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Chin. Phys. B  
  Chin. Phys. B--2008, Vol.17, No.10
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GENERAL

Consensus protocol for multi-agent continuous systems

Tan Fu-Xiao, Guan Xin-Ping, Liu De-Rong
Chin. Phys. B, 2008, 17 (10): 3531-3535 doi: 10.1088/1674-1056/17/10/001
Full Text: [PDF 180 KB] (Downloads:856)
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Based on the algebraic graph theory, the networked multi-agent continuous systems are investigated. Firstly, the digraph (directed graph) represents the topology of a networked system, and then a consensus convergence criterion of system is proposed. Secondly, the issue of stability of multi-agent systems and the consensus convergence problem of information states are all analysed. Furthermore, the consensus equilibrium point of system is proved to be global and asymptotically reach the convex combination of initial states. Finally, two examples are taken to show the effectiveness of the results obtained in this paper.

Information diffusion on adaptive network

Hu Ke, Tang Yi
Chin. Phys. B, 2008, 17 (10): 3536-3541 doi: 10.1088/1674-1056/17/10/002
Full Text: [PDF 264 KB] (Downloads:770)
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Based on the adaptive network, the feedback mechanism and interplay between the network topology and the diffusive process of information are studied. The results reveal that the adaptation of network topology can drive systems into the scale-free one with the assortative or disassortative degree correlations, and the hierarchical clustering. Meanwhile, the processes of the information diffusion are extremely speeded up by the adaptive changes of network topology.

Adiabatic invariants of generalized Lutzky type for disturbed holonomic nonconservative systems

Luo Shao-Kai, Cai Jian-Le, Jia Li-Qun
Chin. Phys. B, 2008, 17 (10): 3542-3548 doi: 10.1088/1674-1056/17/10/003
Full Text: [PDF 153 KB] (Downloads:499)
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Based on the definition of higher-order adiabatic invariants of a mechanical system, a new type of adiabatic invariants,i.e. generalized Lutzky adiabatic invariants, of a disturbed holonomic nonconservative mechanical system are obtained by investigating the perturbation of Lie symmetries for a holonomic nonconservative mechanical system with the action of small disturbance. The adiabatic invariants and the exact invariants of the Lutzky type of some special cases, for example, the Lie point symmetrical transformations, the special Lie symmetrical transformations, and the Lagrange system, are given. And an example is given to illustrate the application of the method and results.

A scheme for demonstration of four-photon de Broglie wavelength

Zhou Xiao-Qi, Yang Tao
Chin. Phys. B, 2008, 17 (10): 3549-3552 doi: 10.1088/1674-1056/17/10/004
Full Text: [PDF 315 KB] (Downloads:490)
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We propose a scheme to effectively generate a four-photon path-entangled number state [the NOON state i.e. \dfrac{1}{\sqrt{2}}(\vert N,0\rangle+\vert 0,N\rangle)] for the demonstration of four-photon de Broglie wavelength. Our scheme requires only linear optical elements, photon detectors and post-selections which are all within the reach of current technology.

Control of entanglement sudden death by Kerr medium

Zheng Qiang, Zhang Xiao-Ping, Ren Zhong-Zhou
Chin. Phys. B, 2008, 17 (10): 3553-3558 doi: 10.1088/1674-1056/17/10/005
Full Text: [PDF 213 KB] (Downloads:661)
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The entanglement dynamics of system, where atoms A and B interact with single mode cavity fields a and b respectively, is studied. The interaction between atom A and cavity a may be described by using the typical Jaynes--Cummings model, while that between the atom B and cavity b filled with a Kerr medium is of a two-photon process. For a certain initial atom entanglement state, there is an entanglement sudden death effect between the two atoms. The Kerr medium in the cavity b can effectively prevent the undesirable entanglement sudden death from occurring. Also, from the viewpoint of the population dynamics, we discuss why the Kerr medium can do so.

Mixedness of the N-qubit states with exchange symmetry

Hu Ming-Liang, Xi Xiao-Qiang
Chin. Phys. B, 2008, 17 (10): 3559-3564 doi: 10.1088/1674-1056/17/10/006
Full Text: [PDF 277 KB] (Downloads:497)
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The mixedness of the $N$-qubit quantum states with exchange symmetry has been studied, and the results show that the linear entropy of the single qubit reduced density matrix (RDM), which can describe the mixedness, is completely determined by the expectation values $\langle S_z \rangle $ and $\langle S_\pm \rangle $ for both the pure and the mixed states. The mixedness of the pure states can be used to describe the bipartite entanglement, as an example we have calculated the mixedness of the Dicke state and the spin squeezed Kitagawa--Ueda state. For the mixed states, we determine the mixedness properties of both the ground states and the thermal states in mean-field clusters of spin-1/2 particles interacting via the anisotropy Heisenberg XXZ interaction, and found for the ferromagnetic case ($J < 0)$, the mixedness will approximate to the pairwise entanglement when the anisotropic parameter ${\it\Delta }> {\it\Delta }_{\rm c} $.

Planar ion chip design for scalable quantum information processing

Wan Jin-Yin, Wang Yu-Zhu, Liu Liang
Chin. Phys. B, 2008, 17 (10): 3565-3573 doi: 10.1088/1674-1056/17/10/007
Full Text: [PDF 902 KB] (Downloads:547)
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We investigate a planar ion chip design with a two-dimensional array of linear ion traps for scalable quantum information processing. Qubits are formed from the internal electronic states of trapped $^{40}$Ca$^{+}$ ions. The segmented electrodes reside in a single plane on a substrate and a grounded metal plate separately, a combination of appropriate rf and DC potentials is applied to them for stable ion confinement. Every two adjacent electrodes can generate a linear ion trap in and between the electrodes above the chip at a distance dependent on the geometrical scale and other considerations. The potential distributions are calculated by using a static electric field qualitatively. This architecture provides a conceptually simple avenue to achieving the microfabrication and large-scale quantum computation based on the arrays of trapped ions.

Inverse scattering method and soliton solutionfamily for the Einstein--Maxwell theory with multiple Abelian gauge fields

Gao Ya-Jun
Chin. Phys. B, 2008, 17 (10): 3574-3579 doi: 10.1088/1674-1056/17/10/008
Full Text: [PDF 182 KB] (Downloads:532)
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A Hauser--Ernst-type extended hyperbolic complex linear system given in our previous paper [Gao Y J 2004 {\it Chin. Phys.} {\bf 13} 602] is slightly modified and used to develop a new inverse scattering method for the stationary axisymmetric Einstein--Maxwell theory with multiple Abelian gauge fields. The reduction procedures in this inverse scattering method are found to be fairly simple, which makes the inverse scattering method be fine and effective in practical application. As an example, a concrete family of soliton solutions for the considered theory is obtained.

Connectivity correlations in three topological spaces of urban bus-transport networks in China

Chen Yong-Zhou, Fu Chun-Hua, Chang Hui, Li Nan, He Da-Ren
Chin. Phys. B, 2008, 17 (10): 3580-3587 doi: 10.1088/1674-1056/17/10/009
Full Text: [PDF 2439 KB] (Downloads:615)
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In this paper, an empirical investigation is presented, which focuses on unveiling the universality of connectivity correlations in three spaces (the route space, the stop geographical space and bus-transferring space) of urban bus-transport networks (BTNs) in four major cities of China. The underlying features of the connectivity correlations are shown in two statistical ways. One is the correlation between the (weighted) average degree of all the nearest neighbouring vertices with degree $k$, ($K^w_{nn}(k)$) $K_{nn}(k)$, and $k$, and the other is the correlations between the assortativity coefficient $r$ and, respectively, the network size $N$, the network diameter $D$, the averaged clustering coefficient $C$, and the averaged distance $\lan l\ran$. The obtained results show qualitatively the same connectivity correlations of all the considered cities under all the three spaces.

Constructing a one-way hash function based on the unified chaotic system

Long Min, Peng Fei, Chen Guan-Rong
Chin. Phys. B, 2008, 17 (10): 3588-3595 doi: 10.1088/1674-1056/17/10/010
Full Text: [PDF 296 KB] (Downloads:506)
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A new one-way hash function based on the unified chaotic system is constructed. With different values of a key parameter, the unified chaotic system represents different chaotic systems, based on which the one-way hash function algorithm is constructed with three round operations and an initial vector on an input message. In each round operation, the parameters are processed by three different chaotic systems generated from the unified chaotic system. Feed-forwards are used at the end of each round operation and at the end of each element of the message processing. Meanwhile, in each round operation, parameter-exchanging operations are implemented. Then, the hash value of length 160 bits is obtained from the last six parameters. Simulation and analysis both demonstrate that the algorithm has great flexibility, satisfactory hash performance, weak collision property, and high security.

Design and FPGA Implementation of a new hyperchaotic system

Wang Guang-Yi, Bao Xu-Lei, Wang Zhong-Lin
Chin. Phys. B, 2008, 17 (10): 3596-3602 doi: 10.1088/1674-1056/17/10/011
Full Text: [PDF 4668 KB] (Downloads:1707)
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In this paper, a new four-dimensional autonomous hyperchaotic system is designed for generating complex chaotic signals. In the design, its parameters are selected according to the requirements for chaos and hyperchaos. The hyperchaotic nature is verified theoretically by using the bifurcation analysis and demonstrated experimentally by the implementation of an analogue electronic circuit. Moreover, the Field Programmable Gate Array (FPGA) technology is applied to implementing a continuous system in a digital form by using a chip of Altera Cyclone II EP2C35F484C8. The digital sequence generated from the FPGA device is observed in our experimental setup.

Adaptive generalized functional synchronization of chaotic systems with unknown parameters

Wang Dong-Feng, Han Pu
Chin. Phys. B, 2008, 17 (10): 3603-3608 doi: 10.1088/1674-1056/17/10/012
Full Text: [PDF 337 KB] (Downloads:608)
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A universal adaptive generalized functional synchronization approach to any two different or identical chaotic systems with unknown parameters is proposed, based on a unified mathematical expression of a large class of chaotic system. Self-adaptive parameter law and control law are given in the form of a theorem. The synchronization between the three-dimensional R\"{o}ssler chaotic system and the four-dimensional Chen's hyper-chaotic system is studied as an example for illustration. The computer simulation results demonstrate the feasibility of the method proposed.

Implementation of LT codes based on chaos

Zhou Qian, Li Liang, Chen Zeng-Qiang, Zhao Jia-Xiang
Chin. Phys. B, 2008, 17 (10): 3609-3615 doi: 10.1088/1674-1056/17/10/013
Full Text: [PDF 577 KB] (Downloads:779)
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Fountain codes provide an efficient way to transfer information over erasure channels like the Internet. LT codes are the first codes fully realizing the digital fountain concept. They are asymptotically optimal rateless erasure codes with highly efficient encoding and decoding algorithms. In theory, for each encoding symbol of LT codes, its degree is randomly chosen according to a predetermined degree distribution, and its neighbours used to generate that encoding symbol are chosen uniformly at random. Practical implementation of LT codes usually realizes the randomness through pseudo-randomness number generator like linear congruential method. This paper applies the pseudo-randomness of chaotic sequence in the implementation of LT codes. Two Kent chaotic maps are used to determine the degree and neighbour(s) of each encoding symbol. It is shown that the implemented LT codes based on chaos perform better than the LT codes implemented by the traditional pseudo-randomness number generator.

A practical approach to robust impulsive lag synchronization between different chaotic systems

Zhang Hua-Guang, Ma Tie-Dong, Yu Wen, Fu Jie
Chin. Phys. B, 2008, 17 (10): 3616-3622 doi: 10.1088/1674-1056/17/10/014
Full Text: [PDF 223 KB] (Downloads:513)
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In this paper, a practical impulsive lag synchronization scheme for different chaotic systems with parametric uncertainties is proposed. By virtue of the new definition of synchronization and the theory of impulsive differential equations, some new and less conservative sufficient conditions are established to guarantee that the error dynamics can converge to a predetermined level. The idea and approach developed in this paper can provide a more practical framework for the synchronization between identical and different chaotic systems in parameter perturbation circumstances. Simulation results finally demonstrate the effectiveness of the method.

Structure-preserving algorithms for the Duffing equation

Gang Tie-Qiang, Mei Feng-Xiang, Xie Jia-Fang
Chin. Phys. B, 2008, 17 (10): 3623-3628 doi: 10.1088/1674-1056/17/10/015
Full Text: [PDF 501 KB] (Downloads:510)
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In this paper, the dissipative and the forced terms of the Duffing equation are considered as the perturbations of nonlinear Hamiltonian equations and the perturbational effect is indicated by parameter $\varepsilon $. Firstly, based on the gradient-Hamiltonian decomposition theory of vector fields, by using splitting methods, this paper constructs structure-preserving algorithms (SPAs) for the Duffing equation. Then, according to the Liouville formula, it proves that the Jacobian matrix determinants of the SPAs are equal to that of the exact flow of the Duffing equation. However, considering the explicit Runge--Kutta methods, this paper finds that there is an error term of order $p$+1 for the Jacobian matrix determinants. The volume evolution law of a given region in phase space is discussed for different algorithms, respectively. As a result, the sum of Lyapunov exponents is exactly invariable for the SPAs proposed in this paper. Finally, through numerical experiments, relative norm errors and absolute energy errors of phase trajectories of the SPAs and the Heun method (a second-order Runge--Kutta method) are compared. Computational results illustrate that the SPAs are evidently better than the Heun method when $\varepsilon $ is small or equal to zero.
NUCLEAR PHYSICS

Judd--Ofelt analysis of spectra and experimental evaluation of laser performance of Tm3+ doped Lu2SiO5 crystal

Yao Bao-Quan, Zheng Liang-Liang, Duan Xiao-Ming, Zhao Guang-Jun, Zong Yan-Hua
Chin. Phys. B, 2008, 17 (10): 3635-3639 doi: 10.1088/1674-1056/17/10/017
Full Text: [PDF 296 KB] (Downloads:524)
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This paper reports that the Tm$^{3 + }$:Lu$_{2}$SiO$_{5}$ (Tm:LSO) crystal is grown by Czochralski technique. The room-temperature absorption spectra of Tm:LSO crystal are measured on a b-cut sample with 4 at.{\%} thulium. According to the obtained Judd--Ofelt intensity parameters $\Om _{2}$=9.3155$\times $10$^{ - 20 }$\,cm$^{2}$, $\Om_{4}$=8.4103$\times $10$^{ - 20 }$\,cm$^{2}$, $\Om_{6}$=1.5908$\times $10$^{ - 20 }$\,cm$^{2}$, the fluorescence lifetime is calculated to be 2.03\,ms for $^{3}$F$_{4} \to {}^{3}$H$_{6}$ transition, and the integrated emission cross section is 5.81$\times $10$^{ - 18 }$\,cm$^{2}$. Room-temperature laser action near 2\,$\mu $m under diode pumping is experimentally evaluated in Tm:LSO. An optical-optical conversion efficiency of 9.1{\%} and a slope efficiency of 16.2{\%} are obtained with continuous-wave maximum output power of 0.67\,W. The emission wavelengths of Tm:LSO laser are centred around 2.06\,$\mu $m with spectral bandwidth of $\sim $13.6\,nm.

Controlling the amplitude of soliton in agrowing Bose--Einstein condensate by means of Feshbach resonance

He Zhang-Ming, Wang Deng-Long, Zhang Wei-Xi, Wang Feng-Jiao, Ding Jian-Wen
Chin. Phys. B, 2008, 17 (10): 3640-3643 doi: 10.1088/1674-1056/17/10/018
Full Text: [PDF 189 KB] (Downloads:486)
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By using Darboux transformation, this paper studies analytically the nonlinear dynamics of a one-dimensional growing Bose--Einstein condensate (BEC). It is shown that the growing model has an important effect on the amplitude of the soliton in the condensates. In the absence of the growing model, there exhibits the stable alternate bright solitons in the condensates. In the presence of the growing model, the obtained results show that the amplitude of the bright soliton decreases (increases) for the BEC growing coefficient $\Om<0$ $(\Om >0)$. Furthermore, we propose experimental protocols to manipulate the amplitude of the bright soliton by varying the scattering length via the Feshbach resonance in the future experiment.

A CVD diamond film detector for pulsed proton detection

Wang Lan, Ouyang Xiao-Ping, Fan Ru-Yu, Jin Yong-Jie, Zhang Zhong-Bing, Pan Hong-Bo, Liu Lin-Yue, Lü Fan-Xiu, Bu Ren-An
Chin. Phys. B, 2008, 17 (10): 3644-3648 doi: 10.1088/1674-1056/17/10/019
Full Text: [PDF 662 KB] (Downloads:438)
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A chemical vapour deposition (CVD) diamond film detector was prepared and the main characteristics for pulsed proton detection were studied at Beijing Tandem Accelerator. The result shows that the charge collection efficiency of the detector increases with increasing electric field intensity and reaches to 9.44{\%} at 5\,V/$\mu $m with the charge collection distance of 15.9\,$\mu $m. The relationship between the sensitivity of the detector and proton energy is consistent with the Monte Carlo (MC) simulation result. Its plasma time for a pulse with 4.85$\times $10$^{5}$ protons is 11.2ns. The dose threshold for onset of damage under 9MeV proton irradiation in the detector is about 10$^{13}$\,cm$^{ - 2}$. All of the results show that a CVD diamond detector has fast time response and high radiation hardness, and can be used in pulsed proton detection.
CLASSICAL AREAS OF PHENOMENOLOGY

Solution of scattering from rough surface with a 2Dtarget above it by a hybrid method based on the reciprocity theorem and the forward--ackward method

Wang Yun-Hua, Zhang Yan-Min, He Ming-Xia, Guo Li-Xin
Chin. Phys. B, 2008, 17 (10): 3696-3703 doi: 10.1088/1674-1056/17/10/027
Full Text: [PDF 1467 KB] (Downloads:445)
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This paper proposes a hybrid method based on the forward--backward method (FBM) and the reciprocity theorem (RT) for evaluating the scattering field from dielectric rough surface with a 2D target above it. Here, the equivalent electric/magnetic current densities on the rough surface as well as the scattering field from it are numerically calculated by FBM, and the scattered field from the isolated target is obtained utilizing the method of moments (MOM). Meanwhile, the rescattered coupling interactions between the target and the surface are evaluated employing the combination of FBM and RT. Our hybrid method is first validated by available MOM results. Then, the functional dependences of bistatic and monostatic scattering from the target above rough surface upon the target altitude, incident and scattering angles are numerically simulated and discussed. This study presents a numerical description for the scattering mechanism associated with rescattered coupling interactions between a target and an underlying randomly rough surface.

Surface relief resonant Brewster filters with multiple channels

Ma Jian-Yong, Liu Shi-Jie, Zhang Da-Wei, Yao Jian-Ke, Xu Cheng, Jin Yun-Xia, Shao Jian-Da, Fan Zheng-Xiu
Chin. Phys. B, 2008, 17 (10): 3704-3707 doi: 10.1088/1674-1056/17/10/028
Full Text: [PDF 1238 KB] (Downloads:559)
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In this paper, a new type of resonant Brewster filters (RBF) with surface relief structure for the multiple channels is first presented by using the rigorous coupled-wave analysis and the $S$-matrix method. By tuning the depth of homogeneous layer which is under the surface relief structure, the multiple channels phenomenon is obtained. Long range, extremely low sidebands and multiple channels are found when the RBF with surface relief structure is illuminated with Transverse Magnetic incident polarization light near the Brewster angle calculated with the effective media theory of sub wavelength grating. Moreover, the wavelengths of RBF with surface relief structure can be easily shifted by changing the depth of homogeneous layer while its optical properties such as low sideband reflection and narrow band are not spoiled when the depth is changed. Furthermore, the variation of the grating thickness does not effectively change the resonant wavelength of RBF, but have a remarkable effect on its line width, which is very useful for designing such filters with different line widths at desired wavelength.

M2 factor of four-petal Gaussian beam

Zhou Guo-Quan, Fan Yan
Chin. Phys. B, 2008, 17 (10): 3708-3712 doi: 10.1088/1674-1056/17/10/029
Full Text: [PDF 822 KB] (Downloads:478)
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Based on the second-order moments, this paper derives an analytical expression of the $M^{2}$ factor of four-petal Gaussian beam. The results show that the $M^{2}$ factor is only determined by the beam order $n$. The corresponding numerical calculations are also given. As the beam order increases, the augment of $M^{2}$ factor is disciplinary. As the expression of $M^{2}$ factor is expressed in series form and becomes more complicated, a new concise formula of $M^{2}$ factor is also presented by using curve fitting of numerical calculations. When $3 \le n \le 200$, the maximum error rate of fitting formula will not exceed 2.6{\%} and the average error rate is 0.28{\%}. This research is helpful to the applications of four-petal Gaussian beam.

Light scattering of nanocrystalline TiO2 film used in dye-sensitized solar cells

Xiong Bi-Tao, Zhou Bao-Xue, Bai Jing, Zheng Qing, Liu Yan-Biao, Cai Wei-Min, Cai Jun
Chin. Phys. B, 2008, 17 (10): 3713-3719 doi: 10.1088/1674-1056/17/10/030
Full Text: [PDF 1652 KB] (Downloads:865)
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This paper studies the light scattering and adsorption of nanocrystalline TiO$_2$ porous films used in dye-sensitized solar cells composed of anatase and/or rutile particles by using an optical four-flux radiative transfer model. These light properties are difficult to measure directly on the functioning solar cells and they can not be calculated easily from the first-principle computational or quantitative theoretical evaluations. These simulation results indicate that the light scattering of 1--25\,nm TiO$_{2}$ particles is negligible, but it is effective in the range of 80 and 180\,nm. A suitable mixture of small particles (10\,nm radius), which are resulted in a large effective surface, and of larger particles (150\,nm radius), which are effective light scatterers, have the potential to enhance solar absorption significantly. The rutile crystals have a larger refractive index and thus the light harvest of the mixtures of such larger rutile and relatively small anatase particles is improved in comparison with that of pure anatase films. The light absorption of the 10\,$\mu$m double-layered films is also examined. A maximal light absorption of double-layered film is gotten when the thickness of the first layer of 10\,nm-sized anatase particles is comparable to that of the second larger rutile layer.

Transverse shift of the transmitted beam of anon-uniformly polarized paraxial light beam at dielectric interfaces

Liu Bao-Ying, Li Chun-Fang
Chin. Phys. B, 2008, 17 (10): 3720-3724 doi: 10.1088/1674-1056/17/10/031
Full Text: [PDF 299 KB] (Downloads:428)
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This paper reports that the central position of the reflected and transmitted beams of a nonlinear polarized light beam at the interface between two media undergoes transverse shifts. It presents a solution to the problem of transverse shift of a non-uniformly polarized paraxial light beam transmitting through interfaces between two homogeneous media by using a two-form amplitude and an extension matrix to represent the vector angular spectrum of a three-dimensional (3D) light beam. It derives general formula for the transverse shift of the transmitted beam, and discusses the shift of a well-collimated beam transmitting through an interface between two homogeneous media and a thin dielectric slab.

High efficient scheme for remote state preparation with cavity QED

Deng Li, Chen Ai-Xi, Xu Yan-Qiu
Chin. Phys. B, 2008, 17 (10): 3725-3728 doi: 10.1088/1674-1056/17/10/032
Full Text: [PDF 152 KB] (Downloads:496)
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In this paper, a scheme is proposed for remote state preparation (RSP) with cavity quantum electrodynamics (QED). In our scheme, two observers share two-atom nonmaximally entangled state as quantum channels and can realize remote preparation of state of an atom. We also propose a generalization for remote preparation of $N$-atom entangled state by ($N$+1)-atom {GHZ-like} state ($N \ge 2)$. By this scheme, one single-atom projective measurement is enough for the RSP of a qubit or $N$-atom entangled state, and the probability of success for RSP is unity. Furthermore, we have considered the case where observers use {W-like} state as quantum channels to realize RSP of a qubit. We compare our scheme with existing ones.

An applicable and resource-economical scheme for the teleportation of W state via spin-path entangled quantum channel

Kang Guo-Dong, Fang Mao-Fa
Chin. Phys. B, 2008, 17 (10): 3729-3733 doi: 10.1088/1674-1056/17/10/033
Full Text: [PDF 474 KB] (Downloads:435)
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In this paper, we accomplish the teleportation of an unknown three-particle maximally entangled $W$ state by using a spin-path entangled quantum channel which may be realized experimentally based on the advanced theory and technique in Bose--Einstein condensate (BEC) of molecule, micro-fabricated wave guide and simple quantum logic gate. Similarly, we can make an arbitrary $n$-particle entangled Greenberger--Horne--Zeilinger (GHZ) state ($n\ge 4$) teleported through this kind of quantum channel. It may have important applications due to its resource-economic and practical features.

Phase modulation of propagation effect with Doppler broadening

Qiao Hong-Xia, Yang Yan-Ling, Tan Xia, Tong Dian-Min, Fan Xi-Jun
Chin. Phys. B, 2008, 17 (10): 3734-3738 doi: 10.1088/1674-1056/17/10/034
Full Text: [PDF 727 KB] (Downloads:403)
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This paper studies the propagation effect in a closed lambda-type three-level atomic system with Doppler broadening. It is shown that, Doppler broadening due to atomic motion and propagation effect associated with driving field depletion along the active medium decreases obviously the gain and output of the lasing without inversion (LWI); the relative phase between the probe and driving fields has a remarkable modulation role to the propagation effect on LWI when Doppler broadening presents; by choosing suitable value of the relative phase, we can get the largest gain and output of LWI.

Generation and classification of robust remote symmetric Dicke states

Zhu Yan-Wu, Gao Ke-Lin
Chin. Phys. B, 2008, 17 (10): 3739-3743 doi: 10.1088/1674-1056/17/10/035
Full Text: [PDF 275 KB] (Downloads:400)
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In this paper, we present an approach to generating arbitrary symmetric Dicke states with distant trapped ions and linear optics. Distant trapped ions can be prepared in the symmetric Dicke states by using two photon-number-resolving detectors and a polarization beam splitter. The atomic symmetric Dicke states are robust against decoherence, for atoms are in a metastable level. We discuss the experimental feasibility of our scheme with current technology. Finally, we discuss the classification of arbitrary $n$-qubit symmetric Dicke states under statistical local operation and classical communication and prove the existence of $[n/2]$ inequivalent classes of genuine entanglement of $n$-qubit symmetric Dicke states.

Photon--photon interactions with inner coupled double-cavity

Lai Wen-Xi, Li Hong-Cai, Yang Rong-Can
Chin. Phys. B, 2008, 17 (10): 3744-3752 doi: 10.1088/1674-1056/17/10/036
Full Text: [PDF 317 KB] (Downloads:505)
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This paper describes the interaction between two spatial modes of the optical fields with a single atom trapped inner coupled double-cavity. Theoretical derivation and numerical simulation with the experimental available parameters show that photon--photon switching and $\pi $ phase shift of single photons may be achieved with current experimental technology. As the probe and control fields are in different spatial modes, the system is superior for implementing cavity QED-based photonic quantum networks.

Trap states in oxidation layer of nanocrystal Si

Huang Wei-Qi, Wang Hai-Xu, Jin Feng, Qin Cao-Jian
Chin. Phys. B, 2008, 17 (10): 3753-3758 doi: 10.1088/1674-1056/17/10/037
Full Text: [PDF 4006 KB] (Downloads:456)
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The photoluminescence (PL) of nanocrystal present in porous silicon shifts from the near infrared to the ultraviolet depending on the size when the surface is passivated with Si-H bonds. After oxidation, the centre wavelength of PL band is pinned in a region of 700--750\,nm and its intensity increases obviously. Calculation shows that trap electronic states appear in the band gap of a smaller nanocrystal when Si = O bonds or Si--O--Si bonds are formed. The changes in PL intensity and wavelength can be explained by both quantum confinement and trap states in an oxidation layer of nanocrystal. In the theoretical model, the most important factor in the enhancement and the pinning effects of PL emission is the relative position between the level of the trap states and the level of the photoexcitation in the silicon nanocrystal.

Performance of gain-switched all-solid-state quasi-continuous-wave tunable Ti:sapphire laser system

Ding Xin, Zhang Heng, Wang Rui, Yu Xuan-Yi, Wen Wu-Qi, Zhang Bai-Gang, Wang Peng, Yao Jian-Quan
Chin. Phys. B, 2008, 17 (10): 3759-3764 doi: 10.1088/1674-1056/17/10/038
Full Text: [PDF 802 KB] (Downloads:495)
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We have made a gain-switched all-solid-state quasi-continuous-wave (QCW) tunable Ti:sapphire laser system, which is pumped by a 532\,nm intracavity frequency-doubled Nd:YAG laser. Based on the theory of gain-switching and the study on the influencing factors of the output pulse width, an effective method for obtaining high power and narrow pulse width output is proposed. Through deliberately designing the pump source and the resonator of the Ti:sapphire laser, when the repetition rate is 6\,kHz and the length of the cavity is 220\,mm, at an incident pump power of 22\,W, the tunable Ti:sapphire laser from 700 to 950\,nm can be achieved. It has a maximum average output power of 5.6\,W at 800\,nm and the pulse width of 13.2\,ns, giving an optical conversion efficiency of 25.5{\%} from the 532\,nm pump laser to the Ti:sapphire laser.

Spectrum evolutions of spontaneous and pump-depleted stimulated Brillouin scatterings in liquid media

Gao Wei, Lü Zhi-Wei, He Wei-Ming, Hasi Wu-Li-Ji, Zhang Zan
Chin. Phys. B, 2008, 17 (10): 3765-3770 doi: 10.1088/1674-1056/17/10/039
Full Text: [PDF 213 KB] (Downloads:449)
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A theoretical model for calculating spontaneous and stimulated Brillouin scattering(SBS) spectra is described. An empirical formula for the Stokes output spectral linewidth, a function of spontaneous Brillouin linewidth and the exponential gain coefficient, is obtained by the calculated data fitting. The formula holds true for two cases involving pump undepletion and depletion. The lineshape change from spontaneous to highly pump-depleted SBS spectra is also investigated. The result shows that for the pump power below the SBS threshold, the Stokes output spectral lineshape evolves from Lorentzian to approximately Gaussian as the pump power increases. For the pump power near or beyond the threshold, the SBS spectrum is in the form of a steady Gaussian profile, and the spectral linewidth comes to a certain value about 7 times narrower than the spontaneous one. The theoretical results are experimentally demonstrated by using several common liquid media.

Temperature effect on dissipative holographicscreening-photovoltaic solitons in a biased dissipative system

Liu Shi-Xiong, Liu Jin-Song, Cai Xin, Fan Ting, Zhang Guang-Yong
Chin. Phys. B, 2008, 17 (10): 3771-3778 doi: 10.1088/1674-1056/17/10/040
Full Text: [PDF 1043 KB] (Downloads:440)
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In a biased dissipative photovoltaic--photorefractive system, this paper investigates the temperature effect on the evolution and the self-deflection of the dissipative holographic screening-photovoltaic (DHSP) solitons. The results reveal that, the evolution and the self-deflection of the bright and dark DHSP solitons are influenced by the system temperature. At a given temperature, for a stable DHSP soliton originally formed in the dissipative system, it attempts to evolve into another DHSP soliton when the temperature change is appropriately small, whereas it will become unstable or break down if the temperature departure is large enough. Moreover, the self-deflection degree of the solitary beam centre increases as temperature rises in some range, while it is decided by the system parameters and is slight under small-signal condition. The system temperature can be adjusted to change the formation and the self-deflection of the solitary beam in order to gain certain optical ends. In a word, the system temperature plays a role for the DHSP solitons in the dissipative system.

Analysis of the special hollow-core photonic crystal fibre by finite element method

Meng Jia, Hou Lan-Tian, Zhou Gui-Yao, Gao Fei, Yuan Jin-Hui, Wei Dong-Bin
Chin. Phys. B, 2008, 17 (10): 3779-3784 doi: 10.1088/1674-1056/17/10/041
Full Text: [PDF 3490 KB] (Downloads:524)
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Two kinds of fabricated hollow-core photonic crystal fibres (HC-PCFs) are studied using finite element method (FEM) because the structures of the fibres are special. Normalized transmission spectra and transverse intensity distribution of the modes are calculated and measured. And the dispersion characteristics of these two kinds of HC-PCFs were analysed from 400\,nm to 800\,nm. Simulated and measured results show that the special structure could affect the properties of HC-PCFs. By comparing the simulated values with the measured results, it can be clarified that FEM is feasible and accurate for analysing photonic crystal fibres whose structures are irregular and complex.

Finite-amplitude vibration of a bubble in water

Qian Zu-Wen, Xiao-Ling
Chin. Phys. B, 2008, 17 (10): 3785-3791 doi: 10.1088/1674-1056/17/10/042
Full Text: [PDF 1077 KB] (Downloads:502)
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The numerical results obtained by Rayleigh--Plesset (R-P) equation failed to agree with the experimental Mie scattering data of a bubble in water without inappropriately increasing the shear viscosity and decreasing the surface tension coefficient. In this paper, a new equation proposed by the present authors (Qian and Xiao) is solved. Numerical solutions obtained by using the symbolic computation program from both the R-P equation and the Qian-Xiao (Q-X) equation clearly demonstrate that Q-X equation yields best results matching the experimental data (in expansion phase). The numerical solutions of R-P equation also demonstrate the oscillation of a bubble in water depends strongly upon the surface tension and the shear viscosity coefficients as well as the amplitude of driving pressure, so that the uniqueness of the numerical solutions may be suspected if they are varied arbitrarily in order to fit the experimental data. If the bubble's vibration accompanies an energy loss such as the light radiation during the contract phase, the mechanism of the energy loss has to be taken into account. We suggest that by use of the bubble's vibration to investigate the state equations of aqueous solutions seem to be possible. We also believe that if one uses this equation instead of R-P equation to deal with the relevant problems such as the `phase diagrams for sonoluminescing bubbles', etc., some different results may be expected.
ATOMIC AND MOLECULAR PHYSICS

The differential interference angle of 2 [Case(a)]diatom on rotational energy transfer in NO(X2 ) collision with He, Ne and Ar system

Li Yong-Qing, Li Jian, Zhao Li-Na, Ni Yan-Qing, Ma Feng-Cai
Chin. Phys. B, 2008, 17 (10): 3649-3654 doi: 10.1088/1674-1056/17/10/020
Full Text: [PDF 230 KB] (Downloads:455)
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To study theoretically the relationship between the differential interference angle and the scattering angle in collisional quantum interference (CQI), we have investigated the differential interference angle of the atom--diatomic [case(a)] molecule system in detail. For the $^2{\it \Pi} $ electronic state in Hund's case (a), the degree of the differential interference is also discussed. The differential interference angles of NO($X{ }^2{\it \Pi})$ are calculated quantitatively for the rotational energy transfer in Hund's case (a) induced by collision with He, Ne and Ar atoms. The method to calculate the differential interference angle is presented. Several factors that affect the differential interference angle are investigated. Finally the variation of the differential interference angle with the impact parameter and relative velocity is discussed.

Studies on odd-parity states of the Sm atom

Guan Feng, Dai Chang-Jian, Zhao Hong-Ying
Chin. Phys. B, 2008, 17 (10): 3655-3661 doi: 10.1088/1674-1056/17/10/021
Full Text: [PDF 236 KB] (Downloads:479)
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Two-step excitation and ionization processes are used to detect Sm atoms in many excited states populated with tunable lasers. The wavelength of the first laser is tuned to the resonances from the Sm 4f$^{6 }$6s$^{2}$ ${}^7F_{J}$ ($J$=0--6) states to many odd-parity states with different electronic configurations, where the atoms are detected by photoionization process using an ultraviolet laser with a wavelength of 355\,nm. Precise measurements on the energy level and intensity for many Sm 4f$^{6}$ 6s6p and 4f$^{5}$5d6s$^{2}$ states have been carried out. In a theoretical analysis on the spectral data, such as peak position, relative intensity, many transitions can be identified as the resonances from the Sm 4f$^{6 }$6s$^2$ $^7F_{J }$ ($J$=0--6) states to the atomic states with 4f$^{6 }$6s6p and 4f$^{5}$5d6s$^{2}$ electronic configurations. This work also reports many spectral data on the odd-parity states that cannot be found in the literature.

Enhanced cooling of a V-type three-level atom in an optical cavity

Liu Li-Wei, Tan Lei, Ding Cai-Ying, Zhang Yu-Qing, Tan Wen-Ting
Chin. Phys. B, 2008, 17 (10): 3662-3667 doi: 10.1088/1674-1056/17/10/022
Full Text: [PDF 1052 KB] (Downloads:415)
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We have studied theoretically and numerically the enhanced cooling of a V-type three-level atom in a high-finesse optical cavity and shown that the cooling rate can be increased by one order of magnitude over that of a two-level atom, and the momentum amplitude tends to a stationary state much smaller than that of a two-level atom. We have further shown that the cooling rate can be significantly improved by using feedback and a time-dependent pump.

Multiphoton resonant ionization of hydrogen atom exposed to two-colour laser pulses

Wang Pei-Jie, Fang Yan
Chin. Phys. B, 2008, 17 (10): 3668-3671 doi: 10.1088/1674-1056/17/10/023
Full Text: [PDF 167 KB] (Downloads:448)
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This paper studies the multiphoton resonant ionization by two-colour laser pulses in the hydrogen atom by solving the time-dependent Schr\"odinger equation. By fixing the parameters of fundamental laser field and scanning the frequency of second laser field, it finds that the ionization probability shows several resonance peaks and is also much larger than the linear superposition of probabilities by applying two lasers separately. The enhancement of the ionization happens when the system is resonantly pumped to the excited states by absorbing two or more colour photons non-sequentially.

Deceleration of a continuous-wave (CW) molecular beam with a single quasi-CW semi-Gaussian laser beam

Yin Ya-Ling, Xia Yong, Yin Jian-Ping
Chin. Phys. B, 2008, 17 (10): 3672-3677 doi: 10.1088/1674-1056/17/10/024
Full Text: [PDF 764 KB] (Downloads:347)
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We propose a promising scheme to decelerate a CW molecular beam by using a red-detuned quasi-cw semi-Gaussian laser beam (SGB). We study the dynamical process of the deceleration for a CW deuterated ammonia (ND$_{3})$ molecular beam by Monte-Carlo simulation method. Our study shows that we can obtain a ND$_{3}$ molecular beam with a relative average kinetic energy loss of about 10{\%} and a relative output molecular number of more than 90{\%} by using a single quasi-cw SGB with a power of 1.5kW and a maximum optical well depth of 7.33mK.

Elastic collisions of sulfur and hydrogen in their ground states at low temperatures and spectroscopic parameters of SH(X2) radical

Shi De-Heng, Zhang Jin-Ping, Sun Jin-Feng, Liu Yu-Fang, Zhu Zun-Lüe, Ma Heng, Yang Xiang-Dong
Chin. Phys. B, 2008, 17 (10): 3678-3686 doi: 10.1088/1674-1056/17/10/025
Full Text: [PDF 233 KB] (Downloads:445)
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This paper constructs the interaction potential of the SH($X^{2}{\it \Pi})$ radical by using the coupled-cluster singles-doubles-approximate-triples theory combining the correlation-consistent quintuple basis set augmented with the diffuse functions, aug-cc-pV5Z, in the valence range. Employing the potential, it accurately determines the spectroscopic parameters. The present $D_{\e}$, $R_{\e}$, \textit{$\omega $}$_{\e}$, \textit{$\omega $}$_{\e}$\textit{$\chi $}$_{\e}$, \textit{$\alpha $}$_{\e}$ and $B_{\e}$ values are of 3.7767\,eV, 0.13424\,nm, 2699.846\,cm$^{ - 1}$, 47.7055\,cm$^{ - 1}$, 0.2639\,cm$^{ - 1}$ and 9.4414\,cm$^{ - 1}$, respectively, which are in excellent agreement with those obtained from the measurements. A total of 19 vibrational states has been found when $J$ = 0 by solving the radial Schr\"{o}dinger equation of nuclear motion. The complete vibrational levels, classical turning points, initial rotation and centrifugal distortion constants when $J$ = 0 are reported for the first time, which are in good accord with the experimental results. The total and various partial-wave cross sections are computed for the elastic collisions of sulfur and hydrogen in their ground states at low temperatures when two atoms approach each other along the SH($X^{2}{\it \Pi} )$ potential energy curve. Over the impact energy range from 1.0$\times $10$^{ - 11}$ to 1.0$\times $10$^{ - 4}$ a.u., eight shape resonances have been found in the total elastic cross sections. For each shape resonance, the resonant energy is accurately calculated. Careful investigations have pointed out that these resonances result from the $l$ = 0, 1, 2, 3, 4, 6, 7, 8 partial-wave contributions.

Equilibrium geometries and electronic properties of BenLi (n=2--15) clusters from first principles

Lei Xue-Ling, Zhu Heng-Jiang, Wang Xian-Ming, Luo You-Hua
Chin. Phys. B, 2008, 17 (10): 3687-3695 doi: 10.1088/1674-1056/17/10/026
Full Text: [PDF 2310 KB] (Downloads:506)
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This paper studies the equilibrium geometries and electronic properties of Be$_{n}$ and Be$_{n}$Li clusters, up to $n$=15, by using density-functional theory(DFT) at B3LYP/6--31G(d) level. The lowest-energy structures of Be$_{n}$ and Be$_{n}$Li clusters were determined. The results indicate that a single lithium impurity enhances the stability and chemical reactivity of the beryllium clusters. It finds that the geometries of the host clusters change significantly after the addition of the lithium atom for $n \ge $8. The lithium impurity prefers to be on the periphery of beryllium clusters, and occupies vertex sites. Both Be$_{4}$Li, Be$_{9}$Li, and Be$_{13}$Li were found to be particularly stable with higher average binding energy, local peaks of second-order energy difference and fragmentation energies. For all the Be$_{n}$Li clusters studied, we found charge transfers from the Li to Be site and co-existence of covalent and metallic bonding characteristics.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Time-domain analytic solutions of two-wire transmission line excited by a plane-wave field

Ni Gu-Yan, Yan Li, Yuan Nai-Chang
Chin. Phys. B, 2008, 17 (10): 3629-3634 doi: 10.1088/1674-1056/17/10/016
Full Text: [PDF 317 KB] (Downloads:572)
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This paper reports that an analytic method is used to calculate the load responses of the two-wire transmission line excited by a plane-wave directly in the time domain. By the frequency-domain Baum--Liu--Tesche (BLT) equation, the time-domain analytic solutions are obtained and expressed in an infinite geometric series. Moreover, it is shown that there exist only finite nonzero terms in the infinite geometric series if the time variate is at a finite interval. In other word, the time-domain analytic solutions are expanded in a finite geometric series indeed if the time variate is at a finite interval. The computed results are subsequently compared with transient responses obtained by using the frequency-domain BLT equation via a fast Fourier transform, and the agreement is excellent.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Mode coupling in nonlinear Kelvin--Helmholtz instability

Wang Li-Feng, Ye Wen-Hua, Li Ying-Jun, Meng Li-Min
Chin. Phys. B, 2008, 17 (10): 3792-3798 doi: 10.1088/1674-1056/17/10/043
Full Text: [PDF 1806 KB] (Downloads:488)
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This paper investigates the interaction of a small number of modes in the two-fluid Kelvin--Helmholtz instability at the nonlinear regime by using a two-dimensional hydrodynamic code. This interaction is found to be relatively long range in wave-number space and also it acts in both directions, i.e.~short wavelengths affect long wavelengths and vice versa. There is no simple equivalent transformation from a band of similar modes to one mode representing their effective amplitude. Three distinct stages of interaction have been identified.

High and low frequency relaxation oscillations in a capacitive discharge plasma

Zhou Zhu-Wen, Sungjin Kim, Ji Shi-Yin, Sun Guang-Yu, Deng Ming-Sen
Chin. Phys. B, 2008, 17 (10): 3799-3806 doi: 10.1088/1674-1056/17/10/044
Full Text: [PDF 762 KB] (Downloads:420)
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Both high and low frequency relaxation oscillations have been observed in an argon capacitive discharge connected to a peripheral grounded chamber through a slot with dielectric spacers. The oscillations, observed from time-varying optical emission of the main discharge chamber, show, for example, a high frequency (46\,kHz) relaxation oscillation at 100\,mTorr, with an absorbed power near the peripheral breakdown, and a low frequency (2.7--3.7\,Hz) oscillation, at a higher absorbed power. The high frequency oscillation is found to ignite a plasma in the slot, but usually not in the periphery. The high frequency oscillation is interpreted by using an electromagnetic model of the slot impedance, combined with the circuit analysis of the system including a matching network. The model is further developed by using a parallel connection of variable peripheral capacitance to analyse the low frequency oscillation. The results obtained from the model are in agreement with the experimental observations and indicate that a variety of behaviours are dependent on the matching conditions.

Comparative research on three types of coaxial slow wave structures

Xiao Ren-Zhen, Liu Guo-Zhi, Chen Chang-Hua
Chin. Phys. B, 2008, 17 (10): 3807-3811 doi: 10.1088/1674-1056/17/10/045
Full Text: [PDF 2410 KB] (Downloads:468)
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This paper studies three types of coaxial slow wave structures (SWSs): (1) with ripples on both the inner and outer conductors; (2) with ripples on the outer conductor and smooth on the inner one; and (3) with ripples on the inner conductor and smooth on the outer one. The frequencies, coupling impedances, time growth rates and beam-wave interaction efficiencies of the three types of coaxial SWSs are obtained by theoretical analysis. Moreover, the relativistic Cerenkov generators (RCGs) with the three types of coaxial SWSs are simulated with a fully electromagnetic particle-in-cell code, and the results verify the theoretical analysis. It is proved that the RCG with double-rippled coaxial SWS has the highest conversion efficiency and the shortest starting time.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Bridge density functional approximation for non-uniform hard core repulsive Yukawa fluid

Zhou Shi-Qi
Chin. Phys. B, 2008, 17 (10): 3812-3821 doi: 10.1088/1674-1056/17/10/046
Full Text: [PDF 1119 KB] (Downloads:530)
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In this work, a bridge density functional approximation (BDFA) (\wx{J. Chem. Phys.} 112, 8079 (2000)) for a non-uniform hard-sphere fluid is extended to a non-uniform hard-core repulsive Yukawa (HCRY) fluid. It is found that the choice of a bulk bridge functional approximation is crucial for both a uniform HCRY fluid and a non-uniform HCRY fluid. A new bridge functional approximation is proposed, which can accurately predict the radial distribution function of the bulk HCRY fluid. With the new bridge functional approximation and its associated bulk second order direct correlation function as input, the BDFA can be used to well calculate the density profile of the HCRY fluid subjected to the influence of varying external fields, and the theoretical predictions are in good agreement with the corresponding simulation data. The calculated results indicate that the present BDFA captures quantitatively the phenomena such as the coexistence of solid-like high density phase and low density gas phase, and the adsorption properties of the HCRY fluid, which qualitatively differ from those of the fluids combining both hard-core repulsion and an attractive tail.

The effect of annealing temperature and film thickness on the phase of pentacene on the p+-Si substrate

Yuan Guang-Cai, Xu Zheng, Zhao Su-Ling, Zhang Fu-Jun, Huang Jin-Zhao, Huang Jin-Ying, Tian Xue-Yan, Xu Xu-Rong
Chin. Phys. B, 2008, 17 (10): 3822-3826 doi: 10.1088/1674-1056/17/10/047
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This paper investigates the morphology and crystallization properties of the two crystalline phases of pentacene grown by thermal evaporation on p$^+$-Si substrates at room temperature by the methods of atomic force microscopy and x-ray diffraction. This kind of substrate induces a thin film phase and a triclinic phase which are formed directly onto p$^+$-Si substrates and constitute a layer consisting of faceted grains with a step height between terraces of 15.8\,{\AA} (1\,\AA=0.1\,nm) and 14.9\,{\AA}, respectively. Above the critical thickness of the thin film phase, lamellar structures are found with an increasing fraction with the increase of the film thickness. When the film thickness is fixed, the fraction of lamellar structures increases with the increase of annealing temperature. These lamellar structures are identified as the second phase with a interplanar distance of 14.9\,{\AA} corresponding to the pentacene triclinic phase. Furthermore, the thin film phase consisting of several micrometre sized uniformly oriented grains at an annealing temperature of less than 80${^\circ}$C and a deposition rate of 0.6\,{\AA}/s is observed.

Formation and photoluminescence properties of boron nanocones

Wang Xing-Jun, Tian Ji-Fa, Bao Li-Hong, Yang Tian-Zhong, Hui Chao, Liu Fei, Shen Cheng-Min, Xu Ning-Sheng, Gao Hong-Jun
Chin. Phys. B, 2008, 17 (10): 3827-3835 doi: 10.1088/1674-1056/17/10/048
Full Text: [PDF 15091 KB] (Downloads:509)
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This paper reports that a simple chemical vapour deposition method has been adopted to fabricate large scale, high density boron nanocones with thermal evaporation of B/B$_{2}$O$_{3}$ powders precursors in an Ar/H$_{2}$ gas mixture at the synthesis temperature of 1000--1200$^{\circ}$C. The lengths of boron nanocones are several micrometres, and the diameters of nanocone tops are in a range of 50--100\,nm. transmission electron microscopy and selected area electron diffraction indicate that the nanocones are single crystalline $\alpha $-tetragonal boron. The vapour--liquid--solid mechanism is the main formation mechanism of boron nanocones. One broad photoluminescence emission peak at the central wavelength of about 650 nm is observed under the 532 nm light excitation. Boron nanocones with good photoluminescence properties are promising candidates for applications in optical emitting devices.

Study of He-induced nano-cavities as sinks of oxygen for forming silicon-on-insulator

Li Bing-Sheng, Zhang Chong-Hong, Hao Xiao-Peng, Wang Dan-Ni, Zhou Li-Hong, Zhang Hong-Hua, Yang Yi-Tao, Zhang Li-Qing
Chin. Phys. B, 2008, 17 (10): 3836-3840 doi: 10.1088/1674-1056/17/10/049
Full Text: [PDF 449 KB] (Downloads:438)
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In the present work, a Cz--Silicon wafer is implanted with helium ions to produce a buried porous layer, and then thermally annealed in a dry oxygen atmosphere to make oxygen transport into the cavities. The formation of the buried oxide layer in the case of internal oxidation (ITOX) of the buried porous layer of cavities in the silicon sample is studied by positron beam annihilation (PBA). The cavities are formed by 15\,keV He implantation at a fluence of $2\ti 10^{16}$\,cm$^{ - 2}$ and followed by thermal annealing at 673\,K for 30 min in vacuum. The internal oxidation is carried out at temperatures ranging from 1073 to 1473\,K for 2\,h in a dry oxygen atmosphere. The layered structures evolved in the silicon are detected by using the PBA and the thicknesses of their layers and nature are also investigated. It is found that rather high temperatures must be chosen to establish a sufficient flux of oxygen into the cavity layer. On the other hand high temperatures lead to coarsening the cavities and removing the cavity layer finally.

Bright and dark small amplitude nonlinear localized modes in a quantum one-dimensional Klein--Gordon chain

Liu Yang, Tang Yi
Chin. Phys. B, 2008, 17 (10): 3841-3846 doi: 10.1088/1674-1056/17/10/050
Full Text: [PDF 169 KB] (Downloads:521)
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By means of the Glauber's coherent state method combined with multiple-scale method, this paper investigates the localized modes in a quantum one-dimensional Klein--Gordon chain and finds that the equation of motion of annihilation operator is reduced to the nonlinear Schr\"{o}dinger equation. Interestingly, the model can support both bright and dark small amplitude travelling and non-travelling nonlinear localized modes in different parameter spaces.

Numerical investigation of the deformation mechanism of a bubble or a drop rising or falling in another fluid

Wang Han, Zhang Zhen-Yu, Yang Yong-Ming, Hu Yüe, Zhang Hui-Sheng
Chin. Phys. B, 2008, 17 (10): 3847-3855 doi: 10.1088/1674-1056/17/10/051
Full Text: [PDF 304 KB] (Downloads:527)
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A numerical method for simulating the motion and deformation of an axisymmetric bubble or drop rising or falling in another infinite and initially stationary fluid is developed based on the volume of fluid (VOF) method in the frame of two incompressible and immiscible viscous fluids under the action of gravity, taking into consideration of surface tension effects. A comparison of the numerical results by this method with those by other works indicates the validity of the method. In the frame of inviscid and incompressible fluids without taking into consideration of surface tension effects, the mechanisms of the generation of the liquid jet and the transition from spherical shape to toroidal shape during the bubble or drop deformation, the increase of the ring diameter of the toroidal bubble or drop and the decrease of its cross-section area during its motion, and the effects of the density ratio of the two fluids on the deformation of the bubble or drop are analysed both theoretically and numerically.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Characterization of Ag adsorption on TiC(001) substrate: an ab initio study

Ma Shang-Yi, Wang Shao-Qing
Chin. Phys. B, 2008, 17 (10): 3856-3866 doi: 10.1088/1674-1056/17/10/052
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Ag adsorptions at 0.25--3 monolayer (ML) coverage on a perfect TiC(001) surface and at 0.25\,ML coverage on C vacancy are separately investigated by using the pseudopotential-based density functional theory. The preferential adsorption sites and the adsorption-induced modifications of electronic structures of both the substrate and adsorbate are analysed. Through the analyses of adsorption energy, ideal work of separation, interface distance, projected local density of states, and the difference electron density, the characteristic evolution of the adatom-surface bonding as a function of the amount of deposited silver is studied. The nature of the Ag/TiC bonding changes as the coverage increases from 0.25 to 3\,MLs. Unlike physisorption in an Ag/MgO system, polar covalent component contributes to the Ag/TiC interfacial adhesion in most cases, however, for the case of 1--3\,ML coverage, an additional electrostatic interaction between the absorption layer and the substrate should be taken into account. The value of ideal work of separation, 1.55\,J/m$^{2}$, for a 3-ML-thick adlayer accords well with other calculations. The calculations predict that Ag does not wet TiC(001) surface and prefers a three-dimensional growth mode in the absence of kinetic factor. This work reports on a clear site and coverage dependence of the measurable physical parameters, which would benefit the understanding of Ag/TiC(001) interface and the analysis of experimental data.

First-principles calculations for electronic, optical and thermodynamic properties of ZnS

Hu Cui-E, Zeng Zhao-Yi, Cheng Yan, Chen Xiang-Rong, Cai Ling-Cang
Chin. Phys. B, 2008, 17 (10): 3867-3874 doi: 10.1088/1674-1056/17/10/053
Full Text: [PDF 286 KB] (Downloads:1049)
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The electronic, optical and thermodynamic properties of ZnS in the zinc-blende (ZB) and wurtzite (WZ) structures are investigated by using the plane-wave pseudopotential density functional theory (DFT). The results obtained are consistent with other theoretical results and the available experimental data. When the pressures are above 20.5 and 27\,GPa, the ZB-ZnS and the WZ-ZnS are converted into indirect gap semiconductors, respectively. The critical point structure of the frequency-dependent complex dielectric function is investigated and analysed to identify the optical transitions. Moreover, the values of heat capacity $C_{V}$ and Debye temperature {$\Th$} at different pressures and different temperatures are also obtained successfully.

Electrical characteristics and optoelectronic properties of metal--semiconductor--metal structure with zinc oxide nanowires across Au electrodes

Wang Ding-Qu, Zhou Zhao-Ying, Zhu Rong, Ye Xiong-Ying
Chin. Phys. B, 2008, 17 (10): 3875-3879 doi: 10.1088/1674-1056/17/10/054
Full Text: [PDF 930 KB] (Downloads:734)
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This paper reports on a method of assembling semiconducting ZnO nanowires onto a pair of Au electrodes to construct a metal--semiconductor--metal (MSM) structure by dielectrophoresis and studying on its electrical characteristics by using current-voltage ($I-V$) measurements. An electronic model with two back to back Schottky diodes in series with a semiconductor of nanowires was established to study the electrical transport of the MSM structures. By fitting the measured $I-V$ characteristics using the proposed model, the parameters of the Schottky contacts and the resistance of nanowires could be acquired. The photoelectric properties of the MSM structures were also investigated by analysing the measurements of the electrical transports under various light intensities. The deduced results demonstrate that ZnO nanowires and their Schottky contacts with Au electrodes both contribute to photosensitivity and the MSM structures with ZnO nanowires are potentially applicable for photonic devices.

Surface plasmon polariton and mode transformation in a nanoscale lossy metallic cylindrical cable

Yang Peng-Fei, Gu Ying, Gong Qi-Huang
Chin. Phys. B, 2008, 17 (10): 3880-3893 doi: 10.1088/1674-1056/17/10/055
Full Text: [PDF 2894 KB] (Downloads:645)
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A theoretical investigation on the surface plasmon polariton in a gold cylindrical nanocable is presented. By solving a complete set of Maxwell's equations in the nanocable (with a $50$\,nm radius gold nanocore, 10--300\,nm silica layer, and 30--200\,nm gold nanocladding), the dispersion relations on the optical frequency and on the silica thickness are discussed. When the silica thickness varies from $50$ to $250$\,nm, at a fixed wavelength, the strong coupling between the gold nanocore and the nanocladding leads to a symmetric-like surface mode and an antisymmetric-like surface mode in the nanocable. The transformation between the surface mode and the waveguide mode in this structure is also investigated. The results will be helpful for understanding the surface waves in the subwavelength structures.

Magnon energy gap in a four-layer ferromagnetic superlattice

Qiu Rong-Ke, Song Pan-Pan, Zhang Zhi-Dong, Guo Lian-Quan
Chin. Phys. B, 2008, 17 (10): 3894-3901 doi: 10.1088/1674-1056/17/10/056
Full Text: [PDF 427 KB] (Downloads:498)
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The magnon energy band in a four-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green's function technique. It is found that three modulated energy gaps exist in the magnon energy band along $K_{x }$ direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the three energy gaps. The magnon energy gaps of the four-layer ferromagnetic superlattice are different from those of the three-layer one. For the four-layer ferromagnetic superlattice, the disappearance of the magnon energy gaps $\Delta \omega _{12} $, $\Delta \omega _{23} $ and $\Delta \omega _{34} $ all correlates with the symmetry of this system. The zero energy gap $\Delta \omega _{23}$ correlates with the symmetry of interlayer exchange couplings, while the vanishing of the magnon energy gaps $\Delta \omega _{12} $ and $\Delta \omega _{34} $ corresponds to a translational symmetry of $x$-direction in the lattice. When the parameters of the system deviate from these symmetries, the three energy gaps will increase.

Growth of Mn5Ge3 ultrathin film on Ge(111)

Chen Li-Jun, Wang De-Yong, Zhan Qing-Feng, He Wei, Li Qing-An, Cheng Zhao-Hua
Chin. Phys. B, 2008, 17 (10): 3902-3906 doi: 10.1088/1674-1056/17/10/057
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The growth of Mn$_{5}$Ge$_{3}$ ultrathin films with different thicknesses, prepared by solid phase epitaxy, is studied. The results of scanning tunnelling microscopy and low energy electron diffraction studies show that the film can be formed and it is terminated with a ($\sqrt 3\times \sqrt 3$) R$30^\circ$ surface reconstruction when the thickness of Mn exceeds 3 monolayers. The magnetic properties show that the Curie temperature is about 300\,K and the $T^{2}$-dependent behaviour is observed to remain up to 220\,K.

Magnetic properties of soft layer/FePt--MgO exchange coupled composite perpendicular recording media

Yin Jin-Hua, Takao Suzuki, Pan Li-Qing
Chin. Phys. B, 2008, 17 (10): 3907-3909 doi: 10.1088/1674-1056/17/10/058
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The magnetic properties of exchange coupled composite (ECC) media that are composed of perpendicular magnetic recording media FePt--MgO and two kinds of soft layers have been studied by using an x-ray diffractometer, a polar Kerr magneto-optical system (PMOKE) and a vibrating sample magnetometer (VSM). The results show that ECC media can reduce the coercivities of perpendicular magnetic recording media FePt--MgO. The ECC media with granular-type soft layers have weaker exchange couplings between magnetic grains and the magnetization process, for ECC media of this kind mainly follow the Stoner--Wohlfarth model.

Multiferroic behaviour of epitaxial NiFe2O4--BaTiO3 heterostructures

Zhang Yi, Deng Chao-Yong, Ma Jing, Lin Yuan-Hua, Nan Ce-Wen
Chin. Phys. B, 2008, 17 (10): 3910-3916 doi: 10.1088/1674-1056/17/10/059
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Multiferroic NiFe2O4--BaTiO3 (BTO) bilayered thin films are epitaxially grown on (001) Nb-doped SrTiO$_{3}$ (STO) substrates by pulsed-laser deposition (PLD). Different growth sequences of NFO and BTO on the substrate yield two kinds of epitaxial heterostructures with (001)-orientation, i.e. (001)-NFO/(001)-BTO/substrate and (001)-BTO/(001)-NFO/substrate. Microstructure studies from x-ray diffraction (XRD) and electron microscopies show differences between these two heterostructures, which result in different multiferroic behaviours. The heterostructured composite films exhibit good coexistence of both ferroelectric and ferromagnetic properties, in particular, obvious magnetoelectric (ME) effect on coupling response.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Effect of pressure grads on convection in inner core of type II supernova

Luo Zhi-Quan, Liu Men-Quan
Chin. Phys. B, 2008, 17 (10): 3917-3921 doi: 10.1088/1674-1056/17/10/060
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By adjusting the pressure grads in the stage of formation of the shock wave, a successful prompt explosion process has been numerically simulated through a progenitor model of 15Msolar, in which the effects of pressure grads on various convections, including the Rayleigh--Taloy (R-T) convection, the lepton driven convection and the negative entropy grads driven convection, in an inner core are analysed. The simulation results show that the increase of the pressure grads in the inner core region may cause a powerful convection, which causes energy transfer from the inner core to the shock wave rapidly and efficiently.
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