the three-level system into an effective two-level system via the quantum Zeno subspace created by exerting strong Raman coupling. We investigate the particle number evolution in the unreduced system to justify the existence of Zeno subspace and find that the effective system can be trusted and the entanglement production is reliable.

Hopf bifurcation and chaotification of Josephson junction with linear delayed feedback

Zhang Li-Sen, Cai Li, Feng Chao-Wen
Acta Physica Sinica. 2011, 60 (6): 060306 doi: 10.7498/aps.60.060306
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In this paper, a resistive-capacitive-shunted Josephson junction with linear delayed feedback is considered. The stability of trivial solution of the controlled system is analyzed using nonlinear dynamics theory, and the theoretical results show that the stable trivial solution of the system will lose its stability via Hopf bifurcation as control parameter varies. The critical parameter condition of Hopf bifurcation is also derived. Numerical analysis of the controlled system is carried out under different parameter conditions, and the results show that the stable periodic solution generated by supercritical Hopf bifurcation may transit to chaos gradually through a process of symmetry-breaking bifurcation and period-doubling bifurcation.

Experimental simulation of quantum entanglement distribution over a high-loss channel Hot!

Yin Juan, Yong Hai-Lin, Wu Yu-Ping, Peng Cheng-Zhi
Acta Physica Sinica. 2011, 60 (6): 060307 doi: 10.7498/aps.60.060307
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We experimentally simulate entanglement distribution and demonstrate the violation of Bell’s inequality over 70 dB channel loss. Imaging a communication system which is composed of a satellite-based entangled photon source at a height of 350 km, two satellite-based transmitting telescopes each with a diameter of 13.5 cm, and two receiving telescopes each with a diameter of 100 cm on the ground station. At a minimum ground elevation angle of 10°, the attenuation for optical links to two ground stations over thousand kilometers is comparable to that we have achieved. Furthermore, theoretical and experimental studies demonstrate the key technology researches in entanglement distribution with high loss. First of all, we should reduce the dark noise and raise the time resolution of the system. On this basis, with the brightness enhancement of the source, the system is tolerant of higher link attenuation and long communication distance.

High-dimensional entanglement for long distance quantum communication Hot!

Yin Juan, Qian Yong, Li Xiao-Qiang, Bao Xiao-Hui, Peng Cheng-Zhi, Yang Tao, Pan Ge-Sheng
Acta Physica Sinica. 2011, 60 (6): 060308 doi: 10.7498/aps.60.060308
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In this paper, we provide a scheme to generate a high-dimensional entanglement source for long distance quantum communication. We utilize a continuous wave pump laser to produce polarization-time two-body four-dimensional entangled photon pairs. Under 20 mW of pump power, we achieve 700 entangled photon pairs per second with a fidelity of 89%±3%. Compared with other known high dimension entangled sources, the developed source in the paper is easy to transmit over a long distance and its phase stability is easy to achieve. Therefore, the source is more suited for the future long distance high-dimensional quantum communication tasks and testing the quantum nonlocality, for example, long distance high dimensional quantum key distribution, experimental testing two-particle Greenberger-Horne-Zeilinger theorem, implementation of two-particle quantum pseudo telepathy, etc.

The thin film model without cutoff and the black hole entropy of Dirac field

Yang Xue-Jun, Zhao Zheng
Acta Physica Sinica. 2011, 60 (6): 060401 doi: 10.7498/aps.60.060401
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The physical idea of thin film model improved from brick-wall model is more direct and clearer than brick-wall model and gives prominence to the significance of the event horizon serving as the characteristic surface of a static or stationary black hole. To remove the divergence of the density of states, an ultraviolet cutoff factor is also introduced into the thin film model. The cutoff is introduced artificially and it has not been understood clearly up to now. There is an indication in a reference that the divergence can be removed without any cutoff when the generalized uncertainty relation is used to calculate black hole entropy. In this paper, thin film model without cutoff and the essential difference between the thin film model without cutoff and the thin film model with cutoff are expounded by the example of calculating the entropy of spherically symmetric static black hole Dirac field.

A method of digital secure communication based on a cellular automata with rapid dispersion of errors

Wang Fu-Lai
Acta Physica Sinica. 2011, 60 (6): 060501 doi: 10.7498/aps.60.060501
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An improved one-dimensional cellular automata is designed in which the key space is large with pseudo random series on a shift map and perturbed terms and thus data expansion is avoided. Random triggering rules are involved. There is no complex computation, but a large amount of information can be processed every time. The stream cipher generated by the automata is proved to be of ideal randomness and avalanche effect with rapid dispersion velocity of errors. Empirical results show that the stream cipher is perfectly random both globally and locally. The chi-square test(confidence 95%) on a set of stream cipher with a length of 24000 and its 400 time iterations shows that the passing rates of frequencies and series are above 95% and 100%, respectively. To test the sensitivity of the data, 1 bit is changed at any position of the key stream and the average variation rate of total bits is 49.99%, ranging from 49% to 51% (theoretical value is 50%), and variance is 1.193 ·10-5, which means that the automata is a good encryption technique.

Langevin equation and its applications in the simulation of protein folding process

Jiang Ze-Nan, Fang Chao, Sun Li-Feng
Acta Physica Sinica. 2011, 60 (6): 060502 doi: 10.7498/aps.60.060502
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Some ideas concerning the properties of Langevin equation and its applications to the protein folding process are introduced in this paper. Continuous mapping of Langevin equation is constructed in the phase space and a clear inhomogeneous distribution at position of the Brownian particles is discovered, which is consistent with the hypothesis of the nonergodicity of space structure of protein molecule in the folding process. Besides, a random coil with the same compactness index as proteins in the denatured state is obtained by simulation under the self-avoiding walk condition. Taking the hydrophobic effects as well as the renormalization model into consideration, we present the method to simulate the process of protein shrinking from a random coil to a molten globule.

Cryptanalysis of a hyper-chaotic image encryption algorithm and its improved version

Wang Jing, Jiang Guo-Ping
Acta Physica Sinica. 2011, 60 (6): 060503 doi: 10.7498/aps.60.060503
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According to the Kerckhoff principle, a kind of image encryption algorithm based on hyper-chaos is discussed through choosing plaintext attack and ciphertext attack. The result shows that the key stream is independent of plaintext and one plain-text word is correlated with single cipher-text word for the algorithm, which makes the ciphertext decrypted easily with little computing by choosing plaintext and ciphertext attack. Considering the above problems, an improved algorithm based on hyper-chaos is proposed and the performance analysis is conducted, including statistical analysis, differential analysis, correlation analysis and key sensitivity testing. Theoretical analysis and simulation results show that the improved algorithm not only can resist the chosen plaintext attack and chosen ciphertext attack, but also can obtain better cryptographic properties, such as statistical characteristics, difference characteristics and so on.

Intermittent synchronizing fractional unified chaotic systems

Hu Jian-Bing, Zhang Guo-An, Zhao Ling-Dong, Zeng Jin-Quan
Acta Physica Sinica. 2011, 60 (6): 060504 doi: 10.7498/aps.60.060504
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Stability about fractional chaotic system is studied and a theory about fractional chaotic system is proposed and proved under intermittent control in this paper. Based on the theorem, a controller is designed to realize the intermittent synchronizing fractional unified chaotic system. Numerical simulation demonstrates the effectiveness of the theorem.

Cellular automaton traffic flow model considering influence of accidents

Qian Yong-Sheng, Zeng Jun-Wei, Du Jia-Wei, Liu Yu-Fei, Wang Min, Wei Jun
Acta Physica Sinica. 2011, 60 (6): 060505 doi: 10.7498/aps.60.060505
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Based on the NaSh model, considering the influence of traffic accident and maintenance of highway sections on traffic flow, the cellular automaton model of highway traffic flow under the lane control is established when accident occurs. And the relevant data of the model are calculated. Through analyzing the results of numerical simulation it is found that the accident has a great influence on the highway traffic flow and considerably on traffic flow density within a certain range. And the influence of the accident blocking point on traffic flow on lane 1 is less than on lane 2. Meanwhile, in this range of traffic flow density, the longer the blocking time and the length of blocking section, the greater the influence of traffic flow is.

Adaptive backstepping control of chaotic property in direct-driveven permanent magnet sychronous generators for wind power

Zheng Gang, Zou Jian-Xiao, Xu Hong-Bing, Qin Gang
Acta Physica Sinica. 2011, 60 (6): 060506 doi: 10.7498/aps.60.060506
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In this paper, a mathematical model of direct-driven permanent magnet synchronous generator(D-PMSG) is derived with taking into account the parametric uncertainty and the disturbance of wind. And also the chaotic property under the condition of certain system parameters and a certain operation is verified. Furthermore,the adaptive backstepping approach is designed to compensate the parametric uncertainty and wind disturbance. The simulation results show that the proposed controller for D-PMSG is effective and robust against the parametric uncertainty and the wind disturbance.

A new smooth quadratic chaotic system and its digital signal processing implementation

Liu Yang-Zheng, Lin Chang-Sheng, Li Xin-Chao
Acta Physica Sinica. 2011, 60 (6): 060507 doi: 10.7498/aps.60.060507
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Developing and changing nonlinear function of Lorenz chaotic system, a new autonomous chaotic system is generated which contains three smooth quadratic terms of system variables and five equilibriums. The characteristics of five equilibriums are discussed and a fractal dimension is calculated. The features of chaotic system are analyzed in detail using bifurcation diagram and Lyapunov exponent. The period doubling bifurcation of the system can occus. The chaotic system is realized based on digital signal processing. Experimental result shows the effectiveness and feasibility of the theoretical analysis and verifies the behaviors of various attractors.

Modified Hénon map generated chaotic pseudorandom-bit sequences and performance analysis

Li Jia-Biao, Zeng Yi-Cheng, Chen Shi-Bi, Chen Jia-Sheng
Acta Physica Sinica. 2011, 60 (6): 060508 doi: 10.7498/aps.60.060508
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A method of improving the traditional Hénon map is proposed in the paper. The internal structure of the system is changed by adopting absolute value term. The linear complexity and sensitivity to initial conditions of the proposed system have been greatly enhanced. The performance of pseudorandom-bit sequences which are generated by the proposed system is analyzed in comparison with the ones that are generated by chaotic system. The performance of the sequence generated by the proposed system is improved compared with the original system. Theoretical analysis and the simulation results show the feasibility of the method.

Maximum trap range and equation of state for Fermi gas in potential trap

Yuan Du-Qi
Acta Physica Sinica. 2011, 60 (6): 060509 doi: 10.7498/aps.60.060509
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In the Thomas-Fermi semi-classical approximation, the maximal trap range and the real trap volume of ideal Fermi gas in an n-dimensional potential trap are gaven, and the relevant equations of state are derived. These results indicate that the maximal trap range and the real pressure of trapped gas are related to the potential field and the chemical potential of the free and ideal Fermi system. When the Thomas-Fermi approximate is valid and the condition ((kT)/())2 ((16π2g)/(9N))2/3<<1 is satisfied, the application of the equation of state to three-dimensional spherical symmetry harmonic trap yields the result that the change of pressure is not obvious when the temperature changes, but the change of pressure is closely related to mass of particle, number of particles and the frequency of harmonic potential.

Analysis of Hopf bifurcation in voltage-controlled boost converter under different switching frequencies

Wang Fa-Qiang, Ma Xi-Kui, Yan Ye
Acta Physica Sinica. 2011, 60 (6): 060510 doi: 10.7498/aps.60.060510
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Due to the absence of the switching frequency in the conventional average model of the voltage-controlled boost converter, this model cannot be used to analyze the influence of the switching frequency on the Hopf bifurcation in the voltage-controlled boost converter. In this paper, the influence of the switching frequency on the Hopf bifurcation in the voltage-controlled boost converter is analyzed by establishing the improved averaged model, which contains the switching frequency. The circuit is designed, and some typical experimental results are given. It is found that it is effective to use the improved average model to analyze the influence of the switching frequency on the Hopf bifurcation in the voltage-controlled boost converter and the Hopf bifurcation is easy to occur when the switching frequency of the voltage-controlled boost converter decreases.

Thermal rectification of asymmetric double-stranded molecular structure

Zhang Mao-Ping, Zhong Wei-Rong, Ai Bao-Quan
Acta Physica Sinica. 2011, 60 (6): 060511 doi: 10.7498/aps.60.060511
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Using nonequilibrium molecular dynamics simulation, we study the thermal rectification of an asymmetric double-stranded molecular structure system. We investigate the influence of temperature, intra- and inter-chain interaction and the system size on the thermal rectification effect of the asymmetric double- chain system. It is reported that the intra- and the inter-chain interaction have an advantage on the rectification efficiency. The rectification efficiency goes to a stable value at a large system size. This phenomenon is also explained by the power spectra of the inter-particles, which is similar to the situation of the single chain system.

Microscopic expression of entransy

Cheng Xue-Tao, Liang Xin-Gang, Xu Xiang-Hua
Acta Physica Sinica. 2011, 60 (6): 060512 doi: 10.7498/aps.60.060512
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Boltzmann found that a proportional relation exists between the entropy and the logarithm of the microstate number in an approximate non-interaction particle system. The relation was expressed as the Boltzmanns entropic equation by Planck later. Boltzmanns work gives a microphysical interpretation of entropy. In this paper, a microscopic expression of entransy is introduced for an ideal gas system of monatomic molecules. The changes of the microstate number, the entropy and the entransy of the system are analyzed and discussed for an isolated ideal gas system of monatomic molecules going through the initial stage of unequilibriun thermal state to the thermal equilibrium state. It is found that the microstate number and the entropy always increase in the process, while the entransy decreases. The microstate number is a basic physical quantity which could measure the disorder degree of the system. The irreversibility of a thermal equilibrium process is attributed to the increase in microstate number. Entropy and entransy both are single value functions of the microstate number and they both could reflect the change of the state for the system. Therefore, both entropy and entransy could describe the irreversibility of thermal processes.

Stochastic bifurcations in Duffing-van der Pol oscillator with Lévy stable noise

Gu Ren-Cai, Xu Yong, Hao Meng-Li, Yang Zhi-Qiang
Acta Physica Sinica. 2011, 60 (6): 060513 doi: 10.7498/aps.60.060513
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This paper aims to investigate the influence of Lévy stable noise on a bistable Duffing-van der Pol oscillator. We obtain the stationary probability density function of amplitude for the Duffing-van der Pol oscillator by use of Monte Carlo method, and analyze the influences of the noise intensity and the stability index on the stationary probability density. Stochastic bifurcations are further discussed though a qualitative change of the stationary probability distribution, which indicates that not only system parameters and noise intensity can be treated as bifurcation parameters, but also the change of the stability index will induce stochastic bifurcations.

Effect of gaussian color-correlated colored noise on stochastic multiresonance of a bistable system

Zhang Xiao-Yan, Xu Wei, Zhou Bing-Chang
Acta Physica Sinica. 2011, 60 (6): 060514 doi: 10.7498/aps.60.060514
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We investigate the stochastic resonance of the bistable system driven by multiplicative and additive colored noises with colored cross-correlation. The expression of signal-to-noise ratio (SNR) is obtained by using the adiabatic limit. Through analyzing SNR with the initial condition of x(0)=x+ , we find the stochastic resonance and the stochastic multiresonance. We also find the effects of the noise intensity, the cross-correlation intensity and the correlation time of the noise on the SNR.

Simultaneous experimental reconstruction of three-dimensional flame soot temperature and volume fraction distributions

Liu Dong, Yan Jian-Hua, Wang Fei, Huang Qun-Xing, Chi Yong, Cen Ke-Fa
Acta Physica Sinica. 2011, 60 (6): 060701 doi: 10.7498/aps.60.060701
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Three-dimensional (3D) flame soot temperature and volume fraction distributions are simultaneously reconstructed experimentally by the simultaneous reconstruction model through using charge-coupled device cameras. The reconstruction model is based on the area reconstruction. The reconstructed 3D soot temperatures and volume fraction distributions are compared with those reported in the literature. The reconstructed temperatures are also compared with those measured by thermocouples. It is shown that the reconstructed temperature distribution and the volume fraction distribution are consistent with the reported results. The reconstructed temperatures in good agreemant with the measured temperatures by thermocouples. So the simultaneous reconstruction model can obtain the soot temperature and volume fraction distributions successfully.

Monte Carlo simulations of the evolution of helium depth distribution in materials

Zhou Yu-Lu, Li Ren-Shun, Zhang Bao-Ling, Deng Ai-Hong, Hou Qing
Acta Physica Sinica. 2011, 60 (6): 060702 doi: 10.7498/aps.60.060702
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Based on the migration-coalescence mechanism for helium bubble growth in a material, the evolution of helium depth distribution during annealing is simulated by the Monte Carlo method. The factors that influence the evolution are studied. The results show that the initial concentration and radius of the helium bubble can affect the evolution of He depth distribution, while the annealing temperature has influence only on the evolution rate but little on the final depth distribution of helium. It is also shown that the evolution of the system turns to slow down gradually with the annealing time going.

Observation on the spatial distribution of air pollutants by active multi-axis differential optical absorption spectroscopy

Wang Zhuo-Ru, Zhou Bin, Wang Shan-Shan, Yang Su-Na
Acta Physica Sinica. 2011, 60 (6): 060703 doi: 10.7498/aps.60.060703
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An active 4-axis differential optical absorption spectroscopy system is developed in the project. The system has 4 telescopes integrated together that can simultaneously project and receive 4 independent light beams for measurement. The 4 beams share one xenon short-arc lamp as the light source. Each telescope can be adjusted individually to point to different reflectors. The angle between different beams can be adjusted up to 28°. A test is conducted on the system with four beams setting to measure the concentration of NO2 in the same area. The comparison shows good consistency between measurement data from different beams: the correlation coefficient (R2) between the data from any two beams is no less than 0.97 and the average difference between different beams is below 1×10-9. The long-term observations on the vertical distributions of NO2 and SO2 around Fudan University reveal the average feature of its daily variation: the concentration of NO2 shows a variation of double-peak in a day, the 2 peaks occur in the early morning and the evening respectively, while the valleys occur in the afternoon and the wee hours; the layer of 44—66 m has the highest NO2 concentration, while the layer of 66—88 m the lowest; during the nighttime, inter-layer difference of NO2 concentration is higher than that during the daytime and can be as high as 17×10-9; the concentration of SO2 shows a variation of single-peak in a day, the peak occurs in the forenoon; the vertical distribution of SO2 is relatively even, with the inter-layer difference below 3×10-9.

Wind retrieval algorithm of Rayleigh Doppler lidar

Shen Fa-Hua, Shu Zhi-Feng, Sun Dong-Song, Wang Zhong-Chun, Xue Xiang-Hui, Chen Ting-Di, Dou Xian-Kang
Acta Physica Sinica. 2011, 60 (6): 060704 doi: 10.7498/aps.60.060704
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The wind measurement principle and the structure of Rayleigh Doppler lidar are introduced. The method for Fabry-Perot(FP) etalon transmission curve calibration is given. The problem is pointed out that to fit the transmission curve by using Lorentz or Voigt function may induce large error: the relative error would be up to 8% by Lorentz fitting especially. A least-square nonlinear fitting procedure is proposed, which can eliminate the fitting error and improve the wind precision. After the dominant role that the temperature uncertainty plays in wind retrieval process is considered, a nonlinear iterative algorithm is proposed, which can retrieve both wind temperature and atmospheric temperature. Simulation results show that the algorithm proposed can improve wind retrieval accuracy effectively compared with the traditional method without the Mie-induced effect, and the wind retrieval accuracy of the algorithm proposed will be degraded with Mie-induced effect but still better than that of traditional method.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Analyses for the stability of multi-gap Hughes-type coupled cavity

Cui Jian, Luo Ji-Run, Zhu Min, Guo Wei
Acta Physica Sinica. 2011, 60 (6): 061101 doi: 10.7498/aps.60.061101
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In this paper, the analytical expressions of the beam-wave coupling coefficient and the beam-loaded conductance in the N-gap Hughes-type coupled cavity used in an extended- interaction klystron are derived based on the space-charge wave theory. The stability of the circuit is discussed through calculating the quality factor of the electron beam. The theoretical analyses show that with the increase of N, the stability of operating mode (2π) becomes more sensitive to the beam voltage, and that the parasitical oscillation may more easily occur and is difficult to suppress. In addition, the increase of the perveance and the decrease of the external loaded quality factor may both cause the instability of the system. The electric field intensities on the gap are greatly different among the modes 2π, π and π/2, which may be a new subject for improving the power capability and the bandwidth in klystron development.
ATOMIC AND MOLECULAR PHYSICS

Spectroscopic parameters and molecular constants of CSe(X1Σ+) radical

Liu Hui, Shi De-Heng, Sun Jin-Feng, Zhu Zun
Acta Physica Sinica. 2011, 60 (6): 063101 doi: 10.7498/aps.60.063101
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The spectroscopic and molecular properties of CSe(X1Σ+) radical are investigated using the complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach. The potential energy curve (PEC) is calculated over the internuclear separation range from 0.08 to 2.5 nm at the basis sets, aug-cc-pV5Z for C and aug-cc-pV5Z-pp for Se atom. The spectroscopic parameters (D0, De, Re, ωe, ωexe, αe and Be) of six isotope molecules (12C74Se, 12C76Se, 12C77Se, 12C78Se, 12C80Se and 12C82Se) are evaluated using the PEC of CSe(X1Σ+) radical. The spectroscopic parameters are compared with those reported in the literature, and excellent agreement is found between them. With the PEC of CSe(X1Σ+) radical obtained here, a total of 81 vibrational states of 12C80Se species are predicted when J = 0 by numerically solving the radical Schrödinger equation of nuclear notion. For each vibrational state of every isotope species, the vibrational levels, classical turning points and inertial rotation constants are reported, which are in agreement with the available experimental data.

Structure and potential energy functionof XF2(X=B,N) molecular ground state

Xiao Xia-Jie, Han Xiao-Qin, Liu Yu-Fang
Acta Physica Sinica. 2011, 60 (6): 063102 doi: 10.7498/aps.60.063102
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Based on the Gaussian03 calculation software, QCISD method is used to optimize the possible ground-state structures of XF2(X=B,N) molecules with the different basis sets. On this basis, the resonant frequencies and force constants are calculated with the D95(df, pd) and D95+(df, pd) basis sets respectively. The potential energy functions of XF2(X=B,N) are derived from the many-body expansion theory. At the same time, according to the potential energy functions, three equivalent potential energy diagrams for the XF2(X=B,N) ground states are drawn. The potential energy surface is verified to be consistent with the three atomic molecular geometry. The structures and the features of XF2(X=B,N) can correctly reappear on the potential surface.

Material opto-electronic properties of In, N co-doped SnO2 studied by first principles

Lu Yao, Wang Pei-Ji, Zhang Chang-Wen, Jiang Lei, Zhang Guo-Lian, Song Peng
Acta Physica Sinica. 2011, 60 (6): 063103 doi: 10.7498/aps.60.063103
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In this paper we use first-principles full potential linearized augmented plane wave method (FP-LAPW) to inwestigate density of states (DOS), band structure and optical properties of the materials that doped with In and N. The results show that the doping structure has fine locat levels in both the spin-down direction and the spin-up direction and both state densities are symmetrical. The local levels are produced in the spin-down direction in the band gap, and co-doped compounds show being semi-metallic. The energy band structure indicates that the two co-doped compounds are still direct band gap semiconductors. The top of valence band shifts toward the low energy with the increase of the concentration of N, so obviously the band gap is widened. The main dielectric peak of imaginary part of dielectric function exists only at 8.58 eV, the position of main peak shifts to ward the right and the peak intensity increases significantly. The static dielectric constants of two different concentrations of N-doped structure also significantly increase, and a strong interaction takes place between the states of N 2p and In 5s. The number of peaks of co-doped absorption spectra reduces and the range of absorption wavelength is broadened.

Atomic-scale study of structural change of TiAl alloy film during the cooling process

Song Cheng-Fen, Fan Qin-Na, Li Wei, Liu Yong-Li, Zhang Lin
Acta Physica Sinica. 2011, 60 (6): 063104 doi: 10.7498/aps.60.063104
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Microstructural changes of molten TiAl films are investigated by using molecular dynamics simulations within the framework of embedded atom method in quenching and continuous cooling processes. Atomic local structures in these films are analyzed by using atom average energy, pair distribution functions, and pair analysis technique. The local structure changes in the TiAl films can be divided in to three stages on quenching, and they are divided in to two stages on continuous cooling.

Influence of an atomic Bose-Einstein condensate on the squeezing properties of V-type three-level atomic lasers

Li Ming
Acta Physica Sinica. 2011, 60 (6): 063201 doi: 10.7498/aps.60.063201
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The Hamiltonian operator of a system of V-type three-level atomic Bose-Einstein condensation interacting with two-mode squeezed coherent light field is analyzed in terms of the lattice-liquid model. It is indicated that the contribution of the interaction between atoms to the Hamiltonian in the literature is irrational,so the Hamiltonian operator is improved and the squeezing properties of atomic laser coupled output from the system of V-type three-level atomic Bose-Einstein condensation interacting with two-mode squeezed coherent light field are studied. The results show that the interaction intensity of light-atoms in the Bose-Eimtein condenation has evident influence on the fluctuations of two quadrature components of the atomic laser.

Characteristics of deposition for neutral atoms in laser standing wave with different velocities

Zhang Wen-Tao, Zhu Bao-Hua, Xiong Xian-Ming, Huang Jing
Acta Physica Sinica. 2011, 60 (6): 063202 doi: 10.7498/aps.60.063202
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The deposition patterns of neutral chromium atoms in a laser standing wave with different longitudinal and transverse velocities are discussed. The simulation results of atoms show that the full width at half maximum (FWHM) of a nanometer stripe is 1.49 nm and the contrast is 62.1 ∶1 when the ideal longitudinal velocity of chromimum atom is the most probable velocity 960 m/s, the FWHM of the stripe is 5.35nm and the contrast is 25.6 ∶1 when the longitudinal velocity of chromimum atom is half the most probable velocity. The simulation results of deposition with different transverse velocities are shown at the same time, the FWHM of the stripe is 4.18nm and the contrast is 20.9 ∶1, with the transverse velocity of chromimum atom being 0.25 m/s; the FWHM of the stripe is 58.4 nm and the contrast is 8.9 ∶1, with the transverse velocity of chromimum atom being 0.50 m/s.

Efficient generation of ultra-broadband supercontinuum in the mid-infrared polarization gating

Liu Kun-Long, Hong Wei-Yi, Wang Shao-Yi, Zhang Qing-Bin, Lu Pei-Xiang
Acta Physica Sinica. 2011, 60 (6): 063203 doi: 10.7498/aps.60.063203
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We theoretically investigate the process of the efficient ultra-broadband supercontinuum generation in the mid-infrared polarization gating. The polarization gating at 2000 nm is adopted to restrict the recombination of the electron into one-half optical cycle and extend the spectrum cut-off to 270 eV. And a 0.5 fs ultraviolet pulse is synthesized to the polarization gating to control the ionization process. Then the harmonic intensity is enhanced by 4—5 orders, and a 240eV supercontinuum is obtained, supporting a 16 as pulse generation. By filtering out different ranges of the supercontinuum, isolated 110 as pulses with tunable central wavelengths are efficiently generated.

P-branch spectral lines of rovibrational transitions of CO molecule in ground state

Fan Qun-Chao, Sun Wei-Guo, Li Hui-Dong, Feng Hao
Acta Physica Sinica. 2011, 60 (6): 063301 doi: 10.7498/aps.60.063301
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An analytical formula is derived from elementary expression of molecular total energy for calculating the accurate P-branch spectral lines of rovibrational transitions for diatomic molecules. Using the constants (Bυ',Bυ″) and a group of fifteen known P-branch experimental transition lines for a transition band, the formula not only reproduces the known experimental transition lines, but also generates the spectral lines that may not be available experimentally. The P-branch emission spectra of the (2,0) band of the CO molecule are studied in this work, and correct values of the unknown spectral lines up to J = 80 for this band are predicted by using the formula.

Spectroscopic parameters and potential energy function of the ground state of TiO (X 3 Δr)

Wei Hong-Yuan, Xiong Xiao-Ling, Liu Guo-Ping, Luo Shun-Zhong
Acta Physica Sinica. 2011, 60 (6): 063401 doi: 10.7498/aps.60.063401
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Based on the theory of atomic and molecular statics, the reasonable dissociation limit for the ground state of TiO is derived.The structural optimization and the frequence analysis for the ground state (X3Δr) of TiO molecule are performed using different density functional theory methods or MP2, MP4 methods with the different basis sets. By comparison with the above calculation results, the conclusion is obtained that the B3LYP method with 6-311+G basis set for O atom and 6-311+ +G** basis set for Ti atom is the most suitable for the geometric structure, vibrational frequence and dissociation energy calculation. The analytical potential energy curve for the ground state (X3Δr) of TiO molecule is scanned using the chosen method, and then fitted to the Murrell-Sortie function using least squares fitting. Finally the spectroscopic constants related to the analytical potential energy function are calculated. All calculation results are in good agreement with the experimental data.

Influence of Sommerfeld parameters on triple differential cross section in non-coplanar geometry

Chen Zhan-Bin, Yang Huan, Wu Xing-Ju, Zhang Sui-Meng
Acta Physica Sinica. 2011, 60 (6): 063402 doi: 10.7498/aps.60.063402
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The effective shield of residual electron in the final state of He+ is further modified for (e, 2e) processes on Helium. Three different amendments to the program are proposed in non-coplanar geometry. The effects of the Sommerfeld parameters on the triple differential cross section and the physical nature of these effects are considered.

A combinative triple-well optical trap for three-species cold atoms or molecules

Lu Jun-Fa, Zhou Qi, Ji Xian-Ming, Yin Jian-Ping
Acta Physica Sinica. 2011, 60 (6): 063701 doi: 10.7498/aps.60.063701
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We propose a scheme to form a combinative triple-well optical trap for cold atoms or molecules in focus plane by using an optical system composed of a lens and a phase-type spatial light modulator (SLM) based on liquid crystal microdisplays illuminated by a plane light wave. The principle of forming a triple-well optical trap is analyzed and the characteristic parameters of optical potential are calculated. We also discuss the evolution between a tripe-well optical trap and a double-well one (or a single-well one). Additionally, the propotential applications of our triple-well trap and its novel optical lattices in four-wave mixing with matter waves, cold collision of three atomic species and so on, are explored.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

A kinetics model for the chemical vapor deposition growth of SiGe/Si heterojunction materials

Dai Xian-Ying, Jin Guo-Qiang, Dong Jie-Qiong, Wang Chuan-Bao, Zhao Xian, Chu Ya-Ping, Xi Peng-Cheng, Deng Wen-Hong, Zhang He-Ming, Hao Yue
Acta Physica Sinica. 2011, 60 (6): 065101 doi: 10.7498/aps.60.065101
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Based on Grove model of CVD(chemical vapor deposition) and Fick’s first law, we propose and build the RPCVD(reduced pressure chemical vapor deposition) growth kinetics model of GeSi/Si heterojunction materials. Different from previous SiGe/Si kinetics model, which only considers surface reaction controlling mechanism, our model simultaneously considers two controlling mechanisms: surface reaction and vapor transport. We also consider the model at these two controlling mechanism limits. This model is suitable for charactering the growth of both strained GeSi/Si heterojunction materials at low temperatures and relaxed GeSi/Si heterojunction materials at high temperatures. The calculated value of the model is compared with experimental results. Whether for the growth of strained SiGe at low temperature of 625 ℃, or for the growth of relaxed SiGe at high temperature of 900 ℃, the model error are both lower than 10%, which is the subject technical target.

Characteristics and structure of magnetotail flux rope recovered from Grad-Shafranov method

Zhang Yong-Cun, Shen Chao, Liu Zhen-Xing
Acta Physica Sinica. 2011, 60 (6): 065201 doi: 10.7498/aps.60.065201
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On 21 February 2009, THEMIS-C satellite observed the classical signal of magnetic flux rope at magnetotail of X=-15.7RE.We take the method of Grad-Shafranov reconstruction to investigate the characteristics and structure of magnetotail flux rope. The results give the characteristic physics parameters such as the invariant axis direction, the cross scale length, the magnetic flux in flux rope, etc. With no constraint from model on shape of the flux rope, we reconstruct the distribution of magnetic field and electric current density in the cross section of magnetic flux rope at magnetotail. Our results show that the magnetic field in the central region of magnetic flux rope can be described as being force-free, while with the increase of radial distance, the fields display no force-free feature in the region where the magnetic fields deviate from the axial symmetric distribution.

Comparison of damage between front and rear surfaces under nanosecond 355nm laser irradiation on fused silica

Liu Hong-Jie, Zhou Xin-Da, Huang Jin, Wang Feng-Rui, Jiang Xiao-Dong, Huang Jing, Wu Wei-Dong, Zheng Wan-Guo
Acta Physica Sinica. 2011, 60 (6): 065202 doi: 10.7498/aps.60.065202
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To investigate the physical mechanism which causes asymmetric damages in front and rear surfaces, time-resolved dynamics of the fused silica’s surface damage induced by the nanosecond ultraviolet laser is studied using shadow graphic technique. The results show that the damage mechanisms in front and rear surfaces under nanosecond laser interaction with fused silica are absolutely different. Although the plasma and the shock waves in air are relatively high, damage is reduced on the front surface because the plasma shielding limits energy deposition of the remnant pulse .While on the rear surface, two factors aggravate the damage, one comes from the impulsion of the plasma after its absorption of the laser energy, the other comes from the interference between the remnant pulse and the reflected pulse from the plasma. It is instructive to understand the damage mechanism.

Features of electron-wall collision frequency with saturated sheath in Hall thruster

Zhang Feng-Kui, Ding Yong-Jie
Acta Physica Sinica. 2011, 60 (6): 065203 doi: 10.7498/aps.60.065203
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In the paper we study the electron-wall collision frequency in Hall thruster using the two-dimensional particle-in-cell method. It is found that electron-wall collision frequency is greatly increased in the state of saturated sheath compared with in the state of classic sheath, and even two orders of magnitude higher. Thus, the contribution of electron-wall collision frequency in the state of saturated sheath to near-wall current will be non-ignorable. In this paper the reason why the electron-wall collision frequency is increased in the state of saturated sheath is further analysed. It is believed that the increase of electron-wall collision frequency is caused by rather low sheath potential drop and the backflow of secondary electron emitted from the wall.

Far field auto-alignment system used in SG-Ⅱ-Up system

Gao Yan-Qi, Zhu Bao-Qiang, Liu Dai-Zhong, Peng Zeng-Yun, Lin Zun-Qi
Acta Physica Sinica. 2011, 60 (6): 065204 doi: 10.7498/aps.60.065204
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The auto alignment system, which is used for the beam adjustment in high power laser system, is not only the key subsystem ensuring the routine operation effectually and safely, but also the key element involved in improving the far-field and near-field beam quality. Based on a skillful design of the grating and illumination-image system, a far field alignment system is realized. This system, which is based on a diffraction function of the grating, is characterized by the high performance and the simultaneous off-axis sample of the focus and the reference. The results, which are obtained when the system is used in pre-amplifier system of the SG-Ⅱ-Up, show that the reposition accuracy of the grating reference is better than 8μm, the jitter amplitude is less than 0.59 μm. After the alignment, the deviation of the beam focus from the grating reference is no more than 10 μm.

Defects in transition between different filament structures in dielectric barrier discharge

Dong Li-Fang, Li Shu-Feng, Fan Wei-Li
Acta Physica Sinica. 2011, 60 (6): 065205 doi: 10.7498/aps.60.065205
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The defects in the transition from square to square grid states are studied in a dielectric barrier discharge. It is found that there exist two kinds of defects in this transition, which are angle defect and dislocation defect. In order to investigate the formation mechanism of the defects, the light emissions from different filaments are measured, which show that the light intensity of filament in the middle of the octagonal cell is larger than that in the side. By introducing the quasi-potential field, the interactions between filaments as well as their influences on the transition between different structures are studied. From above analyses, the defects that could emerge in the transition are suggested, which are in good agreement with that observed in experiments.

Target patterns obtained by suddenly increasing applied voltage in dielectric barrier discharge

Dong Li-Fang, Yue Han, Fan Wei-Li, Li Yuan-Yuan, Yang Yu-Jie, Xiao Hong
Acta Physica Sinica. 2011, 60 (6): 065206 doi: 10.7498/aps.60.065206
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Stable target patterns are produced by suddenly increasing the applied voltage in argon dielectric barrier discharge at atmospheric pressure for the first time. The stability and wavelength selection of target patterns obtained by gradually increasing applied voltage after suddenly increasing applied voltage and by directly suddenly increasing applied voltage are studied respectively. It is found that the target patterns obtained by gradually increasing applied voltage are unstable. There is mutual transformation between target pattern and spiral, in which the target pattern can only survive for several tens milliseconds. The target patterns obtained by directly suddenly increasing applied voltage are much more stable, which can survive for more than 5min. The wavelength selections of target patterns obtained by above two methods are studied. It is found that the wavelength of target patterns obtained by directly suddenly increasing applied voltage decreases more quickly as the applied voltage increases. The results show that the applied voltage increasing way in which the target patterns are obtained plays an important role in the stability and wavelength selection of target pattern.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Variation trend of direct and diffuse radiation in China over recent 50 years

Ma Jin-Yu, Liang Hong, Luo Yong, Li Shi-Kui
Acta Physica Sinica. 2011, 60 (6): 069601 doi: 10.7498/aps.60.069601
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Using the direct and diffuse solar radiation data during 1961—2009 from 14 stations and during 1961—1991 from 49 stations in China, and the method of linear regression (taken time as an independent variable), wavelet analysis and Mann-Kendall statistical test, we analyze the characteristics of the direct and diffusion radiation from different aspects including decadal variation, long-term seasonal change, inter-decadal anomaly, cycle and abrupt change. The results are as follows. 1) The spatial and temporal distribution of the climatic trend for the direct and diffuse radiation are revealed by using the normalized climatic tendency coefficient. At the same time, these results are comparable. 2) The direct solar and diffuse radiation in China show decreasing trend, but there are many differences in region, inter-annual and seasonal trend. 3) Based on the characteristics of the geographical distribution on observation stations and according to the climate zone, the classification and the statistical analysis of the percentage of site occupation the long-term changes of the radiation can be clearly shown to have the characteristics of area and local difference. 4) Using wavelet and Mann-Kendall test method, the statistical results show that the radiations in different regions have different periods and abrupt change. 5)The long-term variations of the direct and diffuse radiation in most big cities turn to decrease more obviously than in other cities. Some. Other studies show that such a climatic phenomenon may be caused by environmental factor change of urbanization related to the difference in development speed between cities.
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