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  • Normalized entropy of rank distribution: a novel measure of heterogeneity of complex networks

    Wu Jun, Tan Yue-Jin, Deng Hong-Zhong, Zhu Da-Zhi
    Chin. Phys. B 2007, 16 (6): 1576-1580
    Many unique properties of complex networks result from heterogeneity. The measure and analysis of heterogeneity are important and desirable to the research of the properties and functions of complex networks. In this paper, the rank distribution is proposed as a new statistic feature of complex netw...

     
Chin. Phys. B  
  Chin. Phys. B--2007, Vol.16, No.6
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GENERAL

Suppression of decoherence by bath ordering

Jing Jun, Ma Hong-Ru
Chin. Phys., 2007, 16 (6): 1489-1504 doi: 10.1088/1009-1963/16/6/001
Full Text: [PDF 7551 KB] (Downloads:734)
Show Abstract
The dynamics of two coupled spins-1/2 coupled to a spin-bath is studied as an extended model of the Tessieri--Wilkie Hamiltonian. The pair of spins served as an open subsystem is prepared in one of the Bell states and the bath consisting of some spins-1/2 is in a thermal equilibrium state from the very beginning. It is found that with increasing coupling strength of the bath spins, the bath forms a resonant antiferromagnetic order. The polarization correlation between the two spins of the subsystem and the concurrence of it are recovered to some extent in the isolated subsystem. This suppression of the subsystem decoherence may be used to control the quantum devices in practical applications.

Pfaffianization of the variable-coefficient Kadomtsev--Petviashvili equation

Zhang Qing-Fan, Fan En-Gui
Chin. Phys., 2007, 16 (6): 1505-1509 doi: 10.1088/1009-1963/16/6/002
Full Text: [PDF 101 KB] (Downloads:466)
Show Abstract
This paper constructs more general exact solutions than $N$-soliton solution and Wronskian solution for variable-coefficient Kadomtsev--Petviashvili (KP) equation. By using the Hirota method and Pfaffian technique, it finds the Grammian determinant-type solution for the variable-coefficient KP equation (VCKP), the Wronski-type Pfaffian solution and the Gram-type Pfaffian solutions for the Pfaffianized VCKP equation.

Energy diffusion controlled reaction rate in dissipative Hamiltonian systems

Deng Mao-Lin, Zhu Wei-Qiu
Chin. Phys., 2007, 16 (6): 1510-1515 doi: 10.1088/1009-1963/16/6/003
Full Text: [PDF 553 KB] (Downloads:706)
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In this paper the energy diffusion controlled reaction rate in dissipative Hamiltonian systems is investigated by using the stochastic averaging method for quasi Hamiltonian systems. The boundary value problem of mean first-passage time (MFPT) of averaged system is formulated and the energy diffusion controlled reaction rate is obtained as the inverse of MFPT. The energy diffusion controlled reaction rate in the classical Kramers bistable potential and in a two-dimensional bistable potential with a heat bath are obtained by using the proposed approach respectively. The obtained results are then compared with those from Monte Carlo simulation of original systems and from the classical Kramers theory. It is shown that the reaction rate obtained by using the proposed approach agrees well with that from Monte Carlo simulation and is more accurate than the classical Kramers rate.

Perturbation to symmetries and Hojman adiabatic invariant for nonholonomic controllable mechanical systems with non-Chetaev type constraints

Xia Li-Li, Li Yuan-Cheng
Chin. Phys., 2007, 16 (6): 1516-1520 doi: 10.1088/1009-1963/16/6/004
Full Text: [PDF 103 KB] (Downloads:436)
Show Abstract
This paper studies the perturbation to symmetries and adiabatic invariant for nonholonomic controllable mechanical systems with non-Chetaev type constraints. It gives the exact invariants introduced by the Lie symmetries of the nonholonomic controllable mechanical system with non-Chetaev type constraints without perturbation. Based on the definition of high-order adiabatic invariants of mechanical system, the perturbation of Lie symmetries for nonholonomic controllable mechanical system with non-Chetaev type constraints with the action of small disturbances is investigated, and a new type of adiabatic invariant of system are obtained. In the end of this paper, an example is given to illustrate the application of the results.

Unified symmetry of the nonholonomic system of non-Chetaev type with unilateral constraints in event space

Hou Qi-Bao, Li Yuan-Cheng, Wang Jing, Xia Li-Li
Chin. Phys., 2007, 16 (6): 1521-1525 doi: 10.1088/1009-1963/16/6/005
Full Text: [PDF 105 KB] (Downloads:493)
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This paper studies the unified symmetry of a nonholonomic system of non-Chetaev type with unilateral constraints in event space under infinitesimal transformations of group. Firstly, it gives the differential equations of motion of the system. Secondly, it obtains the definition and the criterion of the unified symmetry for the system. Thirdly, a new conserved quantity, besides the Noether conserved quantity and the Hojman conserved quantity, is deduced from the unified symmetry of a nonholonomic system of non-Chetaev type with unilateral constraints. Finally, an example is given to illustrate the application of the results.

Propagation of bright femtosecond pulses in a nonlinear optical fibre with the third- and fourth-order dispersions

Ao Sheng-Mei, Yan Jia-Ren, Yu Hui-You
Chin. Phys., 2007, 16 (6): 1526-1533 doi: 10.1088/1009-1963/16/6/006
Full Text: [PDF 2158 KB] (Downloads:479)
Show Abstract
We solve the generalized nonlinear Schr\"{o}dinger equation describing the propagation of femtosecond pulses in a nonlinear optical fibre with higher-order dispersions by using the direct approach to perturbation for bright solitons, and discuss the combined effects of the third- and fourth-order dispersions on velocity, temporal intensity distribution and peak intensity of femtosecond pulses. It is noticeable that the combined effects of the third- and fourth-order dispersions on an initial propagated soliton can partially compensate each other, which seems to be significant for the stability controlling of soliton propagation features.

Lie point symmetry algebras and finite transformation groups of the general Broer--Kaup system

Jia Man
Chin. Phys., 2007, 16 (6): 1534-1544 doi: 10.1088/1009-1963/16/6/007
Full Text: [PDF 127 KB] (Downloads:449)
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Using a new symmetry group theory, the transformation groups and symmetries of the general Broer--Kaup system are obtained. The results are much simpler than those obtained via the standard approaches.

Exact periodic solution in coupled nonlinear Schr?dinger equations

Li Qi-Liang, Chen Jun-Lang, Sun Li-Li, Yu Shu-Yi, Qian Sheng
Chin. Phys., 2007, 16 (6): 1545-1548 doi: 10.1088/1009-1963/16/6/008
Full Text: [PDF 98 KB] (Downloads:560)
Show Abstract
The coupled nonlinear Schr\"{o}dinger equations (CNLSEs) of two symmetrical optical fibres are nonintegrable, however the transformed CNLSEs have integrability. Integrability of the transformed CNLSEs is proved by the Hamilton dynamics theory and Galilei transform. Making use of a transform for CNLSEs and using the ansatz with Jacobi elliptic function form, this paper obtains the exact optical pulse solutions.

Squeezing properties of a trapped ion in the running-wave laser beyond the Lamb--Dicke limit

Pan Chang-Ning, Fang Mao-Fa, Zheng Xiao-Juan, Hu Yao-Hua
Chin. Phys., 2007, 16 (6): 1549-1553 doi: 10.1088/1009-1963/16/6/009
Full Text: [PDF 686 KB] (Downloads:503)
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Beyond the Lamb--Dicke limit, this paper investigates the squeezing properties of the trapped ion in the travelling-wave laser. It shows that the squeezing properties of the trapped ion in the travelling-wave laser are strongly affected by the sideband number $k$, the Lamb--Dicke parameter $\eta$ and the initial average phonon number.

Wigner function of coherent state of N components

Ye Yong-Hua, Zeng Gao-Jian
Chin. Phys., 2007, 16 (6): 1554-1558 doi: 10.1088/1009-1963/16/6/010
Full Text: [PDF 1206 KB] (Downloads:456)
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In this paper, we study the Wigner function of coherent state of $N$ components, especially two components and three components. This function consists of two terms: the Gaussian term and the interference term with the negativity. The first term comprises $N$ Gaussian surfaces evenly centred on a circle of radius $|\beta|=|\alpha|$ with a separate angle of ${2\pi}/{N}$, and the second term is composed of $\frac{1}{2}N(N-1)$ Gaussian-cosine surfaces evenly centred in a circular region of radius $|\beta|<|\alpha|$. Here, $\alpha$ is the eigenvalue of the annihilation operator $a$, and $\beta$ is a variable in some complex space in which the Wigner function is defined. We have proved that the essential condition to eliminate the negativity of the Wigner function is that the mean photon count of the coherent state is equal to that of the Glouber coherent state.

Creating unconventional geometric phase gate using squeeze-like operator assisted by strong driving field

Zhu Ai-Dong, Zhang Shou, Yeon Kyu-Hwang, Yu Seong-Cho, Um Chung-In
Chin. Phys., 2007, 16 (6): 1559-1565 doi: 10.1088/1009-1963/16/6/011
Full Text: [PDF 341 KB] (Downloads:460)
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Based on the idea that a squeezing process can be thought of as a total cumulative effect of a large number of tiny squeezing processes, we define a squeeze-like operator with a time-dependent squeeze parameter. Applying this operator to and combining with a system which includes a two-photon interaction between two atoms and an initial vacuum cavity field, and resorting to a resonant strong driving classical field, we obtain an unconventional geometric phase gate with a shorter gating time.

A scheme of quantum phase gate for trapped ion

Cai Jian-Wu, Fang Mao-Fa, Zheng Xiao-Juan, Liao Xiang-Ping
Chin. Phys., 2007, 16 (6): 1566-1569 doi: 10.1088/1009-1963/16/6/012
Full Text: [PDF 309 KB] (Downloads:458)
Show Abstract
We propose a scheme to implement two-qubit controlled quantum phase gate(CQPG) via a single trapped two-level ion located in the standing wave field of a quantum cavity, in which the trap works beyond the Lamb--Dicke limit. When the light field is resonant with the atomic transition $|g\rangle\leftrightarrow|e\rangle$ of the ion located at the antinode of the standing wave, we can perform CQPG between the internal and external states of the trapped ion; while the frequency of the light field is chosen to be resonant with the first red sideband of the collective vibrational mode of the ion located at the node of the standing wave, we can perform CQPG between the cavity mode and the collective vibrational mode of the trapped ion. Neither the Lamb--Dicke approximation nor the assistant classical laser is needed. Also we can generate a GHZ state if assisted with a classical laser.

Extended speed gradient model for traffic flow on two-lane freeways

Tang Chang-Fu, Jiang Rui, Wu Qing-Song
Chin. Phys., 2007, 16 (6): 1570-1575 doi: 10.1088/1009-1963/16/6/013
Full Text: [PDF 574 KB] (Downloads:694)
Show Abstract
In this paper, the speed gradient (SG) model is extended to describe the traffic flow on two-lane freeways. Terms related to lane change are added into the continuity equations and velocity dynamic equations. The empirically observed two-lane phenomena, such as lane usage inversion and lane change rate versus density, are reproduced by extended SG model. The local cluster effect is also investigated by numerical simulations.

Normalized entropy of rank distribution: a novel measure of heterogeneity of complex networks Hot!

Wu Jun, Tan Yue-Jin, Deng Hong-Zhong, Zhu Da-Zhi
Chin. Phys., 2007, 16 (6): 1576-1580 doi: 10.1088/1009-1963/16/6/014
Full Text: [PDF 284 KB] (Downloads:654)
Show Abstract
Many unique properties of complex networks result from heterogeneity. The measure and analysis of heterogeneity are important and desirable to the research of the properties and functions of complex networks. In this paper, the rank distribution is proposed as a new statistic feature of complex networks. Based on the rank distribution, a novel measure of the heterogeneity called a normalized entropy of rank distribution (NERD) is proposed. The NERD accords with the normal meaning of heterogeneity within the context of complex networks compared with conventional measures. The heterogeneity of scale-free networks is studied using the NERD. It is shown that scale-free networks become more heterogeneous as the scaling exponent decreases and the NERD of scale-free networks is independent of the number of vertices, which indicates that the NERD is a suitable and effective measure of heterogeneity for networks with different sizes.

Evolution of network from node division and generation

Sun Hui-Jun, Wu Jian-Jun
Chin. Phys., 2007, 16 (6): 1581-1585 doi: 10.1088/1009-1963/16/6/015
Full Text: [PDF 716 KB] (Downloads:496)
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Aimed at lowering the effect of `rich get richer' in scale-free networks with the Barab\'{a}si and Albert model, this paper proposes a new evolving mechanism, which includes dividing and preference attachment for the growth of a network. A broad scale characteristic which is independent of the initial network topology is obtained with the proposed model. By simulating, it is found that preferential attachment causes the appearance of the scale-free characteristic, while the dividing will decrease the power-law behaviour and drive the evolution of broad scale networks.

Realization of fractional-order Liu chaotic system by circuit

Lu Jun-Jie, Liu Chong-Xin
Chin. Phys., 2007, 16 (6): 1586-1590 doi: 10.1088/1009-1963/16/6/016
Full Text: [PDF 1512 KB] (Downloads:1034)
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In this paper, chaotic behaviours in the fractional-order Liu system are studied. Based on the approximation theory of fractional-order operator, circuits are designed to simulate the fractional- order Liu system with $q=0.1-0.9$ in a step of 0.1, and an experiment has demonstrated the 2.7-order Liu system. The simulation results prove that the chaos exists indeed in the fractional-order Liu system with an order as low as 0.3. The experimental results prove that the fractional-order chaotic system can be realized by using hardware devices, which lays the foundation for its practical applications.

Chaos control and reduced-order generalized synchronization for the Chen--Liao system

Li Rui-Hong, Xu Wei, Li Shuang
Chin. Phys., 2007, 16 (6): 1591-1596 doi: 10.1088/1009-1963/16/6/017
Full Text: [PDF 430 KB] (Downloads:645)
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This paper deals with the problem of chaos control and synchronization of the Chen--Liao system. From rigorous mathematic justification, the chaotic trajectories of the Chen--Liao system are led to a type of points whose four-dimensional coordinates have a particular functional relation among them. Meanwhile, a new synchronization manner, reduced-order generalized synchronization (RGS), is proposed which has the characteristic of having a functional relation between the slave and the partial master systems. It is shown that this new synchronization phenomenon can be realized by a novel technique. Numerical simulations have verified the effectiveness of the proposed scheme.

Complete synchronization between two bi-directionally coupled chaotic systems via an adaptive feedback controller

Xiao Yu-Zhu, Xu Wei
Chin. Phys., 2007, 16 (6): 1597-1602 doi: 10.1088/1009-1963/16/6/018
Full Text: [PDF 591 KB] (Downloads:597)
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In this paper, we apply a simple adaptive feedback control scheme to synchronize two bi-directionally coupled chaotic systems. Based on the invariance principle of differential equations, sufficient conditions for the global asymptotic synchronization between two bi-directionally coupled chaotic systems via an adaptive feedback controller are given. Unlike other control schemes for bi-directionally coupled systems, this scheme is very simple to implement in practice and need not consider coupling terms. As examples, the autonomous hyperchaotic Chen systems and the new non-autonomous 4D systems are illustrated. Numerical simulations show that the proposed method is effective and robust against the effect of weak noise.

Synchronization between two different chaotic systems with nonlinear feedback control

Lü Ling, Guo Zhi-An, Zhang Chao
Chin. Phys., 2007, 16 (6): 1603-1607 doi: 10.1088/1009-1963/16/6/019
Full Text: [PDF 647 KB] (Downloads:1359)
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This paper presents chaos synchronization between two different chaotic systems by using a nonlinear controller, in which the nonlinear functions of the system are used as a nonlinear feedback term. The feedback controller is designed on the basis of stability theory, and the area of feedback gain is determined. The artificial simulation results show that this control method is commendably effective and feasible.

Behaviours in a dynamical model of traffic assignment with elastic demand

Xu Meng, Gao Zi-You
Chin. Phys., 2007, 16 (6): 1608-1614 doi: 10.1088/1009-1963/16/6/020
Full Text: [PDF 1342 KB] (Downloads:920)
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This paper investigates the dynamical behaviour of network traffic flow. Assume that trip rates may be influenced by the level of service on the network and travellers are willing to take a faster route. A discrete dynamical model for the day-to-day adjustment process of route choice is presented. The model is then applied to a simple network for analysing the day-to-day behaviours of network flow. It finds that equilibrium is arrived if network flow consists of travellers not very sensitive to the differences of travel cost. Oscillations and chaos of network traffic flow are also found when travellers are sensitive to the travel cost and travel demand in a simple network.

Multipartite entanglement in the interaction system between a single-mode microwave cavity field and superconducting charge qubits

Shi Zhen-Gang, Chen Xiong-Wen, Zhu Xi-Xiang, Song Ke-Hui
Chin. Phys., 2007, 16 (6): 1615-1618 doi: 10.1088/1009-1963/16/6/021
Full Text: [PDF 111 KB] (Downloads:530)
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This paper proposes a method of generating multipartite entanglement through using d.c.\ superconducting quantum interference devices (SQUID) inside a standing wave cavity. In this scheme, the d.c.\ SQUID works in the charge region. It is shown that, a large number of important multipartite entangled states can be generated by a controllable interaction between a cavity field and qubits. It is even possible to produce entangled states involving different cavity modes based on the measurement of charge qubits states. After such superpositions states are created, the interaction can be switched off by the classical magnetic field through the SQUID, and there is no information transfer between the cavity field and the charge qubits.

Discrete channel modelling based on genetic algorithm and simulated annealing for training hidden Markov model

Zhao Zhi-Jin, Zheng Shi-Lian, Xu Chun-Yun, Kong Xian-Zheng
Chin. Phys., 2007, 16 (6): 1619-1623 doi: 10.1088/1009-1963/16/6/022
Full Text: [PDF 291 KB] (Downloads:524)
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Hidden Markov models (HMMs) have been used to model burst error sources of wireless channels. This paper proposes a hybrid method of using genetic algorithm (GA) and simulated annealing (SA) to train HMM for discrete channel modelling. The proposed method is compared with pure GA, and experimental results show that the HMMs trained by the hybrid method can better describe the error sequences due to SA's ability of facilitating hill-climbing at the later stage of the search. The burst error statistics of the HMMs trained by the proposed method and the corresponding error sequences are also presented to validate the proposed method.

A shaped annular beam tri-heterodyne confocal microscope with good anti-environmental interference capability

Zhao Wei-Qian, Feng Zheng-De, Qiu Li-Rong
Chin. Phys., 2007, 16 (6): 1624-1631 doi: 10.1088/1009-1963/16/6/023
Full Text: [PDF 1294 KB] (Downloads:515)
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A shaped annular beam tri-heterodyne confocal microscope has been proposed to improve the anti-environmental interference capability and the resolution of a confocal microscope. It simultaneously detects far-, on-, and near-focus signals with given phase differences by dividing the measured light path of the confocal microscope into three sub-paths (signals). Pair-wise real-time heterodyne subtraction of the three signals is used to improve the anti-environmental interference capability, axial resolution, and linearity; and a shaped annular beam super-resolution technique is used to improve lateral resolution. Theoretical analyses and preliminary experiments indicate that an axial resolution of about 1 nm can be achieved with a shaped annular beam tri-heterodyne confocal microscope and its lateral resolution can be better than 0.2 $\mu $m for $\lambda =632.8$~nm, the numerical aperture of the lens of the microscope is NA $=0.85$, and the normalized radius $\varepsilon =0.5$.

Visibility in differential phase-contrast imaging with partial coherence source

Liu Xin, Guo Jin-Chuan, Peng Xiang, Niu Han-Ben
Chin. Phys., 2007, 16 (6): 1632-1636 doi: 10.1088/1009-1963/16/6/024
Full Text: [PDF 794 KB] (Downloads:567)
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This paper gives theoretical analysis of visibility of fringes, which is influenced by distances, temporal and spatial coherence of source, in hard x-ray differential phase-contrast imaging with microfocus x-ray source. According to the character of longitudinal periodicity of the interferogram, the setup is insensitive to mechanical drift and vibrations. The effect of temporal coherence of x-ray source is investigated and its related bandwidth is derived. Based on the theory of partially coherent light, it shows that the requirement for the spatial coherence of x-ray source is not strict and can be met by the general microfocus x-ray tube for x-ray differential phase-contrast imaging.
NUCLEAR PHYSICS

Re-evaluation of the 23Mg(p,γ)24Al reaction rate

Liu Hong-Lin, Liu Men-Quan, Lai Xiang-Jun, Luo Zhi-Quan
Chin. Phys., 2007, 16 (6): 1637-1640 doi: 10.1088/1009-1963/16/6/025
Full Text: [PDF 125 KB] (Downloads:589)
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Based on a new screening Coulomb model, this paper discusses the effect of electron screening on proton capture reaction of $^{23}$Mg. The derived result shows that, in some considerable range of stellar temperatures, the effect of electron screening on resonant reaction is prominent; on the non-resonant reaction the effect is obvious only in the low stellar temperatures. The reaction rates of $^{23}$Mg(p,$\gamma )^{24}$Al would increase 15\%--25{\%} due to the fact that the electron screening are considered in typical temperature range of massive mass white dwarfs, and the results undoubtedly affect the nucleosynthesis of some heavier nuclei in massive mass white dwarfs.
CLASSICAL AREAS OF PHENOMENOLOGY

Diffractive characteristics of the liquid crystal spatial light modulator

Cao Zhao-Liang, Mu Quan-Quan, Hu Li-Fa, Liu Yong-Gang, Xuan Li
Chin. Phys., 2007, 16 (6): 1665-1671 doi: 10.1088/1009-1963/16/6/030
Full Text: [PDF 737 KB] (Downloads:706)
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The liquid crystal spatial light modulator (LC SLM) is very suitable for wavefront correction and optical testing and can produce a wavefront with large phase change and high accuracy. The LC SLM is composed of thousands of pixels and the pixel size and shape have effects on the diffractive characteristics of the LC SLM. This paper investigates the pixel effect on the phase of the wavefront with the scalar diffractive theory. The results show that the maximum optical path difference modulation is 41\,$\mu$m to produce the paraboloid wavefront with the peak to valley accuracy better than $\la$/10. Effects of the mismatch between the pixel and the period, and black matrix on the diffraction efficiency of the LC SLM are also analysed with the Fresnel phase lens model. The ability of the LC SLM is discussed for optical testing and wavefront correction based on the calculated results. It shows that the LC SLM can be used as a wavefront corrector and a compensator.

Influence of degenerate four-wave mixing on the performance of supercontinuum-based multiwavelength optical source

Zhao Xiao-Fan, Yang Yan-Fu, Zhou Hong-Bo, Lou Cai-Yun, Gao Yi-Zhi
Chin. Phys., 2007, 16 (6): 1672-1677 doi: 10.1088/1009-1963/16/6/031
Full Text: [PDF 1526 KB] (Downloads:459)
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The influence of degenerate four-wave mixing (FWM) on the performance of supercontinuum-based multiwavelength optical source has been investigated in detail experimentally and theoretically. Numerical simulation results show that the degenerate FWM effect has a deteriorative influence on the spectral uniformity and the optical signal-to-noise ratio (OSNR) of supercontinuum-based optical source, and by suppressing degenerate FWM effect the performance enhancement of the supercontinuum can be achieved successfully. These results are also confirmed by our experiments. Experimentally, by suppressing degenerate FWM the crosstalk of adjacent channels to the filtered channel can be reduced by as much as 15 dB, and consequently the measured receiver sensitivity at 10 Gbit/s for the filtered optical source is improved from $-1.7$ to $-17.8$~dBm.

Teleportation of a two-atom entangled state via cavity decay

Ye Sai-Yun
Chin. Phys., 2007, 16 (6): 1678-1682 doi: 10.1088/1009-1963/16/6/032
Full Text: [PDF 162 KB] (Downloads:442)
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This paper proposes a scheme for teleporting a two-atom entangled state using leaky cavities. It uses resonant atom--cavity interaction to map the atomic state onto the cavity field. Then it utilizes the interference of polarized photons to establish the correlation between the distant sender and receiver. The advantage of the scheme is that the fidelity is independent of the cavity decay rate, atomic decay and detection efficiency.

Effects of walk-off on cross-phase modulation induced modulation instability in an optical fibre with high-order dispersion

Zhong Xian-Qiong, Xiang An-Ping
Chin. Phys., 2007, 16 (6): 1683-1688 doi: 10.1088/1009-1963/16/6/033
Full Text: [PDF 382 KB] (Downloads:486)
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This paper investigates the effects of walk-off among optical pulses on cross-phase modulation induced modulation instability in the normal dispersion region of an optical fibre with high-order dispersion. The results indicate that, in the case of high-order dispersion, the walk-off effect takes on new characteristics and will influence considerably the shape, position and especially the number of the spectral regions of the gain spectra of modulation instability. Not only the group-velocity mismatch, but also the difference of the third-order dispersion of two optical waves will alter the gain spectra of modulation instability but in different ways. Depending on the values of the walk-off parameters, the number of the spectral regions may increase from two to at most four, and the spectral shape and position may change too.

Controlling the focusing properties of a triangular-lattice metallic photonic-crystal slab

Feng Shuai, Wang Yi-Quan, Li Zhi-Yuan, Cheng Bing-Ying, Zhang Dao-Zhong
Chin. Phys., 2007, 16 (6): 1689-1693 doi: 10.1088/1009-1963/16/6/034
Full Text: [PDF 1621 KB] (Downloads:453)
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This paper studies the focusing properties of a two-dimensional photonic crystal (PC) slab consisting of a triangular lattice of metallic cylinders immersed in a dielectric background. Through the analysis of the equifrequency-surface contours and the field patterns of a point source placed in the vicinity of the PC slab, it finds that both the image distance and image quality can be controlled by simply adjusting the refractive index of the background material.

Temperature or strain induced adjustable-chirp characteristics of uniform fibre grating with tapered metal coating

Liu Yan, Li Bin, Zheng Kai, Tan Zhong-Wei, Chen Yong, Wang Yan Hua, Ren Wen-Hua, Jian Shui-Sheng
Chin. Phys., 2007, 16 (6): 1694-1699 doi: 10.1088/1009-1963/16/6/035
Full Text: [PDF 778 KB] (Downloads:389)
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Temperature and strain characteristics of uniform fibre grating with tapered metal coatings have been analysed theoretically, by which adjustable chirp characteristics of such gratings are shown. Electroplating is adopted to fabricate such gratings, and the tapered metal coating is obtained by gradually drawing the fibre grating out of the solution during the process of electroplating. The gradually changing cross-sectional area of the metal coating is calculated by a newly suggested numerical method. By combining the theoretical and numerical simulation analyses, the gratings' characteristics are given at various temperatures and strains. The results obtained using such a method are also testified by experiments.

The system of L-band 2×10 Gb/s WDM transmission over conventional single mode fibre with 600 km by chirped fibre Bragg gratings dispersion compensation

Yan Feng-Ping, Tong Zhi, Wei Huai, Pei Li, Ning Ti-Gang, Fu Yong-Jun, Zheng Kai, Wang Lin, Li Yi-Fan, Gong Tao-Rong, Jian Shui-Sheng
Chin. Phys., 2007, 16 (6): 1700-1703 doi: 10.1088/1009-1963/16/6/036
Full Text: [PDF 327 KB] (Downloads:511)
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A chirped fibre Bragg grating according to ITU-T suggested L-band (2nd channel $\lambda _{1}=1570.83$~nm; 80th channel $\lambda _{2}=1603.57$ nm) with more than 1800 ps/nm single channel dispersion compensation is presented in this paper, of which the cladding mode loss, the delay curve ripple and the power fluctuation of the reflected spectrum are less than 0.5 dB, 50 ps and 0.25 dB, respectively. With this new FBG as dispersion compensation device, a $2\times 10$ Gb/s wavelength division multiplexing (WDM) L-band transmission of 600 km based on conventional single mode fibre (G.652 fibre) is performed without forward error correction. The bit error rate (BER) is less than 10$^{ - 12}$ and the power penalties of the 2{nd} and 80{th} channel of L-band are 1.8~dB and 2.0~dB, respectively.

Thin film design for advanced thermochromic smart radiator devices

Feng Yu-Dong, Wang Zhi-Min, Ma Ya-Li, Zhang Fu-Jia
Chin. Phys., 2007, 16 (6): 1704-1709 doi: 10.1088/1009-1963/16/6/037
Full Text: [PDF 921 KB] (Downloads:867)
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This paper describes the research on the materials and design methods for advanced smart radiator devices (SRDs) on large-area flexible substrates utilized on spacecraft. The functional material is thermochromic vanadium dioxide. The coating design of SRD is similar to the design of broadband filter coatings in a mid-infrared region. The multilayer coatings have complex structures. Coating materials must be highly transparent in a required spectrum region and also mechanically robust enough to endure the influence from the rigorous environments of outer space. The number of layers must be very small, suitable for the deposition on large-area flexible substrates. All the coatings are designed initially based on optical calculation and practical experience, and then optimized by the TFCALC software. Several designs are described and compared with each other. The results show that the emittance variability of the designed SRDs is great than 400\%, more advanced than the reported ones.

Design and analysis of a novel single-mode single-polarization photonic crystal fibre based on polarization-dependent coupling and absorption effect

Liu Xiao-Yi, Zhang Fang-Di, Zhang Min, Ye Pei-Da
Chin. Phys., 2007, 16 (6): 1710-1718 doi: 10.1088/1009-1963/16/6/038
Full Text: [PDF 590 KB] (Downloads:576)
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A novel single-mode single-polarization (SMSP) photonic crystal fibre has been proposed and analysed based on the polarization-dependent coupling and absorption effect via a full-vector finite element method with perfectly matched layers. The numerical results predict that very efficient SMSP operation can be achieved with both high bandwidth and high extinction ratio at low loss penalty. Effects of the fibre structural parameters on the SMSP bandwidth and extinction ratio have been explored, which will provide useful guide for the design and fabrication of the fibre. The results obtained will be instructive for the realization of new SMSP fibres with high performance.

Polarization properties of elliptical core non-hexagonal symmetry polymer photonic crystal fibre

Zhang Ya-Ni, Miao Run-Cai, Ren Li-Yong, Wang Han-Yi, Wang Li-Li, Zhao Wei
Chin. Phys., 2007, 16 (6): 1719-1724 doi: 10.1088/1009-1963/16/6/039
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In this paper, polarization properties and propagation characteristics of polymer photonic crystal fibres with elliptical core and non-hexagonal symmetry structure are investigated by using the full vectorial plane wave method. The results show that the birefringence of the fibre is induced by asymmetries of both the cladding and the core. Moreover, by adjusting the non-symmetrical ratio factor of cladding $\eta$ from 0.4 to 1 in step 0.1, we find the optimized design parameters of the fibre with high birefringence and limited polarization mode dispersion, operating in a single mode regime at an appropriate wavelength range. The range of wavelength approaches the visible and near-infrared which is consistent with the communication windows of polymer optical fibres.
ATOMIC AND MOLECULAR PHYSICS

Studies on heteronuclear diatomic molecular dissociation energies using algebraic energy method

Fan Kai-Min, Ren Wei-Yi, Liu-Yan, Wang A-Shu, Liu Song-Hong
Chin. Phys., 2007, 16 (6): 1641-1649 doi: 10.1088/1009-1963/16/6/026
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The algebraic energy method (AEM) is applied to the study of molecular dissociation energy $D_e$ for 11 heteronuclear diatomic electronic states: $a^3\Sigma^+$ state of NaK, $X^2\Sigma^+$ state of XeBr, $X^2\Sigma^+$ state of HgI, $X^1\Sigma^+$ state of LiH, $A^3\Pi(1)$ state of ICl, $X^1\Sigma^+$ state of CsH, $A(^3\Pi_1)$ and $B0^+(^3\Pi)$ states of ClF, $2^1\Pi$ state of KRb, $X^1\Sigma^+$ state of CO, and $c^3\Sigma^+$ state of NaK molecule. The results show that the values of $D_e$ computed by using the AEM are satisfactorily accurate compared with experimental ones. The AEM can serve as an economic and useful tool to generate a reliable $D_e$ within an allowed experimental error for the electronic states whose molecular dissociation energies are unavailable from the existing literature.

UV and visible upconversion luminescence in Er3+:YAG under red laser excitation

Yang Hai-Gui, Dai Zhen-Wen, Zu Ning-Ning
Chin. Phys., 2007, 16 (6): 1650-1654 doi: 10.1088/1009-1963/16/6/027
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This paper reports that the ultraviolet and visible upconversion luminescence from the $^{4}\S_{3 / 2}$, $^{2}\G_{9 / 2}$ and $^{2}\P_{3 / 2}$ levels have been observed in Er$^{3 + }$:YAG following 647.2~nm excitation of the $^{4}\F_{9 / 2}$ multiple. Upconversion luminescence intensity dependence on pump power was recorded. The measured decay profiles were theoretically fitted by kinetics theory and the basically good agreements were achieved. The results indicate that some energy transfer processes proposed to explain the observed upconversion phenomena are reasonable.

Absolute differential, elastic integrated and moment transfer cross sections for electron--OCS collisions at intermediate and high energies

Shi De-Heng, Sun Jin-Feng, Zhu Zun-Lue, Ma Heng, Liu Yu-Fang, Yang Xiang-Dong
Chin. Phys., 2007, 16 (6): 1655-1659 doi: 10.1088/1009-1963/16/6/028
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A complex optical model potential modified by incorporating the concept of bonded atom, which takes into consideration the overlapping effect of electron clouds between atoms in a molecule, is firstly employed to calculate the absolute differential, elastic integrated and moment transfer cross sections for electron scattering by OCS over the incident energy range from 200 to 1000\,eV using the additivity rule model at Hartree--Fock level. The calculated results are compared with those obtained by experiment and other theories wherever available, and good agreement is obtained over a wide energy range. It is shown that the additivity rule model together with the modified potential is completely suitable for calculating the absolute differential, elastic integrated and moment transfer cross sections of electron scattering by molecules such as OCS.

Structures and electronic properties of Aun-1Cu and Aun (n≤9) clusters

Wang Hong-Yan, Li Xi-Bo, Tang Yong-Jian, R. Bruce King, Henry F. Schaefer III
Chin. Phys., 2007, 16 (6): 1660-1664 doi: 10.1088/1009-1963/16/6/029
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A systematic study on the structure and electronic properties of gold clusters doped each with one copper atom has been performed using the density functional theory. The average bond lengths in the Au$_{n - 1}$Cu ($n \le 9$) bimetallic clusters are shorter than those in the corresponding pure gold clusters. The ionization potentials of the bimetallic clusters Au$_{n-1}$Cu ($n \le 9$) are larger than those of the corresponding homoatomic gold clusters except for Au$_{5}$. The energy gaps of the Au--Cu binary clusters are narrower than those of the Au$_{n}$ clusters except AuCu and Au$_{3}$Cu. No obvious even--odd effect exists in the variations of the electron affinities and ionization potentials for the Au$_{n - 1}$Cu ($n \le $ 9) clusters, which is in contrast to the case of gold clusters Au$_{n}$.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

The study of the shape anisotropy in patterned permalloy films

Zhang Dong, Zhai Ya, Zhai Hong-Ru
Chin. Phys., 2007, 16 (6): 1725-1727 doi: 10.1088/1009-1963/16/6/040
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In this paper a systematic ferromagnetic resonance study shows that an in-plane magnetic anisotropy in the patterned micron octagon permalloy (Ni$_{80}$Fe$_{20})$ elements is mainly determined by the element geometry. The easy-axis is along the edge of the elements, and the hard-axis is along the diagonal. The shape anisotropy of the octagon elements is determined by square and equilateral octagon, and the theoretical calculation was studied on the shape anisotropy. The shape anisotropy of rectangular was calculated by using the same theory.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Research on factors influencing on the microwave permeability of nanocrystalline FeB alloys

Fu Cheng-Wu, Zhang Shuan-Qin
Chin. Phys., 2007, 16 (6): 1728-1730 doi: 10.1088/1009-1963/16/6/041
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Nanocrystalline FeB alloys have been prepared with optimized grain size and internal stress. Samples prepared under different annealing conditions are analysed by x-ray diffraction, and the permeability $\mu(\omega)$ is measured by HP8510B Vector Network Analyser in the frequency range 2--18GHz. The results show that annealing leads to the growth of the grain size and reduces the internal stress, and smaller grain size and larger internal stress favours the magnetic dissipation.

Micromagnetic simulation for high field sensors with perpendicular magnetizations

Jin Wei, Liu Yao-Wen
Chin. Phys., 2007, 16 (6): 1731-1735 doi: 10.1088/1009-1963/16/6/042
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In this paper, we present a micromagnetic design for high field sensors. The hard layer of the sensors is L1$_{0}$--FePt which is magnetized perpendicularly to film plane and the sense layer is NiFe which is magnetized in the film plane. The magnetization configurations of the hard and sense layers at different external magnetic fields have been simulated. In micromagnetic simulation, the sense field up to one tesla can be reached by using this sensor. We find that whether the sensor has a symmetric or an asymmetric field-sensing window is determined by the coercive field of the hard layer and the demagnetizing field of the sense layer.

Effect of lithium-potassium mixed alkali on spectroscopic properties of Er3+-doped aluminophosphate glasses

Fang Yong-Zheng, Liao Mei-Song, Hu Li-Li
Chin. Phys., 2007, 16 (6): 1736-1742 doi: 10.1088/1009-1963/16/6/043
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Er$^{3+}$-doped lithium-potassium mixed alkali aluminophosphate glasses belonging to the oxide system $x$K$_2$O-(15-$x$)Li$_2$O-4B$_2$O$_3$-11Al$_2$O$_3$-5BaO-65P$_2$O$_5$ are obtained in a semi-continuous melting quenching process. Spectroscopic properties of Er$^{3+}$-doped glass matrix have been analysed by fitting the experimental data with the standard Judd--Ofelt theory. It is observed that Judd--Ofelt intensity parameters ${\it\Omega}_ t (t= 2$, 4 and 6) of Er$^{3+}$ change when the second alkali is introduced into glass matrix. The variation of line strength $S_{\rm ed}$[$^4$I$_{13/2}$,$^4$I$_{15/2}$] follows the same trend as that of the ${\it\Omega}_6$ parameter. The effect of mixed alkali on the spectroscopic properties of the aluminophosphate glasses, such as absorption cross-section, stimulated emission cross-section, spontaneous emission probability, branching ratio and the radiative lifetime, has also been investigated in this paper.

Tradeoff between speed and static power dissipation of ultra-thin body SOI MOSFETs

Tian Yu, Huang Ru, Zhang Xing, Wang Yang-Yuan
Chin. Phys., 2007, 16 (6): 1743-1747 doi: 10.1088/1009-1963/16/6/044
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The speed performance and static power dissipation of the ultra-thin-body (UTB) MOSFETs have been comprehensively investigated, with both DC and AC behaviours considered. Source/drain extension width ($L_{\rm sp})$ and silicon film thickness $(t_{\rm si})$ are two independent parameters that influence the speed and static power dissipation of UTB silicon-on-insulator (SOI) MOSFETs respectively, which can result in great design flexibility. Based on the different effects of physical and geometric parameters on device characteristics, a method to alleviate the contradiction between power dissipated and speed of UTB SOI MOSFETs is proposed. The optimal design regions of $t_{\rm si}$ and $L_{\rm sp}$ for low operating power and high performance logic applications are given, which may shed light on the design of UTB SOI MOSFETs.

Electron transport for a laser-irradiated quantum channel with Rashba spin--orbit coupling

Zhao Hua, Liao Wen-Hu, Zhou Guang-Hui
Chin. Phys., 2007, 16 (6): 1748-1752 doi: 10.1088/1009-1963/16/6/045
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We investigate theoretically the electron transport for a two-level quantum channel (wire) with Rashba spin--orbit coupling under the irradiation of a longitudinally-polarized external laser field at low temperatures. Using the method of equation of motion for Keldysh nonequilibrium Green function, we examine the time-averaged spin polarized conductance for the system with photon polarization parallel to the wire direction. By analytical analysis and a few numerical examples, the interplay effects of the external laser field and the Rashba spin--orbit coupling on the spin-polarized conductance for the system are demonstrated and discussed. It is found that the longitudinally-polarized laser field can adjust the spin polarization rate and produce some photon sideband resonances of the conductance for the system.

The fabrication of nickel silicide ohmic contacts to n-type 6H-silicon carbide

Guo Hui, Zhang Yi-Men, Qiao Da-Yong, Sun Lei, Zhang Yu-Ming
Chin. Phys., 2007, 16 (6): 1753-1756 doi: 10.1088/1009-1963/16/6/046
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This paper reports that the nickel silicide ohmic contacts to n-type 6H-SiC have been fabricated. Transfer length method test patterns with NiSi/SiC and NiSi$_{2}$/SiC structure are formed on N-wells created by N$^{ + }$ ion implantation into Si-faced p-type 6H-SiC epilayer respectively. NiSi and NiSi$_{2}$ films are prepared by annealing the Ni and Si films separately deposited. A two-step annealing technology is performed for decreasing of oxidation problems occurred during high temperature processes. The specific contact resistance $\rho _{c}$ of NiSi contact to n-type 6H-SiC as low as 1.78$\times $10$^{ - 6}\Omega $cm$^{2}$ is achieved after a two-step annealing at 350~${^\circ}$C for 20 min and 950${^\circ}$C for 3 min in N$_{2}$. And 3.84$\times $10$^{ - 6}\Omega $cm$^{2}$ for NiSi$_{2}$ contact is achieved. The result for sheet resistance $R_{\rm sh}$ of the N$^{ + }$ implanted layers is about 1210$\Omega /\square$. X-ray diffraction analysis shows the formation of nickel silicide phases at the metal/n-SiC interface after thermal annealing. The surfaces of the nickel silicide after thermal annealing are analysed by scanning electron microscope.

A threshold voltage model for high-k gate-dielectric MOSFETs considering fringing-field effect

Ji Feng, Xu Jing-Ping, Lai Pui-To
Chin. Phys., 2007, 16 (6): 1757-1763 doi: 10.1088/1009-1963/16/6/047
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In this paper, a threshold voltage model for high-$k$ gate-dielectric metal--oxide--semiconductor field-effect transistors (MOSFETs) is developed, with more accurate boundary conditions of the gate dielectric derived through a conformal mapping transformation method to consider the fringing-field effects including the influences of high-$k$ gate-dielectric and sidewall spacer. Comparing with similar models, the proposed model can be applied to general situations where the gate dielectric and sidewall spacer can have different dielectric constants. The influences of sidewall spacer and high-$k$ gate dielectric on fringing field distribution of the gate dielectric and thus threshold voltage behaviours of a MOSFET are discussed in detail.

Magnetization study of ITER-type internal-Sn Nb3Sn superconducting wire

Zhang Chao-Wu, Zhou Lian, Andre Sulpice, Jean-Louis Soubeyroux, Christophe Verwaerde, Gia Ky Hoang, Zhang Ping-Xiang, Lu Ya-Feng, Tang Xian-De
Chin. Phys., 2007, 16 (6): 1764-1769 doi: 10.1088/1009-1963/16/6/048
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Through magnetization measurement with a SQUID magnetometer the heat treatment optimization of an international thermonuclear experimental reactor (ITER)-type internal-Sn Nb$_{3}$Sn superconducting wire has been investigated. The irreversibility temperature $T^*(H)$, which is mainly dependent on A15 phase composition, was obtained by a warming and cooling cycle at a fixed field. The hysteresis width $\Delta M(H)$ which reflects the flux pinning situation of the A15 phase is determined by the sweeping of magnetic field at a constant temperature. The results obtained from differently heat-treated samples show that the combination of $T^*(H)$ with $\Delta M(H)$ measurement is very effective for optimizing the heat reaction process. The heat treatment condition of the ITER-type wire is optimized at 675$\,^\circ$C/128~h, which results in a composition closer to stoichiometric Nb$_{3}$Sn and a state with best flux pinning.

Difference in magnetic properties between Co-doped ZnO powder and thin film

Liu Xue-Chao, Shi Er-Wei, Chen Zhi-Zhan, Zhang Hua-Wei, Zhang Tao, Song Li-Xin
Chin. Phys., 2007, 16 (6): 1770-1775 doi: 10.1088/1009-1963/16/6/049
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This paper reports that the Zn$_{0.95}$Co$_{0.05}$O polycrystalline powder and thin film were prepared by sol-gel technique under the similar preparation conditions. The former does not show typical ferromagnetic behaviour, while the latter exhibits obvious ferromagnetic properties at 5 K and room temperature. The UV--vis spectra and x-ray absorption spectra show that Co$^{2 + }$ ions are homogeneously incorporated into ZnO lattice without forming secondary phases. The distinct difference between film and powder sample is the $c$-axis (002) preferential orientation indicated by the x-ray diffraction pattern and field emission scanning electron microscopy measurement, which may be the reason why Zn$_{0.95}$Co$_{0.05}$O film shows ferromagnetic behaviour.

Resonant tunnelling of the magnetization in molecular crystal of [(Mn1-xCrx)12O12(CH3COO)16(H2O)4]?2CH3COOH?4H2O (x=0,0.03,0

He Guang, He Lun-Hua, Zhang Jun-Rong, Cao Hui-Bo, Yan Li-Qin, Wang Fang-Wei, Yan Qi-Wei
Chin. Phys., 2007, 16 (6): 1776-1779 doi: 10.1088/1009-1963/16/6/050
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The quantum tunnelling of magnetization (QTM) in single crystals of the single molecule magnet (Mn$_{1-x}$Cr$_x$)12-Ac ($x$=0, 0.03, 0.04, 0.05) has been investigated. In comparison with its parent Mn12-Ac, a greater rate of magnetization relaxation and a lower effective potential-energy barrier have been observed in Cr-doping samples. This modulation of QTM due to the Cr-doping could be attributed to the small change of $S_z$ due to the smaller spin of Cr itself and additional intrinsic but distributed transverse and longitudinal anisotropy raised by a subtle change of the local environment in the magnetic Mn12 core.

The first-principles study of ferroelectric behaviours of PbTiO3/SrTiO3 and BaTiO3/SrTiO3 superlattices

Zhu Zhen-Ye, Wang Biao, Wang Hai, Zheng Yue, Li Qing-Kun
Chin. Phys., 2007, 16 (6): 1780-1785 doi: 10.1088/1009-1963/16/6/051
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We have performed the first-principles calculation to investigate the origins of ferroelectricities and different polarization behaviours of superlattices BaTiO$_{3}$/SrTiO$_{3}$ and PbTiO$_{3}$/SrTiO$_{3}$. The density of state (DOS) and electronic charge profiles show that there are strong hybridizations between atoms Ti and O and between atoms Pb and O which play very important roles in producing the ferroelectricities of superlattices BaTiO$_{3}$/SrTiO$_{3}$ and PbTiO$_{3}$/SrTiO$_{3}$. Owing to the decline of internal electric field in SrTiO$_{3}$ (ST) layer, the tetragonality and polarizations of superlattices decrease with increasing the fraction of SrTiO$_{3}$ in the superlattices. We find that the polarization of PbTiO$_{3}$/SrTiO$_{3}$ is larger$_{ }$than that of BaTiO$_{3}$/SrTiO$_{3}$ at the same ratio of components, because the polarization mismatch between PbTiO$_{3}$ and SrTiO$_{3}$ is larger than that between BaTiO$_{3}$ and SrTiO$_{3}$. The polarization and tetragonality are enhanced with respect to those of bulk tetragonal BaTiO$_{3}$ in the superlattices BaTiO$_{3}$/SrTiO$_{3}$, while the polarization and tetragonality are reduced with respect to those of bulk tetragonal PbTiO$_{3}$ in superlattices PbTiO$_{3}$/SrTiO$_{3}$.

Spectroscopic investigation of a new crystal: Nd3+,Yb3+:YVO4

Wang Su-Mei, Du Shi-Feng, Lu Jian, Zhang Dong-Xiang, Feng Bao-Hua
Chin. Phys., 2007, 16 (6): 1786-1789 doi: 10.1088/1009-1963/16/6/052
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The absorption and emission spectra of the YVO$_4$ single crystal co-doped with 1 at.\% Nd$^{3+}$ and 1 at.\% Yb$^{3+}$ are investigated. The efficient Nd$^{3+}$ $\rightarrow$ Yb$^{3+}$ energy transfer and the back transfer (Yb$^{3+}\rightarrow$ Nd$^{3+}$) are observed at room temperature. The fluorescence lifetime of the $^4$F$_{3/2}$ level of Nd$^{3+}$ in Nd,Yb:YVO$_4$ is measured under 808\,nm laser light excitation. The efficiency of Nd$^{3+}\rightarrow$ Yb$^{3+}$ energy transfer in YVO$_4$ is determined to be about 34\%.

Photoluminescence and electroluminescence properties of ZnO films on p-type silicon wafers

Wang Fei-Fei, Cao Li, Liu Rui-Bin, Pan An-Lian, Zou Bing-Suo
Chin. Phys., 2007, 16 (6): 1790-1795 doi: 10.1088/1009-1963/16/6/053
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A simplified n-ZnO/p-Si heterojunction has been prepared by growing n-type ZnO rods on p-type silicon wafer through the chemical vapour deposition method. The reflectance spectrum of the sample shows an independent absorption peak at 384 nm, which may be originated from the bound states at the junction. In the photoluminescence spectrum a new emission band is shown at 393 nm, besides the bandedge emission at 380 nm. The electroluminescence spectrum of the n-ZnO/p-Si heterojunction shows a stable yellow luminescence band centred at 560 nm,which can be attributed to the emission from trapped states. Another kind of discrete ZnO rod has also been prepared on such silicon wafer and is encapsulated with carbonated polystyrene for electroluminescence detection. This composite structure shows a weak ultraviolet electroluminescence band at 395 nm and a yellow electroluminescence band. These data prove that surface modification which blocks the transverse movement of carriers between neighbouring nanorods plays important roles in the ultraviolet emission of ZnO nanorods. These findings are vital for future display device design.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Origination of gamma-ray burst pulses associated with the Doppler effect of spherical fireballs or uniform jet

Lu Rui-Jing, Qin Yi-Ping, Zhang Fu-Wen
Chin. Phys., 2007, 16 (6): 1806-1816 doi: 10.1088/1009-1963/16/6/055
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Ryde and Petrosian have pointed out that the rise phases of gamma-ray burst (GRB) pulses originate from the widths of the intrinsic pulses and their decay phases are determined by the curvature effect of the expanding fireball surface based on their simplified formula. In this paper we investigate in detail the issue based on the formula in Ref.[20], which is derived based on a model of highly symmetric expanding fireballs, where the Doppler effect is the key factor to be concerned about, and no terms are omitted in their derivation. Our analyses show that the decay phases of the observed pulses originate from the contributions from both the curvature effect of the expanding fireball and the two timescales of the local pulses, and the rise phases of the observed pulses only come from the two timescales of the local pulses. Associated with a local pulse with both rise and decay portions, the light curve of GRBs in the rise portion is expected to undergo a concave phase and then a convex one, whereas that in the decay portion is expected to evolve by an opposite process. And the ratio of the concave timescale to the convex one in the rise phase of the observed pulse linearly increases with the ratio of the rising timescale to the decay one of the local pulse ($r_{\rm rd}$), whereas the ratio of the convex timescale to the concave timescale in its decay phase linearly decreases with $r_{\rm rd}$. The two correlations are independent of the local pulse forms and the rest-frame radiation forms. But the different forms of local pulses and the different values of $r_{\rm rd}$ gives rise to the diversity of the light curve pulse shapes. We test a sample of 86 GRB pulses detected by the BATSE instrument on board the Compton Gamma Ray Observatory and find that the characteristics do exist in the light curve of GRBs.
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