Chin. Phys. B

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Algebraic structure and Poisson's theory of mechanico-electrical systems

Liu Hong-Ji, Tang Yi-Fa, Fu Jing-Li

Chin. Phys., 2006, 15 (8): 1653-1661 doi: 10.1088/1009-1963/15/8/001
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The algebraic structure and Poisson's integral theory of mechanico-electrical systems are studied. The Hamilton canonical equations and generalized Hamilton canonical equations and their the contravariant algebraic forms for mechanico-electrical systems are obtained. The Lie algebraic structure and the Poisson's integral theory of Lagrange mechanico-electrical systems are derived. The Lie algebraic structure admitted and Poisson's integral theory of the Lagrange--Maxwell mechanico-electrical systems are presented. Two examples are presented to illustrate these results.

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Hamilton--Jacobi method for solving ordinary differential equations

Mei Feng-Xiang, Wu Hui-Bin, Zhang Yong-Fa

Chin. Phys., 2006, 15 (8): 1662-1664 doi: 10.1088/1009-1963/15/8/002
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[PDF 86 KB] (Downloads:737)

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The Hamilton--Jacobi method for solving ordinary differential equations is presented in this paper. A system of ordinary differential equations of first order or second order can be expressed as a Hamilton system under certain conditions. Then the Hamilton--Jacobi method is used in the integration of the Hamilton system and the solution of the original ordinary differential equations can be found. Finally, an example is given to illustrate the application of the result.

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Lie-form invariance of non-holonomic systems with unilateral constraints

Wang Jing, Li Yuan-Cheng, Xia Li-Li, Hou Qi-Bao

Chin. Phys., 2006, 15 (8): 1665-1668 doi: 10.1088/1009-1963/15/8/003
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In this paper the Lie-form invariance of the non-holonomic systems with unilateral constraints is studied. The definition and the criterion of the Lie-form invariance of the system are given. The generalized Hojman conserved quantity and a new type of conserved quantity deduced from the Lie-form invariance are obtained. Finally, an example is presented to illustrate the application of the results.

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An inverse problem in analytical dynamics

Li Guang-Cheng, Mei-Feng-Xiang

Chin. Phys., 2006, 15 (8): 1669-1671 doi: 10.1088/1009-1963/15/8/004
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This paper presents an inverse problem in analytical dynamics. The inverse problem is to construct the Lagrangian when the integrals of a system are given. Firstly, the differential equations are obtained by using the time derivative of the integrals. Secondly, the differential equations can be written in the Lagrange equations under certain conditions and the Lagrangian can be obtained. Finally, two examples are given to illustrate the application of the result.

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Three-order form invariance and conserved quantity

Yang Xue-Hui, Ma Shan-Jun

Chin. Phys., 2006, 15 (8): 1672-1677 doi: 10.1088/1009-1963/15/8/005
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In this paper, the definition of three-order form invariance is given. Then the relation between the three-order form invariance and the three-order Lie symmetry is discussed and the sufficient and necessary condition of Lie symmetry, which comes from the three-order form invariance, is obtained. Finally a three-order Hojman conserved quantity is studied and an example is given to illustrate the application of the obtained results.

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A symmetry and a conserved quantity for the Birkhoff system

Mei Feng-Xiang, Gang Tie-Qiang, Xie Jia-Fang

Chin. Phys., 2006, 15 (8): 1678-1681 doi: 10.1088/1009-1963/15/8/006
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A symmetry and a conserved quantity of the Birkhoff system are studied. The symmetry is called the Birkhoff symmetry. Its definition and criterion are given in this paper. A conserved quantity can be deduced by using the symmetry. An example is given to illustrate the application of the result.

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Multi-party dense coding in non-symmetric quantum channel

Fu Chang-Bao, Xia Yan, Zhang Shou

Chin. Phys., 2006, 15 (8): 1682-1685 doi: 10.1088/1009-1963/15/8/007
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A three- and an (N+1)-party dense coding scheme in the case of non-symmetric Hilbert spaces of the particles of a quantum channel are investigated by using a multipartite entangled state. In the case of the (N+1)-party dense coding scheme, we show that the amount of classical information transmitted from N senders to one receiver is improved.

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Simple experimental scheme of teleporting a two-qubit state via linear optical elements

Yuan Hong-Chun, Li Heng-Mei, Qi Kai-Guo

Chin. Phys., 2006, 15 (8): 1686-1689 doi: 10.1088/1009-1963/15/8/008
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We propose a simple experimental scheme in which an unknown two-qubit state is faithfully and deterministically teleported from Alice to Bob. The scheme is constructed with four photons from parametric down conversion, linear optical elements, and conventional photon detectors, all of which are available in current technology. It is shown that the probability of successful teleportation ideally reaches 100% based on single-photon two-qubit-assisted Bell-state measurement, which can distinguish all four Bell-states simultaneously via conventional photon detectors. By generalizing the scheme, the teleportation of an unknown multi-qubit system can also be realized.

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A quantum encryption scheme using d-level systems

Guo Fen-Zhuo, Gao Fei, Wen Qiao-Yan, Zhu Fu-Chen

Chin. Phys., 2006, 15 (8): 1690-1694 doi: 10.1088/1009-1963/15/8/009
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Using the generalized Bell states and quantum gates, we introduce a quantum encryption scheme of d-level states (qudits). The scheme can detect and correct arbitrary transmission errors using only local operations and classical communications between the communicators. In addition, the entanglement key used to encrypt can be recycled. The protocol is informationally secure, because the output state is a totally mixed one for every input state \rho .

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Protocol for multi-party superdense coding by using multi-atom in cavity QED

Tan Jia, Fang Mao-Fa

Chin. Phys., 2006, 15 (8): 1695-1699 doi: 10.1088/1009-1963/15/8/010
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We present a protocol for multi-party superdense coding by using multi-atom in cavity quantum electrodynamics (QED). It is shown that, with a highly detuned cavity mode and a strong driving field, the protocol is insensitive to both cavity decay and thermal field. It is even certain to identify GHZ states via detecting the atomic states. Therefore we can realize the quantum dense coding in a simple way in the multiparty system.

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Remote atomic information concentration without Bell-state measurement

Wu Zhen-Zhen, Fang Mao-Fa

Chin. Phys., 2006, 15 (8): 1700-1704 doi: 10.1088/1009-1963/15/8/011
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This paper proposes a scheme for information concentration of two remote two-level atoms in cavity QED. This scheme does not involve the Bell-state measurement. During the interaction between atom and cavity, the cavity frequency is large-detuned from the atomic transition frequency, thus the scheme is insensitive to both the cavity decay and the thermal field. This idea can directly be generalized in the case of multi-atom information concentration.

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Chaos feature of test particle in the gravitational field with a quadrupole

Chen Ju-Hua, Wang Yong-Jiu

Chin. Phys., 2006, 15 (8): 1705-1708 doi: 10.1088/1009-1963/15/8/012
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[PDF 116 KB] (Downloads:510)

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In this paper we investigate the dynamics of a test particle in the gravitational field with a quadrupole. By constructing Poincaré sections for different values of the parameters and initial conditions, we find a chaotic evolution. From these Poincaré sections, we further confirm that the chaotic evolution of the test particle originates from the quadrupole.

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The Hawking radiation of the charged particle via tunnelling from the axisymmetric Sen black hole

Jiang Qing-Quan, Yang Shu-Zheng, Chen De-You

Chin. Phys., 2006, 15 (8): 1709-1714 doi: 10.1088/1009-1963/15/8/013
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Extending Parikh's semi-classical quantum tunnelling model, this paper has studied the Hawking radiation of the charged particle via tunnelling from the horizon of the axisymmetric Sen black hole. Different from the uncharged massless particle, the geodesics of the charged massive particle tunnelling from the horizon is not light-like. The derived result supports Parikh's opinion and provides a correct modification to Hawking strictly thermal spectrum developed by the fixed background space-time and not considering the energy conservation and the self-gravitation interaction.

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Adaptive passive equivalence of uncertain Lü system

Qi Dong-Lian

Chin. Phys., 2006, 15 (8): 1715-1718 doi: 10.1088/1009-1963/15/8/014
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An adaptive passive strategy for controlling uncertain L\"{u} system is proposed. Since the uncertain L\"{u} system is minimum phase and the uncertain parameters are from a bounded compact set, the essential conditions are studied by which uncertain L\"{u} system could be equivalent to a passive system, and the adaptive control law is given. Using passive theory, the uncertain L\"{u} system could be globally asymptotically stabilized at different equilibria by the smooth state feedback.

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Pole placement method of controlling chaos in DC--DC buck converters

Zou Yan-Li, Luo Xiao-Shu, Chen Guan-Rong

Chin. Phys., 2006, 15 (8): 1719-1724 doi: 10.1088/1009-1963/15/8/015
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[PDF 191 KB] (Downloads:740)

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Based on the mechanism for the generation of chaos in a buck converter, a pole placement method is proposed and applied to controlling the chaos in a circuit. The control circuit is designed and tested. Numerical calculation and circuit implementation demonstrate the validity of this chaos control method.

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Effect of the mutation of carotenoids on the dynamics of energy transfer in light-harvesting complexes (LH2) from Rhodobacter sphaeroides 601 at room temperature

Liu Wei-Min, Liu Yuan, Liu Kang-Jun, Yan Yong-Li, Guo Li-Jun, Xu Chun-He, Qian Shi-Xiong

Chin. Phys., 2006, 15 (8): 1725-1730 doi: 10.1088/1009-1963/15/8/016
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Energy transfers in two kinds of peripheral light-harvesting complexes (LH2) of {Rhodobacter sphaeroides} (RS) 601 are studied by using femtosecond pump--probe spectroscopy with tunable laser wavelength at room temperature. These two complexes are native LH2 (RS601) and green carotenoid mutated LH2 (GM309). The obtained results demonstrate that, compared with spheroidenes with ten conjugated double bonds in native RS601, carotenoid in GM309 containing neurosporenes with nine conjugated double bonds can lead to a reduction in energy transfer rate in the B800-to-B850 band and the disturbance in the energy relaxation processes within the excitonic B850 band.

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In-line phase contrast for weakly absorbing materials with a microfocus x-ray source

Zhang Di, Li Zheng, Huang Zhi-Feng, Yu Ai-Min, Sha Wei

Chin. Phys., 2006, 15 (8): 1731-1737 doi: 10.1088/1009-1963/15/8/017
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[PDF 200 KB] (Downloads:419)

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For weakly absorbing materials, image contrast can be enhanced by phase contrast in formation. The effectiveness of the in-line phase contrast technique relies on its ability to record intensity data which contain information on the x-ray's phase shift. Four kinds of approaches to the relationship between intensity distribution and phase shift are reviewed and discussed. A micro-focal x-ray source with high geometrical magnification is used to acquire phase contrast images. A great improvement on image quality is shown and geometrical parameters are modified for comparison between different imaging positions.

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High-T_c planar SQUID gradiometer for eddy current non-destructive evaluation

Zhang Ming-Jian, Lang Pei-Lin, Peng Zhi-Hui, Chen Ying-Fei, Chen Ke, Zheng Dong-Ning

Chin. Phys., 2006, 15 (8): 1903-1908 doi: 10.1088/1009-1963/15/8/046
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This paper reports the fabrication and test of a high-T_c SQUID planar gradiometer which is patterned from YBCO thin film deposited on a SrTiO\xj{3} bicrystal substrate. The measurement of noise spectrum at 77K shows that the white noise at 200 Hz is about 1×10^-4{\Phi₀/\sqrt Hz. The minimal magnetic gradient is measured and the results suggest that the minimal magnetic gradient is 94 pT/m. The planar gradiometer is used in non-destructive evaluation (NDE) experiments to detect the artifacts in conducting aluminium plates by performing eddy current testing in an unshielded environment. The effect of the exciting coil dimension on the NDE results is investigated. By mapping out the induced field distribution, flaws about 10mm below the plate surface can be clearly identified.

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Isospin- and momentum-dependent interaction in isospin-dependent quantum molecular dynamics

Liu Jian-Ye, Guo Wen-Jun, Ren Zhong-Zhou, Xing Yong-Zhong, Zuo Wei, Lee Xi-Guo

Chin. Phys., 2006, 15 (8): 1738-1745 doi: 10.1088/1009-1963/15/8/018
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[PDF 252 KB] (Downloads:480)

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An isospin-dependent quantum molecular dynamical model (IQMD) is developed, with the isospin degree of freedom in the momentum-dependent interaction(MDI) included in IQMD, to obtain an isospin- and momentum-dependent interaction (IMDI) in IQMD. We investigate the effect of IMDI on the isospin fractionation ratio and its dynamical mechanism in the intermediate energy heavy ion collisions. It is found that the IMDI induces the significant reductions in the isospin fractionation ratio for all of beam energies, impact parameters, neutron--proton ratios and mass number of colliding systems. However, the strong dependence of isospin fractionation ratio on the symmetrical potential is preserved, with the isospin degree of freedom included in the MDI, i.e. the isospin fractionation ratio is still a good probe for extracting the information about the equation of state of isospin asymmetrical nuclear matter.

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A possible mechanism of current in medium under electromagnetic wave

Zhang Tao

Chin. Phys., 2006, 15 (8): 1752-1754 doi: 10.1088/1009-1963/15/8/020
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In this paper a possible mechanism of current in medium is presented. Comparison between this current and the magnetization current was made. Expression for this current was derived. This work is helpful to understanding the interaction between medium and electromagnetic wave.

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Electromagnetic scattering from two parallel 2D targets arbitrarily located in a Gaussian beam

Wang Yun-Hua, Guo Li-Xin, Wu Qiong

Chin. Phys., 2006, 15 (8): 1755-1765 doi: 10.1088/1009-1963/15/8/021
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In this paper based on the equivalence principle and the reciprocity theorem, the scattered field up to second-order by two parallel 2D targets arbitrarily located in a Gaussian beam is considered. The first-order solution can easily be obtained by calculating the scattered field from isolated targets when illuminated by a Gaussian beam. However, because of the difficulty in formulating the couple scattering field, it is almost impossible to find an analytical solution for the second-order scattered field if the shapes of 2D targets are not canonical geometries. In order to overcome this problem, in this paper, the second-order solution is derived by using the technique based on the reciprocity theorem and the equivalence principle. Meanwhile, the relation between the secondary scattered field from target #1 and target {\#}2 is obtained. Specifically, the bi- and mono-static scattering of Gaussian beam by two parallel adjacent inhomogeneous plasma-coated conducting circular cylinders is calculated and the dependence of attenuation of the scattering width on the thickness of the coated layer, electron number density, collision frequency and radar frequency is discussed in detail.

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Continuous-variable quantum teleportation of even and odd coherent states through varied gain channels

Li Ying, Zhang Jing, Zhang Jun-Xiang, Zhang Tian-Cai

Chin. Phys., 2006, 15 (8): 1766-1771 doi: 10.1088/1009-1963/15/8/022
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This paper has investigated quantum teleportation of even and odd coherent states in terms of the EPR entanglement states for continuous variables. It discusses the relationship between the fidelity and the entanglement of EPR states, which is characterized by the degree of squeezing and the gain of classical channels. It shows that the quality of teleporting quantum states also depends on the characteristics of the states themselves. The properties of teleporting even and odd coherent states at different intensities are investigated. The difference of teleporting two such kinds of quantum states are analysed based on the quantum distance function.

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Numerical simulations of negative-index refraction in a lamellar composite with alternating single negative layers

Dong Zheng-Gao, Zhu Shi-Ning, Liu Hui

Chin. Phys., 2006, 15 (8): 1772-1776 doi: 10.1088/1009-1963/15/8/023
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[PDF 373 KB] (Downloads:631)

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Negative-index refraction is demonstrated in a lamellar composite with epsilon-negative (ENG) and mu-negative (MNG) materials stacked alternatively. Based on the effective medium approximation, simultaneously negative effective permittivity and permeability of such a lamellar composite are obtained theoretically and further proven by full-wave simulations. Consequently, the renowned left-handed metamaterial comprising split ring resonators and wires is interpreted as an analogy of such ENG--MNG layers. In addition, beyond the effective medium approximation, the propagating field squeezed near the ENG/MNG interface is demonstrated to be left-handed surface waves with backward phase velocity.

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Analysis of spectrum characteristics of optical scintillation in stack gas flow

Liu Wen-Qing, Liu He-Lai, Zeng Zong-Yong, Jiang Yu

Chin. Phys., 2006, 15 (8): 1777-1782 doi: 10.1088/1009-1963/15/8/024
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[PDF 136 KB] (Downloads:408)

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Based on the analysis of spectrum characteristics of intensity fluctuations while light beams pass through stack gas flow in an industrial setting, this paper puts emphasis upon discussing the spectrum of optical intensity fluctuations by the variety of particle concentration in stack gas flow. This paper also gives the primary theoretical explanation of the measurement results in the stack of coal-fired utility boilers. Meanwhile, the cross-correlation formula is given as the theoretical basis of velocity measurement by using particle concentration scintillation.

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Restriction of shot noise and material noise in a multilevel photochromic memory on signal-to-noise ratio

Zhang Qi-Cheng, Ni Yi, Xu Duan-Yi, Hu Heng

Chin. Phys., 2006, 15 (8): 1783-1787 doi: 10.1088/1009-1963/15/8/025
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[PDF 329 KB] (Downloads:348)

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The recording density of multilevel photochromic memory is limited by the signal-to-noise ratio (SNR) of the readout signal. In this paper, shot noise and material noise are investigated through theoretical analysis of SNR. When the bandwidth of a system is less than 1MHz, the material noise takes a prominent position; when the bandwidth of the system is more than 10MHz, the shot noise becomes dominant. The thickness of recording layer can be optimized to maximize the SNR and reduce the influence of the bandwidth of the system on SNR.

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Multilevel read-only optical recording methods

Song Jie, Xu Duan-Yi, Qi Guo-Sheng, Hu Hua, Zhang Qi-Cheng, Xiong Jian-Ping

Chin. Phys., 2006, 15 (8): 1788-1792 doi: 10.1088/1009-1963/15/8/026
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[PDF 507 KB] (Downloads:401)

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The advantages of read-only storage is the predominance of optical recording relative to magnetic and other rewritable methods. Multilevel (ML) read-only technology has been a trend to improve the data capacity and transfer rate. Based on the principle and coding method of ML, this paper demonstrates some ML read-only recording methods, of which a new ML read-only recording is developed. This recording method integrates amplitude modulation achieved by the reaction mechanism of physics and chemistry of photoresist with the run-length-limited technology. The discs can be achieved using standard photoresist mastering and replication techniques with great compatibility to conventional binary read-only discs.

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Entanglement swapping with atoms separated by long distance

Yuan Chun-Hua, Ou Yong-Cheng, Zhang Zhi-Ming

Chin. Phys., 2006, 15 (8): 1793-1797 doi: 10.1088/1009-1963/15/8/027
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[PDF 123 KB] (Downloads:431)

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This paper proposes a scheme for entanglement swapping based on cavity QED. The two atoms to be entanglement-swapped can be separated over long distance. The scheme is a non-post-selection one with the success probability of 1/2.

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High index of refraction via quantum interference in a three-level system of Er³⁺-doped yttrium aluminium garnet crystal

He Qiong-Yi, Wang Tie-Jun, Gao Jin-Yue

Chin. Phys., 2006, 15 (8): 1798-1805 doi: 10.1088/1009-1963/15/8/028
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A simple three-level system is proposed to produce high index of refraction with zero absorption in an Er³⁺-doped yttrium aluminium garnet (YAG) crystal, which is achieved for a probe field between the excited state ⁴I_13/2 and ground state ⁴I_15/2 by adjusting a strong coherent driving field between the upper excited state ⁴I_11/2 and ⁴I_15/2. It is found that the changes of the frequency of the coherent driving field and the concentration of Er³⁺ ions in the YAG crystal can maximize the index of refraction accompanied by vanishing absorption. This result could be useful for the dispersion compensation in fibre communication, laser particle acceleration, high precision magnetometry and so on.

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Characteristics of selective oxidation during the fabrication of vertical cavity surface emitting laser

Hao Yong-Qin, Zhong Jing-Chang, Ma Jian-Li, Zhang Yong-Ming, Wang Li-Jun

Chin. Phys., 2006, 15 (8): 1806-1809 doi: 10.1088/1009-1963/15/8/029
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[PDF 219 KB] (Downloads:584)

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Taking into account oxidation temperature, N₂ carrier gas flow, and the geometry of the mesa structures this paper investigates the characteristics of selective oxidation during the fabrication of the vertical cavity surface emitting laser (VCSEL) in detail. Results show that the selective oxidation follows a law which differs from any reported in the literature. Below 435℃ selective oxidation of Al_0.98Ga_0.02As follows a linear growth law for the two mesa structures employed in VCSEL. Above 435℃ approximately increasing parabolic growth is found, which is influenced by the geometry of the mesa structures. Theoretical analysis on the difference between the two structures for the initial oxidation has been performed, which demonstrates that the geometry of the mesa structures does influence on the growth rate of oxide at higher temperatures.

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Nonlinear optical properties in double-sided nonlinear media with Z-scan technique based on the Huygens--Fresnel principle

Ouyang Qiu-Yun, Zhang Xue-Ru, Jiang Li, Chang Qing, Wang Yu-Xiao, Song Ying-Lin

Chin. Phys., 2006, 15 (8): 1810-1814 doi: 10.1088/1009-1963/15/8/030
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We present a theoretical model to analyse the propagation of a Gaussian laser beam through double-sided nonlinear media. This model is based on the Huygens--Fresnel diffraction integral method. This theoretical model is not only consistent with the cascade structure model for a small nonlinear phase-shift but also can be used for a large nonlinear phase-shift. It has been verified that it is suitable to characterize the double-sided nonlinear media compared with the cascade structure model. A good agreement between the experimental data and the results from the theoretical model is obtained. It will be useful for the design of multi-sided nonlinear materials.

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Optical properties of carbon nanotubes and BaTiO₃ composite thin films

Lü Guo-Wei, Cheng Bo-Li, Shen Hong, Chen Yu-Jin, Zhou Yue-Liang, Chen Zheng-Hao, Yang Guo-Zhen

Chin. Phys., 2006, 15 (8): 1815-1818 doi: 10.1088/1009-1963/15/8/031
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Multiwalled carbon nanotubes and BaTiO₃ composite films have been prepared by pulsed-laser deposition technique at room temperature and high temperature of 600℃, separately. The structures of the composite films are investigated by using scanning electron microscopy and x-ray diffraction. The optical behaviours of the samples produced at different temperatures are compared with Raman spectroscopy, and UV-visible absorption. And the observation by Z-scan technique reveals that the composite films have a larger optical nonlinearity, and the samples prepared at high temperatures have better transmittance and opposite sign imaginary part of optical third-order nonlinearity.

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Suppression of the interactions between fibre gratings used as dispersion compensators in dense wavelength-division multiplexing systems

Tan Zhong-Wei, Ning Ti-Gang, Liu Yan, Tong Zhi, Jian Shui-Sheng

Chin. Phys., 2006, 15 (8): 1819-1823 doi: 10.1088/1009-1963/15/8/032
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[PDF 180 KB] (Downloads:489)

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Chirped fibre Bragg gratings (CFBGs) are required to be concatenated to compensate the fibre dispersion in the dense wavelength-division multiplexing (DWDM) systems. When the channel spacing is small, the performance of CFBGs is degraded, which restricts the usage of fibre gratings. The origin of the interactions between the gratings is analysed and methods of suppressing the interactions are also proposed.

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Full-vectorial finite-difference beam propagation method based on the modified alternating direction implicit method

Xiao Jin-Biao, Sun Xiao-Han

Chin. Phys., 2006, 15 (8): 1824-1830 doi: 10.1088/1009-1963/15/8/033
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[PDF 209 KB] (Downloads:711)

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A modified alternating direction implicit algorithm is proposed to solve the full-vectorial finite-difference beam propagation method formulation based on $H$ fields. The cross-coupling terms are neglected in the first sub-step, but evaluated and doubly used in the second sub-step. The order of two sub-steps is reversed for each transverse magnetic field component so that the cross-coupling terms are always expressed in implicit form, thus the calculation is very efficient and stable. Moreover, an improved six-point finite-difference scheme with high accuracy independent of specific structures of waveguide is also constructed to approximate the cross-coupling terms along the transverse directions. The imaginary-distance procedure is used to assess the validity and utility of the present method. The field patterns and the normalized propagation constants of the fundamental mode for a buried rectangular waveguide and a rib waveguide are presented. Solutions are in excellent agreement with the benchmark results from the modal transverse resonance method.

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Effects of initial frequency chirp on the linear propagation characteristics of the exponential optical pulse

Zheng Hong-Jun, Liu Shan-Liang

Chin. Phys., 2006, 15 (8): 1831-1837 doi: 10.1088/1009-1963/15/8/034
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[PDF 218 KB] (Downloads:601)

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In this paper, the linear propagation characteristics of the exponential optical pulse with initial linear and nonlinear frequency chirp are numerically studied in a single mode fibre for \be₂<0. It can be found that the temporal full width at half maximum and time-bandwidth product of exponential pulse monotonically increase with the increase of propagation distance and decrease with the increase of linear chirp C for C<0.5, go through an initial decreasing stage near \zeta=1, then increase with the increase of propagation distance and linear chirp C for C\geq0.5. The broadening of pulses with negative chirp is faster than that with positive chirp. The exponential pulse with linear chirp gradually evolves into a near-Gaussian pulse. The effect of nonlinear chirp on waveform of the pulse is much greater than that of linear chirp. The temporal waveform breaking of exponential pulse with nonlinear chirp is first observed in linear propagation. Furthermore, the expressions of the spectral width and time-bandwidth product of the exponential optical pulse with the frequency chirp are given by use of the numerical analysis method.

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Design and analysis of a kind of large flattened mode optical fibre

Zhao Chu-Jun, Peng Run-Wu, Tang Zhi-Xiang, Ye Yun-Xia, Fan Dian-Yuan

Chin. Phys., 2006, 15 (8): 1838-1842 doi: 10.1088/1009-1963/15/8/035
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[PDF 150 KB] (Downloads:423)

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In this paper, a refractive index profile design enabling us to obtain a flat modal field around the fibre centre is investigated. The theoretical approach for designing such multilayer large flattened mode (LFM) optical fibres is presented. A comparison is made between the properties of a three-layer LFM structure and a standard step-index profile with the same core size. The obtained results indicate that the effective area of the LFM fibre is about twice as large as that of the standard step-index fibre, but the LFM fibre has less effective ability to filter out the higher order modes than the standard step-index fibre with the same bending radius.

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Accurate evaluation of lowest band gaps in ternary locally resonant phononic crystals

Wang Gang, Shao Li-Hui, Liu Yao-Zong, Wen Ji-Hong

Chin. Phys., 2006, 15 (8): 1843-1848 doi: 10.1088/1009-1963/15/8/036
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[PDF 418 KB] (Downloads:749)

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Based on a better understanding of the lattice vibration modes, two simple spring--mass models are constructed in order to evaluate the frequencies on both the lower and upper edges of the lowest locally resonant band gaps of the ternary locally resonant phononic crystals. The parameters of the models are given in a reasonable way based on the physical insight into the band gap mechanism. Both the lumped-mass methods and our models are used in the study of the influences of structural and the material parameters on frequencies on both edges of the lowest gaps in the ternary locally resonant phononic crystals. The analytical evaluations with our models and the theoretical predictions with the lumped-mass method are in good agreement with each other. The newly proposed heuristic models are helpful for a better understanding of the locally resonant band gap mechanism, as well as more accurate evaluation of the band edge frequencies.

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Study on the delamination of tungsten thin films on Sb₂Te₃

Xu Jia-Qing, Liu Bo, Song Zhi-Tang, Feng Song-Lin, Chen Bomy

Chin. Phys., 2006, 15 (8): 1849-1854 doi: 10.1088/1009-1963/15/8/037
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[PDF 2218 KB] (Downloads:361)

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To investigate the reliability of electrode materials for chalcogenide random access memory (C-RAM) applications, the geometry and time evolution of the worm-like delamination patterns on a tungsten/Sb$_{2}$Te$_{3}$ bilayer system surface are observed by field emission scanning electronic microscope (FESEM) and optical microscopy. The tungsten film stress and interface toughness are estimated using a straight-side model. After confirming the instability of this system being due to large compressive stress stored in the tungsten film and relative poor interface adhesion, a preliminary solution as the inset of a TiN adhesion layer is presented to improve the system performances.

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Simulating high Reynolds number flow in two-dimensional lid-driven cavity by multi-relaxation-time lattice Boltzmann method

Chai Zhen-Hua, Shi Bao-Chang, Zheng Lin

Chin. Phys., 2006, 15 (8): 1855-1863 doi: 10.1088/1009-1963/15/8/038
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By coupling the non-equilibrium extrapolation scheme for boundary condition with the multi-relaxation-time lattice Boltzmann method, this paper finds that the stability of the multi-relaxation-time model can be improved greatly, especially on simulating high Reynolds number (Re) flow. As a discovery, the super-stability analysed by Lallemand and Luo is verified and the complex structure of the cavity flow is also exhibited in our numerical simulation when Re is high enough. To the best knowledge of the authors, the maximum of Re which has been investigated by direct numerical simulation is only around 50,000 in the literature; however, this paper can readily extend the maximum to 1000,000 with the above combination.

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The aerosol penetration through an electret fibrous filter

Jiang Wei, Cheung Chun-Shun, Chan Cheong-Ki, Zhu Chao

Chin. Phys., 2006, 15 (8): 1864-1870 doi: 10.1088/1009-1963/15/8/039
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The aim of this paper is to present a theoretical study of the aerosol penetration through an electret fibrous filter, using a numerical approach. The aerosol sizes considered in this study were in the submicron range, and in the numerical model, the conventional mechanical mechanisms (impaction, interception, diffusion and gravitationally settling) were taken into consideration along with the electrostatic mechanisms, including the Coulombic and dielectrophoretic effects. The aerosol penetration through an electret fibrous filter is heavily dependent on the aerosol penetration of a single fibre. The aerosol penetration through a single electret fibre under various filtration conditions was calculated. The effects of aerosol diameter, aerosol and fibre charge state, face velocity, packing density and aerosol dielectric constant on the aerosol penetration were investigated.

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Continuously transferring cold atoms in caesium double magneto-optical trap

Yan Shu-Bin, Geng Tao, Zhang Tian-Cai, Wang Jun-Min

Chin. Phys., 2006, 15 (8): 1746-1751 doi: 10.1088/1009-1963/15/8/019
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We have established a caesium double magneto-optical trap (MOT) system for cavity-QED experiment, and demonstrated the continuous transfer of cold caesium atoms from the vapour-cell MOT with a pressure of ～ 1×10^-6 Pa to the ultra-high-vacuum (UHV) MOT with a pressure of ～ 8×10^-8 Pa via a focused continuous-wave transfer laser beam. The effect of frequency detuning as well as the intensity of the transfer beam is systematically investigated, which makes the transverse cooling adequate before the atoms leak out of the vapour-cell MOT to reduce divergence of the cold atomic beam. The typical cold atomic flux got from vapour-cell MOT is ～2×10⁷ atoms/s. About 5×10⁶ caesium atoms are recaptured in the UHV MOT.

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Landau damping of collective modes in a harmonically trapped Bose--Einstein condensate

Ma Xiao-Dong, Zhou Yu, Ma Yong-Li, Huang Guo-Xiang

Chin. Phys., 2006, 15 (8): 1871-1878 doi: 10.1088/1009-1963/15/8/040
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This paper proposes a method for calculating the Landau damping of a low-energy collective mode in a harmonically trapped Bose--Einstein condensate. Based on the divergence-free analytical solutions for ground-state wavefunction of the condensate and eigenvalues and eigenfunctions for thermally excited quasiparticles, obtained beyond Thomas--Fermi approximation, this paper calculates the coupling matrix elements describing the interaction between the collective mode and the quasiparticles. With these analytical results this paper evaluates the Landau damping rate of a monopole mode in a spherical trap and discusses its dependence on temperature, particle number and trapping frequency of the system.

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Electrical characteristics of MOS capacitor with HfTiON gate dielectric and HfTiSiON interlayer

Chen Wei-Bing, Xu Jing-Ping, Lai Pui-To, Li Yan-Ping, Xu Sheng-Guo, Chan Chu-Lok

Chin. Phys., 2006, 15 (8): 1879-1882 doi: 10.1088/1009-1963/15/8/041
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The paper reports that HfTiO dielectric is deposited by reactive co-sputtering of Hf and Ti targets in an Ar/O₂ ambience, followed by an annealing in different gas ambiences of N₂, NO and NH₃ at 600℃ for 2 min. Capacitance--voltage and gate-leakage properties are characterized and compared. The results indicate that the NO-annealed sample exhibits the lowest interface-state and dielectric-charge densities and best device reliability. This is attributed to the fact that nitridation can create strong Si \equiv \!\!\equivN bonds to passivate dangling Si bonds and replace strained Si--O bonds, thus the sample forms a hardened dielectric/Si interface with high reliability.

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Simultaneous determination of trap depth and the ratio of the rate of recombination to that of capture from thermo-luminescence

Xu Zheng, Zhang Fu-Jun, Zhao Su-Ling, Wang Li-Wei, Georgobiani A. N., Gutan V. B., Meng Li-Jian

Chin. Phys., 2006, 15 (8): 1883-1887 doi: 10.1088/1009-1963/15/8/042
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Thermo-luminescence (TL) is a kind of luminescence decay measured with varying temperature. In the process of TL the decay parameter itself involves the temperature effect of traps. Thus the trap depth is inseparable from the decay parameter. There are two separate peaks in the TL curve of ZnS:Cu,Co if the measurement starts from liquid nitrogen temperature. In the experiment we started from zero Celsius temperature to isolate the deeper traps. We have proposed and realized three methods for simultaneous determination of trap depth and decay parameter based on the quasi-equilibrium model and experimental data. If we treat the case of kinetic order \alpha =1 as \alpha =2, the error might be as large as 100%.