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Chin. Phys. B  
  Chin. Phys. B--2008, Vol.17, No.3
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The homotopic method of travelling wave solution for El Ni?o tropic sea--air coupled oscillator

Mo Jia-Qi, Lin Wan-Tao
Chin. Phys. B 2008, 17 (3): 0743;  doi: 10.1088/1674-1056/17/3/001
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The EI Ni?o and Southern Oscillation (ENSO) is an interannual phenomenon involved in the tropical Pacific sea--air interactions. In this paper, an asymptotic method of solving nonlinear equations for the ENSO model is proposed. And based on a class of oscillator of the ENSO model and by employing the method of homotopic mapping, the approximate solution of equations for the corresponding ENSO model is studied. It is proved from the results that homotopic method can be used for analysing the sea surface temperature anomaly in the equatorial Pacific of the sea--air oscillator for the ENSO model.

Kac--Moody--Virasoro symmetry algebra of a (2+1)-dimensional bilinear system

Li Jin-Hua, Lou Sen-Yue
Chin. Phys. B 2008, 17 (3): 0747;  doi: 10.1088/1674-1056/17/3/002
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Based on some known facts of integrable models, this paper proposes a new (2+1)-dimensional bilinear model equation. By virtue of the formal series symmetry approach, the new model is proved to be integrable because of the existence of the higher order symmetries. The Lie point symmetries of the model constitute an infinite dimensional Kac--Moody--Virasoro symmetry algebra. Making use of the infinite Lie point symmetries, the possible symmetry reductions of the model are also studied.

The Lie symmetries and Noether conserved quantities of discrete mechanical systems with variable mass

Shi Shen-Yang, Fu Jing-Li, Huang Xiao-Hong, Chen Li-Qun, Zhang Xiao-Bo
Chin. Phys. B 2008, 17 (3): 0754;  doi: 10.1088/1674-1056/17/3/003
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This paper studies the Lie symmetries and Noether conserved quantities of discrete mechanical systems with variable mass. The discrete Euler--Lagrange equation and energy evolution equation are derived by using a total variational principle. The invariance of discrete equations under infinitesimal transformation groups is defined to be Lie symmetry. The condition of obtaining the Noether conserved quantities from the Lie symmetries is also presented. An example is discussed for applications of the results.

Exact self-similar solitary waves and collisions in nonlinear optical media

Li Hua-Mei
Chin. Phys. B 2008, 17 (3): 0759;  doi: 10.1088/1674-1056/17/3/004
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This paper analyses bright and dark spatial self-similar waves propagation and collision in graded-index nonlinear waveguide amplifiers with self-focusing and self-defocusing Kerr nonlinearities. It finds an appropriate transformation for the first time such that the nonlinear Schr\"odinger equation (NLSE) with varying coefficients transform into standard NLSE. It obtains one-solitonlike, two-solitonlike and multi-solitonlike self-similar wave solutions by using the transformation. Furthermore, it analyses the features of the self-similar waves and their collisions.

The dynamics of triple-well trapped Bose--Einstein condensates with atoms feeding and loss effects

Mu Ai-Xia, Zhou Xiao-Yan, Xue Ju-Kui
Chin. Phys. B 2008, 17 (3): 0764;  doi: 10.1088/1674-1056/17/3/005
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In this paper, we consider the macroscopic quantum tunnelling and self-trapping phenomena of Bose--Einstein condensates (BECs) with three-body recombination losses and atoms feeding from thermal cloud in triple-well potential. Using the three-mode approximation, three coupled Gross--Pitaevskii equations (GPEs), which describe the dynamics of the system, are obtained. The corresponding numerical results reveal some interesting characteristics of BECs for different scattering lengths. The self-trapping and quantum tunnelling both are found in zero-phase and \pi-phase modes. Furthermore, we observe the quantum beating phenomenon and the resonance character during the self-trapping and quantum tunnelling. It is also shown that the initial phase has a significant effect on the dynamics of the system.

Probabilistic teleportation of multi-particle partially entangled state

Chen Xiu-Bo, Du Jian-Zhong, Wen Qiao-Yan, Zhu Fu-Chen
Chin. Phys. B 2008, 17 (3): 0771;  doi: 10.1088/1674-1056/17/3/006
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Utilizing the generalized measurement described by positive operator-valued measure, this paper comes up with a protocol for teleportation of an unknown multi-particle entangled (GHZ) state with a certain probability. The feature of the present protocol is to weaken requirement for the quantum channel initially shared by sender and receiver. All unitary transformations performed by receiver are summarized into a formula. On the other hand, this paper explicitly constructs the efficient quantum circuits for implementing the proposed teleportation by means of universal quantum logic operations in quantum computation.

Remote interactions on two distributed quantum systems: nonlocal unambiguous quantum-state discrimination

Chen Li-Bing, Jin Rui-Bo, Lu Hong
Chin. Phys. B 2008, 17 (3): 0778;  doi: 10.1088/1674-1056/17/3/007
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Remote quantum-state discrimination is a critical step for the implementation of quantum communication network and distributed quantum computation. We present a protocol for remotely implementing the unambiguous discrimination between nonorthogonal states using quantum entanglements, local operations, and classical communications. This protocol consists of a remote generalized measurement described by a positive operator valued measurement (POVM). We explicitly construct the required remote POVM. The remote POVM can be realized by performing a nonlocal controlled-rotation operation on two spatially separated qubits, one is an ancillary qubit and the other is the qubit which is encoded by two nonorthogonal states to be distinguished, and a conventional local Von Neumann orthogonal measurement on the ancilla. The particular pair of states that can be remotely and unambiguously distinguished is specified by the state of the ancilla. The probability of successful discrimination is not optimal for all admissible pairs. However, for some subset it can be very close to an optimal value in an ordinary local POVM.

Feasible schemes for preparation of all five-atom graph states

Zhang Jin
Chin. Phys. B 2008, 17 (3): 0785;  doi: 10.1088/1674-1056/17/3/008
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We propose feasible schemes for preparation of all five-atom graph states by cavity quantum electrodynamics (QED). Our schemes require only the atom--cavity interaction with a large detuning which is available in current experiment so that these schemes are within the reach of the current technology.

Generation of nonclassical states in a large detuning cavity

Zhang Ying-Jie, Ren Ting-Qi, Xia Yun-Jie
Chin. Phys. B 2008, 17 (3): 0789;  doi: 10.1088/1674-1056/17/3/009
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By using the theory of cavity QED, we study the system in which a two-level atom interacts with a cavity in the case of large detuning. Through the selective detecting of atomic state, Schr\"{o}dinger cat states and entangled coherent states are easily generated. When the atom is driven by a weak classical field and the cavity field is in the Schr\"{o}dinger cat state, we study the conditions of generating the Fock states and the maximal success probability. The maximal success probability in our scheme is larger than the previous one.

Entanglement control in one-dimensional s=1/2 random XY spin chain

Shan Chuan-Jia, Cheng Wei-Wen, Liu Tang-Kun, Huang Yan-Xia, Li Hong, Xia Yun-Jie
Chin. Phys. B 2008, 17 (3): 0794;  doi: 10.1088/1674-1056/17/3/010
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The entanglement in one-dimensional random XY spin systems where the impurities of exchange couplings and the external magnetic fields are considered as random variables is investigated by solving the different spin--spin correlation functions and the average magnetization per spin. The entanglement dynamics near particular locations of the system is also studied when the exchange couplings (or the external magnetic fields) satisfy three different distributions (the Gaussian distribution, double-Gaussian distribution, and bimodal distribution). We find that the entanglement can be controlled by varying the strength of external magnetic field and the distributions of impurities. Moreover, the entanglement of some nearest-neighbouring qubits can be increased for certain parameter values of the three different distributions.

Short-ranged potential effects on the recurrence spectra of lithium M = 1 atoms in parallel electric and magnetic fields

Wang Wen-Peng, Li Hong-Yun, Wang Shu-Bao, Lin Sheng-Lu
Chin. Phys. B 2008, 17 (3): 0801;  doi: 10.1088/1674-1056/17/3/011
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This paper presents recurrence spectra of highly excited lithium atoms with M = 1 state in parallel electric and magnetic fields at a fixed scaled energy \varepsilon = - 0.03. Short-ranged potentials including ionic core potential and centrifugal barrier are taken into account. Their effects on the states and photo-absorption spectrum are analysed in detail. This demonstrates that the geometric features of classical orbits are of special importance for modulations of the spectral pattern. Thus the weak polarization as well as the reduction of correlation of electrons induced by short-ranged potentials give rise to the recurrence spectra of lithium M = 1 atoms more compact than that of the M = 0 one, which is in good agreement with the experimental prediction.

Teleportation of an arbitrary mixture of diagonal states of multiqudit

Du Qian-Hua, Lin Xiu-Min, Chen Zhi-Hua, Lin Gong-Wei, Chen Li-Bo, Gu Yong-Jian
Chin. Phys. B 2008, 17 (3): 0807;  doi: 10.1088/1674-1056/17/3/012
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This paper proposes a scheme to teleport an arbitrary mixture of diagonal states of multiqutrit via classical correlation and classical communication. To teleport an arbitrary mixture of diagonal states of N qutrits, N classically correlated pairs of two qutrits are used as channel. The sender (Alice) makes Fourier transform and conditional gate (i.e., XOR^{(3)} gate) on her qutrits and does measurement in appropriate computation bases. Then she sends N ctrits to the receiver (Bob). Based on the received information, Bob performs the corresponding unitary transformation on his qutrits and obtains the teleported state. Teleportation of an arbitrary mixture of diagonal states of multiqudit is also discussed.

Formation of three-body entanglement via a vacuum optical cavity induction in Tavis--Cummings model

Li Yu-Liang, Li Xue-Mei
Chin. Phys. B 2008, 17 (3): 0812;  doi: 10.1088/1674-1056/17/3/013
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After briefly introducing Akhtarshenas, concurrence vector and subvector for describing many-body entanglement, we investigate the entanglement formation for a system which contains three bodies, i.e. two identical atoms and a single-model cavity field, in the Tavis--Cummings model by calculating the concurrences. The results show that the coupling strength between two atoms, the decay cavity and the atomic spontaneous emission can change the entanglement of formation according to different modes: these factors destroy periodicity and symmetry of all concurrences, and that the coupling strength of two atoms does not change the peak value of concurrence (C), but the strength of decay cavity and the atomic spontaneous emission decline in the peak value of concurrence (C) and the latter is more serious than the former under the same strengths. The concurrence vector and subvector are a useful measure of entanglement for a pure state of the many-body system, in that it can give novel pictures about the entanglements for the entire system and between its inner bodies.

Tunnelling effect of the non-stationary Kerr black hole

Yang Shu-Zheng, Chen De-You
Chin. Phys. B 2008, 17 (3): 0817;  doi: 10.1088/1674-1056/17/3/014
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Extending Parikh and Wilczek's work to the non-stationary black hole, we study the Hawking radiation of the non-stationary Kerr black hole by the Hamilton--Jacobi method. The result shows that the radiation spectrum is not purely thermal and the tunnelling probability is related to the change of Bekenstein--Hawking entropy, which gives a correction to the Hawking thermal radiation of the black hole.

Noether's and Poisson's methods for solving differential equation xs(m)= Fs(t,xk(m-2),xk(m-1)

He Guang, Mei Feng-Xiang
Chin. Phys. B 2008, 17 (3): 0822;  doi: 10.1088/1674-1056/17/3/015
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This paper studies integration of a higher-order differential equation which can be reduced to a second-order ordinary differential equation. The solution of the second-order equation can be obtained by the Noether method and the Poisson method. Then the solution of the higher-order equation can be obtained by integrating the solution of the second-order equation.

Hawking radiation from the Schwarzschild black hole with a global monopole via gravitational anomaly

Peng Jun-Jin, Wu Shuang-Qing
Chin. Phys. B 2008, 17 (3): 0825;  doi: 10.1088/1674-1056/17/3/016
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This paper derives the Hawking flux from the Schwarzschild black hole with a global monopole by using Robinson and Wilczek's method. Adopting a dimensional reduction technique, it can describe the effective quantum field in the (3+1)-dimensional global monopole background by an infinite collection of the (1+1)-dimensional massless fields if neglecting the ingoing modes near the horizon, where the gravitational anomaly can be cancelled by the (1+1)-dimensional black body radiation at the Hawking temperature.

Instantaneous information propagation in free flow, synchronized flow, stop-and-go waves in a cellular automaton model

Jiang Rui, Jin Wen-Long, Wu Qing-Song
Chin. Phys. B 2008, 17 (3): 0829;  doi: 10.1088/1674-1056/17/3/017
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Recently, a number of efforts are underway to investigate inter-vehicle communications (IVC). This paper studies the instantaneous information propagation behaviours based on IVC in three different traffic situations (free flow, synchronized flow and stop-and-go waves) in a cellular automaton model. It is shown that different behaviours appear in stop-and-go waves from those in free flow and synchronized flow. While the distribution of Multi-hop Communication Distance (MhCD) is either exponential or uniform in free flow and synchronized flow, the distribution of MhCD is either exponential or with a single peak in stop-and-go waves.

Adaptive coupled synchronization of non-autonomous systems in ring networks

Guo Liu-Xiao, Xu Zhen-Yuan, Hu Man-Feng
Chin. Phys. B 2008, 17 (3): 0836;  doi: 10.1088/1674-1056/17/3/018
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The adaptive coupled synchronization method for non-autonomous systems is proposed. This method can avoid estimating the value of coupling coefficient. Under the uniform Lipschitz assumption, we derive the asymptotical synchronization for a general coupling ring network with N identical non-autonomous systems, even when N is large enough. Strict theoretical proofs are given. Numerical simulations illustrate the effectiveness of the present method.

Exponential stability of Takagi--Sugeno fuzzy systems with impulsive effects and small delays

Yu Yong-Bin, Zhong Qi-Shui, Liao Xiao-Feng, Yu Jue-Bang
Chin. Phys. B 2008, 17 (3): 0842;  doi: 10.1088/1674-1056/17/3/019
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This paper deals with the exponential stability of impulsive Takagi--Sugeno fuzzy systems with delay. Impulsive control and delayed fuzzy control are applied to the system, and the criterion on exponential stability expressed in terms of linear matrix inequalities (LMIs) is presented.

Chaotic attractor transforming control of hybrid Lorenz--Chen system

Qi Dong-Lian, Wang Qiao, Gu Hong
Chin. Phys. B 2008, 17 (3): 0847;  doi: 10.1088/1674-1056/17/3/020
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Based on passive theory, this paper studies a hybrid chaotic dynamical system from the mathematics perspective to implement the control of system stabilization. According to the Jacobian matrix of the nonlinear system, the stabilization control region is gotten. The controller is designed to stabilize fast the minimum phase Lorenz--Chen chaotic system after equivalently transforming from chaotic system to passive system. The simulation results show that the system not only can be controlled at the different equilibria, but also can be transformed between the different chaotic attractors.

Decrease in Hurst exponent of human gait with aging and neurodegenerative diseases

Zhuang Jian-Jun, Ning Xin-Bao, Yang Xiao-Dong, Hou Feng-Zhen, Huo Cheng-Yu
Chin. Phys. B 2008, 17 (3): 0852;  doi: 10.1088/1674-1056/17/3/021
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In this paper the decrease in the Hurst exponent of human gait with aging and neurodegenerative diseases was observed by using an improved rescaled range (R/S) analysis method. It indicates that the long-range correlations of gait rhythm from young healthy people are stronger than those from the healthy elderly and the diseased. The result further implies that fractal dynamics in human gait will be altered due to weakening or impairment of neural control on locomotion resulting from aging and neurodegenerative diseases. Due to analysing short-term data sequences rather than long datasets required by most nonlinear methods, the algorithm has the characteristics of simplicity and sensitivity, most importantly, fast calculation as well as powerful anti-noise capacities. These findings have implications for modelling locomotor control and also for quantifying gait dynamics in varying physiologic and pathologic states.

Stochastic period-doubling bifurcation in biharmonic driven Duffing system with random parameter

Xu Wei, Ma Shao-Juan, Xie Wen-Xian
Chin. Phys. B 2008, 17 (3): 0857;  doi: 10.1088/1674-1056/17/3/022
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Stochastic period-doubling bifurcation is explored in a forced Duffing system with a bounded random parameter as an additional weak harmonic perturbation added to the system. Firstly, the biharmonic driven Duffing system with a random parameter is reduced to its equivalent deterministic one, and then the responses of the stochastic system can be obtained by available effective numerical methods. Finally,numerical simulations show that the phase of the additional weak harmonic perturbation has great influence on the stochastic period-doubling bifurcation in the biharmonic driven Duffing system. It is emphasized that, different from the deterministic biharmonic driven Duffing system, the intensity of random parameter in the Duffing system can also be taken as a bifurcation parameter, which can lead to the stochastic period-doubling bifurcations.

Approximate entropy---a new statistic to quantify arc and welding process stability in short-circuiting gas metal arc welding

Cao Biao, Xiang Yuan-Peng, Lü Xiao-Qing, Zeng Min, Huang Shi-Sheng
Chin. Phys. B 2008, 17 (3): 0865;  doi: 10.1088/1674-1056/17/3/023
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Based on the phase state reconstruction of welding current in short-circuiting gas metal arc welding using carbon dioxide as shielding gas, the approximate entropy of welding current as well as its standard deviation has been calculated and analysed to investigate their relation with the stability of electric arc and welding process. The extensive experimental and calculated results show that the approximate entropy of welding current is significantly and positively correlated with arc and welding process stability, whereas its standard deviation is correlated with them negatively. A larger approximate entropy and a smaller standard deviation imply a more stable arc and welding process, and vice versa. As a result, the approximate entropy of welding current promises well in assessing and quantifying the stability of electric arc and welding process in short-circuiting gas metal arc welding.

Numeral eddy current sensor modelling based on genetic neural network

Yu A-Long
Chin. Phys. B 2008, 17 (3): 0878;  doi: 10.1088/1674-1056/17/3/024
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This paper presents a method used to the numeral eddy current sensor modelling based on the genetic neural network to settle its nonlinear problem. The principle and algorithms of genetic neural network are introduced. In this method, the nonlinear model parameters of the numeral eddy current sensor are optimized by genetic neural network (GNN) according to measurement data. So the method remains both the global searching ability of genetic algorithm and the good local searching ability of neural network. The nonlinear model has the advantages of strong robustness, on-line modelling and high precision. The maximum nonlinearity error can be reduced to 0.037{\%} by using GNN. However, the maximum nonlinearity error is 0.075$^{ }${\%} using the least square method.

Anisotropic emission of charged mesons and structure characteristic of emission source in heavy ion collisions at 1--2A GeV

Liu Fu-Hu
Chin. Phys. B 2008, 17 (3): 0883;  doi: 10.1088/1674-1056/17/3/025
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Angular distributions of pions and kaons produced in heavy ion collisions at the low-energy end of high energies (1--2\,A GeV) have been investigated by using a multisource ideal gas model. The model covers the expansions and movements of the emission sources, and it is related to the collective flows. By using the analytic expression and the Monte Carlo method, the azimuthal and polar angle distributions of mesons are calculated by the model and compared with the experimental data of the KaoS Collaboration.

The influence of reactor core parameters on effective breeding coefficient Keff

Liu Li-Po, Liu Yi-Bao, Wang Juan, Yang Bo, Zhang Tao
Chin. Phys. B 2008, 17 (3): 0896;  doi: 10.1088/1674-1056/17/3/026
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The values of effective breeding coefficient Keff in a reactor core of nuclear power plant are calculated for different values of parameters (core structure, fuel assembly component) by using the Monte Carlo method. The obtained values of Keff are compared and analysed, which can provide theoretical basis for reactor design.

Slice emittance and projected emittance

Li Zheng-Hong
Chin. Phys. B 2008, 17 (3): 0901;  doi: 10.1088/1674-1056/17/3/027
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This paper presents an analytical description for the growth of the projected emittance (here just referred to the transverse emittance) based on the concept of the slice emittance in an RF photoinjector. In the RF photoinjector, the slice emittance undergoes small changes, but the projected emittance changes significantly even in the drift space after the injector. Carefully adjusting the parameters of the RF photoinjector, which usually means emittance compensation, the projected emittance can be minimized to the value of the slice emittance. The relation between slice emittance and projected emittance is explained in this paper. An emittance function, which shows such a relation, is also introduced. A model about the emittance growth in the RF photoinjector is established, which accords with the particle simulation results by using the code ASTRA. The condition to minimize the emittance is also given by using the emittance function, which means the emittance compensation in the RF photoinjector.

Behaviours of the excited states 1s2np along lithium isoelectronic sequence from Z=11 to 20

Hu Mu-Hong, Wang Zhi-Wen
Chin. Phys. B 2008, 17 (3): 0908;  doi: 10.1088/1674-1056/17/3/028
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Based on the obtained energy values of 1s$^{2}n$p ($n \le $ 9) states for lithium-like systems from $Z$=11 to 20 (by the authors of this paper: Hu M H and Wang Z W 2004 \textit{Chin. Phys.} \textbf{13} 662), this paper determines the quantum defects, as slowly varying function of energy, of this Rydberg series. Using them as input, it can predict the energies of any highly excited states below the ionization threshold for this series according to the quantum defect theory. The regularities of variation for quantum defects of the series along this isoelectronic sequence are physically analysed and discussed. The screening parameters, which are equal to the effective screening charge of the core-electrons, are also obtained.

Heteronuclear intermolecular single-quantum coherences in liquid nuclear agnetic resonance

Chen Song, Zhu Xiao-Qin, Cai Shu-Hui, Chen Zhong
Chin. Phys. B 2008, 17 (3): 0915;  doi: 10.1088/1674-1056/17/3/029
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This paper analyses the heteronuclear Cosy Revamped by Asymmetric Z-gradient Echo Detection pulse sequence. General theoretical expressions of the pulse sequence with arbitrary flip angles were derived by using dipolar field treatment and signals originating from heteronuclear intermolecular single-quantum coherences (iSQCs) in highly-polarized two spin-1/2 systems were mainly discussed in order to find the optimal flip angles. The results show that signals from heteronuclear iSQCs decay slower than those from intermolecular double-quantum coherences or intermolecular zero-quantum coherences. Magical angle experiments validate that the signals are from heteronuclear iSQCs and insensitive to the imperfection of radio-frequency flip angles. All experimental observations are in excellent agreement with theoretical predictions. The quantum-mechanical treatment leads to similar predictions to the dipolar field treatment.

Parametric resonance and cooling on an atom chip

Yan Bo, Li Xiao-Lin, Ke Min, Wang Yu-Zhu
Chin. Phys. B 2008, 17 (3): 0921;  doi: 10.1088/1674-1056/17/3/030
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This paper observes the parametric excitation on atom chip by measuring the trap loss when applying a parametric modulation. By modulating the current in chip wires, it modulates not only the trap frequency but also the trap position. It shows that the strongest resonance occurs when the modulation frequency equals to the trap frequency. The resonance amplitude increases exponentially with modulation depth. Because the Z-trap is an anharmonic trap, there exists energy selective excitation which would cause parametric cooling. We confirm this effect by observing the temperature of atom cloud dropping.

The interaction between multiple bubbles and the free surface

Zhang A-Man, Yao Xiong-Liang
Chin. Phys. B 2008, 17 (3): 0927;  doi: 10.1088/1674-1056/17/3/031
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The flow is assumed to be potential, and a boundary integral method is used to solve the Laplace equation for the velocity potential to investigate the shape and the position of the bubble. A 3D code to study the bubble dynamics is developed, and the calculation results agree well with the experimental data. Numerical analyses are carried out for the interaction between multiple bubbles near the free surface including in-phase and out-of-phase bubbles. The calculation result shows that the bubble period increases with the decrease of the distance between bubble centres because of the depression effect between multiple bubbles. The depression has no relationship with the free surface and it is more apparent for out-of-phase bubbles. There are great differences in dynamic behaviour between the in-phase bubbles and the out-of-phase bubbles due to the depression effect. Furthermore, the interaction among eight bubbles is simulated with a three-dimensional model, and the evolving process and the relevant physical phenomena are presented. These phenomena can give a reference to the future work on the power of bubbles induced by multiple charges exploding simultaneously or continuously.

Theoretical investigation of an electron beam propagating through a wide gap cavity

Song Wei, Lin Yu-Zheng, Liu Guo-Zhi, Shao Hao
Chin. Phys. B 2008, 17 (3): 0939;  doi: 10.1088/1674-1056/17/3/032
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This paper presents a self-consistent nonlinear theory of the current and energy modulations when an electron beam propagates through an inductively-loaded wide gap cavity. The integro-differential equations are obtained to describe the modulation of the beam current and kinetic energy. A relativistic klystron amplifier (RKA) model is introduced, which uses an inductively-loaded wide gap cavity as an input cavity. And a numerical code is developed for the extended model based on the equations, from which some relations about the modulated current and modulated energy are numerically given.

Nonparaxial propagation of phase-flipped Gaussian beams

Gao Zeng-Hui, Lü Bai-Da
Chin. Phys. B 2008, 17 (3): 0943;  doi: 10.1088/1674-1056/17/3/033
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This paper derives the closed-form expressions for nonparaxial phase flipped Gaussian (PFG) beams propagating in free space, through a knife edge and an aperture, which enable us to study nonparaxial propagation properties of PFG beams and to compare nonparaxial results with paraxial ones. It is found that the $f$ parameter, offsetting distance of the knife edge and truncation parameter affect the nonparaxial beam propagation properties. Only under certain conditions the paraxial approximation is applicable. The results are illustrated by numerical examples.

Novel cell parameter determination of a twisted-nematic liquid crystal display

Huang Xia, Jing Hai, Fu Guo-Zhu
Chin. Phys. B 2008, 17 (3): 0950;  doi: 10.1088/1674-1056/17/3/034
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In this paper a novel method is proposed to determine the cell parameters including the twist angle, optic retardation and rubbing direction of twisted-nematic liquid crystal displays (TNLCD) by rotating the TNLCD. It is a single-wavelength method. Because using subtraction equation of transmittance as curve fitting equation, the influence of the light from environment and the absorption by polarizer, the sample of TNLCD and analyser on the transmittance is eliminated. Accurate results can also be obtained in imperfect darkness. By large numbers of experiments, we found that not only the experimental setup is quite simple and can be easily adopted to be carried out, but also the results are accurate.

Aberration-free two-thin-lens systems based on negative-index materials

Lin Zhi-Li, Ding Jie-Chen, Zhang Pu
Chin. Phys. B 2008, 17 (3): 0954;  doi: 10.1088/1674-1056/17/3/035
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Since the complete correction of all five monochromatic Seidel aberrations for a singlet lens with random shape or a two-thin-lens system is unprocurable merely by using the conventional positive-index materials both in theory and practice, this paper proposes that when one or both of the two lenses is/are made from negative-index materials, an imaging system composed of a pair of spherical thin lenses is possible to form a real image, in air, free from all five monochromatic Seidel aberrations. The calculated numerical solutions to the structural parameters of such lens systems possessing superior performance are provided and examples of them are illustrated for the given combinations of the two lenses' refractive indices, including an ultimately-remote imaging system.

Instantaneous coherent polarization and coherent polarimetric spectra

Liu Tao, Wang Xue-Song, Xiao Shun-Ping
Chin. Phys. B 2008, 17 (3): 0960;  doi: 10.1088/1674-1056/17/3/036
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The statistics of polarization in electromagnetic waves or target vector has been studied deeply, generally using Stokes parameters. Unfortunately, all the data-processing includes the assumption that the sampling data are independent of time, without a consideration of the time coherence of the polarization data, such as instantaneous Stokes parameters. In this paper, the definitions of the instantaneous coherent polarization function and polarimetric spectrum are presented for the first time, which shows the coherences of the instantaneous Stokes parameters in both time and frequency domain, even in spatial coherence. The new formula of definition can be extended to spatial propagation coherence, both in free space or any linear medium.

Scheme for the implementation of 1→3 optimal phase-covariant quantum cloning in ion-trap systems

Yang Rong-Can, Li Hong-Cai, Lin Xiu, Huang Zhi-Ping, Xie Hong
Chin. Phys. B 2008, 17 (3): 0967;  doi: 10.1088/1674-1056/17/3/037
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This paper proposes a scheme for the implementation of $1 \to 3$ optimal phase-covariant quantum cloning with trapped ions. In the present protocol, the required time for the whole procedure is short due to the resonant interaction, which is important in view of decoherence. Furthermore, the scheme is feasible based on current technologies.

Effects of dipole--dipole interaction on entanglement transfer

Guo Hong, Xiong Heng-Na
Chin. Phys. B 2008, 17 (3): 0971;  doi: 10.1088/1674-1056/17/3/038
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A system consisting of two different atoms interacting with a two-mode vacuum, where each atom is resonant only with one cavity mode, is considered. The effects of dipole--dipole ({dd}) interaction between two atoms on the atom--atom entanglement and mode--mode entanglement are investigated. For a weak {dd} interaction, when the atoms are initially separable, the entanglement between them can be induced by the {dd} interaction, and the entanglement transfer between the atoms and the modes occurs efficiently; when the atoms are initially entangled, the entanglement transfer is almost not influenced by the {dd} interaction. However, for a strong {dd} interaction, it is difficult to transfer the entanglement from the atoms to the modes, but the atom--atom entanglement can be maintained when the atoms are initially entangled.

Fifth-order phase-sensitive detection of ultrafast polarization beats in cascade four-level system

Nie Zhi-Qiang, Li Pei-Zhe, Yu Xiao-Jun, Zhang Yan-Peng, Jiang Tong, Li Ling, Gan Chen-Li, Zuo Cui-Cui, Zhang Peng-Fei, Song Jian-Ping, Lu Ke-Qing
Chin. Phys. B 2008, 17 (3): 0978;  doi: 10.1088/1674-1056/17/3/039
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We study the colour-locked twin-noisy-field correlation effects in the fifth-order nonlinear susceptibility of ultrafast polarization beats in a cascade four-level system. More importantly, the fifth-order phase-sensitive heterodyne detection of ultrafast polarization beats has been exploited. The fifth-order nonlinear optical response can be controlled and modified through the colour-locked correlation of twin noisy fields. Thus, this method with the phase dispersion information is a good way to measure the real and imaginary parts of the fifth-order nonlinear susceptibility.

Surface solitons supported by one-dimensional composite Bessel optical lattices

Dong Liang-Wei, Yang Xiao-Yu, Chen Hai-Yun
Chin. Phys. B 2008, 17 (3): 0988;  doi: 10.1088/1674-1056/17/3/040
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We address the existence of surface solitons at an interface in a defocusing cubic medium with an imprinted one-dimensional ($1$D) composite Bessel optical lattice. This setting is composed of two Bessel lattices with different orders and different modulation depths, separated beside both sides of an interface. Stability analysis and numerical propagation simulations prove that solitons supported by the model are dynamically stable in the entire domain of their existence. The order of lattice determines the shape of soliton, and the amplitude of soliton depends on the lattice modulation depth. The experimental realization of the scheme is also proposed. Our results may provide another effective way of controlling the shapes of surface solitons and thus their evolutions by introducing a new freedom degree.

Polarization dependent dispersion and its impact on optical parametric process in high nonlinear microstructure fibre

Xiao Li, Zhang Wei, Huang Yi-Dong, Peng Jiang-De
Chin. Phys. B 2008, 17 (3): 0995;  doi: 10.1088/1674-1056/17/3/041
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High nonlinear microstructure fibre (HNMF) is preferred in nonlinear fibre optics, especially in the applications of optical parametric effects, due to its high optical nonlinear coefficient. However, polarization dependent dispersion will impact the nonlinear optical parametric process in HNMFs. In this paper, modulation instability (MI) method is used to measure the polarization dependent dispersion of a piece of commercial HNMF, including the group velocity dispersion, the dispersion slope, the fourth-order dispersion and group birefringence. It also experimentally demonstrates the impact of the polarization dependent dispersion on the continuous wave supercontinuum (SC) generation. On one axis MI sidebands with symmetric frequency detunings are generated, while on the other axis with larger MI frequency detuning, SC is generated by soliton self-frequency shift.

Towards 640Gbit/s wavelength conversion based on nonlinear polarization rotation in a semiconductor optical amplifier

Feng Chuan-Fen, Wu Jian, Zhang Jun-Yi, Xu Kun, Lin Jin-Tong
Chin. Phys. B 2008, 17 (3): 01000;  doi: 10.1088/1674-1056/17/3/042
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Taking into account ultra-fast carrier dynamics, this paper models 640\,Gbit/s wavelength conversion scheme based on nonlinear polarization rotation (NPR) in a single semiconductor optical amplifier (SOA) and investigates the performance of this kind of wavelength conversion scheme in detail. In this model, two carrier temperature equations are introduced to substitute two energy density equations, which reduce the complexity of calculation in comparison with the previous model. The temporary gain and phase shift dynamics induced by ultra-short optical pulses are numerically simulated and the simulated results are qualitatively in good agreement with reported experimental results. Simulated results show that non-inverted and inverted 640\,Gbit/s wavelength conversions based on NPR are achieved with clear open eye diagrams. To further investigate the performance of the non-inverted wavelength conversion scheme, the dependence of output extinction ratio (ER) on some key parameters used in simulation is illustrated. Furthermore, simulated analyses show that high performance non-inverted wavelength conversion based on NPR can be achieved by using a red-shifted filtering scheme.

Energy exchange between (3+1)D colliding spatiotemporal optical solitons in dispersive media with cubic--quintic nonlinearity

Yang Hong, Tang Yi
Chin. Phys. B 2008, 17 (3): 01008;  doi: 10.1088/1674-1056/17/3/043
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We investigate the energy exchange between (3+1)D colliding spatiotemporal solitons (STSs) in dispersive media with cubic--quintic (CQ) nonlinearity by numerical simulations. Energy exchange between two (3+1)D head on colliding STSs caused by their phase difference is observed, just as occurring in other optical media. Moreover, energy exchange between two head-on colliding STSs with different speeds is firstly shown in the CQ and saturable media. This phenomenon, we believe, may arouse some interest in the future studies of soliton collision in optical media.

The two photorefractive centres in iron doped nearly stoichiometric lithium niobate crystals

Li Xiao-Chun, Kong Yong-Fa, Wang Li-Zhong, Liu Hong-De
Chin. Phys. B 2008, 17 (3): 01014;  doi: 10.1088/1674-1056/17/3/044
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This paper investigates the photorefractive properties of iron doped lithium niobate with different [Li]/[Nb] ratios. The experimental results show two photorefractive centres for iron doped near-stoichiometric lithium niobate crystal. Besides Fe$^{2 + }$ and Fe$^{3 + }$ ions, small polarons and bipolarons are considered as another photoactive centre.

Photonic crystal fibre Brillouin laser based on Bragg grating Fabry--Perot cavity

Geng Dan, Yang Dong-Xiao, Shen Guo-Feng, Zhang Xian-Min
Chin. Phys. B 2008, 17 (3): 01020;  doi: 10.1088/1674-1056/17/3/045
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A photonic crystal fibre Brillouin laser based on fibre Bragg grating Fabry--Perot cavity is presented. A highly nonlinear photonic crystal fibre 25\,m in length is used as Brillouin gain medium and fibre Bragg grating Fabry--Perot cavity is chosen in order to enhance the laser conversion efficiency and suppress the higher-order Stokes waves. The laser reaches the threshold at input power of 35\,mW, and the experimental laser conversion efficiency achieves 18{\%} of the input power of 140\,mW and does not show higher-order Stokes waves. A photonic crystal fibre Brillouin laser with shorter fibre length and lower threshold is experimentally realized.

Higher-order effects on self-similar parabolic pulse in the microstructured fibre amplifier

Liu Wei-Ci, Xu Wen-Cheng, Feng Jie, Chen Wei-Cheng, Li Shu-Xian, Liu Song-Hao
Chin. Phys. B 2008, 17 (3): 01025;  doi: 10.1088/1674-1056/17/3/046
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By considering higher-order effects, the properties of self-similar parabolic pulses propagating in the microstructured fibre amplifier with a normal group-velocity dispersion have been investigated. The numerical results indicate that the higher-order effects can badly distort self-similar parabolic pulse shape and optical spectrum, and at the same time the peak shift and oscillation appear, while the pulse still reveals highly linear chirp but grows into asymmetry. The influence of different higher-order effects on self-similar parabolic pulse propagation has been analysed. It shows that the self-steepening plays a more important role. We can manipulate the geometrical parameters of the microstructured fibre amplifier to gain a suitable dispersion and nonlinearity coefficient which will keep high-quality self-similar parabolic pulse propagation. These results are significant for the further study of self-similar parabolic pulse propagation.

All-fibre micro-ring resonator based on tapered microfibre

Dong Xiao-Wei, Lu Shao-Hua, Feng Su-Chun, Xu Ou, Jian Shui-Sheng
Chin. Phys. B 2008, 17 (3): 01029;  doi: 10.1088/1674-1056/17/3/047
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In this paper, bendloss characteristics of an optical fibre are investigated in detail, and the results show that the resonator with a smaller ring radius, wider free spectrum range (FSR), higher fineness ($f$) and quality-factor ($Q$) can be achieved by using microfibres. Based on the improved fused taper technique, a high-quality microfibre with 5\,$\mu$m radius has been fabricated, and an all-fibre micro-ring resonator with a radius of only 500\,$\mu$m is realized using self-coiling coupling method. The good-resonant characteristic makes the all-fibre device be expected to avoid bendloss and connection loss associated with planar waveguide integration.

Vertical rotation effect on turbulence characteristics in an open channel flow

Zou Li-Yong, Bai Jing-Song, Li Bu-Yang, Tan Duo-Wang, Li Ping, Liu Cang-Li
Chin. Phys. B 2008, 17 (3): 01034;  doi: 10.1088/1674-1056/17/3/048
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This paper solves the three-dimensional Navier--Stokes equation by a fractional-step method with the Reynolds number Re$_\tau $=194 and the rotation number $N_\tau $=0--0.12. When $N_\tau $ is less than 0.06, the turbulence statistics relevant to the spanwise velocity fluctuation are enhanced, but other statistics are suppressed. When $N_\tau $ is larger than 0.06, all the turbulence statistics decrease significantly. Reynolds stress budgets elucidate that turbulence kinetic energy in the vertical direction is transferred into the streamwise and spanwise directions. The flow structures exhibit that the bursting processes near the bottom wall are ejected toward the free surface. Evident change of near-surface streak structures of the velocity fluctuations are revealed.

Three-dimensional lattice Boltzmann method for simulating blood flow in aortic arch

Kang Xiu-Ying, Ji Yu-Pin, Liu Da-He, Jin Yong-Juan
Chin. Phys. B 2008, 17 (3): 01041;  doi: 10.1088/1674-1056/17/3/049
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The three-dimensional (3D) lattice Boltzmann models, 3DQ15, 3DQ19 and 3DQ27, under different wall boundary conditions and lattice resolutions have been investigated by simulating Poiseuille flow in a circular cylinder for a wide range of Reynolds numbers. The 3DQ19 model with improved Fillippova and Hanel (FH) curved boundary condition represents a good compromise between computational efficiency and reliability. Blood flow in an aortic arch is then simulated as a typical haemodynamic application. Axial and secondary fluid velocity and effective wall shear stress profiles in a 180$^\circ$ bend are obtained, and the results also demonstrate that the lattice Boltzmann method is suitable for simulating the flow in 3D large-curved vessels.

Intense Cherenkov-type terahertz electromagnetic radiation from ultrafast laser--plasma interaction

Hu Qiang-Lin, Liu Shi-Bing, Li Wei
Chin. Phys. B 2008, 17 (3): 01050;  doi: 10.1088/1674-1056/17/3/050
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A Cherenkov-type terahertz electromagnetic radiation is revealed, which results efficiently from the collective effects in the time-domain of ultrafast pulsed electron current produced by ultrafast intense laser--plasma interaction. The emitted pulse waveform and spectrum, and the dependence of laser pulse parameters on the structure of the radiation field are investigated numerically. The condition of THz radiation generation in this regime and Cherenkov geometry of the radiation field are studied analytically.

STM study of In nanostructures formation on Ge(001) surface at different coverages and temperatures

Qin Zhi-Hui, Shi Dong-Xia, Pang Shi-Jin, Gao Hong-Jun
Chin. Phys. B 2008, 17 (3): 01055;  doi: 10.1088/1674-1056/17/3/051
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Different In/Ge(001) nanostructures have been obtained by annealing the samples at 320\du\ with different coverages of In. Annealing a sample with a critical coverage of 2.1 monolayer of In, different In/Ge(001) nanostructures can be obtained at different temperatures. It is found that thermal annealing treatments first make In atoms form elongated Ge{\{}103{\}}-faceted In-clusters, which will grow wider and longer with increasing temperature, and finally cover the surface completely.

Theory of nine elastic constants of biaxial nematics

Liu Hong
Chin. Phys. B 2008, 17 (3): 01060;  doi: 10.1088/1674-1056/17/3/052
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In this paper, a rotational invariant of interaction energy between two biaxial-shaped molecules is assumed and in the mean field approximation, nine elastic constants for simple distortion patterns in biaxial nematics are derived in terms of the thermal average $\langle {D_{mn}^{(l)} } \rangle \langle {D_{{m}'{n}'}^{({l}')} } \rangle $, where $D_{mn}^{(l)} $ is the Wigner rotation matrix. In the lowest order terms, the elastic constants depend on coefficients $\Ga$, ${\Ga'}$, $\lambda $, order parameters $\bar {Q}_0 = Q_0 \langle {D_{00}^{(2)} } \rangle + Q_2 \langle {D_{02}^{(2)} + D_{0 - 2}^{(2)} } \rangle $ and $\bar {Q}_2 = Q_0 \langle {D_{20}^{(2)} } \rangle + Q_2 \langle {D_{22}^{(2)} + D_{2 - 2}^{(2)} } \rangle $. Here $\Ga $ and ${\Ga'}$ depend on the function form of molecular interaction energy $v_{j'j''j} ( {r_{12} } )$ and probability function $f_{k'k''k} ( {r_{12} } )$, where $r_{12} $ is the distance between two molecules, and $\lambda $ is proportional to temperature. $Q_0 $ and $Q_2 $ are parameters related to multiple moments of molecules. Comparing these results with those obtained from Landau--de Gennes theory, we have obtained relationships between coefficients, order parameters used in both theories. In the special case of uniaxial nematics, both results are reduced to a degenerate case where $K_{11} = K_{33}$.

Formation of high density TiN nanocrystals and its application in non-volatile memories

Li Xue-Lin, Feng Shun-Shan, Chen Guo-Guang
Chin. Phys. B 2008, 17 (3): 01070;  doi: 10.1088/1674-1056/17/3/053
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Non-volatile memory based on TiN nanocrystal (TiN--NC) charge storage nodes embedded in SiO$_{2}$ has been fabricated and its electrical properties have been measured. It was found that the density and size distribution of TiN--NCs can be controlled by annealing temperature. The formation of well separated crystalline TiN nano-dots with an average size of 5\,nm is confirmed by transmission electron microscopy and x-ray diffraction. x-ray photoelectron spectroscopy confirms the existence of a transition layer of TiN$_{x}$O$_{y}$/SiON oxide between TiN--NC and SiO$_{2}$, which reduces the barrier height of tunnel oxide and thereby enhances programming/erasing speed. The memory device shows a memory window of 2.5\,V and an endurance cycle throughout 10$^{5}$. Its charging mechanism, which is interpreted from the analysis of programming speed (d$V_{\rm th}$/d$t$) and the gate leakage versus voltage characteristics ($I_{\rm g}$ vs $V_{\rm g})$, has been explained by direct tunnelling for tunnel oxide and Fowler--Nordheim tunnelling for control oxide at programming voltages lower than 9V, and by Fowler--Nordheim tunnelling for both the oxides at programming voltages higher than 9\,V.

Phase-field simulation of dendritic growth in a binary alloy with thermodynamics data

Long Wen-Yuan, Xia Chun, Xiong Bo-Wen, Fang Li-Gao
Chin. Phys. B 2008, 17 (3): 01078;  doi: 10.1088/1674-1056/17/3/054
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This paper simulates the dendrite growth process during non-isothermal solidification in the Al--Cu binary alloy by using the phase-field model. The heat transfer equation is solved simultaneously. The thermodynamic and kinetic parameters are directly obtained from existing database by using the Calculation of Phase Diagram (CALPHAD) method. The effects of the latent heat and undercooling on the dendrite growth, solute and temperature profile during the solidification of binary alloy are investigated. The results indicate that the dendrite growing morphologies could be simulated realistically by linking the phase-field method to CALPHAD. The secondary arms of solidification dendritic are better developed with the increase of undercooling. Correspondingly, the tip speed and the solute segregation in solid--liquid interface increase, but the tip radius decreases.

Optically induced phase transition of excitons in coupled quantum dots

Chen Zi-Dong
Chin. Phys. B 2008, 17 (3): 01084;  doi: 10.1088/1674-1056/17/3/055
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The weak classical light excitations in many semiconductor quantum dots have been chosen as important solid-state quantum systems for processing quantum information and implementing quantum computing. For strong classical light we predict theoretically a novel phase transition as a function of magnitude of this classical light from the deformed to the normal phases in resonance case, and the essential features of criticality such as the scaling behaviour, critical exponent and universality are also present in this paper.

Fusion curves and thermodynamic properties of carbon tetrachloride, chloroform, bromoform and silicon tetrachloride at pressure up to 3500Mpa

Zhu Rong-Jiao, Xu Wei, Tian Yi-Ling, Hao Ji-Shuang
Chin. Phys. B 2008, 17 (3): 01088;  doi: 10.1088/1674-1056/17/3/056
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The fusion temperature as a function of pressure for carbon tetrachloride, chloroform, bromoform and silicon tetrachloride at pressures up to 3500MPa has been determined. The experimental data were fitted by the equation $T_{{\rm fus}} = T_0 (1 + \Delta p / a_1 )^{a_2 }\exp ( - a_3 \Delta p)$ and the changes of the molar enthalpy and molar internal energy on fusion were calculated using the parameters of the fitted equation. Comparisons with the data from the literature show that the experimental data, parameters of fitted equations, changes of the molar enthalpy and molar internal energy are reliable.

The spreading behaviour of perfluoropolyether droplets on solid surfaces

Guo Xiao-Yan, Li Xin, Hu Yuan-Zhong, Wang Hui
Chin. Phys. B 2008, 17 (3): 01094;  doi: 10.1088/1674-1056/17/3/057
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The spread of perfluoropolyether (PFPE) droplets on solid surfaces has been measured from the top-down view through a microscope system. Effects of substrates, molecular weight and end-group functionality on spreading of the PFPE droplets have been studied experimentally and the results were compared with those by molecular dynamics (MD) simulations. Silicon wafer and diamond-like carbon (DLC) substrates were used to study the effect of substrates on spreading. Two types of PFPE, Z-dol and Z-tetraol, with the same chain structure and various molecular weights (2000 and 4000\,g/mol) were employed in experiments. Effect of molecular weight has been investigated through comparing the spreading of Z-dol 2000 and Z-dol 4000, and it is found that the increase of molecular weight will decrease the mobility of PFPE. Comparison between spreading of Z-dol and Z-tetraol of the same molecular weight proved that functional end group plays a significant role on the spreading of PFPE, which confirmed the MD simulation results.

Effect of the defect on the focusing in a two-dimensional photonic-crystal-based flat lens

Feng Zhi-Fang, Wang Xiu-Guo, Li Zhi-Yuan, Zhang Dao-Zhong
Chin. Phys. B 2008, 17 (3): 01101;  doi: 10.1088/1674-1056/17/3/058
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We have investigated in detail the influence of defect on the focusing of electromagnetic waves in a two-dimensional photonic-crystal flat lens by using the finite-difference time-domain method. The result shows that many focusings can be observed at the symmetrical positions when a defect is introduced into the lens. Furthermore, the wave-guides in the lens can confine the transmission wave effectively and improve the quality of the focusing.

Investigation on the thermal radiation properties of antimony doped tin oxide particles

Fu Cheng-Wu, Zhang Shuan-Qin, Chen Ming-Qing
Chin. Phys. B 2008, 17 (3): 01107;  doi: 10.1088/1674-1056/17/3/059
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This paper reports the preparation of antimony doped tin oxide crystalline powders by chemical coprecipitation method. The influence of sintering temperature and the sintering retention time on the thermal infrared emissivity is analysed. The thermal infrared reflectivity is measured and the optimum doping concentration is proposed.

Quantum diffusion in semi-infinite periodic and quasiperiodic systems

Zhang Kai-Wang
Chin. Phys. B 2008, 17 (3): 01113;  doi: 10.1088/1674-1056/17/3/060
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This paper studies quantum diffusion in semi-infinite one-dimensional periodic lattice and quasiperiodic Fibonacci lattice. It finds that the quantum diffusion in the semi-infinite periodic lattice shows the same properties as that for the infinite periodic lattice. Different behaviour is found for the semi-infinite Fibonacci lattice. In this case, there are still $C(t)\sim t^{ - \delta }$ and $d(t)\sim t^{\beta }$. However, it finds that $0 < \delta < 1$ for smaller time, and $\delta = 0$ for larger time due to the influence of surface localized states. Moreover, $\beta $ for the semi-infinite Fibonacci lattice is much smaller than that for the infinite Fibonacci lattice. Effects of disorder on the quantum diffusion are also discussed.

Influence of V/III ratio on the structural and photoluminescence properties of In0.52AlAs/ In0.53GaAs metamorphic high electron mobility transistor grown by olecular beam epitaxy

Gao Hong-Ling, Zeng Yi-Ping, Wang Bao-Qiang, Zhu Zhan-Ping, Wang Zhan-Guo
Chin. Phys. B 2008, 17 (3): 01119;  doi: 10.1088/1674-1056/17/3/061
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A series of metamorphic high electron mobility transistors (MMHEMTs) with different V/III flux ratios are grown on GaAs (001) substrates by molecular beam epitaxy (MBE). The samples are analysed by using atomic force microscopy (AFM), Hall measurement, and low temperature photoluminescence (PL). The optimum V/III ratio in a range from 15 to 60 for the growth of MMHEMTs is found to be around 40. At this ratio, the root mean square (RMS) roughness of the material is only 2.02 nm; a room-temperature mobility and a sheet electron density are obtained to be 10610.0cm$^{2}$/(V$\cdot$s) and 3.26$\times $10$^{12}$cm$^{ - 2}$ respectively. These results are equivalent to those obtained for the same structure grown on InP substrate. There are two peaks in the PL spectrum of the structure, corresponding to two sub-energy levels of the In$_{0.53}$Ga$_{0.47}$As quantum well. It is found that the photoluminescence intensities of the two peaks vary with the V/III ratio, for which the reasons are discussed.

Rapid preparation of Mg(B1-xCx)2 superconductor using hybrid microwave method

Guo Juan, Dong Cheng, Gao Hong, Wen Hai-Hu, Yang Li-Hong, Zeng Fu, Chen Hong
Chin. Phys. B 2008, 17 (3): 01124;  doi: 10.1088/1674-1056/17/3/062
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The crystal structure and the superconductivity for samples Mg(B1-xCx)2 (0 \le x \le 0.09) prepared by a hybrid microwave synthesis have been investigated. The starting material B10C is also obtained by using the microwave method. The carbon can distribute uniformly in the Mg(B1-xCx)2 samples because boron and carbon are mixed on an atomic scale in the staring material B10C. The dependences of both lattice parameters and superconducting transition temperature Tc on carbon content accord with those reported in the literature. The upper critical field Hc2 at 20K can be enhanced from about 4.3T for x=0 to 10\,T for x=0.05. The critical current density Jc of Mg(B0.95C0.05)2 is 1.05×104A/cm2 at 20K and 1T.

Angular dependence of coercivity of grains in nanocrystalline permanent magnets

Gong Yi-Min, Lan Zhi-Huan, Yan Yu, Du Xiao-Bo, Wang Wen-Quan, Wang Xue-Feng, Su Feng, Lu Lei, Zhang Zhi-Sheng, Jin Han-Min, Wen Ge-Hui
Chin. Phys. B 2008, 17 (3): 01130;  doi: 10.1088/1674-1056/17/3/063
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In this paper magnetization remanence curves were studied for nanocrystalline Pr8Fe87B5, Pr12Fe82B6 and Pr15Fe77B8. Initially the sample was at remanence following saturation along $z$-axis. After rotating the magnet by $5n$ degrees (n=0, 1, ..., 18) a field H was applied along $z$-axis and then decreased to zero, and the remanence Jr^{n} $ was measured as a function of $H$. The curves were compared with those calculated based on the nucleation of reverse domain model and domain wall pinning model. The latter model succeeds in simulation much better than the former, and it is concluded that the magnetization reversal is dominated by domain wall pinning for all the samples. The nucleation mechanism contribution, while remains small, increases with the increase of Pr content.

Preparation and luminescence characteristics of Eu2+ activated silicate phosphor

Li Pan-Lai, Yang Zhi-Ping, Wang Zhi-Jun, Guo Qing-Lin
Chin. Phys. B 2008, 17 (3): 01135;  doi: 10.1088/1674-1056/17/3/064
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This paper synthesizes the Sr$_{2}$SiO$_{4}$\,:\,Eu$^{2 + }$ phosphor by high temperature solid-state reaction. The emission spectrum of Sr$_{2}$SiO$_{4}$\,:\,Eu$^{2 + }$ shows two bands centred at 480 and 547\,nm, which agree well with the calculation values of emission spectrum, and the location of yellow emission of Sr$_{2}$SiO$_{4}$\,:\,Eu$^{2 + }$ is influenced by the Eu$^{2 + }$ concentration. The excitation spectrum for 547\,nm emission has two bands at 363 and 402\,nm. The emission spectrum of white light emitting diodes (w-LEDs) based on Sr$_{2}$SiO$_{4}$\,:\,Eu$^{2 + }$ phosphor + InGaN LED was investigated.

The theory of interaction between wave and basic flow

Ran Ling-Kun, John P.Boyd
Chin. Phys. B 2008, 17 (3): 01138;  doi: 10.1088/1674-1056/17/3/065
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This paper investigates the interaction between transient wave and non-stationary and non-conservative basic flow. An interaction equation is derived from the zonally symmetric and non-hydrostatic primitive equations in Cartesian coordinates by using the Momentum--Casimir method. In the derivation, it is assumed that the transient disturbances satisfy the linear perturbation equations and the basic states are non-conservative and slowly vary in time and space. The diabatic heating composed of basic-state heating and perturbation heating is also introduced. Since the theory of wave--flow interaction is constructed in non-hydrostatic and ageostrophic dynamical framework, it is applicable to diagnosing the interaction between the meso-scale convective system in front and the background flow. It follows from the local interaction equation that the local tendency of pseudomomentum wave-activity density depends on the combination of the perturbation flux divergence second-order in disturbance amplitude, the local change of basic-state pseudomomentum density, the basic-state flux divergence and the forcing effect of diabatic heating. Furthermore, the tendency of pseudomomentum wave-activity density is opposite to that of basic-state pseudomomentum density. The globally integrated basic-state pseudomomentum equation and wave-activity equation reveal that the global development of basic-state pseudomomentum is only dominated by the basic-state diabatic heating while it is the forcing effect of total diabatic heating from which the global evolution of pseudomomentum wave activity results. Therefore, the interaction between the transient wave and the non-stationary and non-conservative basic flow is realized in virtue of the basic-state diabatic heating.

Re-research on the size of proto-neutron star in core-collapse supernova

Luo Zhi-Quan, Liu Men-Quan
Chin. Phys. B 2008, 17 (3): 01147;  doi: 10.1088/1674-1056/17/3/066
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The electron capture timescale may be shorter than hydrodynamic timescale in inner iron core of core-collapse supernova according to a recent new idea. Based on the new idea, this paper carries out a numerical simulation on supernova explosion for the progenitor model Ws15M$_{\odot}$. The numerical result shows that the size of proto-neutron star has a significant change (decrease about 20{\%}), which may affects the propagation of the shock wave and the final explosion energy.
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