Chin. Phys. B
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CN 11-5639/O4
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Chin. Phys. B  
  Chin. Phys. B--2008, Vol.17, No.1
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GENERAL

A new supersymmetric classical Boussinesq equation

Zhang Meng-Xia, Liu Qing-Ping, Wang Juan, Wu Ke
Chin. Phys. B, 2008, 17 (1): 10-16 doi: 10.1088/1674-1056/17/1/002
Full Text: [PDF 122 KB] (Downloads:901)
Show Abstract
In this paper, we obtain a supersymmetric generalization for the classical Boussinesq equation. We show that the supersymmetric equation system passes the Painlev\'{e test and we also calculate its one- and two-soliton solutions.

Structure equation and Mei conserved quantity for Mei symmetry of Appell equation

Jia Li-Qun, Xie Jia-Fang, Zheng Shi-Wang
Chin. Phys. B, 2008, 17 (1): 17-22 doi: 10.1088/1674-1056/17/1/003
Full Text: [PDF 114 KB] (Downloads:798)
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This paper investigates structure equation and Mei conserved quantity of Mei symmetry of Appell equations for non-Chetaev nonholonomic systems. Appell equations and differential equations of motion for non-Chetaev nonholonomic mechanical systems are established. A new expression of the total derivative of the function with respect to time $t$ along the trajectory of a curve of the system is obtained, the definition and the criterion of Mei symmetry of Appell equations under the infinitesimal transformations of groups are also given. The expressions of the structure equation and the Mei conserved quantity of Mei symmetry in the Appell function are obtained. An example is given to illustrate the application of the results.

The density wave in a new anisotropic continuum model

Ge Hong-Xia, Dai Shi-Qiang, Dong Li-Yun
Chin. Phys. B, 2008, 17 (1): 23-26 doi: 10.1088/1674-1056/17/1/004
Full Text: [PDF 103 KB] (Downloads:527)
Show Abstract
In this paper the new continuum traffic flow model proposed by Jiang {\it et al is developed based on an improved car-following model, in which the speed gradient term replaces the density gradient term in the equation of motion. It overcomes the wrong-way travel which exists in many high-order continuum models. Based on the continuum version of car-following model, the condition for stable traffic flow is derived. Nonlinear analysis shows that the density fluctuation in traffic flow induces a variety of density waves. Near the onset of instability, a small disturbance could lead to solitons determined by the Korteweg--de-Vries (KdV) equation, and the soliton solution is derived.

Remote preparation of an entangled two-qubit state with three parties

Dai Hong-Yi, Chen Ping-Xing, Zhang Ming, Li Cheng-Zu
Chin. Phys. B, 2008, 17 (1): 27-33 doi: 10.1088/1674-1056/17/1/005
Full Text: [PDF 136 KB] (Downloads:777)
Show Abstract
We present a scheme for probabilistic remote preparation of an entangled two-qubit state with three parties from a sender to either of two receivers. The quantum channel is composed of a partially entangled two-qubit state and a partially entangled three-qubit state. We calculate the successful total probabilities of the scheme in general and particular cases, respectively. We also calculate total classical communication cost in a general case and two particular cases, respectively.

A quantum dense coding implementation in an ion trap

Pan Chang-Ning, Fang Mao-Fa
Chin. Phys. B, 2008, 17 (1): 34-37 doi: 10.1088/1674-1056/17/1/006
Full Text: [PDF 94 KB] (Downloads:413)
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This paper reports that a quantum dense coding can be implemented with ions confined in a linear trap and interacting with laser beams. The scheme is insensitive to the interaction between the quantum channel and the environment. The Bell-state measurement is not involved and the probability of success in our scheme is $1.0$.

Berry phase in a generalized nonlinear two-level system

Liu Ji-Bing, Li Jia-Hua, Song Pei-Jun, Li Wei-Bin
Chin. Phys. B, 2008, 17 (1): 38-42 doi: 10.1088/1674-1056/17/1/007
Full Text: [PDF 138 KB] (Downloads:531)
Show Abstract
In this paper, we investigate the behaviour of the geometric phase of a more generalized nonlinear system composed of an effective two-level system interacting with a single-mode quantized cavity field. Both the field nonlinearity and the atom--field coupling nonlinearity are considered. We find that the geometric phase depends on whether the index $k$ is an odd number or an even number in the resonant case. In addition, we also find that the geometric phase may be easily observed when the field nonlinearity is not considered. The fractional statistical phenomenon appears in this system if the strong nonlinear atom--field coupling is considered. We have also investigated the geometric phase of an effective two-level system interacting with a two-mode quantized cavity field.

Cluster-state preparation in thermal cavities without single-qubit operation

Zhang Xiao-Long, Feng Mang, Gao Ke-Lin
Chin. Phys. B, 2008, 17 (1): 43-48 doi: 10.1088/1674-1056/17/1/008
Full Text: [PDF 138 KB] (Downloads:521)
Show Abstract
A potential scheme is proposed for generating cluster states of many atoms in cavity quantum electradynamics (QED), in which an unorthodox encoding is employed with the ground state being qubit $\left\vert 0\right\rangle $ while two closely spaced upper states being qubit $\left\vert 1\right\rangle $. Throughout the scheme the cavities can be in thermal states but are only virtually excited. We show how to create the cluster states by performing a two-step but no single-qubit operation. Discussion is also carried out on the experimental feasibility of our scheme.

Cavity loss induced generation of W states

Wu Huai-Zhi, Yang Zhen-Biao, Su Wan-Jun, Zhong Zhi-Rong, Zheng Shi-Biao
Chin. Phys. B, 2008, 17 (1): 49-54 doi: 10.1088/1674-1056/17/1/009
Full Text: [PDF 1162 KB] (Downloads:452)
Show Abstract
The existence of decoherence-free subspace (DFS) has been discussed widely. In this paper, we propose an alternative scheme for generating the four-atom $W$ states by manipulating DF qubits. The atoms are divided into two pairs and trapped in two separate optical cavities. Manipulation of atoms within DFS may generate a two-atom maximally entangled state in an individual cavity, which is a stable state. After driving the system out of DFS, the atoms will interact resonantly with the cavity field. The photons leaking from the cavities interfere at the beamsplitter, which destroys which-path information, and are finally detected by one of the detectors, leading to the generation of a $W$ state. In addition, the numerical simulation indicates that the fidelity of the prepared state can, for a very wide parameter regime, be very close to unity.

Scheme for teleportation of an unknown atomic state via a cluster state in cavity QED

Cao Zhuo-Liang, Li Da-Chuang
Chin. Phys. B, 2008, 17 (1): 55-59 doi: 10.1088/1674-1056/17/1/010
Full Text: [PDF 108 KB] (Downloads:539)
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This paper proposes an experimentally feasible scheme for teleportation of an unknown two-atom entangled state, where a cluster state is used as the quantum channel. This scheme does not need any joint measurement. In addition, the successful probability and fidelity of teleportation can both reach 1.0. The current scheme can be realized within the current experimental technology.

Total teleportation of zero- and one-photon entangled states in running waves

W. B. Cardoso, A. T. Avelar, B.Baseia, N. G. de Almeida
Chin. Phys. B, 2008, 17 (1): 60-63 doi: 10.1088/1674-1056/17/1/011
Full Text: [PDF 169 KB] (Downloads:439)
Show Abstract
Inspired by a recent paper [2002 {\it J. Opt. B {\bf 4 316] we present an alternative scheme to teleport an entanglement of zero- and one-photon states of a running-wave field. The scheme employs only linear optical elements plus single-photon sources and detectors.

Generation of multiple-particle cluster state via cavity QED

Lin Gong-Wei, Lin Xiu-Min, Chen Li-Bo, Du Qian-Hua, Chen Zhi-Hua
Chin. Phys. B, 2008, 17 (1): 64-69 doi: 10.1088/1674-1056/17/1/012
Full Text: [PDF 330 KB] (Downloads:1086)
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This paper proposes schemes for generating multiple-photon and multiple-atom cluster states, respectively. The schemes are based on the cavity input--output process and atomic or photonic states measurement, and the successful probabilities approach unity in the ideal case. The numerical simulations show that the produced multiple-particle cluster states have high fidelity even if the Lamb--Dicke condition is not satisfied. Some practical imperfections, such as atomic spontaneous emission and output coupling inefficiency, only decrease the success probability but exert no influence on the fidelity of generated multiple-particle cluster states. From the experimental point of view, smaller operation number and lack of need for individual addressing keeps the schemes easy to implement. These schemes may offer a promising approach to the generation of a large-scale cluster state.

Extra dimensions and atomic transition frequencies

Li Zhi-Gang, Ni Wei-Tou, Antonio Pulido Patón
Chin. Phys. B, 2008, 17 (1): 70-75 doi: 10.1088/1674-1056/17/1/013
Full Text: [PDF 137 KB] (Downloads:375)
Show Abstract
New unification theories predict large extra dimensions (LEDs). If that is the case, gravity would be stronger at short ranges than what Newtonian gravity predicts. LEDs could also have effects at atomic level. In this paper we propose a new method to constrain the size of `gravity-only' LEDs by analysing how these LEDs modify the energy of the atomic transitions 1s--2s and 2s--2p (Lamb shift), in the particular case of the hydrogen and muonium atoms. We estimate these effects by using Bethe's non-relativistic treatment of Lamb shift. In the particular case of three LEDs, which may be a candidate to explain the interaction mechanism of dark matter particles, we have found that current knowledge in atomic spectroscopy could constrain their sizes to less than 10\,$\mu$m. Although our contributions do not reach the sensitivity given by SN1987a, they are still slightly better than recent constraints given by Inverse Square Law tests of the E\"{o}t--Wash group at Washington University, which gave $R_{3} < 36.6\,\mu$m.

Effects of correlations between the real and imaginary parts of quantum noise on intensity fluctuation for a saturation laser model

Li Yue-Hong, Mei Dong-Cheng
Chin. Phys. B, 2008, 17 (1): 76-79 doi: 10.1088/1674-1056/17/1/014
Full Text: [PDF 223 KB] (Downloads:456)
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This paper studies the effects of cross-correlations between the real and imaginary parts of quantum noise on the laser intensity in a saturation laser model. It derives the analytic expressions of the intensity correlation function ${C(\tau)}$ and the associated relaxation time ${T({C})}$ in the case of a stable locked phase resulting from the cross-correlation ${\lambda_q}$ between the real and imaginary parts of quantum noise. Based on numerical computations it finds that the presence of cross correlations between the real and imaginary parts of quantum noise slow down the decay of intensity fluctuation, i.e., it causes the increase of intensity fluctuation.

Complete synchronization of uncertain chaotic dynamical network via a simple adaptive control

Xiao Yu-Zhu, Xu Wei, Li Xiu-Chun, Tang Su-Fang
Chin. Phys. B, 2008, 17 (1): 80-86 doi: 10.1088/1674-1056/17/1/015
Full Text: [PDF 513 KB] (Downloads:627)
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In this paper, based on the invariance principle of differential equations, we propose a simple adaptive control method to synchronize the network with coupling of the general form. Comparing with other control approaches, this scheme only depends on each node's state output. So we need not to know the concrete network structure and the solutions of the isolate nodes of the network in advance. In order to demonstrate the effectiveness of the method, a special example is provided and numerical simulations are performed. The numerical results show that our control scheme is very effective and robust against the weak noise.

Design of output feedback controller for a unified chaotic system

Li Wen-Lin, Chen Xiu-Qin, Shen Zhi-Ping
Chin. Phys. B, 2008, 17 (1): 87-91 doi: 10.1088/1674-1056/17/1/016
Full Text: [PDF 199 KB] (Downloads:526)
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In this paper, the synchronization of a unified chaotic system is investigated by the use of output feedback controllers; a two-input single-output feedback controller and single-input single-output feedback controller are presented to synchronize the unified chaotic system when the states are not all measurable. Compared with the existing results, the controllers designed in this paper have some advantages such as small feedback gain, simple structure and less conservation. Finally, numerical simulations results are provided to demonstrate the validity and effectiveness of the proposed method.

Passive adaptive control of chaos in synchronous reluctance motor

Wei Du-Qu, Luo Xiao-Shu
Chin. Phys. B, 2008, 17 (1): 92-97 doi: 10.1088/1674-1056/17/1/017
Full Text: [PDF 166 KB] (Downloads:667)
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The performance of synchronous reluctance motor (SynRM) degrades due to chaos when its systemic parameters fall into a certain area. To control the undesirable chaos in SynRM, a passive control law is presented in this paper, which transforms the chaotic SynRM into an equivalent passive system. It is proved that the equivalent system can be asymptotically stabilized at the set equilibrium point, namely, chaos in SynRM can be controlled. Moreover, in order to eliminate the influence of undeterministic parameters, an adaptive law is introduced into the designed controller. Computer simulation results show that the proposed controller is very effective and robust against the uncertainties in systemic parameters. The present study may help to maintain the secure operation of industrial servo drive system.

A function cascade synchronization method with unknown parameters and applications

An Hong-Li, Chen Yong
Chin. Phys. B, 2008, 17 (1): 98-104 doi: 10.1088/1674-1056/17/1/018
Full Text: [PDF 761 KB] (Downloads:464)
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This paper investigates the function cascade synchronization of chaos system. Combining cascade synchronization scheme, parametric adaptive control and projective synchronization scheme, it proposes a new function cascade synchronization scheme to address a generalized-type synchronization problem of three famous chaotic systems: the Lorenz system, Liu system and R\"{o}ssler system, the states of two identical chaotic systems with unknown parameters can be asymptotically synchronized by choosing different special suitable error functions. Numerical simulations are used to verify the effectiveness of the proposed synchronization techniques.

Hybrid control of bifurcation and chaos in stroboscopic model of Internet congestion control system

Ding Da-Wei, Zhu Jie, Luo Xiao-Shu
Chin. Phys. B, 2008, 17 (1): 105-110 doi: 10.1088/1674-1056/17/1/019
Full Text: [PDF 212 KB] (Downloads:655)
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Interaction between transmission control protocol (TCP) and random early detection (RED) gateway in the Internet congestion control system has been modelled as a discrete-time dynamic system which exhibits complex bifurcating and chaotic behaviours. In this paper, a hybrid control strategy using both state feedback and parameter perturbation is employed to control the bifurcation and stabilize the chaotic orbits embedded in this discrete-time dynamic system of TCP/RED. Theoretical analysis and numerical simulations show that the bifurcation is delayed and the chaotic orbits are stabilized to a fixed point, which reliably achieves a stable average queue size in an extended range of parameters and even completely eliminates the chaotic behaviour in a particular range of parameters. Therefore it is possible to decrease the sensitivity of RED to parameters. By using the hybrid strategy, we may improve the stability and performance of TCP/RED congestion control system significantly.

Controlling chaos in RCL-shunted Josephson junction by delayed linear feedback

Feng Yu-Ling, Shen Ke
Chin. Phys. B, 2008, 17 (1): 111-116 doi: 10.1088/1674-1056/17/1/020
Full Text: [PDF 736 KB] (Downloads:1375)
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The resistively--capacitively--inductively-shunted (RCL-shunted) Josephson junction (RCLSJJ) shows chaotic behaviour under some parameter conditions. Here a scheme for controlling chaos in the RCLSJJ is presented based on the linear feedback theory. Numerical simulations show that this scheme can be effectively used to control chaotic states in this junction into stable periodic states. Moreover, the different stable period states with different period numbers can be obtained by appropriately adjusting the feedback intensity and delay time without any pre-knowledge of this system required.

New bifurcations of basin boundaries involving Wada and a smooth Wada basin boundary

Zou Hai-Lin, Xu Jian-Xue, Jiang Jun
Chin. Phys. B, 2008, 17 (1): 117-124 doi: 10.1088/1674-1056/17/1/021
Full Text: [PDF 1128 KB] (Downloads:466)
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This paper demonstrates and analyses double heteroclinic tangency in a three-well potential model, which can produce three new types of bifurcations of basin boundaries including from smooth to Wada basin boundaries, from fractal to Wada basin boundaries in which no changes of accessible periodic orbits happen, and from Wada to Wada basin boundaries. In a model of mechanical oscillator, it shows that a Wada basin boundary can be smooth.

More relaxed condition for dynamics of discrete time delayed Hopfield neural networks

Zhang Qiang
Chin. Phys. B, 2008, 17 (1): 125-128 doi: 10.1088/1674-1056/17/1/022
Full Text: [PDF 101 KB] (Downloads:406)
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The dynamics of discrete time delayed Hopfield neural networks is investigated. By using a difference inequality combining with the linear matrix inequality, a sufficient condition ensuring global exponential stability of the unique equilibrium point of the networks is found. The result obtained holds not only for constant delay but also for time-varying delays.

Analysis of two-torus in a new four-dimensional autonomous system

Wu Wen-Juan, Chen Zeng-Qiang, Yuan Zhu-Zhi
Chin. Phys. B, 2008, 17 (1): 129-134 doi: 10.1088/1674-1056/17/1/023
Full Text: [PDF 877 KB] (Downloads:498)
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In this paper, we report the dynamical behaviours of a four-dimensional autonomous continuous dissipative system analysed when the parameter is varied in the range we are interested in. The system changes its dynamical modes between periodic motion and quasiperiodic motion. Furthermore, the existence of two-torus is investigated numerically by means of Lyapunov exponents. By taking advantage of phase portraits and Poincar\'{e} sections, two types of the two-torus are observed and proved to have the structure of ring torus and horn torus, both of which are known to be the standard tori.

Equilibrium points and bifurcation control of a chaotic system

Liang Cui-Xiang, Tang Jia-Shi
Chin. Phys. B, 2008, 17 (1): 135-139 doi: 10.1088/1674-1056/17/1/024
Full Text: [PDF 613 KB] (Downloads:1533)
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Based on the Routh--Hurwitz criterion, this paper investigates the stability of a new chaotic system. State feedback controllers are designed to control the chaotic system to the unsteady equilibrium points and limit cycle. Theoretical analyses give the range of value of control parameters to stabilize the unsteady equilibrium points of the chaotic system and its critical parameter for generating Hopf bifurcation. Certain nP periodic orbits can be stabilized by parameter adjustment. Numerical simulations indicate that the method can effectively guide the system trajectories to unsteady equilibrium points and periodic orbits.
RAPID COMMUNICATION

SAD phasing by OASIS at different resolutions down to 0.30nm and below

Yao De-Qiang, Li He, Chen Qiang, Gu Yuan-Xin, Zheng Chao-De, Lin Zheng-Jiong, Fan Hai-Fu, Nobuhisa Watanabe, Sha Bing-Dong
Chin. Phys. B, 2008, 17 (1): 1-9 doi: 10.1088/1674-1056/17/1/001
Full Text: [PDF 2709 KB] (Downloads:2568)
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Single-wavelength anomalous diffraction (SAD) phasing is increasingly important in solving de novo protein structures. Direct methods have been proved very efficient in SAD phasing. This paper aims at probing the low-resolution limit of direct-method SAD phasing. Two known proteins TT0570 and Tom70p were used as test samples. Sulfur-SAD data of the protein TT0570 were collected with conventional Cu-K\alpha source at 0.18nm resolution. Its truncated subsets respectively at 0.21, 0.30, 0.35 and 0.40nm resolutions were used in the test. TT0570 Cu-K$\alpha$ sulfur-SAD data have an expected Bijvoet ratio <\vert\Delta F\vert>/\ \sim 0.55%. In the 0.21nm case, a single run of OASIS-DM-ARP/wARP led automatically to a model containing 1178 of the total 1206 residues all docked into the sequence. In 0.30 and 0.35nm cases, SAD phasing by OASIS-DM led to traceable electron density maps. In the 0.40nm case, SAD phasing by OASIS-DM resulted in a degraded electron density map, which may be difficult to trace but still contains useful secondary-structure information. Test on real 0.33nm selenium-SAD data of the protein Tom70p showed that even automatic model building was not successful, the combination of manual tracing and direct-method fragment extension was capable of significantly improving the electron-density map. This provides the possibility of effectively improving the manually built model before structure refinement is performed.
NUCLEAR PHYSICS

Resonances of a hydrogen atom in strong parallel electric and magnetic fields using B-spline basis sets

Zhang Yue-Xia, Meng Hui-Yan, Shi Ting-Yun
Chin. Phys. B, 2008, 17 (1): 140-147 doi: 10.1088/1674-1056/17/1/025
Full Text: [PDF 136 KB] (Downloads:520)
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The B-spline basis set plus complex scaling method is applied to the numerical calculation of the exact resonance parameters $E_r}$ and $\Ga/2$ of a hydrogen atom in parallel electric and magnetic fields. The method can calculate the ground and higher excited resonances accurately and efficiently. The resonance parameters with accuracies of $10^{-9}-10^{-12}$ for hydrogen atom in parallel fields with different field strengths and symmetries are presented and compared with previous ones. Extension to the calculation of Rydberg atom in crossed electric and magnetic fields and of atomic double excited states in external electric fields is discussed.

Study on charge equilibration time of highly charged ions in carbon foils

Fang Yan, Xiao Guo-Qing, Xu Hu-Shan, Sun Zhi-Yu, Zhao Yong-Tao, Hu Zheng-Guo, Xu Hua-Gen, Huang Tian-Heng, Wang Yu-Yu
Chin. Phys. B, 2008, 17 (1): 148-151 doi: 10.1088/1674-1056/17/1/026
Full Text: [PDF 306 KB] (Downloads:374)
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Charge state distribution of 0.8MeV/u uranium ions after transmission through a thin carbon foil has been studied. It is observed that the charge state distribution is equilibrated after the uranium ions have passed through a 15 $\mu $g/cm$^{2}$ carbon foil. The equilibrated average charge state is 33.72 and the charge equilibration time of uranium ions in carbon foil is less than 5.4fs.
CLASSICAL AREAS OF PHENOMENOLOGY

Super energy flows in a waveguide filled with air and left-handed materials

Yu Guan-Xia, Cui Tie-Jun
Chin. Phys. B, 2008, 17 (1): 164-169 doi: 10.1088/1674-1056/17/1/029
Full Text: [PDF 1061 KB] (Downloads:438)
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The phenomena of super energy flows are studied theoretically and numerically in a parallel-plate waveguide which is filled with two layered equally-thick different media, i.e. air and specific left-handed materials (LHM) with $\epsilon_{{\rm r}1}=-1/(1+\delta)+\i\gamma$ and $\mu_{{\rm r}1}=-(1+\delta)+\i\gamma$. In this special waveguide, two-directional super-energy flows are excited by a three-dimensional horizontal electric dipole at the same time, which has transmission patterns different from those of two-dimensional source and three-dimensional vertical electric dipole. We also show that the retardation and loss in LHM are sensitive to the amplitude of super power densities, and the dimensions of waveguide determine the propagating modes, which makes super energy flows more practical.

Wavelet--fractional Fourier transforms

Yuan Lin
Chin. Phys. B, 2008, 17 (1): 170-179 doi: 10.1088/1674-1056/17/1/030
Full Text: [PDF 1651 KB] (Downloads:510)
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This paper extends the definition of fractional Fourier transform (FRFT) proposed by Namias V by using other orthonormal bases for $L^{2}\left( R \right)$ instead of Hermite--Gaussian functions. The new orthonormal basis is gained indirectly from multiresolution analysis and orthonormal wavelets. The so defined FRFT is called wavelets-fractional Fourier transform.

Implementing remote controlled-NOT gates and entanglement swapping via geometric phase gates in ion-trap systems

Yang Rong-Can, Li Hong-Cai, Lin Xiu, Huang Zhi-Ping
Chin. Phys. B, 2008, 17 (1): 180-184 doi: 10.1088/1674-1056/17/1/031
Full Text: [PDF 119 KB] (Downloads:416)
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We propose a scheme for the implementation of remote controlled-NOT gates and entanglement swapping via geometric phase gates in ion-trap systems. The proposed scheme uses the two ground states of the $\Lambda$-type ions as memory instead of the vibrational mode. And the system is robust against the spontaneous radiation and the dephasing.

Influences of decoherence on the generation of a macroscopic superposition state using weak cross-Kerr effect

Wu Shao-Ping, Zhang Li-Juan, Li Gao-Xiang
Chin. Phys. B, 2008, 17 (1): 185-189 doi: 10.1088/1674-1056/17/1/032
Full Text: [PDF 295 KB] (Downloads:538)
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Considering a system in which a single photon and a coherent field propagate through a Kerr medium, when the weak cross-Kerr interaction between the coherent state and the single photon under decoherence is involved, this paper derives analytically a macroscopic superposition state by the superoperator method and investigates the influences of decoherence on the coherence properties of the obtained state. It finds that the macroscopic superposition state will experience evolution from a pure superposition state to a mixed state in a dissipative environment and the Kerr effect makes the field display a periodic revival from decoherence for a short time.

Efficient scheme of quantum SWAP gate and multi-atom cluster state via cavity QED

Jiang Chun-Lei, Fang Mao-Fa, Hu Yao-Hua
Chin. Phys. B, 2008, 17 (1): 190-193 doi: 10.1088/1674-1056/17/1/033
Full Text: [PDF 133 KB] (Downloads:492)
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In this paper, we propose a physical scheme to realize quantum SWAP gate by using a large-detuned single-mode cavity field and two identical Rydberg atoms. It is shown that the scheme can also be used to create multi-atom cluster state. During the interaction between atom and cavity, the cavity is only virtually excited and thus the scheme is insensitive to the cavity field states and cavity decay. With the help of our scheme it is very simple to prepare the $N$-atom cluster state with perfect fidelity and probability. The practical feasibility of this method is also discussed.

Quantum analysis on the four-photon interference

Wang Ruo-Peng, Zhang Hui-Rong
Chin. Phys. B, 2008, 17 (1): 194-198 doi: 10.1088/1674-1056/17/1/034
Full Text: [PDF 265 KB] (Downloads:374)
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We present a theory for quantum interference of four photons generated by spontaneous parametric down-conversion. Detailed investigation of the dependence of fourfold coincidence count rate on time delay between the incident and the reflective pump laser pulses is carried out. Gaussian type dependence is found, and good agreement between our theoretical results and experimental data reported in the literature is achieved.

The relation between composition in laser absorption region and ambient pressure

Yang Bo, Zhu Jin-Rong, Yang Yan-Nan, Shen Zhong-Hua, Lu Jian, Ni Xiao-Wu
Chin. Phys. B, 2008, 17 (1): 199-204 doi: 10.1088/1674-1056/17/1/035
Full Text: [PDF 152 KB] (Downloads:358)
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In this paper, the compositions in a laser absorption region can be determined from the experiment of laser impulse coupling. When the ambient pressure varies from 9325 to 33325Pa, the compositions are vapour and plasma; while from 35325 to 101325Pa, they are ambient air and plasma. By analysing the relation between the degree of compression and the ambient pressure, the compositions can be determined and the variation of plasma can be explained.

Widely tunable dual-pump parametric amplifiers with photonic crystal fibres

Li Yong-Zhong, Qian Lie-Jia, Lu Da-Quan, Fan Dian-Yuan, Chen Guang-Hui
Chin. Phys. B, 2008, 17 (1): 205-210 doi: 10.1088/1674-1056/17/1/036
Full Text: [PDF 460 KB] (Downloads:471)
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This paper theoretically studies the double-pumped fibre-optical parametric amplifiers (FOPAs) in photonic crystal fibres. Two distinct working regimes of FOPAs are researched, which depend on the dispersion at the central wavelength of the two pumps. Extremely broad tuning range can be obtained when the central pump wavelength is in the normal dispersion regime and is insensitive to the wavelength separation between the two pumps, while the tuning range is narrow in the anomalous dispersion regime and can be significantly enhanced by increasing the wavelength separation. Impacts of higher-order dispersions and temporal walk-off on the gain spectra are also discussed.

Continuous-wave mid-infrared intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate

Ding Xin, Zhang Shao-Min, Ma Hong-Mei, Pang Ming, Yao Jian-Quan, Li Zhuo
Chin. Phys. B, 2008, 17 (1): 211-216 doi: 10.1088/1674-1056/17/1/037
Full Text: [PDF 598 KB] (Downloads:481)
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This paper reports a continuous-wave (CW) mid-infrared intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate (PPLN) pumped by a diode-end-pumped CW Nd:YVO$_{4}$ laser. Considering the thermal lens effects, it adopted an optical ballast lens and the near-concentric cavity for better operation. At the PPLN's grating period of 28.5\,$\mu$m and the temperature of 140\du, the maximum idler output power of 155\,mW at 3.86\,$\mu$m has been achieved when the 808\,nm pump power is 8.5\,W, leading to an optical-to-optical conversion efficiency of 1.82{\%}.

Theoretical modelling of the effect of photon lifetime on the output dynamics of Er-doped distributed feedback fibre lasers

Wang Li, Chen Bai, Chen Jia-Lin, Chang Li-Ping, Li Guo-Yang, Sun An, Lin Zun-Qi
Chin. Phys. B, 2008, 17 (1): 217-223 doi: 10.1088/1674-1056/17/1/038
Full Text: [PDF 370 KB] (Downloads:505)
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By employing a simple model of describing three-level lasers, we have theoretically investigated the effect of photon lifetime on the output dynamics of Er-doped distributed feedback fibre lasers. And based on the theoretical analysis we have proposed a promising method to suppress self-pulsing behaviour in the fibre lasers.

Green and red up-conversion emissions and thermometric application of Er3+-doped silicate glass

Li Cheng-Ren, Dong Bin, Li Lei, Lei Ming-Kai
Chin. Phys. B, 2008, 17 (1): 224-227 doi: 10.1088/1674-1056/17/1/039
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The green and red up-conversion emissions centred at about 534, 549 and 663\,nm of wavelength, corresponding respectively to the ${^{2}}H_{11 / 2} \to {^{4}}I_{15 / 2}$, ${^{4}}S_{3 / 2} \to {^{4}}I_{15 / 2}$ and ${^{4}}F_{9 / 2} \to {^{4}}I_{15 / 2}$ transitions of Er$^{3 + }$ ions, have been observed for the Er$^{3 + }$-doped silicate glass excited by a 978\,nm semiconductor laser beam. Excitation power dependent behaviour of the up-conversion emission intensity indicates that a two-photon absorption up-conversion process is responsible for the green and red up-conversion emissions. The temperature dependence of the green up-conversion emissions is also studied in a temperature range of 296--673\,K, which shows that Er$^{3 + }$-doped silicate glass can be used as a sensor in high-temperature measurement.

A ministop band in a single-defect photonic crystal waveguide based on silicon on insulator

Tang Hai-Xia, Zuo Yu-Hua, Yu Jin-Zhong, Wang Qi-Ming
Chin. Phys. B, 2008, 17 (1): 228-231 doi: 10.1088/1674-1056/17/1/040
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This paper reports that a two-dimensional single-defect photonic crystal waveguide in the \textit{$\Ga$-K} direction with triangular lattice on a silicon-on-insulator substrate is fabricated by the combination of electron beam lithography and inductively coupled plasma etching. A ministop band (MSB) is observed by the measurement of transmission characteristics. It results from the coupling between the two modes with the same symmetry, which is analysed from the stimulated band diagram by the effective index and the two-dimensional plane wave expansion methods. The parameter working on the MSB is the ratio of the radius of air holes to the lattice constant, $r/a$. It is obtained that the critical $r/a$ value determining the occurrence or disappearance of MSB is 0.36. When $r/a $ is larger than or equal to 0.36, the MSB occurs. However, when $r/a $ is smaller than 0.36, the MSB disappears.

A simple model for approximate bandgap structure calculation of all-solid photonic bandgap fibre based on an array of rings

Fang Hong, Lou Shu-Qin, Guo Tie-Ying, Yao Lei, Li Hong-Lei, Jian Shui-Sheng
Chin. Phys. B, 2008, 17 (1): 232-237 doi: 10.1088/1674-1056/17/1/041
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A simple model for approximate bandgap structure calculation of all-solid photonic bandgap fibre based on an array of rings is proposed. In this model calculated are only the potential modes of a unit cell, which is a high-index ring in the low-index background for this fibre, rather than the whole cladding periodic structure based on Bloch's theorem to find the bandgap. Its accuracy is proved by comparing its results with the results obtained by using the accurate full-vector plane-wave method. High speed in computation is its great advantage over the other exact methods, because it only needs to find the roots of one-dimensional analytical expressions. And the results of this model, mode plots, offer an ideal environment to explore the basic properties of photonic bandgap clearly.

Lattice Boltzmann method with the cell-population equilibrium

Zhou Xiao-Yang, Cheng Bing, Shi Bao-Chang
Chin. Phys. B, 2008, 17 (1): 238-248 doi: 10.1088/1674-1056/17/1/042
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The central problem of the lattice Boltzmann method (LBM) is to construct a discrete equilibrium. In this paper, a multi-speed 1D cell-model of Boltzmann equation is proposed, in which the cell-population equilibrium, a direct non-negative approximation to the continuous Maxwellian distribution, plays an important part. By applying the explicit one-order Chapman--Enskog distribution, the model reduces the transportation and collision, two basic evolution steps in LBM, to the transportation of the non-equilibrium distribution. Furthermore, 1D dam-break problem is performed and the numerical results agree well with the analytic solutions.
ATOMIC AND MOLECULAR PHYSICS

Analysis of the influence of various effects on frequency shifts of the acetylene saturated absorption lines

Dong Lei, Zhang Lei, Dou Hai-Peng, Yin Wang-Bao, Jia Suo-Tang
Chin. Phys. B, 2008, 17 (1): 152-157 doi: 10.1088/1674-1056/17/1/027
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Frequency shifts of the acetylene saturated absorption lines at 1.5\,$\mu$m with temperature, gas pressure and laser power have been investigated in detail. The second-order Doppler effect, the recoil effect, the Zeeman effect, the pressure shift and the power shift are taken into consideration. The magnitudes of those shifts caused by various effects are evaluated. In order to reproduce the stability of $5.7\times10^{ - 14}$ obtained by Edwards, all necessary conditions are given. The results show that when there is a larger external magnetic field, the Zeeman shift could not be neglected, so that the shield should be employed. And the design of a long cavity is advantageous to reduce the influence of the second-order Doppler effect. The results also show that at least $\pm $2.5\du\ temperature control for cavity can effectively prevent several effects and improve the frequency stability.

Line intensities of the asymptotic asymmetric-top radical HO2 at high temperatures

Song Xiao-Shu, Cheng Xin-Lu, Yang Xiang-Dong, Linghu Rong-Feng, Lü Bing
Chin. Phys. B, 2008, 17 (1): 158-163 doi: 10.1088/1674-1056/17/1/028
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The total internal partition sums were calculated in the product approximation at temperatures up to 5000\,K for the asymptotic asymmetric-top HO$_{2}$ molecule. The calculations of the rotational partition function and the vibrational partition function were carried out with the rigid-top model and in the harmonic oscillator approximation, respectively. Our values of the total internal partition sums are consistent with the data of HITRAN database with $-$0.14{\%} at 296\,K. Using the calculated partition functions, we have calculated the line intensities of $\nu _{2}$ band of HO$_{2}$ at several high temperatures. The results showed that the calculated line intensities are in very good agreement with those of HITRAN database at temperatures up to 3000\,K, which provides a strong support for the calculations of partition functions and line intensities at high temperatures. Then we have extended the calculation to higher temperatures. The simulated spectra of $\nu_{2}$ band of the asymptotic asymmetric-top HO$_{2}$ molecule at 4000 and 5000\,K are also obtained.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

New criterion in predicting glass forming ability of various glass-forming systems

X. H. Du, J. C. Huang
Chin. Phys. B, 2008, 17 (1): 249-254 doi: 10.1088/1674-1056/17/1/043
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It has been confirmed that glass-forming ability (GFA) of supercooled liquids is related to not only liquid phase stability but also the crystallization resistance. In this paper, it is found that the liquid region interval ($T_{\rm l}-T_{\rm g})$ characterized by the normalized parameter of $T_{\rm g}$/$T_{\rm l}$ could reflect the stability of glass-forming liquids at the equilibrium state, whilst the normalization of supercooled liquid region $\Delta T_{\rm x}$=($T_{\rm x}-T_{\rm g})$, i.e. $\Delta T_{\rm x}$/$T_{\rm x}$ (wherein $T_{\rm l}$ is the liquidus temperature, $T_{\rm g}$ the glass transition temperature, and $T_{\rm x}$ the onset crystallization temperature) could indicate the crystallization resistance during glass formation. Thus, a new parameter, defined as $\xi =T_{\rm g}$/$T_{\rm l}+\Delta T_{\rm x}$/$T_{\rm x}$ is established to predict the GFA of supercooled liquids. In comparison with other commonly used criteria, this parameter demonstrates a better statistical correlation with the GFA for various glass-forming systems including metallic glasses, oxide glasses and cryoprotectants.

Temperature dependence of ratio between dielectric anisotropy and order parameter in fluorinated nematic liquid crystals

Ma Heng, Sun Rui-Zhi, Li Zhen-Xin, Liu Yu-Fang
Chin. Phys. B, 2008, 17 (1): 255-258 doi: 10.1088/1674-1056/17/1/044
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Temperature dependence of ratio between dielectric anisotropy and order parameter of fluorinated nematic liquid crystal is investigated by using a semi-empirical molecular orbital package that can accurately calculate an angle between molecular dipole moment and long axis. We optimize the molecular conformations with three semi-empirical Hamiltonians AM1, PM3 and PM5, and then make a comparison between computational results and experimental measurements. It is shown that the results obtained from AM1 method are in good agreement with the measurements. The present study offers an applicable method to predict the dielectric properties of liquid crystal material.

Study of mechanical properties of amorphous copper with molecular dynamics simulation

Wang Guang-Hai, Pan Hui, Ke Fu-Jiu, Xia Meng-Fen, Bai Yi-Long
Chin. Phys. B, 2008, 17 (1): 259-263 doi: 10.1088/1674-1056/17/1/045
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The formation and mechanical properties of amorphous copper are studied using molecular dynamics simulation. The simulations of tension and shearing show that more pronounced plasticity is found under shearing, compared to tension. Apparent strain hardening and strain rate effect are observed. Interestingly, the variations of number density of atoms during deformation indicate free volume creation, especially under higher strain rate. In particular, it is found that shear induced dilatation does appear in the amorphous metal.

Shear modulus of shock-compressed LY12 aluminium up to melting point

Yu Yu-Ying, Tan Hua, Hu Jian-Bo, Dai Cheng-Da
Chin. Phys. B, 2008, 17 (1): 264-269 doi: 10.1088/1674-1056/17/1/046
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Asymmetric plate impact experiments are conducted on LY12 aluminium alloy in a pressure range of 85--131\,GPa. The longitudinal sound speeds are obtained from the time-resolved particle speed profiles of the specimen measured with Velocity Interferometer System for Any Reflector (VISAR) technique, and they are shown to be good agreement with our previously reported data of this alloy in a pressure range of 20--70\,GPa, and also with those of 2024 aluminium reported by McQueen. Using all of the longitudinal speeds and the corresponding bulk speeds calculated from the Gruneisen equation of state (EOS), shear moduli of LY12 aluminium alloy are obtained. A comparison of the shear moduli in the solid phase region with those estimated from the Steinberg model demonstrate that the latter are systematically lower than the measurements. By re-analysing the pressure effect on the shear modulus, a modified equation is proposed, in which the pressure term of $P/\eta^{1/3}$ in the Steinberg model is replaced by a linear term. Good agreement between experiments and the modified equation is obtained, which implies that the shear modulus of LY12 aluminium varies linearly both with pressure and with temperature throughout the whole solid phase region. On the other hand, shear modulus of aluminium in a solid-liquid mixed phrase region decreases gradually and smoothly, a feature that is very different from the drastic dropping at the melting point under static conditions.

Lattice dynamics study of low energy guest--host coupling in clathrate hydrate

Yang Yue-Hai, Dong Shun-Le, Wang Lin
Chin. Phys. B, 2008, 17 (1): 270-273 doi: 10.1088/1674-1056/17/1/047
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Our lattice dynamics simulation of Xe-hydrate with four-site TIP4P oxygen-shell model can accurately reproduce each peak position in the inelastic incoherent neutron scattering spectrum at the acoustic band (below 15\,meV) and yield correct relative intensity. Based on the results, the uncertain profile at $\sim $6\,meV is assigned to anharmonic guest modes coupled strongly to small cages. Blue shift is proposed in phonon dispersion sheet in the case of anticrossing and found to be an evident signal for guest--host coupling that explains the anomalous thermal conductivity of clathrate hydrate.

Surface rumples and band gap reductions of cubic BaZrO3 (001) surface studied by means of first-principles calculations

Zhang Chao, Wang Chun-Lei, Li Ji-Chao, Yang Kun, Zhang Yan-Fei, Wu Qing-Zao
Chin. Phys. B, 2008, 17 (1): 274-280 doi: 10.1088/1674-1056/17/1/048
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Electronic properties of the (001) surface of cubic BaZrO$_{3}$ with BaO and ZrO$_{2}$ terminations have been studied using first-principles calculations. Surface structure, partial density of states, band structure and surface energy have been obtained. We find that the largest relaxation appears in the first layer of atoms, and the relaxation of the BaO-terminated surface is larger than that of the ZrO$_{2}$-terminated surface. The surface rumpling of the BaO-terminated surface is also larger than that of the ZrO$_{2}$-terminated surface. Results of surface energy calculations reveal that the BaZrO$_{3}$ surface is likely to be more stable than the PbZrO$_{3}$ surface.

Synthesis, characterization of the pentacene and fabrication of pentacene field-effect transistors

Tao Chun-Lan, Zhang Xu-Hui, Dong Mao-Jun, Liu Yi-Yang, Sun Shuo, Ou Gu-Ping, Zhang Fu-Jia, Zhang Hao-Li
Chin. Phys. B, 2008, 17 (1): 281-285 doi: 10.1088/1674-1056/17/1/049
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A comprehensive understanding of the organic semiconductor material pentacene is meaningful for organic field-effect transistors (OFETs). Thin films of pentacene are the most mobile molecular films known to date. This paper reported that the pentacene sample was successfully synthesized. The purity of pentacene is up to 95\%. The results of a joint experimental investigation based on a combination of infrared absorption spectra, mass spectra (MS), element analysis, x-ray diffraction (XRD) and atom force microscopy (AFM). The authors fabricated OFET with the synthesized pentacene. Its field effect mobility is about 1.23\,cm$^2$/(V$\cdot$s) and on--off ratio is above 10$^{6}$.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Ab initio calculation of the growth of Te nanorods and Bi2Te3 nanoplatelets

Tian Xiao-Qing, Du Shi-Xuan, Gao Hong-Jun
Chin. Phys. B, 2008, 17 (1): 286-289 doi: 10.1088/1674-1056/17/1/050
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In this paper the growth mechanism of a Te/Bi$_{2}$Te$_{3}$ novel structure is studied by \textit{ab-initio} calculations. The results show that the growth of Te nanorods is determined by the adsorption energy of Te atoms on different crystalline Te surfaces. The adsorption energy of Te on the Te (001) surface is 3.29 eV, which is about 0.25 eV higher than that of Te on the Te (110). This energy difference makes the preferential growth direction along the $<001>$ direction. In addition, the higher surface energy of Bi$_{2}$Te$_{3}$ (110) and the lattice misfit between crystalline Bi$_{2}$Te$_{3}$ and Te along $<001>$ direction are considered to explain the growth of the Bi$_{2}$Te$_{3}$ nanoplatelets, in which Volmer--Weber model is used. The theoretical results are in agreement with experimental observation.

Calculations of two dimensional electron gas distributions in AlGaN/GaN material system

Guo Bao-Zeng, Gong Na, Yu Fu-Qiang
Chin. Phys. B, 2008, 17 (1): 290-295 doi: 10.1088/1674-1056/17/1/051
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This paper presents calculating results of the two-dimensional electron gas (2DEG) distributions in AlGaN/GaN material system by solving the Schr\"{o}dinger and Poisson equations self-consistently. Due to high 2DEG density in the AlGaN/GaN heterojunction interface, the exchange correlation potential should be considered among the potential energy item of Schr\"{o}dinger equation. Analysis of the exchange correlation potential is given. The dependencies of the conduction band edge, 2DEG density on the Al mole fraction are presented. The polarization fields have strong influence on 2DEG density in the AlGaN/GaN heterojunction, so the dependency of the conduction band edge on the polarization is also given.

Spin-flip process through double quantum dots coupled to two half-metallic ferromagnetic leads

Yan Cong-Hua, Wu Shao-Quan, Huang Rui, Sun Wei-Li
Chin. Phys. B, 2008, 17 (1): 296-302 doi: 10.1088/1674-1056/17/1/052
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We investigate the spin-flip process through double quantum dots coupled to two half-metallic ferromagnetic leads in series. By means of the slave-boson mean-field approximation, we calculate the density of states in the Kondo regime for two different configurations of the leads. It is found that the transport shows some remarkable properties depending on the spin-flip strength. These effects may be useful in exploiting the role of electronic correlation in spintronics.

The origin of blue photoluminescence from nc-Si/SiO2 multilayers

Ma Zhong-Yuan, Guo Si-Hua, Chen De-Yuan, Wei De-Yuan, Yao Yao, Zhou Jiang, Huang Rui, Li Wei, Xu Jun, Xu Ling, Huang Xin-Fan, Chen Kun-Ji, Feng Duan
Chin. Phys. B, 2008, 17 (1): 303-306 doi: 10.1088/1674-1056/17/1/053
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Intensive blue photoluminescence (PL) was observed at room temperature from the nanocrystalline-Si/SiO$_{2}$ (nc-Si/SiO$_{2})$ multilayers (MLs) obtained by thermal annealing of SiO/SiO$_{2}$\,MLs for the first time. By controlling the size of nc-Si formed in SiO sublayer from 3.5 to 1.5 nm, the PL peak blueshifts from 457 to 411 nm. Combining the analysis of TEM, Raman and absorption measurement, this paper attributes the blue PL to multiple luminescent centres at the interface of nc-Si and SiO$_{2}$.

The scalability of the tunnel-regenerated multi-active-region light-emitting diode structure

Guo Xia, Shen Guang-Di
Chin. Phys. B, 2008, 17 (1): 307-310 doi: 10.1088/1674-1056/17/1/054
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The scalability of the tunnel-regenerated multi-active-region (TRMAR) structure has been investigated for the application in light-emitting diodes (LEDs). The use of the TRMAR structure was proved theoretically to have unique advantages over conventional single-active-layer structures in virtually every aspect, such as high quantum efficiency, high power and low leakage. Our study showed that the TRMAR LED structure could obtain high output power under low current injection and high wall-plug efficiency compared with the conventional single-active-layer LED structure.

Magnetic field induced phase branches of the superconducting transition in two-dimensional square π-loop arrays

Liu Dang-Ting, Tian Ye, Chen Geng-Hua, Yang Qian-Sheng
Chin. Phys. B, 2008, 17 (1): 311-316 doi: 10.1088/1674-1056/17/1/055
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Based on the results of explicit forms of free energy density for each possible arrangement of magnetization fluxes in large-scale two-dimensional (2D) square $\pi $-loop arrays given by Li \textit{et al} [2007 {\em Chin. Phys.} {\bf 16} 1450], the field-cooled superconducting phase transition is further investigated by analysing the free energy of the arrays with a simplified symmetrical model. Our analytical result is exactly the same as that obtained in Li's paper by means of numerical calculations. It is shown that the phase transition splits into two branches with either ferromagnetic or anti-ferromagnetic flux ordering, which depends periodically on the strength of external magnetic flux $\phi_{\e}$ through each loop and monotonically on the screen parameter $\beta $ of the loops in the arrays. In principle, the diagram of the phase branches is similar to that of its one-dimensional counterpart. The influence of thermal fluctuation on the flux ordering during the transition from normal to superconducting states of the $\pi $-loop arrays is also discussed.

Chemical composition and magnetism of Ag doped LaMnO3

Zhang Ning, Geng Tao, Cao Hong-Xia, Bao Jian-Chun
Chin. Phys. B, 2008, 17 (1): 317-322 doi: 10.1088/1674-1056/17/1/056
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By using a sol-gel clue, a set of polycrystalline perovskite samples La$_{1 - x}$Ag$_{x}$MnO$_{3}$ with a nominal doping level $x$ ranging from 0.05 to 0.45 has been synthesized. The chemical composition and the magnetism of the samples were investigated. A little Ag was found seeping from the samples in the sintering process when the doping level exceeded 0.05 and the sintering temperature was higher than 700\du\, resulting in the samples being in multiphase. The magnetic transition points of the samples have been found to decrease with increasing sintering temperature. A concentration-dependent $T_{\rm c}$ similar to that of bivalent metal ion doped perovskite, has been obtained. We believe that the Ag seeping in the sintering process is responsible for those magnetic characteristics.

High-density and narrow size-distribution InAs quantum dots formed by a modified two-step growth

Huang She-Song, Niu Zhi-Chuan, Zhan Feng, Ni Hai-Qiao, Zhao Huan, Wu Dong-Hai, Sun Zheng
Chin. Phys. B, 2008, 17 (1): 323-327 doi: 10.1088/1674-1056/17/1/057
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We develop a modified two-step method of growing high-density and narrow size-distribution InAs/GaAs quantum dots (QDs) by molecular beam epitaxy. In the first step, high-density small InAs QDs are formed by optimizing the continuous deposition amount. In the second step, deposition is carried out with a long growth interruption for every 0.1 InAs monolayer. Atomic force microscope images show that the high-density ($\sim $5.9$\times $10$^{10}$\,cm$^{ - 2})$ good size-uniformity InAs QDs are achieved. The strong intensity and narrow linewidth (27.7\,meV) of the photoluminescence spectrum show that the QDs grown in this two-step method have a good optical quality.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Capability of Raman lidar for monitoring the variation of atmospheric CO2 profile

Zhao Pei-Tao, Zhang Yin-Chao, Wang Lian, Hu Shun-Xing, Su Jia, Cao Kai-Fa, Zhao Yue-Feng, Hu Huan-Ling
Chin. Phys. B, 2008, 17 (1): 335-342 doi: 10.1088/1674-1056/17/1/059
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Lidar (Light detection and ranging) has special capabilities for remote sensing of many different behaviours of the atmosphere. One of the techniques which show a great deal of promise for several applications is Raman scattering. The detecting capability, including maximum operation range and minimum detectable gas concentration is one of the most significant parameters for lidar remote sensing of pollutants. In this paper, based on the new method for evaluating the capabilities of a Raman lidar system, we present an evaluation of detecting capability of Raman lidar for monitoring atmospheric CO$_{2}$ in Hefei. Numerical simulations about the influence of atmospheric conditions on lidar detecting capability were carried out, and a conclusion can be drawn that the maximum difference of the operation ranges caused by the weather conditions alone can reach about 0.4 to 0.5km with a measuring precision within 30ppmv. The range of minimum detectable concentration caused by the weather conditions alone can reach about 20 to 35 ppmv in vertical direction for 20000 shots at a distance of 1 km on the assumption that other parameters are kept constant. The other corresponding parameters under different conditions are also given. The capability of Raman lidar operated in vertical direction was found to be superior to that operated in horizontal direction. During practical measurement with the Raman lidar whose hardware components were fixed, aerosol scattering extinction effect would be a significant factor that influenced the capability of Raman lidar. This work may be a valuable reference for lidar system designing, measurement accuracy improving and data processing.

An ergodic algorithm for long-term coverage of elliptical orbits

Xu Ming, Xu Shi-Jie
Chin. Phys. B, 2008, 17 (1): 343-349 doi: 10.1088/1674-1056/17/1/060
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This paper deals with the coverage analysis problem of elliptical orbits. An algorithm based on ergodic theory, for long-term coverage of elliptical orbits, is proposed. The differential form of the invariant measure is constructed via the perturbation on mean orbital elements resulted from the $J_{2}$ term of non-spherical shape of the earth. A rigorous proof for this is then given. Different from the case of circular orbits, here the flow and its space of the dynamical system are defined on a physical space, and the real-value function is defined as the characteristic function on station mask. Therefore, the long-term coverage is reduced to a double integral via Birkhoff--Khinchin theorem. The numerical implementation indicates that the ergodic algorithm developed is available for a wide range of eccentricities.

Optimized transfer trajectories in the earth--moon system

Xie Wen-Xian, Xu Wei, Cai Li
Chin. Phys. B, 2008, 17 (1): 350-355 doi: 10.1088/1674-1056/17/1/061
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Investigations of low energy transfer trajectories are important for both celestial mechanics and astronautics. Methodologies using the theories from dynamical systems are developed in recent years. This paper investigates the dynamics of the earth--moon system. Low energy transfer trajectories are solved numerically by employing a hybrid strategy: first, a genetic hide and seek method performs a search in large domain to confine the global minimum $f({\eta})$ (objective function) region; then, a deterministic Nelder--Mead method is utilized to refine the minimum quickly. Some transfer trajectories of the spacecraft in the earth--moon system are successfully simulated which verify the desired efficiency and robustness of the method of this paper.

Modification of gravitational redshift of x-ray burst produced by pulsar surface magnetoplasma

Zhu Jun, Ji Pei-Yong
Chin. Phys. B, 2008, 17 (1): 356-361 doi: 10.1088/1674-1056/17/1/062
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In this paper, the propagation of x-ray bursts in the magnetoplasma of pulsar magnetosphere is discussed. The electromagnetic interaction between x-ray bursts and magnetoplasma is described as some geometry. The electromagnetic effects of surface superstrong magnetic field and dynamic effects of outflowing magnetoplasma of pulsars are treated as an optical metric. The Gordon metric is introduced to represent the gravitational metric and optical metric. So the propagation of x-ray bursts in magnetoplasma of pulsars can be described as x-ray bursts transmitting in an effective space characterized by Gordon metric. The modification of gravitational redshift, attributed to the flowing magnetoplasma of pulsars, is obtained and it is shown that the modification is of redshift and can reach the same magnitude as the gravitational redshift for ordinary pulsars.
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