Acta Physica Sinica

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Propagation of electromagnetic wave in a lossy cylindrical waveguide

Jiao Chong-Qing, Luo Ji-Run

Acta Physica Sinica. 2006, 55 (12): 6360 doi: 10.7498/aps.55.6360
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Based on the dispersion equation of electromagnetic mode, the propagation characteristics in a lossy cylindrical waveguide are studied. The analytic formula of propagation constant for all modes in the waveguide is presented, which includes the effects of the thickness of the lossy layer. A large uumber of numerical calculations using the analytic formula and the dispersion equation have been carried out on the relations of the attenuation and phase constant with wave frequency, thickness and conductivity of the lossy layer. The analytic calculation results are in good agreement with those of the dispersion equation. This research is useful for selecting appropriate distributed wall losses for the stable and wide-band operation of gyrotron traveling wave amplifiers.

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Investigation on the miniaturization of the microstrip antenna based on the back ward wave property of left-handed medium

Wu Ming-Feng, Meng Fan-Yi, Wu Qun, Wu Jian

Acta Physica Sinica. 2006, 55 (12): 6368 doi: 10.7498/aps.55.6368
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Based on a left-handed medium (LHM) structure unit with smooth dispersion, broadband property and of electrical small dimensions, a microstrip antenna (MSA) substrate is designed partially loaded by both the LHM and the conventional dielectric medium for the miniaturization of MSAs, in which the backward wave property of LHM is employed to compensate for the phase shift resulting from waves propagating in the conventional dielectric medium. Both the analytical and numerical results demonstrate that the physical dimensions of a 4.70 GHz MSA have been significantly reduced by 37.92%, and can be no longer proportional to the working wavelength, while its bandwidth and gain can be equivalent to that of a conventional MSA. All above results indicate the practical capability of LHM in the miniaturization of MSAs.

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The transmittance of Savart polariscope in polarization interference imaging spectrometer

Peng Zhi-Hong, Zhang Chun-Min, Zhao Bao-Chang, Li Ying-Cai, Wu Fu-Quan

Acta Physica Sinica. 2006, 55 (12): 6374 doi: 10.7498/aps.55.6374
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The Savart polariscope is the key spectroscopic component of the static polarization interference imaging spectrometer (SPIIS) that we have developed. The principle of beam splitting of Savart polariscope is described. This paper mainly studies the reflection and refraction of light incident from one medium to another when incident plane and the principle section of the left plate are coincident or perpendicular, according to electromagnetic boundary conditions. The transmission coefficient of each interface is deduced, and the total transmittance is given as a function of angle and wavelength of the incident light which is analyzed through computer simulation. It is proved in theory and by experiment that the Savart polariscope has the advantages of both high flux and large field of view, and can be used as high performance lateral shearing beam splitter in static interferometer and SPIIS. This will provide the theoretical basis for the development of new polarization interference imaging spectral systems.

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Hydrodynamic model of transient Ni-like X-ray lasers driven by Gaussian laser pulse

Pang Hai-Long, Li Ying-Jun, Lu Xin, Zhang Jie

Acta Physica Sinica. 2006, 55 (12): 6382 doi: 10.7498/aps.55.6382
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The self-similarity model of hydrodynamics of transient collisional excitation X-ray lasers is modified for drive laser pulse with a Gaussian temporal profile. The results show that the modified model can more accurately describe the hydrodynamic process of tramsient collision emission X-ray laser than the self-similarity model. Using the modified model, the experimental design of the Ni-like Mo X-ray lasers is optimized.

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Application of quantitative imaging to elimination of scattering effect on X-ray in-line outline imaging

Liu Li-Xiang, Du Guo-Hao, Hu Wen, Luo Yu-Yu, Xie Hong-Lan, Chen Min, Xiao Ti-Qiao

Acta Physica Sinica. 2006, 55 (12): 6387 doi: 10.7498/aps.55.6387
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X-ray in-line outline imaging (XILOI) attracts much attention in recent years, for its simple setup compared with other approaches. Unfortunately, scattering effect cannot be removed directly, which restricts seriously the applications of this method to fields like biomedical radiography. The scattering effect in XILOI was investigated by digital simulation, in which the sample-detector distance (SDD) was changed step by step. The results show that there is a best imaging distance for the direct outline imaging and it is impossible to eliminate the scattering by arbitrarily changing the distance in this case. This difficulty could be overcome by quantitative phase contrast imaging(QPCI), in which SDD can be adjusted freely using a reconstruction algorithm. According to the investigation using QPCI, the scattering effect can be reduced to a minimum by increasing the SDD to a critical value, at which distinct improvement of the image quality can be achieved.

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Measurement of refractive index profile of holey fiber using quantitative phase tomography

Huang Yan-Ping, Qi Chun-Yuan

Acta Physica Sinica. 2006, 55 (12): 6395 doi: 10.7498/aps.55.6395
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A method to determine three-dimensional refractive index profile of holey fiber using a combination of quantitative phase microscopy and tomographic reconstruction techniques is described. Results show that the method based on the transport-of-intensity equation for phase retrieval is straightforward to measure phase profile, nondestructive to the measured fiber, and valuable to determine three-dimensional refractive index profile of holey fiber.

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Intelligent control of video monitoring system based on the color histogram analysis

Zhang Bian-Li, Chang Sheng-Jiang, Li Jiang-Wei, Wang Kai, Shen Hui-Ting, Zhang Yan-Xin, Zhai Hong-Chen

Acta Physica Sinica. 2006, 55 (12): 6399 doi: 10.7498/aps.55.6399
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The intelligent control of video monitoring system in a fixed background scene is realized by comparing color histogram distance between reference image and objective image. The impacts on reference images caused by the variation with time and sunlight are eliminated by renewing reference images on-line. In order to reduce computational complexity and speed up the processing, a uniform compressional algorithm of real color space based on fuzzy method is proposed. The simulations show that an image can be processed in 10 ms, which meets the requirement of real-time processing.

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Design and fabrication of holographic variable line-spacing gratings for position sensor

Lou Jun, Fu Shao-Jun, Xu Xiang-Dong, He Shi-Ping

Acta Physica Sinica. 2006, 55 (12): 6405 doi: 10.7498/aps.55.6405
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Variable line-spacing gratings are widely used in spacial spectroscopic and synchrotron radiation devices, but their design and fabrication are difficult. In this paper, the geometrical theory of aspheric wave-front recording optics is briefly reviewed. The genetic algorithm is introduced to optimize parameters of holographic variable line-spacing gratings. In order to improve the efficiency of calculation. the integral expression of the objective function is also derived. Design example of holographic variable line-spacing gratings for position sensor is given to demonstrate the capability of this method. Holographic variable line-spacing gratings with large density gradient are fabricated successfully.

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The hole burning and optical bistability of quasi-Λ-type four-level atom system

Chen Jun, Liu Zheng-Dong, You Su-Ping

Acta Physica Sinica. 2006, 55 (12): 6410 doi: 10.7498/aps.55.6410
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In this paper we study the quantum interference effects of a quasi-Λ-type four-level atom system interacting with two light fields. When the probe field is weak, our calculations show that along with the change of Rabi frequencies of the driving field, the system appears to be hole burning in the dispersion curve,and two big electromagnetic induced transparency windows with approximately the same width are demonstrated. In addition, the evolution of dispersion with the Rabi phase of probe field shows optical bistability.

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Spectroscopic characteristics of Nd³⁺-doped yttrium lanthanum oxide trans parent ceramics

Ding Jun, Yang Qiu-Hong, Tang Zai-Feng, Xu Jun, Su Liang-Bi

Acta Physica Sinica. 2006, 55 (12): 6414 doi: 10.7498/aps.55.6414
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Nd³⁺-doped Y_2-2x La_2x O₃ (x=0.08) transparent ceramics were fabricated by conventional fabrication process. Spectroscopic properties of the samples were investigated. The absorption band of Nd³⁺: Y_1.84La_0.16O₃ was broad covering the wavelength range 780—850 nm. When doped with 1.5at% Nd³⁺, the cross sections of the sample at 820 nm and laser diode pumped 808 nm were 1.81×10^-20cm² and 1.54×10^-20cm², respectively. The strongest emission peak of the sample was centered at 1078 nm with long fluorescent lifetime, broad emission bandwidth and high quantum efficiency. Because of the additive La₂O₃, the spectroscopic quality parameter (X_Nd) of matrix was decreased from 1.6 to 0.46, thus the fluorescence branch ratio of ⁴F_3/2—⁴I_11/2 transition was increased to 56.82%. These properties of Nd³⁺: Y_1.84La_0.16O₃ transparent ceramic are benefitial to achieve high efficient laser output and ultrashort modelocked pulse.

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Influence of introducing chirp on bistable characteristics of linear negative tapered Bragg gratings

Tian Jian-Feng, Wu Zheng-Mao, Xia Guang-Qiong

Acta Physica Sinica. 2006, 55 (12): 6419 doi: 10.7498/aps.55.6419
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Based on the coupled mode theory, the influence of introducing the chirp on the bistable characteristics of linear negative tapered Bragg gratings is investigated. The results show that introducing positive chirp improves the bistable performance of linear negative tapered Bragg gratings, and the bistable performance can be further optimized by reasonably selecting the length of the linear negative tapered Bragg gratings with positive chirp.

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Spectral properties of hydrogen-containing organic solution of neodymium chelate

Ye Yun-Xia, Yu Ke-Han, Qian Lie-Jia, Fan Dian-Yuan, Peng Bo

Acta Physica Sinica. 2006, 55 (12): 6424 doi: 10.7498/aps.55.6424
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Tris-thenoyltrifluroacetonate of Nd³⁺ has been prepared and dissolved in DMF solation with very high concentration, and the contained hydrogen has not been substituted by deuterium. The absorption spectrum, emission spectrum, and fluorescence lifetime of the solution were measured. Very obvious characteristic fluorescence peaks were observed at 898 and 1058 nm. Based on Judd-Ofelt theory, three intensity parameters were obtained: Ω₂=4.9×10^-20 cm², Ω₄=5.1×10^-20 cm² and Ω₆=2.5×10^-20 cm². Line strengths S_cal, oscillator strengths f_cal, radiative transition probabilities A_ed, radiative lifetimes τ_r and branch ratios β were calculated too. The measured lifetime τ of 1058 nm peak is 460 μs, and that of 898 nm 505 μs. Comparison between theoretically computed radiative lifetime τ_r (682 μs) and the measured lifetime indicates that the non-radiative transition probability of the solution is very low and the fluorescence quantum efficiency very high. High values of three intensity parameters prove the high asymmetric surroundings of Nd³⁺, which is important for Nd³⁺ to absorb the excitation energy. Spectropic quality factor Ω₄/Ω₆>1 makes radiation at 898 nm stronger than at 1058 nm.

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Photon localization in amorphous photonic crystal

Xu Xing-Sheng, Chen Hong-Da, Zhang Dao-Zhong

Acta Physica Sinica. 2006, 55 (12): 6430 doi: 10.7498/aps.55.6430
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The photon localization in disordered two-dimensional photonic crystal is studied by use of multiple-scattering method. The disorder degree can be controlled by adjusting the random rotating angle of the square cell. It is found that the transmission in the band decreases and that in the gap increases as the disorder degree increases, and localization induced by disorder will spread from the band gap edge to the band center and the gap center. Moreover, the mean transmission of the band will decrease exponentially with disorder increasing.

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Microwave transmission behavior of the single dissymmetrical hexagonal split-ring resonators

Yao Yuan, Zhao Xiao-Peng, Zhao Jing, Zhou Xin

Acta Physica Sinica. 2006, 55 (12): 6435 doi: 10.7498/aps.55.6435
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Inspired by the dendritic geometry in nature, we designed the single dissymmetrical hexagonal split ring resonators (SRRs). The SRRs were fabricated on one side of the dielectric substrate using shadow mask/etching technique. By experiments and computer simulations, we have researched the microwave transmission behavior of the SRRs in the frequency band of 7—12 GHz. The results show that, for an individual hexagonal SRR, the resonance frequency is affected by the size of the SRR; for two SRRs, there are two resonance peaks in the transmittion curve when they are close to each other. For three SRRs or the radialized rings, the resonance frequency of the structure with high-level branches shifts towards lower values compared with that with no branches. The simulations are in agreement with the experimental results.

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Regulating ability of defects on the negative refraction of left-handed metamaterials

Zheng Qing, Zhao Xiao-Peng, Li Ming-Ming, Zhao Jing

Acta Physica Sinica. 2006, 55 (12): 6441 doi: 10.7498/aps.55.6441
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We have investigated the defect effect on negative refraction of the left-handed metamaterials (LHMs). The printed circuit boards with LHMs are fabricated using a shadow mask/etching technique. The negative refraction of wedge-shaped LHMs samples with and without defects is investigated respectively. The experimental result shows that when two kinds of point defects are introduced into the sample, the ratio of the maximum power of samples with point defects to that without defects are 1.035 and 1.256, and the absolute value of the negative refraction index increases by 9.6% and 19.6%, respectively. When three kinds of vacant defects are introduced into the sample, the ratios of the maximum power of samples with vacant defects to that without defects have the highest value of 1.973 and the lowest value of 0.364, and the absolute values of the negative refraction index have increased by 68.33% and 9.6% accordingly. We think that the defect breaks the periodic structure of the sample, resulting in a new condition of the electromagnetism resonance which leads to the changes of the negative refraction index and the maximum power. So we can regulate the negative refraction index of LHMs by adjusting the defects.

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Numerical simulation of a novel rectangular-lattice single-polarization single-mode photonic crystal fiber

Zhang Fang-Di, Liu Xiao-Yi, Zhang Min, Ye Pei-Da

Acta Physica Sinica. 2006, 55 (12): 6447 doi: 10.7498/aps.55.6447
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A novel structure of single-polarization single-mode (SPSM) photonic crystal fiber (PCF) is proposed and analyzed numerically based on a full-vector finite element method with anisotropic perfectly matched layers. Through optimization a fiber with confinement loss less than 0.1 dB/km in the wavelengths range of 1.38 to 1.61 μm is obtained. The corresponding design procedures for the novel SPSM-PCF are also presented.

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Time-frequency analysis for phase retrieval from traces of frequency resolved optical gating

Deng Yu-Qiang, Wang Qing-Yue, Zhang Zhi-Gang

Acta Physica Sinica. 2006, 55 (12): 6454 doi: 10.7498/aps.55.6454
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Based on the theory of wavelet-transform analysis for spectral phase retrieval from spectral shearing interferogram, we extract phases from the traces of frequency resolved optical gating (FROG) with time-frequency analysis method. The method enables the phases to be extracted from the ridges of FROG traces directly, and requires no iterative algorithm. For the flap ridges, accurate phases can be extracted. However, for the frequency-varying ridges, the results have great error at the tails of the pulses, and the reasons for error generation are analyzed.

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Study on the mechanism and measurement of stress of TiO₂ and SiO₂ thin-films

Gu Pei-Fu, Zheng Zhen-Rong, Zhao Yong-Jiang, Liu Xu

Acta Physica Sinica. 2006, 55 (12): 6459 doi: 10.7498/aps.55.6459
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The stress of TiO₂ and SiO₂ thin films has been researched, including stress model, measurement method and experimental results for different preparation conditions. Based on the model of curvature of deformed substrate, the stress of the films deposited with and without ion assist as well as with different substrate temperature has been measured and some useful results for both single layers and multilayer system of TiO₂ and SiO₂ have been obtained. The effect of packing density of the layer on stress is found as follows: the film with lower packing density shows a tensile and that with high pacing density shows a compress stress. The accumulated stress in multilayer system even can be diminished to zero by adjusting the preparation parameters.

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Experimental research of coherent combining of three fiber amplifiers

Xiao Rui, Hou Jing, Jiang Zong-Fu, Liu Ming

Acta Physica Sinica. 2006, 55 (12): 6464 doi: 10.7498/aps.55.6464
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Combining coherent laser beams is an important and challenging area of laser science and is now still in a state of laboratory. We have succeeded in the coherent combination of three-element fiber-laser array based on ytterbium-doped polarization-maintaining single-mode power amplifiers with good experimental results. In this paper, we introduce the experimental setup and detailedly describe the method of measurement and control of phase noise. A single signal arm is taken as example, the measured phase noise are presented. At last, we give the results of coherent combination in the far field and briefly discuss a few factors having effect on the far field properties. We conclude that the combining method can be scaled to a large number of lasers.

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Transmission properties of one-dimensional qusi-periodical phononic crystal

Cao Yong-Jun, Dong Chun-Hong, Zhou Pei-Qin

Acta Physica Sinica. 2006, 55 (12): 6470 doi: 10.7498/aps.55.6470
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In this paper, the model of a one-dimensional (1D) phononic crystal with quasi-periodical structure is proposed. The transmission coefficients of elastic waves through the 1D qusi-periodical phononic crystal are numerically calculated, and the obtained transmission coefficients are compared with those of the phononic crystal with periodical structure. The results show that the band gap can also be found in the phononic crystal with quasi-periodical structure, and the frequency range of the gap is the same as that of the periodical structure. However, the only difference is that strongly localized resonant modes appear in the gap of the qusi-periodical phononic crystal. This study to the properties of the localized modes is useful to the fabrication of the acoustic or elastic wave filters.

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Investigation of bubble dynamics in ultrasonic sonoporation

Chen Qian, Zou Xin-Ye, Cheng Jian-Chun

Acta Physica Sinica. 2006, 55 (12): 6476 doi: 10.7498/aps.55.6476
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During the process of quickly producing pathologic sections of the living tissues with ultrasonic sonoporation, it has been found that the exciting ultrasonic signal has an evident effect on the pathologic section. For the sake of understanding the effect and obtaining the best state of quickly producing pathologic section, the bubble dynamics in ultrasonic sonoporation is investigated by constructing a model of cavitated bubbles and altering the parameters, such as the ultrasonic signal frequency, acoustic pressure, bubbles' original radius and viscosity of the fluid. Numerical simulations indicate that radial vibration of cavitating bubble can keep on a steady process of expanding, shrinking, and vibrating in a given rang of frequencies, and one can find out the best original radius for obtaining the maximal cavitation. There exist a best cavitation regions which are determined by the parameters, i.e., the ultrasonic signal frequency, acoustic pressure, bubbles' original radius and viscosity of body fluid.

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Harmonic velocity noise and its frequency resonance with the potential

Song Yan-Li

Acta Physica Sinica. 2006, 55 (12): 6482 doi: 10.7498/aps.55.6482
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A noise with frequency structure, i.e. the harmonic velocity noise is investigated to describe the complicated noise environment. We studied the noise's occurrence, correlation function, power spectrum, as well as some behaviors caused by its frequency characteristics when it acts as a thermal noise. The results show that the harmonic velocity noise is band-passing in frequency spectral space with a peak frequency and the band width is determined by Γ. If a Brownian particle in a harmonic potential is driven by a thermal harmonic velocity noise, its maximum energy appears when the two frequencies are equal. This testifies that there is a dynamical resonance between the frequencies of the noise and the potential, which controls the particle's energy.

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On the nonlinear oscillation of internal sliding friction in particulate matter

Du Xue-Neng, Hu Lin, Kong Wei-Shu, Wang Wei-Ming, Wu Yu

Acta Physica Sinica. 2006, 55 (12): 6488 doi: 10.7498/aps.55.6488
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Experiments are designed to explore the sliding friction that the particulate material bears in the movement when the detecting rod goes vertically through the material contained in a round tube. The research result shows that the sliding friction makes nonlinear oscillations about an average value when the depth of the particulate pile with 2 mm particulate diameter is greater than 0.5 to 2 times the diameter of the container. When the detecting rod goes up with the uniform velocity of less than 2×10^-3 m/s, the average value of the sliding friction is 0.2 to 0.5 times greater than the maximum static friction F₀ and the value fluctuates within the range from F₀ to 2F₀. When the frequency is lower than 1.35 Hz, the intensity of various frequencies goes down exponentially with increasing frequency. The average period T of the main frequency is inversely proportional to the velocity v of the detecting rode.

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Static properties of a femtosecond electron diffraction system

Liu Yun-Quan, Liang Wen-Xi, Zhang Jie, Wu Jian-Jun, Tian Jin-Shou, Wang Jun-Feng, Zhao Bao-Sheng

Acta Physica Sinica. 2006, 55 (12): 6500 doi: 10.7498/aps.55.6500
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Ultrafast electron diffraction is an important technique to study the ultrafast phenomenon in physical, chemical and biological processes. This paper introduces a femtosecond electron diffractometer. The diameter of electron beam and deflection sensitivity of X-Y deflection plates are reported. We also demonstrate the static diffraction pattern of a 300 nm thick gold film taken by the femtosecond electron diffractometer.

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The structure and X-ray photoelectron spectroscopy analysis of double-atom filled skutterudite compounds

Li Han, Tang Xin-Feng, Zhao Wen-Yu, Zhang Qing-Jie

Acta Physica Sinica. 2006, 55 (12): 6506 doi: 10.7498/aps.55.6506
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Double-atom filled single-phase Ca_mCe_nFe_xCo_4-xSb₁₂ compounds were synthesized through a melting—quenching—diffusion—annealing procedure. Ca and Ce were used as filling atoms. The structure of double-atom filled skutterudite compounds was investigated via Rietveld refinement and X-ray photoelectron spectroscopy analysis. The results of Rietveld refinement indicate that Ca_mCe_nFe_xCo_4-xSb₁₂ compounds have skutterudite structure, and the Sb-icosahedron voids were filled with Ca or Ce. The thermal parameter (B) of Ca/Ce is much larger than those of Sb and Fe/Co in the compounds. The specific chemical states of atoms were obtained from X-ray photoelectron spectroscopy quantitative analysis, the results show that the Sb atoms have five chemical states, and the relative percentages of Sb atoms in different chemical states are correlative with the total filling fraction. The filling atoms tend to be located at the center of the voids of the Sb-icosahedrons preferentially.

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Molds for nanoimprinting made by modified photoresist

Chen Lei-Ming, Guo Yan-Feng, Guo Xi, Tang Wei-Hua

Acta Physica Sinica. 2006, 55 (12): 6511 doi: 10.7498/aps.55.6511
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The molds for nanoimprint is very important for nanoimprinting. Many hard materials have been used to make molds. But these materials are difficult to fabricate. In this paper we present a novel technique for making molds based on the modification of polymer by focused ion beam irradiation. This technique is very fast and simple. It can be used in many other domainus of nanofabrication.

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Structure, magnetic properties and atomic immigration of CoFe₂O₄ nanoparticles

Wang Li, Wang Hai-Bo, Wang Tao, Li Fa-Shen

Acta Physica Sinica. 2006, 55 (12): 6515 doi: 10.7498/aps.55.6515
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CoFe₂O₄ nanoparticles have been prepared by sol-gel method. M?ssbauer spectra at temperature varying from 80 to 873 K showed that the atomic site preference of nanoparticles is different from that of the bulk material. The results also showed that the T_c of nanosized CoFe₂O₄ is much lower than that of the bulk counterpart. This decrease of T_c in the nanoparticles may be attributed to the redistribution of Fe and Co cations at the A and B sites. The M?ssbauer spectra also revealed that the hyperfine field varied with the temperature and the hyperfine interaction follows T^3/2+T^5/2 law approximately. The average isomer shift decreases almost linearly with increasing temperature.

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Atomic modeling on the elastic properties of double-walled carbon nanotubes under tension

Ni Xiang-Gui, Yin Jian-Wei

Acta Physica Sinica. 2006, 55 (12): 6522 doi: 10.7498/aps.55.6522
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The stress versus strain relations and the Poisson's ratios under tension of 4 double-walled carbon nanotubes (DWCNTs) with diameters greater than 1 nm were numerically studied with the molecular dynamics method. The simulation shows that in the elastic range the stress and the strain have nonlinear relation, and the tangent elastic moduli of the DWCNTs decrease from 720 to 570 GPa with increasing strain. As the strain increases, the value of Poisson's ratio changes from 0.3 to 0.17, and the sizes of the DWCNTs have little influences on the Poisson's ratio.

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The effects of axial magnetic field on electronic properties of carbon nanotubes ^Hot!

Zhang Zhu-Hua, Guo Wan-Lin, Guo Yu-Feng

Acta Physica Sinica. 2006, 55 (12): 6526 doi: 10.7498/aps.55.6526
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The effects of the external magnetic field on the energy gap of carbon nanotubes were investigated by using the tight-bonding method. It was found that, under the applied magnetic field, the peak of energy gap induced by magnetic field and the slope of energy gap versus magnetic field depend on their diameters tightly; when tubes with the same diameters are used, the metal type tubes have the highest energy gap peak. Furthermore, under the magnetic field, the density of states of carbon nanotubes near the Fermi level are also calculated, showing that the Van Hove singularities will exhibit a periodic phenomenon of splitting, moving and merging. Our calculations meet the results from Green's function method, so they are reasonable.

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Single crystal growth and magnetic properties of strong geometric frustrated magnetic pyrochlore Dy₂Ti₂O₇

Tang Zheng, Li Chang-Zhen, Yin Di, Zhu Ben-Peng, Wang Li-Li, Wang Jun-Feng, Xiong Rui, Wang Qu-Quan, Shi Jing

Acta Physica Sinica. 2006, 55 (12): 6532 doi: 10.7498/aps.55.6532
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Large, high quality single crystals of Dy₂Ti₂O₇ have been successfully grown by the floating zone technique in an infrared image furnace. The obtained single crystal has been characterized by X-ray diffraction at room temperature and is shown to have the face centred cubic structure, Fd3m, with a room temperature lattice parameter a＝1.0112(2) nm. The full-width at half-maximum of rocking curves of ［111］ and ［400］ Bragg peaks are 0.07° and 0.05°, respectively. Magnetic susceptibility measurements give a Van Vleck paramagnetic parameter of 2.46×10^-5m³/mol, the effective moment μ_eff＝10.24(4)μ_B and Cure-Weiss temperature Θ_CW＝1.1 K, indicating weak ferromagnetism for the Dy₂Ti₂O₇ single crystal. The comparative studies of the experiment and theoretical analysis reveal that the long-ranged dipole-dipole interactions dominate the magnetic behaviors of this kind of spin ice system, and the dipolar energy scale D_nn=3.00 K.

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Phase transition from amorphous carbon to diamond nanocrystalline induced by ⁴⁰Ar⁺

Hu Jian-Gang, Wang Zhen-Xia, Yong Zhen-Zhong, Li Qin-Tao, Zhu Zhi-Yuan

Acta Physica Sinica. 2006, 55 (12): 6538 doi: 10.7498/aps.55.6538
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Large-scale diamond nanocrystals of different sizes were synthesized by 60 keV ⁴⁰Ar⁺ irradiation on amorphous carbon. Investigated by high-resolution transmission electron microscopy, energy diffraction X-ray spectrum, electron diffraction and Raman spectrum, the diamond crystallites embeded in graphitic film have a high nucleation density (about 10¹³/cm²) and can grow to large sizes even of the micrometer order. The mechanism of phase transition is discussed preliminarily.

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Thermodynamic characteristics of metallic glass-forming liquids

Xia Ming-Xu, Meng Qing-Ge, Zhang Shu-Guang, Ma Chao-Li, Li Jian-Guo

Acta Physica Sinica. 2006, 55 (12): 6543 doi: 10.7498/aps.55.6543
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On the basis of analyzing the thermodynamic model of regular melt, the mixing enthalpy ΔH^mix and the mixing entropy ΔS^mix of typical metallic glass melts were calculated. The distribution of ΔH^mix vs. ΔS^mix for typical metallic glasses was generalized, and a strategy for pinpointing metallic glass formers has been proposed by combining the critical cooling rate R_c based on the atomic intrinsic characteristics of the alloys including atom size, composition, and mixing enthalpy of binary systems among the components. On the condition of ΔS^mix greater than 0.6 J·K^-1mol^-1 and ΔH less than -15 kJ·mol^-1, the alloy tends to form a bulk metallic glass(BMG). It shows that R_c is intimately related with ΔS^mix, and can be expressed as R_c=42.24×10⁴ exp(-13.91 ΔS^mix)+19.66. Two new glass formers, Zr₄₀Al₁₀Ni₁₅Cu₃₅, located far from the glass forming area of the existing Zr-Al-Ni-Cu BMGs with a content of 55at%—65at% zirconium, and Fe₅₃Co₅Nd₁₂B₃₀ of quaternary Fe-B-based BMG, were successfully prepared with this approach.

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Diffusion and interface reaction of Cu and Si in Cu/SiO₂/Si (111) systems

Cao Bo, Bao Liang-Man, Li Gong-Ping, He Shan-Hu

Acta Physica Sinica. 2006, 55 (12): 6550 doi: 10.7498/aps.55.6550
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The Cu thin films were deposited on p-type Si (111) substrates by magnetron sputtering at room temperature. The diffusion and interface reaction of Cu/SiO₂/Si (111) systems were studied for different annealing temperatures by X-ray diffraction (XRD) and Rutherford backscattering (RBS).We obtained some useful results in the following aspects：The onset temperature of interdiffusion was 450℃ for the Cu/SiO₂/Si (111) systems.With the increase of annealing temperature, the interdiffusion was more apparent. There were no copper silicides formed below annealing temperature of 450℃ for the Cu/SiO₂/Si (111) systems. The onset temperature of silicification was 500℃. Copper silicides were formed on the samples after annealing at 500℃.

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Heat conduction in one-dimensional systems with damping

Li Xin-Xia, Tang Yi

Acta Physica Sinica. 2006, 55 (12): 6556 doi: 10.7498/aps.55.6556
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By making use of the method of molecular dynamics, we study the behaviors of heat conduction in one-dimensional systems under the influence of damping. The results show that when the integrability of the systems is destroyed by the damping, linear temperature profiles appear even in the harmonic lattices. Weak damping acts as a sort of perturbation in nonintegable systems and does not substantially change their temperature profiles and the thermal conductivity, while it causes essential change in integrable systems. However, in the case of strong damping, because of the excessive dissipation of energy, temperature profiles in a sunken shape and the convergent thermal conductivity appear.

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Study of the stability of gallium-arsenic ion clusters

Yang Jian-Song, Li Bao-Xing

Acta Physica Sinica. 2006, 55 (12): 6562 doi: 10.7498/aps.55.6562
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Using full-muffin-tin-orbital molecular-dynamics method, the electronic and geometric structures of Ga_nAs_n (n=4,5,6) ion clusters and their stability have been investigated in detail. The lowest energy structures are found. Our calculations suggest that they are obviously different from the ground state structures of their corresponding neutral clusters. In addition, the stable ionic structures have more severe structural distortion than the neutral structures. Gallium atoms occupy the cap atom positions more easily than arsenic atoms in the mixed Ga_nAs_n clusters.

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Electronic theoretical study on the influence of rare earth on the stress corrosion in magnesium alloy

Liu Gui-Li

Acta Physica Sinica. 2006, 55 (12): 6570 doi: 10.7498/aps.55.6570
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The atomic models of pure boundary and that with Mg₁₇Al₁₂ of α phase in magnesium alloy were set up. The segregation energies of Al and rare earth atoms, the interaction energies between Al and/or rare earth atoms, and the Fermi energy levels of different systems were calculated by using recursion method. The Al and rare earth segregation at the grain boundaries, the relationship between the interaction of Al or rare earth atoms and the ordering tendency, as well as the physical nature of the influence of rare earth on the stress corrosion of magnesium alloy were discussed. Calculation results show that: Al and rare earth atoms segregate at grain boundaries, and Al atoms repel each other, leading to the formation of the ordered Mg₁₇Al₁₂ phases in the grain boundaries. But rare earth atoms attract each other, so atom clusters are formed in the grain boundaries. The rare earth atom cluster can attract Al atoms, make the Al atoms to infiltrate into the rare earth atom cluster, forming rare earth compound. Therefore, rare earth have the effect of restraining the forming of Mg₁₇Al₁₂ along grain boundaries which functions as the cathode of magnesium alloy that leads to corrosion, this reducing the sensibility of stress corrosion.

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Electronic structure of intrinsic defects and mechanism of donor-acceptor pair luminescence in CuI crystal

Liu Hai-Lan, Gu Mu, Zhang Rui, Xu Rong-Kun, Li Guang-Wu, Ouyang Xiao-Ping

Acta Physica Sinica. 2006, 55 (12): 6574 doi: 10.7498/aps.55.6574
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The electronic structures of γ phase copper iodide crystal and the intrinsic point defects associated with iodine and copper have been studied with relativistic density functional theory and embedded cluster method. The simulations for point defects show that the tetrahedron interstitial copper atoms and copper vacancies may lead to the shallow donor and acceptor levels in the energy gap, which is related with the origins of the broad donor-acceptor pair recombination luminescence band 420—430 nm of CuI crystal.

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Virtual-crystal doping study in novel superconductor MgCNi₃

Ma Rong, Zhang Jia-Hong, Du Jin-Li, Liu Su, Liu Mei

Acta Physica Sinica. 2006, 55 (12): 6580 doi: 10.7498/aps.55.6580
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Using full potential linearized augmented plane wave method and considering local spin density approximation, we study superconducting and magnetic properties in virtual-crystal doped MgCNi₃. The electronic band structure, bulk modulus and its pressure derivative, magnetic moment and its variation rate are calculated. It is found that: for electron-doped Mg_1-xAl_xCNi₃(0≤x≤0.5), the superconductivity and magnetic fluctuations decrease gradually with increasing doping. For hole-doped Mg_1-xNa_xCNi₃ with x=0.12, a ferromagnetic phase transition occurs and superconductivity disappears. In the hole doping range of 0≤x<0.12, there is the unstable superconducting state with spin fluctuations.

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Study of single-walled carbon nanotube's differential conductance in high magnetic field under high pressure

Cai Jian-Zhen, Zhu Hong-Wei, Wu De-Hai, Liu Feng, Lü Li

Acta Physica Sinica. 2006, 55 (12): 6585 doi: 10.7498/aps.55.6585
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Accompanied by the structural phase transition, the electron transport properties of single-walled carbon nanotubes bundles undergo a metal-semiconductor transition at a hydrostatic pressure of 1.5 GPa. In the semiconducting phase there coexist two effects——electron phase coherence which leads to two-dimensional electron weak localization, and Coulomb correlation which leads to the environmental quantum fluctuation of charge transport. We applied hydrostatic pressure up to 10 GPa to single-walled carbon nanotube bundles, and studied the bias voltage dependence of the differential conductance at low temperatures and in strong magnetic fields. Our results show that phase coherence and Coulomb correlation are two effects that independently influence on the electron transport process in the semiconducting phase of the single walled carbon nanotube bundles.

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The division of iron's core and valence states under high pressures via first-principles calculation

Sun Bo, Liu Shao-Jun, Zhu Wen-Jun

Acta Physica Sinica. 2006, 55 (12): 6589 doi: 10.7498/aps.55.6589
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We performed first-principles calculation for the body-centered cubic iron based on density-function theory, employing the pseudopotentionals and plane-wave method. We set the computational precision of the energy of one atom to 0.01 eV and make the spin-polarized total-energy calculation. The calculated results show that the 3p state should be treated as valence state when pressure is higher than 140 GPa, while the contribution to the total energy due to the dispersion of 3s state can be ignored for the whole range of earth's core condition.

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Effects of nonlinearity on the transmission property of superlattices

Liu Bing-Can, Pan Xue-Qin, Ren Zhi-Ming

Acta Physica Sinica. 2006, 55 (12): 6595 doi: 10.7498/aps.55.6595
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We investigate the effects of nonlinearity on the transmission property of superlattices. The nonlinear Schr?dinger equation leads to a second order nonlinear difference equation, and we obtain transmission spectrum of wave by iterating the difference equation. The transmission spectrum shows that the nonlinear coefficient has a distinctive modulation effect on the transmission coefficient.

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Research of two-dimensional hole gas in p-GaN/Al_0.35Ga_0.65N/GaN strained quantum-well

You Da, Xu Jin-Tong, Tang Ying-Wen, He Zheng, Xu Yun-Hua, Gong Hai-Mei

Acta Physica Sinica. 2006, 55 (12): 6600 doi: 10.7498/aps.55.6600
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In this paper, the two-dimensional hole gas (2DHG) induced in the heterojunction were investigated in detail. The density of the 2DHG was calculated at first, then, based on the semiconductor-insulator-semiconductor and superlattice critical thickness model and using the self consistent Poisson-Schrdinger calculations, the influence of the AlGaN barrier and the top GaN layer thickness on the distribution of the 2DHG were calculated when the barrier layer is fully strained and half strained. The Schottky device with this structure was fabricated and C-V measurement was made to verify the existence of the 2DHG and the validity of calculation results. Finally, the 2DHG effects on p-GaN/AlGaN/GaN Schottky photodetector were investigated. Due to the polarization and Stark effect, the spectral responses with the 10nm blue shift are observed. Under zero bias, the peak responsivity of the device is about 0.022A/W, and increases to 0.19A/W under 1V reverse bias, which approaches the theoretical limit.

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Quantum tunnelling time of cold atom passing through a laser beam

Tang Lin, Huang Jian-Hua, Duan Zheng-Lu, Zhang Wei-Ping, Zhou Zhao-Ying, Feng Yan-Ying, Zhu Rong

Acta Physica Sinica. 2006, 55 (12): 6606 doi: 10.7498/aps.55.6606
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Atoms can be prepared at low temperatures by laser cooling. The center of mass motion of the cold atoms exhibits wave nature of quantum mechanics. In this paper, we study the quantum tunneling effect of a cold atomic beam propagating through a laser beam which is blue detuned. The blue detuned laser beam is physically equal to a quantum potential barrier. According to two-level model of atom, we systematically analyze the quantum reflection and transmission of the vector atomic matter wave with internal structures propagating through a laser beam. Quantum tunneling time the atomic beam spends in transmitting the laser beam is studied in details. Because of quantum wave nature, cold atoms tunneling through a laser beam can obviously have a completely different feature from that of a classical particle (hot atom).

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Investigation on stability of microcrystalline silicon thin film transistors

Li Juan, Wu Chun-Ya, Zhao Shu-Yun, Liu Jian-Ping, Meng Zhi-Guo, Xiong Shao-Zhen, Zhang Fang

Acta Physica Sinica. 2006, 55 (12): 6612 doi: 10.7498/aps.55.6612
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Instability of a bottom gate microcrystalline silicon (μc-Si) thin film transistor (TFT), of which the active layer was deposited by very high frequency-plasma enhanced chemical vapor deposition with silane concentration of 4% diluted by H₂, was measured and compared under two different gate bias stress conditions. A new instability phenomenon of TFT under the voltage bias stress of V_gs=V_ds=10 V was found, where the ratio of the source-drain current of μc-Si TFT to its initial value decreases first, then stays flat for a period of time, then increases. However, under the voltage bias stress of V_gs=10 V(V_ds＝0 V), the source-drain current of μc-Si TFT decreases as normal exponential decay. Analysis on the change of sub-threshold swing S and threshold voltage V_th with stress time indicated the recoverable degradation could have resulted from the electron trapping and releasing in μc-Si TFT treated by gate-bias stress with V_ds≠0.

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Transport properties and photo-induced effect in La_0.82Te_0.18MnO₃ thin film

Wang Jian-Yuan, Chen Chang-Le, Gao Guo-Mian, Han Li-An, Jin Ke-Xin

Acta Physica Sinica. 2006, 55 (12): 6617 doi: 10.7498/aps.55.6617
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The transition from the metallic phase to the nonconductive phase occurred at 283 K in La_0.82Te_0.18MnO₃ thin film prepared by pulse laser deposition method. The transport results show that the data satisfy the formula of electro-electro and electro-magnon scattering for T<T_MI; when T>T_MI it agrees with small polaron transport model. The effect of the continuous wave laser(532 nm，40 mW) on the film was also investigated. Below T_MI, the resistivity has a photo-induced increase. The maximum rate of resistivity changes(Δρ/ρ₀) can reach 51.1%， which is much greater than that of hole-doped manganites. Above T_MI there is a photoconduction. The relaxation was observed in the experiment when the laser was turned on and off. The resistively is exponentially related with the time.

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The distribution and origination of electric field and charge in interface layer of superconductor

Yang Peng-Fei, Chen Wen-Xue

Acta Physica Sinica. 2006, 55 (12): 6622 doi: 10.7498/aps.55.6622
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Based on relativistic field equations of superconducting state, the structure and forming mechanism of interface layer of superconductor are studied for the condition of weak magnetic field. It is shown that electric field, potential difference, Hall effect and sandwich of charge density exist in this layer,which originate from the measurable effect of potential field limited by relativistic covariance. In order to verify the result of this paper, a design of experiment is given.

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Synthesis and thermoelectric properties of Sb-doped type-Ⅰ Ge clathrates Ba₈Ga_16-xSb_xGe₃₀

Xiong Cong, Tang Xin-Feng, Qi Qiong, Deng Shu-Kang, Zhang Qing-Jie

Acta Physica Sinica. 2006, 55 (12): 6630 doi: 10.7498/aps.55.6630
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The single-phase Sb-doped n-type Ba₈Ga_16-xSb_xGe₃₀ compounds were synthesized by melting reaction combined with spark plasma sintering. Influences of substituting Sb for Ga on the thermoelectric properties of the compounds were investigated. The results indicate that with the increase of Sb substitution fraction the Seebeck coefficient is decreased gradually, and the temperature which corresponds to the peak value of Seebeck coefficient moves to low-temperature. The electrical conductivity of the compounds increases at first and then decreases with the increase of x; when x=2, it reaches maximum. Substituting Sb for Ga has a great influence on the thermal properties of the compounds. Both the thermal conductivity and lattice thermal conductivity decrease in various degrees. Of all n-type Ba₈Ga_16-xSb_xGe₃₀ compounds, the compound Ba₈Ga₁₄Sb₂Ge₃₀ has the greatest ZT value, the maximal value of which reaches 1.1 at about 950 K.

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The dc Josephson current in superconductor-ferromagnet/insulator/spin-triplet p-wave superconductor junctions

Li Xiao-Wei

Acta Physica Sinica. 2006, 55 (12): 6637 doi: 10.7498/aps.55.6637
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From the Bogoliubov-de Gennes equations, we obtain the self-consistent equation for a ferromagnetic superconductor. Using the Furusaki-Tsukada formula, we calculate the dc Josephson current in superconductor-ferromagnet/insulator/spin-triplet p-wave superconductor (FS/I/p) junctions. It is found that the dc Josephson currents in FS/I/p are suppressed by the presence of exchange field and insulating barrier scattering. The period of oscillation curves of the Josephson current is π when there exist p_x-wave symmetries for the pairing symmetries of spin-triplet superconductor.

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Kondo interactions in the CeOs₄Sb₁₂ skutterudite studied by inelastic neutron scattering

Yang Chang-Ping, Zhou Zhi-Hui, Wang Hao, K. Iwasa, M. Kohgi

Acta Physica Sinica. 2006, 55 (12): 6643 doi: 10.7498/aps.55.6643
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The energy gap near Fermi surface due to the hybridization of Ce³⁺ 4f¹ and conduction electrons is the key to understand the physical properties of the CeOs₄Sb₁₂ compound, such as Kondo insulating behavior, moment quench of Ce³⁺ at low temperatures and the characteristics of heavy fermion. In this work, inelastic neutron scattering spectra of powder CeOs₄Sb₁₂ sample were collected at different temperatures using LAM-D neutron spectrometer at KEK pulsed neutron source. The result indicates that the CeOs₄Sb₁₂ skutterudite is a Kondo insulator with a c-f interaction of 3.1 meV. The Debye temperature is determined as 317 K.

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The formation and thermal stability of exchange bias in NiFe/PtMn bilayers

Li Yan, Chen Qing-Yong, Jiang Hong-Wei, Wang Ai-Ling, Zheng Wu

Acta Physica Sinica. 2006, 55 (12): 6647 doi: 10.7498/aps.55.6647
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(Ni_0.81Fe_0.19)_1-xCr_x/NiFe/PtMn films were prepared by magnetron sputtering. The formation and thermal stablitity of NiFe/PtMn bilayers were systematically investigated. The experiment shows that the grain size of PtMn layer depends strongly on the change in Cr concent ration. Thermal stability of exchange bias indicates that (Ni_0.81Fe_0.19)_1-xCr_x/NiFe/PtMn films with larger PtMn grains have a higher blocking temperature, and the bigger grain size is helpful in reducing the critical thickness of PtMn layer, which is consistent with Mauri's model.

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Room-temperature ferromagnetism in Co-doped ZnO diluted magnetic semiconductor

Wang Yi, Sun Lei, Han De-Dong, Liu Li-Feng, Kang Jin-Feng, Liu Xiao-Yan, Zhang Xing, Han Ru-Qi

Acta Physica Sinica. 2006, 55 (12): 6651 doi: 10.7498/aps.55.6651
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The room-temperature ferromagnetism (RTFM) of Co-doped zinc oxide are reported in this paper. The Zn_1-xCo_xO (x=0.02, 0.06, 0.10) specimens were synthesized by solid state reaction of the mixture of ZnO and Co₂O₃ powders. The specimens were then annealed in the hydrogenation ambience. The RTFM was found in the hydrogenated samples, and the hysteresis loops of the hydrogenated Co-doped ZnO samples were measured at 300 K by using the superconducting quantum interference device magnetometer. The samples were further measured by X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy.

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The effect of a Bi underlayer on FePt thin film

Feng Chun, Li Bao-He, Han Gang, Teng Jiao, Jiang Yong, Liu Quan-Lin, Yu Guang-Hua

Acta Physica Sinica. 2006, 55 (12): 6656 doi: 10.7498/aps.55.6656
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In this paper, the FePt films with Bi underlayer were prepared by dc magnetron sputtering on glass substrates. The L1₀-FePt films were obtained after the deposited samples were subjected to vacuum annealing at various temperatures. The effect of a Bi underlayer on the ordering temperature and magnetic properties of FePt films was studied. Experimental results show that the FePt film can realize the low-temperature ordering at 350℃ after introduction of a Bi underlayer. Moreover, the Bi underlayer can also obviously enhance the coercivity H_c of the film and enlarge the concentration range of FePt films with high H_c. We studied the distribution of Bi atoms by X-ray photoelectron spectroscopy and the change of crystal structure of FePt films by X-ray diffraction. The cause of the above observatious is associated with enhanced ordering degree of FePt films by the Bi diffusion during annealing process.

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Microstructures and electrical properties of CaCu₃Ti₄O₁₂ ceramics

Shao Shou-Fu, Zheng Peng, Zhang Jia-Liang, Niu Xiao-Kun, Wang Chun-Lei, Zhong Wei-Lie

Acta Physica Sinica. 2006, 55 (12): 6661 doi: 10.7498/aps.55.6661
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CaCu₃Ti₄O₁₂ ceramics are prepared by the conventional solid-state reaction method with various sintering temperatures. Microstructures are examined by scanning electronic microscopy, and it is found that they could be categorized into three different types. Dielectric properties and complex impedances are investigated in the frequency range of 40 Hz—110 MHz over a temperature range of 25—280℃. The room temperature dielectric constant increases with sintering temperature. With increasing the measuring temperature, ceramics with different microstructures show diverse electrical properties. However, some common features exist among the electrical properties. For all of the ceramics, dielectric dispersion shows a low-frequency response and two Debye-type relaxations, and there exist three semicircles in the complex impedance plane at high temperatures. The observed electrical properties are ascribed to the detailed internal polycrystalline microstructure, i.e., to come from the contributions of the domains, the grain boundaries and defects inside grains such as domain boundaries, etc.

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Tong Yong-Zai, Wang Xi-An, Yu Ben-Hai, Hu Xue-Hui

Acta Physica Sinica. 2006, 55 (12): 6667 doi: 10.7498/aps.55.6667
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Based on the electro-optical coefficients, the Miller-δ coefficients of KNbO₃, LiNbO₃, BaTiO₃ and several semiconductor crystals were calculated. The results show that the coefficients are frequency independent and are the same for unclamped and clamped values, so it is feasible to take the Miller-δ coefficients to characterize the nonlinear optical properties. Furthermore, a novel mechanism of the electro-optical effects is presented which maintains that the electro-optical effect results from the self-similarity of the nonlinear system, manifested as the recopy of the linear properties and the Miller-δ coefficients are the proportion factors of self-copy.

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Small angle X-ray scattering research of the relaxation and crystallization process in Cu₆₀Zr₃₀Ti₁₀ amorphous alloy

Cheng Wei-Dong, Sun Min-Hua, Li Jia-Yun, Wang Ai-Ping, Sun Yong-Li, Liu Fang, Liu Xiong-Jun

Acta Physica Sinica. 2006, 55 (12): 6673 doi: 10.7498/aps.55.6673
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Small angle X-ray scattering technique was used to investigate the evolution of microstructure in Cu₆₀Zr₃₀Ti₁₀ amorphous alloy heated at temperatures from 300 to 813 K. It is confirmed that the Cu-rich domains in the diameter range about 30 nm exist in the as-quenched state. The structural relaxation can be divided into the low temperature structure relaxation in the temperature range from 300 to 573 K and the high temperature structure relaxation in the temperature range from 573 K to the temperature of glass transition. The Cu-rich domains with ordered clusters are the basis of crystallization. Porod curves indicate that there is a sharp boundary between the nano body-centred-cubic CuZr precipitates and the matrix.

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Improved performance of the dispenser cathode with a Re intermediate layer

Li Yu-Tao, Zhang Hong-Lai, Liu Pu-Kun, Zhang Ming-Chen

Acta Physica Sinica. 2006, 55 (12): 6677 doi: 10.7498/aps.55.6677
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A new type dispenser cathode with Os-W/Re dual-layer has been developed. Emission performance and surface microstructure of the cathode with the dual-layer before and after ageing were studied. The performance of the dispenser cathode is improved by introducing a Re intermediate leyer. DC current density of the dispenser cathodes coated with Os-W alloy and Os-W/Re were compared. It is found that the cathode with Os-W/Re shows better emission performance than the cathode with Os-W alloy. Both cathodes were investigated using X-ray photoelectron spectroscopy after full activation. Ternary alloy coating being formed for the cathode with Os-W/Re is the major reason for its better emission performance. Scanning electron microscopy was used for investigating surface microstructures of both kinds of cathodes and the results show that the emitting surface of the cathode with Os-W alloy after ageing appeared non-adherent (flaking) in localized areas. This is one of the reasons for its non-uniform emission. However, surface of the cathode with Os-W/Re does not suffer from peeling under the same conditions, thus ensuring better emission uniformity and functional reliability of the dispenser cathode.

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Investigation on the crystal structure, optical and electrical properties of Er³⁺ implanted CdTe thin film

Hou Juan, Zheng Yu-Feng, Dong You-Zhong, Kuang Dai-Hong, Sun Yan-Fei, Li Qiang

Acta Physica Sinica. 2006, 55 (12): 6684 doi: 10.7498/aps.55.6684
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The structure, optical and electrical properties of the CdTe polycrystalline thin film prepared by close-space sublimation and doped with rare earth element erbium using ion implantation had been investigated by means of X-ray diffraction, scanning electron microscopy, ultraviolet visible spectroscopy, Hall effect and impedance measurement. The results indicate that the crystallinity of the samples can be improved with suitable doping concentration. It is believed that the grain-boundary barrier of the thin film CdTe:Er can be decreased due to the appearance of electron traps at grain boundaries. It is found that the implantation of Er³⁺ in CdTe thin film causes a great change in conductivity but only a little influence on optical energy band gap of the samples.

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The critical phenomena of the dilute-to-dense transition in two-dimensional granular flow

Zhong Jie, Peng Zheng, Wu Yao-Yu, Shi Qing-Fan, Lu Kun-Quan, Hou Mei-Ying

Acta Physica Sinica. 2006, 55 (12): 6691 doi: 10.7498/aps.55.6691
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The criticality of the dilute-to-dense transition in an inclined two-dimensional(2D) granular channel flow is investigated. The waiting time t before the transition occurs and after the flow is initiated is recorded. It is found that the probability function C(t) for the flow remaining dilute at time t decays exponentially with a characteristic time α^-1(d). The characteristic time is found to be fitted well by a power law a(d_c-d)^-γ, where d_c is the critical opening size: as for d>d_c, the transition will never happen. The existence of a critical opening size at the exit confirms that the dilute-to-dense transition in 2D granular flow is a critical transition.

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Investigation of improved conversion efficiency of microcrystalline silicon thin film solar cells

Zhang Xiao-Dan, Zhao Ying, Gao Yan-Tao, Chen Fei, Zhu Feng, Wei Chang-Chun, Sun Jian, Geng Xin-Hua, Xiong Shao-Zhen

Acta Physica Sinica. 2006, 55 (12): 6697 doi: 10.7498/aps.55.6697
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A series of microcrystalline silicon thin films solar cells were fabricated by very high frequency plasma enhanced chemical vapor deposition at different total gas flow rates and on different back reflectors. The results of I-V measurements of solar cells showed that the characteristic parameters of solar cells were all improved with the increase of total flow rate, so conversion efficiency of solar cells were increased. In addition, short circuit current (J_sc) of solar cells was greatly reduced, as a result, conversion efficiency of solar cells were improved when ZnO/Ag/Al back reflector were incorporated into solar cells. The details can be seen in the paper.

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Information processing of multidimensional simultaneity fluorescence with two-photon array excitation

Lin Zi-Yang, Fu Zhe, Liu Li-Xin, Hu Tao, Qu Jun-Le, Guo Bao-Ping, Niu Han-Ben

Acta Physica Sinica. 2006, 55 (12): 6701 doi: 10.7498/aps.55.6701
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Microscopical imaging method of five-dimensional simultaneity fluorescence information is a new technology for acquiring fluorescence information, which makes use of two-photon array excitation to acquire information of fluorescence position, fluorescence spectrum and fluorescence lifetime for each array element. It removes the limitation on existing fluorescence detection technology in which different functional informations are not obtained simultaneously. In this paper, the methods for deriving geometrical intensity image, different spectral intensity images and different spectral life-time images from the complex information of the new technology are presented. Because of array excitation, there is asymmetry in the array excitation intensity, which influences the excited fluorescence intensity. A method based on the excitation fluorescence intensity correction coefficient matrix is put forward, which eliminates effectively the influence of the asymmetry of array excitation intensity. Data collection and processing for actual samples are made and imaging results are got. The experimental results show the validity of the processing methods and some unsolved problems in the processing methods are discussed.

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Unified symmetry of Poincaré-Chetaev equations

Ding Ning, Fang Jian-Hui, Zhang Peng-Yu, Wang Peng

Acta Physica Sinica. 2006, 55 (12): 6197 doi: 10.7498/aps.55.6197
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The unified symmetry and conserved quantities of Poincaré-Chetaev equations are studied. The definition and criterion of the unified symmetry are given. The Noether conserved quantity, the Hojman conserved quantity, and the Mei conserved quantity induced from the symmetry are obtained.

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The sinking depth of a projectile in granular media under gravity

Zhang Quan-Yi, Wu Yao-Yu, Peng Zheng, Liu Rui, Lu Kun-Quan, Hou Mei-Ying

Acta Physica Sinica. 2006, 55 (12): 6203 doi: 10.7498/aps.55.6203
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The process of impact and penetration of a projectile with velocity u₀ in a fine, loose granular system under acceleration due to gravity has been recorded experimentally by using fast video photography. The measured penetration depth as a function of the projectile mass agrees with the prediction of our previous drag force model in that at low impact velocity the penetration depth is linearly proportional to the mass of the projectile.

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Thomson scattering with few-cycle laser pulses

Zhang Peng, Song Yan-Rong, Zhang Zhi-Gang

Acta Physica Sinica. 2006, 55 (12): 6208 doi: 10.7498/aps.55.6208
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In this paper, we analyze the relativistic Thomson scattering with few-cycle laser pulses. We conclude that scattering of high energy electrons with mono-cycle laser pulses is capable of producing attosecond pulses. The calculation shows that with a 1.5 cycle pulse at the wavelength of 1 μm, the normalized electric field intensity of 0.01,and the electron relativistic factor of 50, X-ray pulses of 0.2 as can be obtained. We also discussed the influence of the carrier-envelop phase offset and the initial phase φ_in of electrons starting to interact with the optical field on the radiation spectrum. The calculation results demonstrate that proper values of phase can result in single attosecond pulse generation, as well as the possibility of frequency tuning.

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The method for constructing the exact solutions to the nonlinear evolution equation

Taogetusang, Sirendaoerji

Acta Physica Sinica. 2006, 55 (12): 6214 doi: 10.7498/aps.55.6214
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Based on tanh-function method, homogeneous balance method and auxiliary equation, a new auxiliary equation was introduced in the paper, meanwhile, a new invariance solution was obtained, and a new exact solitary wave solution for Benjamin-Bona-Mahoney(BBM) equation and modified BBM equation was constructed using the symbolic calculation system of Mathematica. The method introduced in the paper has general significance in searching for exact solutions to the nonlinear developing equation.

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Teleportation of entangled coherent state through bipartite entangled quantum channels

Liu Chuan-Long, Zheng Yi-Zhuang

Acta Physica Sinica. 2006, 55 (12): 6222 doi: 10.7498/aps.55.6222
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We propose a scheme for teleportation of an entangled coherent state through bipartite entangled quantum channels. We study the problem in both coherent state picture and orthogonal basis picture composed of coherent states, and find that in the coherent state picture teleportation can be implemented using only linear elements, but the probability of success is less than 1/2, while in the orthogonal basis picture the probability of successful teleportation reaches 1 as long as the four Bell states can be discriminated.

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Bound state solutions of the Dirac equation with the Makarov potentials

Zhang Min-Cang, Wang Zhen-Bang

Acta Physica Sinica. 2006, 55 (12): 6229 doi: 10.7498/aps.55.6229
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[PDF 178 KB] Download:(1134)

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The bound state solutions of the Dirac equation with equal scalar and vector Makarov potentials are obtained. It is shown that angular component of the Dirac equation can be solved with the gactorization method， which enables us to find immediately the eigenvalues and at the same time the manipulation process for the normalized eigenfunctions. The radial bound state solutions are expressed in terms of the confluent hypergeometric functions and the energy equation is derived from the boundary condition satisfied by the radial wavefunctions.

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Generalized master equation for the nonextensive reaction-diffusion systems

Wu Jun-Lin, Huang Xin-Min

Acta Physica Sinica. 2006, 55 (12): 6234 doi: 10.7498/aps.55.6234
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[PDF 130 KB] Download:(1159)

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Based on the theory of nonequilibrium statistics and density operator equation, the generalized master equation satisfied by characteristic function for the nonextensive reaction-diffusion systems affected by pressure is derived by calculating the time variation of probability distribution function, where the pressure of the nonextensive systems is given in the framework of Tsallis statistics. This new equation not only depends on the nonextensive parameter but also has more nonlinear terms as compared with the master equation in the phenomenological theory, and is thus more general.

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Stochastic resonance of amplitude modulated wave in a linear model of single-mode laser

Zhang Liang-Ying, Cao Li, Jin Guo-Xiang

Acta Physica Sinica. 2006, 55 (12): 6238 doi: 10.7498/aps.55.6238
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[PDF 196 KB] Download:(1052)

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By adding modulated wave to the equation of the laser intensity of the gain-noise model of the single-mode lasers, we use the linear approximation method to calculate the power spectrum and signal-to-noise ratio(SNR) of the laser intensity, which is driven by two white noises correlated in the form of δ function. The result show that the SNR shows stochastic resonance with the varing of not only intensities of the pump noise and quantum noise，but also the frequency of a high frequency carrier signal and frequency of a low frequency periodical signal.

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Cryptanalysis of multiple chaotic systems based public key encryption technique

Wang Kai, Pei Wen-Jiang, Zou Liu-Hua, He Zhen-Ya

Acta Physica Sinica. 2006, 55 (12): 6243 doi: 10.7498/aps.55.6243
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[PDF 191 KB] Download:(1417)

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A novel public key encryption technique based on multiple chaotic systems has been proposed. This scheme employs m-chaotic systems and a set of linear functions for key exchange over an insecure channel. The security of the proposed algorithm grows as (NP)^m, where N, P are the size of the key and the computational complexity of the linear functions, respectively. In this paper, the fundamental weakness of the cryptosystem is pointed out and a successful attack is described. Given the fact that any complex linear transformations on a vector will make the norm of the vector approximate linear growth, we present an attack that permits recovering the corresponding secret key from the public key and the initial value. Both theoretical and experimental results show that the attacker can access the secret key without any difficulty. The lack of security discourages the use of such algorithm for practical applications.

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Synchronization control based on feedback precise linearization

Zhu Zhi-Yu

Acta Physica Sinica. 2006, 55 (12): 6248 doi: 10.7498/aps.55.6248
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[PDF 185 KB] Download:(1334)

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Precise linearity method which is applied to linearize nonlinear chaotic system through strict state transform and feedback strategy is discussed. Considering that some of the state variables can not be measured, the nonlinear feedback method including state observer is researched, and the corresponding control law is deduced. This kind of control method is adopted to chaos synchronization control of the Lorenz system, the simulation results show that the synchronization error of the three state variables can convergence to zero in a short time, which indicates that the control procedure proposed in this paper can guarantee high convergence speed and precision of synchronization under the prerequisite of close-loop stability.

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Stochastic chaos in stochastic Duffing systems and its control by delayed feedback

Wu Cun-Li, Ma Shao-Juan, Sun Zhong-Kui, Fang Tong

Acta Physica Sinica. 2006, 55 (12): 6253 doi: 10.7498/aps.55.6253
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[PDF 332 KB] Download:(1686)

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The problem of stochastic chaos and its control by delayed feedback in a Duffing system with bounded random parameters (a stochastic Duffing system in short) under harmonic excitations is considered in detail. At first, the stochastic Duffing system is transformed into its equivalent deterministic nonlinear system by the Gegenbauer polynomial approximation. Thus, the problem of chaotic response and its control in stochastic Duffing system can be reduced to that in an equivalent deterministic system. So the available effective mathematical methods and control strategies can be applied to the latter. Then, the main feature of stochastic chaos is fully explored, where the top Lyapunov exponent of the equivalent system obtained by Wolf's algorithm is used to identify the dynamic behavior of stochastic Duffing system. Finally, the control strategy of delayed feedback is applied to suppress or to induce chaotic response in the system. The results of numerical simulation show that by proper choice of feedback intensity and time delay, either suppressing or inducing stochastic chaos can be achieved. Hence, the strategy of delayed feedback control is also effective to stochastic chaos.

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Chaos synchronization of the new hyperchaotic Chen system via nonlinear control

Wu Xiang-Jun, Wang Xing-Yuan

Acta Physica Sinica. 2006, 55 (12): 6261 doi: 10.7498/aps.55.6261
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[PDF 263 KB] Download:(2142)

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This paper studies chaos synchronization of the new hyperchaotic Chen system via nonlinear control. A new method for improving the Lyapunov function of error dynamics of synchronization designed by Jiang and Huang et al is presented. The method removes the limitation occasioned by the Lyapunov function having only one form. Based on Lyapunov theory, a nonlinear controller is designed to synchronize two identical systems and two different chaotic systems. Chaos synchronization of two identical hyperchaotic Chen systems and two different chaotic systems (the hyperchaotic Chen system and the hyperchaotic R?ssler system) have been proved theoretically. Numerical simulations show the effectiveness of the proposed method.

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Studies on chaotic modulation performance and internal phase shifting key encoding in injection semiconductor lasers

Yan Sen-Lin

Acta Physica Sinica. 2006, 55 (12): 6267 doi: 10.7498/aps.55.6267
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The chaotic modulation and demodulation in injected semiconductor lasers are studied, and a method of chaotic encoding is presented by modulating the phase of external optical injection light in semiconductor lasers. The modulation response function, demodulation response function and demodulation response factor are analyzed by small-signal analysis. It is found there are peak values about 60 MHz and the response functions and the demodulation factor decrease at high modulation frequency. A chaotic modulation-demodulation equation is theoretically deduced and its roots are given. It is found that there is a peak value at low modulation frequency and the demodulation perfomance declines at high frequency, however, modulation-demodulation of 10⁹ Hz frequency is relalized. Synchronization is achieved and is proved feasible numerically in larger parameter range. Secure communication applications are numerically simulated with chaotic modulations of 200 Mb/s rate and 1.4 GHz frequency. Chaotic encoding is also achieved by shifting key on or off a phase-controller to encode chaotic laser state and decoding is realized under the condition of synchronization or unsynchronization. Chaotic phase key shifting is numerically simulated with a bit rate of 10 Mb/s.

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The study of a cellular automaton NS and WWH mixed model for traffic flow on a two-lane roadway

Wu Ke-Fei, Kong Ling-Jiang, Liu Mu-Ren

Acta Physica Sinica. 2006, 55 (12): 6275 doi: 10.7498/aps.55.6275
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Based on the NS model and the WWH model for one-dimensional cellular automaton traffic flow, and taking into account the drivers adopting different driving rules, we present a cellular automaton NS and WWH mixed model for traffic flow on a two-lane roadway. By using numerical simulation, we study the effect of the mixed proportion coefficient f_NS on the velocity-density and flow-density diagrams of the mixed traffic flow and the lane-change frequency of the vehicles.

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Time-resolved two-photon excitation fluorescence spectroscopy

Liu Li-Xin, Qu Jun-Le, Lin Zi-Yang, Chen Dan-Ni, Xu Gai-Xia, Hu Tao, Guo Bao-Ping, Niu Han-Ben

Acta Physica Sinica. 2006, 55 (12): 6281 doi: 10.7498/aps.55.6281
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[PDF 290 KB] Download:(2706)

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A novel time-resolved two-photon excitation fluorescence spectroscopic system based on a high repetition rate streak camera and capable of simultaneous measurement of fluorescence spectrum and lifetime of the samples is presented. The system has high temporal (6.5—200 ps) and spectral (1—3 nm) resolutions and permits rapid data acquisition and reliable and reproducible lifetime and spectrum determinations. The system is tested with standard fluorescent dyes (rhodamine 6G, coumarin 314 and their mixtures) and the lifetimes and spectra obtained agree well with those reported in the literatures. Experimental results indicate that our system provides a unique contrast mechanism for discriminating multi-fluorophore or multi-component of biological tissues through spectrally and temporally resolved information and may find extensive applications in multispectral fluorescence lifetime imaging and fluorescence resonance energy transfer imaging.

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Study of X-ray detector system characteristics on the 3B3 medium energy beamline in BSRF

Yi Rong-Qing, Yang Guo-Hong, Cui Yan-Li, Du Hua-Bing, Wei Min-Xi, Dong Jian-Jun, Zhao Yi-Dong, Cui Ming-Qi, Zheng Lei

Acta Physica Sinica. 2006, 55 (12): 6287 doi: 10.7498/aps.55.6287
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On the 3B3 medium energy X-ray beamline, a new monochromatic X-ray source tunable in the 2—6 keV energy range bas been constructed and implemented. The characteristic parameters of the X-ray source having been determined, with the help of the light source, we have calibrated the sensitivity of X-ray detector,thickness of filter,diffraction efficiency of crystals and energy response of the BAS5000-RS, which showed the high performance of the monochromator and detecter system.

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Two-photon spectroscopy and Dicke narrowing of a thin atomic vapor film

Li Yuan-Yuan, Bai Jin-Tao, Zhang Gui-Zhong, Zhou Yu, Zhang Yan-Peng, Gan Chen-Li

Acta Physica Sinica. 2006, 55 (12): 6293 doi: 10.7498/aps.55.6293
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One-photon Dick-narrowing absorption spectroscopy from a thin atomic vapor film can be extended to the two-photon case, in which the sub-Doppler absorption structures are obtained in a cascade three-level system. The periodic line shapes of two photon spectroscopy are similar to one-photon case. It is found that Dicke-narrowing is apparent when L/λ=(2n+1)/2 (n an integer, L the film thickness, and λ the wavelength of the probe field)in the case of one-photon process, and this feature is maintained in the case of two-photon process but not in the one-photon process when L/λ=2n/2. Due to the contribution of atom-wall collision in the cell and the pump-probe scheme, a very narrow structure can be obtained when the pump and the probe fields are in counter-propagation regime.

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Relation between dynamic parameters and limiting current in separated function radio frequency quadrupole accelerator

Wang Zhi, Chen Jia-Er, Yan Xue-Qing, Lu Yuan-Rong, Fang Jia-Xun, Guo Zhi-Yu

Acta Physica Sinica. 2006, 55 (12): 6298 doi: 10.7498/aps.55.6298
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The particles' motion in separated function radio frequency quadrupole (SFRFQ) accelerator is analyzed in this paper. Compared to conventional radio frequency quadrupole accelerator, the SFRFQ structure has higher accelerating efficiency, and the particles are focused or defocused by the quadrupole outside the diaphragms. The relation between limiting current and dynamic parameters has been deduced, so the transverse and longitudinal stability of particles in SFRFQ is ensured by selecting proper dynamic parameters.

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Potentional energy function of CrHⁿ(n=0,+1,+2)

Huang Ping, Zhu Zheng-He

Acta Physica Sinica. 2006, 55 (12): 6302 doi: 10.7498/aps.55.6302
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[PDF 238 KB] Download:(1031)

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Based on the atomic and molecular reaction statics, the ground electronic states of CrH(X⁶Σ⁺), CrH⁺(⁵Σ⁺), CrH²⁺ (⁶Σ⁺) and their dissociation limits have been derived. Using density functional method (B3PW91), 6-311++G^** basis sets for H and split valence polarization basis sets for Cr, the molecular equilibrium geometry and dissociation energies for CrH⁺(⁵Σ⁺) and CrH²⁺ (⁶Σ⁺) have been calculated. The analytical potential energy functions for CrH(X⁶Σ⁺), CrH⁺(⁵Σ⁺) and CrH²⁺ (⁶Σ⁺) are determined. The force fields and spectroscopic parameters have been worked out from these analytical potential energy functions. For the ground state of CrH⁺, the calculated results of R_e, f₂, f₃, f₄, B_e, α_e, ω_e and ω_eχ_e are 0.16200 nm, 1.52574 aJ/nm², -7.81171 aJ/nm³, 28.61613 aJ/nm⁴, 6.71181, 0.28792, 1624.6297 and 53.55394 cm^-1, respectively; and for the ground state of CrH²⁺, the corresponding parameters are 0.24005 nm, 0.42946 aJ/nm², -0.97766 aJ/nm³, 2.40438 aJ/nm⁴, 2.9562, 0.050184, 858.059 and 6.46813 cm^-1, respectively. The theoretical results show minimum points in the potential energy curves of CrH⁺(⁵Σ⁺) and CrH(X⁶Σ⁺), so we conclude that CrH(X⁶Σ⁺) and CrH⁺(⁵Σ⁺) are stable.But there are no minimum points in the potential energy curves of CrH²⁺ (⁶Σ⁺), so CrH²⁺ (⁶Σ⁺) is not stable.

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Study on potential energy functions and spectrum constants of VO^n±(n=0,1,2)

Du Quan, Wang Ling, Shen Xiao-Hong, Gao Tao

Acta Physica Sinica. 2006, 55 (12): 6308 doi: 10.7498/aps.55.6308
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[PDF 267 KB] Download:(1191)

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The potential energy functions and spectrum constants of VO^n±(n=0,1,2) have been analyzed by the density functional method (B3LYP/6-311++G(d, p) and using the relativistic effective core potential (Lanl2dz). The results show that all of them can exist stably. Their ground electronic states are ⁴Σ (VO^2-), ³Σ (VO^-), ⁴Σ(VO), ³Σ(VO⁺) and ²Σ(VO²⁺). Among them, the potential energy curves of VO²⁺ and VO^2- have the form of a volcanic crater. The molecules of VO²⁺ and VO^2- are in meta-stable states. The potential energy curves of VO²⁺ and VO^2- have been fitted with the seven-parameter Murell-Sorbie functions. It has been found that the fitting cures of the meta-stable ions VO²⁺ and VO^2- are well in accordance with their potential energy curves. However, the four-parameter Murell-Sorbie functions are not suitable for VO²⁺ and VO^2-. At the same time, the effect of charge on the potential energy functions and energy levels have been discussed.

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A study of the surface enhanced Raman bond polarizability derivatives of ethylene thiourea：electromagnetic and charge transfer mechanisms

Liu Zhao-Jun, Wu Guo-Zhen

Acta Physica Sinica. 2006, 55 (12): 6315 doi: 10.7498/aps.55.6315
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The surface enhanced Raman spectra of ethylene thiourea adsorbed on the silver electrode were measured at different electrode potentials. Based on the analysis of the Raman spectra, especially the bond polarizability derivatives elucidated from the Raman intensities by our algorithm, important information on the surface enhancement mechanisms was collected. The results show that both the electromagnetic and charge transfer mechanisms are responsible for the large enhancement, the former operating in the whole potential range between -0.3 and -1.2 V while the latter only in the range lower than -0.7 V.

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The classical dissociation of HF molecule by chirped laser pulse

Chi Yu-Hua, Liu Xue-Shen, Ding Pei-Zhu

Acta Physica Sinica. 2006, 55 (12): 6320 doi: 10.7498/aps.55.6320
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[PDF 222 KB] Download:(1019)

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The classical dissociation of a diatomic molecule by chirped laser pulses is evaluated by means of symplectic algorithm. We discuss the effect of the vibro-rotational energy level transition on the dissociation probability.

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Cascade decays and final charge-state distribution of hollow argon ions

Hu Hong-Wei, Dong Chen-Zhong

Acta Physica Sinica. 2006, 55 (12): 6326 doi: 10.7498/aps.55.6326
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[PDF 203 KB] Download:(1152)

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On the basis of a previous model of radiative-Auger-cascade for calculation of final-charge-state distributions of hollow ions, a new model of radiative-Auger-double Auger-cascade has been constructed by including double Auger process, and was applied to study the final-charge-state distribution in the production of Ar⁺(1s^-1) (argon ion with an initial 1s hole) and Ar⁺(2s^-1) (argon ion with an initial 2s hole). Comparing with the previous calculations and experiments, the present results show excellent agreement.

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Generation of controllable double-well optical trap for cold atoms (molecules) and its experimental studies

Mu Ren-Wang, Li Ya-Li, Ji Xian-Ming, Yin Jian-Ping

Acta Physica Sinica. 2006, 55 (12): 6333 doi: 10.7498/aps.55.6333
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[PDF 561 KB] Download:(1475)

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In this paper, an experimental scheme of a controllable double-well optical trap for cold atoms (molecules) is briefly introduced, and the fabrication method of a binary π-phase plate and the experimental results to generate a controllable double-well optical trap are reported. In the experiment, we investigated the dependence of the double-well parameters (such as the spatial position of optical double-well, the spacing between the centers of two wells and the relative intensity distributions and so on) on the phase errors of the π-phase plate, and the change of double-well intensities resulting from errors in the engraving depth of the binary π-phase plate as well as the evolution of the optical trap from two wells to single one are studied both theoretically and experimentally. Experimental results consistent with theoretical prediction are obtained.

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A laser diode system for ⁴⁰K-⁸⁷Rb atomic cooling

Wei Dong, Chen Hai-Xia, Xiong De-Zhi, Zhang Jing

Acta Physica Sinica. 2006, 55 (12): 6342 doi: 10.7498/aps.55.6342
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We have developed a semiconductor laser system used in ⁴⁰K-⁸⁷Rb trapping and cooling experiment. The laser diode system is composed of three external cavity diode lasers and four injection diode lasers and a tapered amplifier. Four laser beams used for ⁴⁰K and ⁸⁷Rb cooling and repump lights are obtained by using acoustic optic modulators to offset the frequencies from the three external cavity diode lasers. Four light beams with different frequencies are injected into four slave lasers for injection locking. Then Rb cooling light, K cooling light and K repump light are injected into a semiconductor tapered amplifier in a master oscillator-power configuration. This configuration is flexible and stable and can simultaneously produce the cooling and repump light for ⁴⁰K and ⁸⁷Rb trapping and cooling experiment.

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Applicability of the reaction window theory

Chen Lan-Fang, Ma Xin-Wen, Zhu Xiao-Long

Acta Physica Sinica. 2006, 55 (12): 6347 doi: 10.7498/aps.55.6347
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[PDF 314 KB] Download:(1110)

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Based on the molecular Coulombic over barrier model for description of slow ion-atom collisions, the reaction window theory related to projectile velocity is presented briefly. According to the theory, the state-selective differential cross sections of single electron capture in O⁸⁺-H, Ar⁸⁺-H, Ar⁸⁺-He, Ne¹⁰⁺-He and Ar¹⁸⁺-He collisions at different collision velocities are calculated and compared with experimental results. Calculations are also done for single, double, and triple electron capture in ¹⁵N⁷⁺-Ne collisions at fixed velocity of 0.53　a.u., and are compared with experimental data. It is found that the predictions of the final electronic state distribution of captured electron(s) are in agreement with experimental data, and both theory and experiments show that the widths of the reaction window increase with the projectile velocity. The differential cross sections predicted by the theory are larger for smaller Q-values, vice versa, when compared with experimental data.

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Theoretical investigation of optical heterodyne cavity ring down spectroscopy

Cao Lin, Wang Chun-Mei, Chen Yang-Qin, Yang Xiao-Hua

Acta Physica Sinica. 2006, 55 (12): 6354 doi: 10.7498/aps.55.6354
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A simplified optical heterodyne cavity ring down spectroscopy, which is relatively easy to implement and more suitable for molecular ro-vibrational spectrum study, is suggested in the present paper. It avoids measuring the ring down time directly, and in addition cancels the DC common mode signal resulting from the loss of the cavity mirrors. Theoretically, it could reach the quantum noise detection limit. Furthermore, its lineshape of the first derivative of Gaussian profile is theoretically analyzed, and the dependence of the spectral intensity and lineshape on some experimental parameters are also discussed, and thus the optimal parameters are obtained.

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Numerical simulation of the internal flow in microwave plasma thruster in magnetic field

Yang Juan, Su Wei-Yi, Mao Gen-Wang, Xia Guang-Qing

Acta Physica Sinica. 2006, 55 (12): 6494 doi: 10.7498/aps.55.6494
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[PDF 273 KB] Download:(1382)

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Recent experiments show that the performance of microwave plasma thruster is a little too low because the energy absorbed by plasma depends on the relationship of plasma and microwave frequency. One potential solution is to use external magnetic field to improve the transfer process of microwave in plasma. This paper presents numerical study about how a magnetic field affects the thermal plasma flow field and its temperature in microwave plasma thruster. Out purpose is to see if the magnetic field can enhance the thermal plasma core temperature. Assuming that the plasma within the thruster is under the condition of local thermal equilibrium and the external magnetic fields is uniform, coupled Navier-Stokes, Maxwell and Saha equations are set up to describe the plasma flow under microwave electromagnetic and external magnetic fields. Solving Navier-Stokes equations with semi-implicit method for pressure-linked equations and Maxwell equations with finite-difference time-domain method, the result shows that when the magnetic field intensity is 0.5 T the temperature of plasma core is increased by 24% compared with that at zero magnetic field. Thus the magnetic field improves the performance of microwave plasma thruster.

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Approaches to convergence enhancement of multiframe blind deconvolution of astronomical images

Luo Lin, Wang Li, Cheng Wei-Dong, Shen Mang-Zuo

Acta Physica Sinica. 2006, 55 (12): 6708 doi: 10.7498/aps.55.6708
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[PDF 286 KB] Download:(2297)

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The convergence property of multiframe blind deconvolution applied to improve the resolution of astronomical images is influenced by initial object estimate, constraint conditions and photon noise. A method of determining band limitation of the point-spread function from the optical imaging system parameters is proposed. The initial object estimate of blind deconvolution algorithm is formed by using Knox-Thompson method to reconstruct object phase from short-exposure images. A novel method，which is used to decrease photon noise, edge effects and ringing of restoration images is developed. An improved multiframe blind deconvolution algorithm with a strict constrained optimization method of the expectation-maximization based on maximum-likelihood estimation is presented. The restored images of the simulation data,and real Mars and solar-granulation data show that the proposed multiframe blind deconvolution algorithm is valid for overcoming effects of atmospheric turbulence and photon noise and improving the resolution of real observed astronomical images, and capabel of partly removing th diffraction effect of optical system on restored images.

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Numerical analysis of the scaling laws about focused beam spreading induced by the atmosphere

Huang Yin-Bo, Wang Ying-Jian

Acta Physica Sinica. 2006, 55 (12): 6715 doi: 10.7498/aps.55.6715
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Using typical sets of numerical parameters under characteristic laser beam propagation conditions, focused beam spreading induced by atmospheric turbulence and thermal blooming is analyzed by numerical simulation. In the analysis of the combined effect, we assume that the thermal blooming effect arises in consequence of the increase in beam radius induced by atmospheric turbulence and beam jitter. The scaling relations between the laser propagation effects and characteristic parameters describing the propagation in atmosphere are obtained. Based upon these relations, we can efficiently estimate atmospheric propagation effects and learn the performance of a particular system design under various environmental conditions, as well as conduct laser system design optimization.

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The new algorithm for standalone positioning with global positioning system and numerical experiments

Huang Si-Xun, Sheng Zheng

Acta Physica Sinica. 2006, 55 (12): 6720 doi: 10.7498/aps.55.6720
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[PDF 274 KB] Download:(2226)

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To determine the approximate position of a global positioning system receiver, the Bancroft method can provide the initial value for linearization of the observation equation, which can then be solved by the least-square (LS) method. Because the solution of LS method is not unique and the observation data have noise, the solution is ill-posed. In order to solve the problem, we introduce the regularization method combined with the optimum choice of regularization parameter. The experimental result indicates that it can enhance the resistance to bad errors, which has significance in real-time fast positioning.