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CN 11-5639/O4
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  • Complete Bell-state analysis for single-photon hybrid entangled state

    Sheng Yu-Bo, Zhou Lan, Cheng Wei-Wen, Gong Long-Yan, Wang Lei, Zhao Sheng-Mei
    Chin. Phys. B 2013, 22 (3): 030314
    We propose a scheme capable of performing complete Bell-state analysis for single-photon hybrid entangled state. Our single-photon state is encoded in both polarization and frequency degrees of freedom. The setup of scheme is composed of polarizing beam splitters, half wave plates, frequency shifter...

     
  • Average position in quantum walks with a U(2) coin

    Li Min, Zhang Yong-Sheng, Guo Guang-Can
    Chin. Phys. B 2013, 22 (3): 030310
    We investigated discrete-time quantum walks with an arbitary unitary coin. Here we discover that the average position〈x〉=max(〈x〉)sin(α+γ), while the initial state is 1/√2(|0L〉+ i|0R〉). We verify the result, and obtain some symmetry properties of quantum walks with a U(2) coin with ...

     
  • Magnetic properties and magnetostriction of PrxNd1-xFe1.9 (0≤x≤1.0) alloys at low temperature

    Wang Yong, Tang Shao-Long, Li Yu-Long, Xie Ren, Du You-Wei
    Chin. Phys. B 2013, 22 (3): 037503
    The crystal structure, magnetic and magnetostrictive properties of high-pressure synthesized PrxNd1-xFe1.9 (0≤x≤1.0) alloys were studied. The alloys exhibit single cubic Laves phase with MgCu2-type structure. The initial magnetization curve reveals that Pr0.2Nd0.8Fe1.9 has a minimum magnetocry...

     
Chin. Phys. B  
  Chin. Phys. B--2013, Vol.22, No.3
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Mathematical structure of the three-dimensional (3D) Ising model

Zhang Zhi-Dong
Chin. Phys. B, 2013, 22 (3): 030513 doi: 10.1088/1674-1056/22/3/030513
Full Text: [PDF 394 KB] (Downloads:3129)
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An overview of the mathematical structure of the three-dimensional (3D) Ising model is given from the viewpoints of topology, algebra, and geometry. By analyzing the relationships among transfer matrices of the 3D Ising model, Reidemeister moves in the knot theory, Yang-Baxter and tetrahedron equations, the following facts are illustrated for the 3D Ising model. 1) The complexified quaternion basis constructed for the 3D Ising model naturally represents the rotation in a (3+1)-dimensional space-time as a relativistic quantum statistical mechanics model, which is consistent with the 4-fold integrand of the partition function obtained by taking the time average. 2) A unitary transformation with a matrix that is a spin representation in 2n·l·o-space corresponds to a rotation in 2n·l·o-space, which serves to smooth all the crossings in the transfer matrices and contributes the non-trivial topological part of the partition function of the 3D Ising model. 3) A tetrahedron relation would ensure the commutativity of the transfer matrices and the integrability of the 3D Ising model, and its existence is guaranteed by the Jordan algebra and the Jordan-von Neumann-Wigner procedures. 4) The unitary transformation for smoothing the crossings in the transfer matrices changes the wave functions by complex phases φx, φy, and φz. The relationship with quantum field and gauge theories and the physical significance of the weight factors are discussed in detail. The conjectured exact solution is compared with numerical results, and the singularities at/near infinite temperature are inspected. The analyticity in β=1/(kBT) of both the hard-core and the Ising models has been proved only for β>0, not for β=0. Thus the high-temperature series cannot serve as a standard for judging a putative exact solution of the 3D Ising model.
GENERAL

Mei symmetry and conservation laws of discrete nonholonomic dynamical systems with regular and irregular lattices

Zhao Gang-Ling, Chen Li-Qun, Fu Jing-Li, Hong Fang-Yu
Chin. Phys. B, 2013, 22 (3): 030201 doi: 10.1088/1674-1056/22/3/030201
Full Text: [PDF 240 KB] (Downloads:476)
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In this paper, Noether symmetry and Mei symmetry of discrete nonholonomic dynamical systems with regular and the irregular lattices are investigated. Firstly, the equations of motion of discrete nonholonomic systems are introduced on the regular and rregular lattices. Secondly, for cases of the two lattices, based on the invariance of the Hamiltomian functional under the infinitesimal transformation of time and generalized coordinates, we present the quasi-extremal equation, the discrete analogues of Noether identity, Noether theorems, and the Noether conservation laws of the systems. Thirdly, in cases of the two lattices, we study the Mei symmetry in which we give the discrete analogues of the criterion, the theorem, and the conservative laws of Mei symmetry for the systems. Finally, an example is discussed for applications of the results.

Melting phenomenon in magneto hydro-dynamics steady flow and heat transfer over a moving surfacein the presence of thermal radiation

Reda G. Abdel-Rahman, M. M. Khader, Ahmed M. Megahed
Chin. Phys. B, 2013, 22 (3): 030202 doi: 10.1088/1674-1056/22/3/030202
Full Text: [PDF 270 KB] (Downloads:680)
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The Lie group method is applied to present an analysis of the magneto hydro-dynamics (MHD) steady laminar flow and the heat transfer from a warm laminar liquid flow to a melting moving surface in the presence of thermal radiation. By using the Lie group method, we have presented the transformation groups for the problem with a part from the scaling group. The application of this method reduces the partial differential equations (PDEs) with their boundary conditions governing the flow and heat transfer to a system of nonlinear ordinary differential equations (ODEs) with appropriate boundary conditions. The resulting nonlinear system of ODEs is solved numerically using an implicit finite difference method (FDM). The local skin-friction coefficients and the local Nusselt numbers for different physical parameters are presented in a table.

Two new discrete integrable systems

Chen Xiao-Hong, Zhang Hong-Qing
Chin. Phys. B, 2013, 22 (3): 030203 doi: 10.1088/1674-1056/22/3/030203
Full Text: [PDF 183 KB] (Downloads:386)
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In this paper, we focus on the construction of new (1+1)-dimensional discrete integrable systems according to a subalgebra of loop algebra Â1. By designing two new (1+1)-dimensional discrete spectral problems, two new discrete integrable systems are obtained, namely, a 2-field lattice hierarchy and a 3-field lattice hierarchy. When deriving the two new discrete integrable systems, we find the generalized relativistic Toda lattice hierarchy and the generalized modified Toda lattice hierarchy. Moreover, we also obtain the Hamiltonian structures of the two lattice hierarchies by means of the discrete trace identity.

Stability and Neimark-Sacker bifurcation analysis of food-limited population model with time delay

Jiang Xiao-Wei, Guan Zhi-Hong, Zhang Xian-He, Zhang Ding-Xue, Liu Feng
Chin. Phys. B, 2013, 22 (3): 030204 doi: 10.1088/1674-1056/22/3/030204
Full Text: [PDF 387 KB] (Downloads:706)
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In this paper, a kind of discrete delay food-limited model obtained by Euler method is investigated, where the discrete delay τ is regarded as a parameter. By analyzing the associated characteristic equation, the linear stability of this model is studied. It is shown that Neimark–Sacker bifurcation occurs when τ crosses some critical values. The explicit formulae which determine the stability, direction, and other properties of bifurcating periodic solution are derived by means of the theory of center manifold and normal form. Finally, numerical simulations are performed to verify the analytical results.

Asymptotic solution of weak nonlinear model for mid-latitude stationary wind field of two-layer barotropic ocean

Lin Wan-Tao, Zhang Yu, Mo Jia-Qi
Chin. Phys. B, 2013, 22 (3): 030205 doi: 10.1088/1674-1056/22/3/030205
Full Text: [PDF 463 KB] (Downloads:331)
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The weak nonlinear model of two-layer barotropic ocean with Rayleigh dissipation is built. The analytic asymptotic solution is derived in mid-latitude stationary wind field, and the physical meaning of the corresponding problem is discussed.

Stability analysis and control synthesis of uncertain Roesser-type discrete-time two-dimensional systems

Wang Jia, Hui Guo-Tao, Xie Xiang-Peng
Chin. Phys. B, 2013, 22 (3): 030206 doi: 10.1088/1674-1056/22/3/030206
Full Text: [PDF 1000 KB] (Downloads:838)
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We study the stability analysis and control synthesis of uncertain discrete-time two-dimensional (2D) systems. The mathematical model of the discrete-time 2D system is established upon the well-known Roesser model, and the uncertainty phenomenon, which appears typically in practical environments, is modeled by a convex bounded (polytope type) uncertain domain. Then, the stability analysis and control synthesis of uncertain discrete-time 2D systems are developed by applying the Lyapunov stability theory. In the processes of stability analysis and control synthesis, the obtained stability/stabilzaition conditions become less conservative by applying some novel relaxed techniques. Moreover, the obtained results are formulated in the form of linear matrix inequalities, which can be easily solved via the standard numerical software. Finally, numerical examples are given to demonstrate the effectiveness of the obtained results.

Dynamical analysis of a sexually transmitted disease model on complex networks

Yuan Xin-Peng, Xue Ya-Kui, Liu Mao-Xing
Chin. Phys. B, 2013, 22 (3): 030207 doi: 10.1088/1674-1056/22/3/030207
Full Text: [PDF 3715 KB] (Downloads:573)
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In this paper, a sexually transmitted disease model is proposed on complex networks, where contacts between humans are treated as a scale-free social network. There are three groups in our model, which are dangerous male, non-dangerous male, and female. By mathematical analysis, we obtain the basic reproduction number for the existence of endemic equilibrium and study the effects of various immunization schemes about different groups. Furthermore, numerical simulations are undertook to reach and verify more conclusions.

A new complex variable meshless method for advection–diffusion problems

Wang Jian-Fei, Cheng Yu-Min
Chin. Phys. B, 2013, 22 (3): 030208 doi: 10.1088/1674-1056/22/3/030208
Full Text: [PDF 317 KB] (Downloads:480)
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In this paper, based on the improved complex variable moving least-square (ICVMLS) approximation, an improved complex variable meshless method (ICVMM) for two-dimensional advection–diffusion problems is developed. The equivalent functional of two-dimensional advection–diffusion problems is formed, the variation method is used to obtain the equation system, and the penalty method is employed to impose the essential boundary conditions. The difference method for two-point boundary value problems is used to obtain the discrete equations. Then the corresponding formulas of the ICVMM for advection–diffusion problems are presented. Two numerical examples with different node distributions are used to validate and investigate the accuracy and efficiency of the new method in this paper. It is shown that the ICVMM is very effective for advection–diffusion problems, and has good convergent character, accuracy, and computational efficiency.

Multisymplectic implicit and explicit methods for Klein–Gordon–Schrödinger equations

Cai Jia-Xiang, Yang Bin, Liang Hua
Chin. Phys. B, 2013, 22 (3): 030209 doi: 10.1088/1674-1056/22/3/030209
Full Text: [PDF 1830 KB] (Downloads:435)
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We propose multisymplectic implicit and explicit Fourier pseudospectral methods for the Klein–Gordon–Schrödinger equations. We prove that the implicit method satisfies the charge conservation law exactly. Both methods provide accurate solutions in long-time computations and simulate the soliton collision well. Numerical results show the abilities of the two methods in preserving charge, energy, and momentum conservation laws.

Modified Burgers equation by local discontinuous Galerkin method

Zhang Rong-Pei, Yu Xi-Jun, Zhao Guo-Zhong
Chin. Phys. B, 2013, 22 (3): 030210 doi: 10.1088/1674-1056/22/3/030210
Full Text: [PDF 279 KB] (Downloads:989)
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In this paper, we present the local discontinuous Galerkin method for solving Burgers’ equation and the modified Burgers’ equation. We describe the algorithm formulation and practical implementation of the local discontinuous Galerkin method in detail. The method is applied to the solution of the one-dimensional viscous Burgers’ equation and two forms of the modified Burgers’ equation. The numerical results indicate that the method is very accurate and efficient.

Complex Maxwell's equations

A. I. Arbab
Chin. Phys. B, 2013, 22 (3): 030301 doi: 10.1088/1674-1056/22/3/030301
Full Text: [PDF 218 KB] (Downloads:4077)
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A unified complex model of Maxwell's equations is presented. The wave nature of electromagnetic field vector is related to the temporal and spatial distributions and the circulation of charge and current densities. A new vacuum solution is obtained. A new transformation under which Maxwell's equations are invariant is proposed. This transformation extends the ordinary gauge transformation to include charge-current besides scalar-vector potential. An electric dipole moment is found to be related to magnetic charges. The Dirac's quantization is found to determine an uncertainty relation expressing the indeterminacy of electric and magnetic charges. We generalize Maxwell's equations to include longitudinal waves. A formal analogy between this formulation and Dirac's equation is discussed.

Exact solutions of Dirac equation with Pöschl–Teller double-ring-shaped Coulomb potential via Nikiforov–Uvarov method

E. Maghsoodi, H. Hassanabadi, S. Zarrinkamar
Chin. Phys. B, 2013, 22 (3): 030302 doi: 10.1088/1674-1056/22/3/030302
Full Text: [PDF 196 KB] (Downloads:534)
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Exact analytical solutions of the Dirac equation are reported for the Pöschl–Teller double-ring-shaped Coulomb potential. The radial, polar, and azimuthal parts of the Dirac equation are solved by using the Nikiforov–Uvarov method, and exact bound state energy eigenvalues and the corresponding two-component spinor wavefunctions are reported.

Relativistic symmetry of position-dependent mass particle in Coulomb field including tensor interaction

M. Eshghi, M. Hamzavi, S. M. Ikhdair
Chin. Phys. B, 2013, 22 (3): 030303 doi: 10.1088/1674-1056/22/3/030303
Full Text: [PDF 230 KB] (Downloads:462)
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The spatially-dependent mass Dirac equation is solved exactly for attractive scalar and repulsive vector Coulomb potentials including a tensor interaction under the spin and pseudospin symmetric limit. Closed forms of the energy eigenvalue equation and wave functions are obtained for arbitrary spin-orbit quantum number κ. Some numerical results are given too. The effect of the tensor interaction on the bound states is presented. It is shown that the tensor interaction removes the degeneracy between two states in the spin doublets. We also investigate the effects of the spatially-dependent mass on the bound states under the conditions of the spin symmetric limit in the absence of tensor interaction.

Comparison between non-Markovian dynamics with and without rotating wave approximation

Tang Ning, Xu Tian-Tian, Zeng Hao-Sheng
Chin. Phys. B, 2013, 22 (3): 030304 doi: 10.1088/1674-1056/22/3/030304
Full Text: [PDF 621 KB] (Downloads:503)
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In the limit of weak coupling between the system and its reservoir, we derive the time-convolutionless (TCL) non-Markovian master equation for a two-level system interacting with a zero-temperature structured environment with no rotating wave approximation (NRWA). By comparing with the dynamics with RWA, we demonstrate the impact of the RWA on the system dynamics, as well as the effects of non-Markovianity on the preservation of atomic coherence, squeezing, and entanglement.

Efficient three-step entanglement concentration for an arbitrary four-photon cluster state

Si Bin, Su Shi-Lei, Sun Li-Li, Cheng Liu-Yong, Wang Hong-Fu, Zhang Shou
Chin. Phys. B, 2013, 22 (3): 030305 doi: 10.1088/1674-1056/22/3/030305
Full Text: [PDF 266 KB] (Downloads:886)
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We propose an entanglement concentration protocol (ECP) to concentrate an arbitrary partially-entangled four-photon cluster state. As a pioneering three-step entanglement concentration scheme, our protocol only needs single-photon resource to assist the concentration in each step, which makes this protocol more economical. With the help of the linear optical elements and weak cross-Kerr nonlinearity, one can obtain a maximally-entangled cluster state via local operations and classical communication. Moreover, the protocol can be iterated to obtain a higher success probability and is feasible under the current experimental conditions.

Squeezing entangled state of two particles with unequal masses

Yang Yang, Fan Hong-Yi
Chin. Phys. B, 2013, 22 (3): 030306 doi: 10.1088/1674-1056/22/3/030306
Full Text: [PDF 176 KB] (Downloads:347)
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For two unequal-mass particles, we construct the entangled state representation and then derive the corresponding squeezing operator. This squeezing operator has a natural realization in the entangled state representation, which exhibits the intrinsic relation between squeezing and quantum entanglement. This squeezing operator involves both two-mode squeezing and the direct product of two single-mode squeezings. The maximum squeezing occurs when the two particles possess equal mass. When two particles' mass difference becomes large, the component of the two single-mode squeezings becomes dominant.

New approach for deriving the exact time evolution of density operator for diffusive anharmonic oscillator and its Wigner distribution function

Meng Xiang-Guo, Wang Ji-Suo, Liang Bao-Long
Chin. Phys. B, 2013, 22 (3): 030307 doi: 10.1088/1674-1056/22/3/030307
Full Text: [PDF 239 KB] (Downloads:406)
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Using the thermal entangled state representation, we solve the master equation of a diffusive anharmonic oscillator (AHO) to obtain the exact time evolution formula for the density operator in the infinitive operator-sum representation. We present a new evolution formula of the Wigner function (WF) for any initial state of the diffusive AHO by converting the calculation of the WF to an overlap between two pure states in an enlarged Fock space. It is found that this formula brings us much convenience to investigate the WF's evolution of any known initial state. As applications, this formula is used to obtain the evolution of the WF for a coherent state and the evolution of the photon-number distribution of the diffusive AHO.

Induced modification of geometric phase of a qubit coupled to an XY spin chain by the Dzyaloshinsky–Moriya interaction

Zhang Ai-Ping, Li Fu-Li
Chin. Phys. B, 2013, 22 (3): 030308 doi: 10.1088/1674-1056/22/3/030308
Full Text: [PDF 331 KB] (Downloads:444)
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We consider a qubit symmetrically and transversely coupled to an XY spin chain with Dzyaloshinsky–Moriya (DM) interaction in the presence of a transverse magnetic field. An analytical expression for the geometric phase of the qubit is obtained in the weak coupling limit. We find that the modification of the geometrical phase induced by the spin chain environment is greatly enhanced by the DM interaction in the weak coupling limit around the quantum phase transition point of the spin chain.

Electromagnetically induced transparency of single Λ-type three-level atom in high-finesse optical cavity

Sun Yan-Fen, Tan Lei, Xu Yan
Chin. Phys. B, 2013, 22 (3): 030309 doi: 10.1088/1674-1056/22/3/030309
Full Text: [PDF 497 KB] (Downloads:1215)
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We study the features of the electromagnetically induced transparency (EIT) in a single Λ-type three-level atom placed in a high finesse cavity under the action of a coupling laser and a probe laser. Our calculations show that three transparency windows appear when the pump strength is big enough. It can be explained by the residual pump in the cavity resulting mostly in the energy splitting. Level |3〉is split into four slightly different energy levels. An interference takes place between excitation pathways. Furthermore, it is also shown that the frequencies of the EIT windows can be tuned by changing the coupling field detuning Δ2 and the reflection profile is very sensitive to the cavity field detuning Δc.

Nonclassicality and decoherence of coherent superposition operation of photon subtraction and photon addition on squeezed state

Xu Li-Juan, Tan Guo-Bin, Ma Shan-Jun, Guo Qin
Chin. Phys. B, 2013, 22 (3): 030311 doi: 10.1088/1674-1056/22/3/030311
Full Text: [PDF 13850 KB] (Downloads:353)
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The statistical properties of m-coherent superposition operation (μa+νa+)m on the single-mode squeezed vacuum state (M-SSVS) and its decoherence in a thermal environment have been studied. Converting the M-SSVS to a squeezed Hermite polynomial excitation state, we obtain a compact expression for the normalization factor of M-SSVS, which is the Legendre polynomial of the squeezing parameter. We also derive the explicit expression of Wigner function (WF) of M-SSVS, and find the negative region of WF in phase space. The decoherence effect on this state is then discussed by deriving the time evolution of the WF. Using the negativity of WF, the loss of nonclassicality has been discussed.

Maximum confidence measurements via probabilistic quantum cloning

Zhang Wen-Hai, Yu Long-Bao, Cao Zhuo-Liang, Ye Liu
Chin. Phys. B, 2013, 22 (3): 030312 doi: 10.1088/1674-1056/22/3/030312
Full Text: [PDF 196 KB] (Downloads:429)
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Probabilistic quantum cloning (PQC) cannot copy a set of linearly dependent quantum states. In this paper, we show that if incorrect copies are allowed to be produced, linearly dependent quantum states may also be cloned by the PQC. By exploiting this kind of PQC to clone a special set of three linearly dependent quantum states, we derive the upper bound of the maximum confidence measure of a set. An explicit transformation of the maximum confidence measure is presented.

Two-qubit and three-qubit controlled gates with cross-Kerr nonlinearity

Zhao Rui-Tong, Guo Qi, Cheng Liu-Yong, Sun Li-Li, Wang Hong-Fu, Zhang Shou
Chin. Phys. B, 2013, 22 (3): 030313 doi: 10.1088/1674-1056/22/3/030313
Full Text: [PDF 247 KB] (Downloads:833)
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Schemes for two-qubit and three-qubit controlled gates based on cross-Kerr nonlinearity are proposed in this paper. The success probability of these gates can be increased by the quantum nondemolition detectors which are used to judge which paths the signal photons pass through. These schemes are nearly deterministic and require no ancilla photon. The advantages of these gates over the existing ones include Less resource consumption and higher success probability, which make our schemes more feasible with current technology.

Complete Bell-state analysis for single-photon hybrid entangled state Hot!

Sheng Yu-Bo, Zhou Lan, Cheng Wei-Wen, Gong Long-Yan, Wang Lei, Zhao Sheng-Mei
Chin. Phys. B, 2013, 22 (3): 030314 doi: 10.1088/1674-1056/22/3/030314
Full Text: [PDF 257 KB] (Downloads:573)
Show Abstract
We propose a scheme capable of performing complete Bell-state analysis for single-photon hybrid entangled state. Our single-photon state is encoded in both polarization and frequency degrees of freedom. The setup of scheme is composed of polarizing beam splitters, half wave plates, frequency shifters, and independent wavelength division multiplexers, which are feasible with current technology. We also show that, with this setup, we can perform the schemes for complete two-photon Bell-state analysis for polarization degree of freedom. Moreover, it can also be used to perform the teleportation scheme between different degrees of freedom. This setup may allow extensive applications in current quantum communications.

Three-dimensional Bose–Einstein condensate vortex soliton sunder optical lattice and harmonic confinements

Wang Ying, Zong Feng-De, Li Feng-Bo
Chin. Phys. B, 2013, 22 (3): 030315 doi: 10.1088/1674-1056/22/3/030315
Full Text: [PDF 1183 KB] (Downloads:618)
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We predict three-dimensional vortex solitons in a Bose–Einstein condensate under a complex potential which is the combination of a two-dimensional parabolic trap along the transverse radial direction and a one-dimensional optical-lattice potential along the z axis direction. The vortex solitons are built in the form of layer-chain structure made up of several fundamental vortices along the optical-lattice direction, which were not reported before in the three-dimensional Bose–Einstein condensate. By using the combination of the energy density functional method with the direct numerical simulation, we find three-dimensional vortex solitons with topological charge χ=1, χ=2, and χ=3. Moreover, the macroscopic quantum tunneling and the chirp phenomena of the vortex solitons are shown in the evolution. Thereinto, the occurrence of the macroscopic quantum tunneling provides a possibility for the realization of the quantum tunneling in experiment. Specifically, we manipulate the vortex solitons along the optical lattice direction successfully. The stability limits for dragging the vortex solitons from an initial fixed position to a prescribed location are further pursued.

Singularities of noncompact charged objects

M. Sharif, G. Abbas
Chin. Phys. B, 2013, 22 (3): 030401 doi: 10.1088/1674-1056/22/3/030401
Full Text: [PDF 187 KB] (Downloads:361)
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We formulate a model of noncompact spherical charged objects in the framework of noncommutative field theory. The Einstein–Maxwell field equations are solved with charged anisotropic fluid. We choose matter and charge densities as functions of two parameters instead of defining these quantities in terms of Gaussian distribution function. It is found that the corresponding densities and the Ricci scalar are singular at origin, whereas the metric is nonsingular, indicating a spacelike singularity. The numerical solution of the horizon equation implies that there are two or one or no horizon(s) depending on the mass. We also evaluate the Hawking temperature, and find that a black hole with two horizons is evaporated to an extremal black hole with one horizon.

Thermodynamic properties of Reissner–Nordström–de Sitter quintessence black holes

Wei Yi-Huan, Ren Jun
Chin. Phys. B, 2013, 22 (3): 030402 doi: 10.1088/1674-1056/22/3/030402
Full Text: [PDF 225 KB] (Downloads:437)
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Mass, electric charge, and temperature of black holes in the Reissner–Nordström–de Sitter quintessence (RN–dSQ) spacetime are obtained. The heat capacities of the RN–dSQ black hole for certain electric charge and mass are analyzed. The electrostatic energy and the dark energy in the RN–dSQ black hole are also calculated.

Quantum mechanical version of classical Liouville theorem

Xie Chuan-Mei, Fan Hong-Yi
Chin. Phys. B, 2013, 22 (3): 030501 doi: 10.1088/1674-1056/22/3/030501
Full Text: [PDF 192 KB] (Downloads:1484)
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In terms of the coherent state evolution in phase space, we present a quantum mechanical version of the classical Liouville theorem. The evolution of coherent state from |z〉to |sz-rz*〉angle corresponds to the motion from a point z(q,p) to another point sz-rz* with |s|2-|r|2=1. The evolution is governed by the so-called Fresnel operator U(s,r) recently proposed in quantum optics theory, which classically corresponds to the matrix optics law and the optical Fresnel transformation and obeys the group product rules. In another word, we can recapitulate the Liouville theorem in the context of quantum mechanics by virtue of coherent state evolution in phase space, which seems to be a combination of quantum statistics and quantum optics.

Noise destroys the coexisting of periodic orbits of a piecewise linear map

Wang Can-Jun, Yang Ke-Li, Qu Shi-Xian
Chin. Phys. B, 2013, 22 (3): 030502 doi: 10.1088/1674-1056/22/3/030502
Full Text: [PDF 406 KB] (Downloads:368)
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The effects of the Gaussian white noise and the Gaussian colored noise on the periodic orbits of period-5 (P-5) and period-6 (P-6) in their coexisting domain of a piecewise linear map are investigated numerically. The probability densities of some orbits are calculated. When the noise intensity is D=0.0001, only the orbits of P-5 exist, and the coexisting phenomenon is destroyed. On the other hand, the self-correlation time τ of the colored noise also affects the coexisting phenomenon. When τc<τ<τc', only the orbits of P-5 appear, and the stability of the orbits of P-5 is enhanced. However, when τ>τc' (τc and τc' are critical values), only the orbits of P-6 exist, and the stability of the orbits of P-6 is enhanced greatly. When τ<τc, the orbits of P-5 and P-6 coexist, but the stability of the orbits of P-5 is enhanced and that of P-6 is weakened with τ increasing.

High frequency forcing on nonlinear systems

Yao Cheng-Gui, He Zhi-Wei, Zhan Meng
Chin. Phys. B, 2013, 22 (3): 030503 doi: 10.1088/1674-1056/22/3/030503
Full Text: [PDF 3954 KB] (Downloads:804)
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High-frequency signals are pervasive in many science and engineering fields. In this work, the effect of high-frequency driving on general nonlinear systems is investigated, and an effective equation for the slow motion is derived by extending the inertial approximation for the direct separation of fast and slow motions. Based on this theory, a high-frequency force can induce various phase transitions of a system by changing its amplitude and frequency. Numerical simulations on several nonlinear oscillator systems show very good agreements with the theoretic result. These findings may shed light on our understanding of the dynamics of nonlinear systems subject to a periodic force.

Correlation between detrended fluctuation analysis and the Lempel–Ziv complexity in nonlinear time series analysis

Tang You-Fu, Liu Shu-Lin, Jiang Rui-Hong, Liu Ying-Hui
Chin. Phys. B, 2013, 22 (3): 030504 doi: 10.1088/1674-1056/22/3/030504
Full Text: [PDF 724 KB] (Downloads:664)
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We focus on the study of the correlation between the detrended fluctuation analysis (DFA) and the Lempel–Ziv complexity (LZC) in nonlinear time series analysis in this paper. Typical dynamical systems including logistic map and Duffing model are investigated. Moreover, the influences of the Gaussian random noise on both DFA and LZC are analyzed. The results show a high correlation between DFA and LZC, which can quantify the non-stationarity and the nonlinearity of the time series, respectively. With the enhancement of the random component, the exponent α and the normalized complexity index C show increasing trends. In addition, C is found to be more sensitive to the fluctuation in the nonlinear time series than α. Finally, the correlation between DFA and LZC is applied to the feature extraction of vibration signals for a reciprocating compressor gas valve, and an effective fault diagnosis result is obtained.

Hybrid three-dimensional variation and particle filtering for nonlinear systems

Leng Hong-Ze, Song Jun-Qiang
Chin. Phys. B, 2013, 22 (3): 030505 doi: 10.1088/1674-1056/22/3/030505
Full Text: [PDF 415 KB] (Downloads:393)
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This work addresses the problem of estimating the states of nonlinear dynamic systems with sparse observations. We present a hybrid three-dimensional variation (3DVar) and particle piltering (PF) method, which combines the advantages of 3DVar and particle-based filters. By minimizing the cost function, this approach will produce a better proposal distribution of the state. Afterwards the stochastic resampling step in standard PF can be avoided through a deterministic scheme. The simulation results show that the performance of the new method is superior to the traditional ensemble Kalman filtering (EnKF) and the standard PF, especially in highly nonlinear systems.

Transfer function modeling and analysis of the open-loop Buck converter using the fractional calculus

Wang Fa-Qiang, Ma Xi-Kui
Chin. Phys. B, 2013, 22 (3): 030506 doi: 10.1088/1674-1056/22/3/030506
Full Text: [PDF 457 KB] (Downloads:19054)
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Based on the fact that the real inductor and the real capacitor are fractional order in nature and the fractional calculus, the transfer function modeling and analysis of the open-loop Buck converter in continuous conduction mode (CCM) operation are carried out in this paper. The fractional order small signal model and the corresponding equivalent circuit of the open-loop Buck converter in CCM operation are presented. The transfer functions from the input voltage to the output voltage, from the input voltage to the inductor current, from the duty cycle to the output voltage, from the duty cycle to the inductor current, and the output impedance of the open-loop Buck converter in CCM operation are derived, and their bode diagrams and step responses are calculated, respectively. It is found that all the derived fractional order transfer functions of the system are influenced by the fractional orders of the inductor and the capacitor. Finally, the realization of the fractional order inductor and the fractional order capacitor is designed, and the corresponding PSIM circuit simulation results of the open-loop Buck converter in CCM operation are given to confirm the correctness of the derivations and the theoretical analysis.

Generation of transient chaos from two-dimensional systems via a switching approach

Sun Chang-Chun, Xu Qi-Cheng, Sui Ying
Chin. Phys. B, 2013, 22 (3): 030507 doi: 10.1088/1674-1056/22/3/030507
Full Text: [PDF 334 KB] (Downloads:500)
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A new approach of generating transient chaos from two-dimensional (2D) continuous autonomous systems within finite time is presented. Based on an absolute-value switching law, the phenomenon of transient chaos takes place by switching between three 2D systems. Basic dynamical behaviors of the systems are investigated. Numerical examples illustrate the validity of the results.

Adaptive control of bifurcation and chaos in a time-delayed system

Li Ning, Yuan Hui-Qun, Sun Hai-Yi, Zhang Qing-Ling
Chin. Phys. B, 2013, 22 (3): 030508 doi: 10.1088/1674-1056/22/3/030508
Full Text: [PDF 391 KB] (Downloads:672)
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In this paper, the stabilization of a continuous time-delayed system is considered. To control the bifurcation and chaos in a time-delayed system, a parameter perturbation control and a hybrid control are proposed. Then, to ensure the asymptotic stability of the system in the presence of unexpected system parameter changes, the adaptive control idea is introduced, i.e., the perturbation control parameter and the hybrid control parameter are automatically tuned according to the adaptation laws, respectively. The adaptation algorithms are constructed based on the Lyapunov–Krasovskii stability theorem. The adaptive parameter perturbation control and the adaptive hybrid control methods improve the corresponding constant control methods. They have the advantages of increased stability, adaptability to the changes of the system parameters, control cost saving, and simplicity. Numerical simulations for a well-known chaotic time-delayed system are performed to demonstrate the feasibility and superiority of the proposed control methods. Besides, comparison of the two adaptive control methods are made in an experimental study.

Chaotic dynamic behavior analysis and control for a financial risk system

Zhang Xiao-Dan, Liu Xiang-Dong, Zheng Yuan, Liu Cheng
Chin. Phys. B, 2013, 22 (3): 030509 doi: 10.1088/1674-1056/22/3/030509
Full Text: [PDF 1490 KB] (Downloads:1681)
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According to the risk management process of financial market, a financial risk dynamic system is constructed in this paper. Through analyzing the basic dynamic property, we obtain the conditions for stability and bifurcation of the system based on Hopf bifurcation theory of nonlinear dynamical systems. In order to make the system's chaos disappear, we select the feedback gain matrix to design a class of chaotic controller. Numerical simulations are performed to reveal the change process of financial market risk. It is shown that, when the parameter of risk transmission rate changes, the system gradually comes into chaos from the asymptotically stable state through bifurcation. Besides, the controller can control chaos effectively.

Average consensus of multi-agent systems with communication time delays and noisy links

Sun Yong-Zheng, Li Wang, Ruan Jiong
Chin. Phys. B, 2013, 22 (3): 030510 doi: 10.1088/1674-1056/22/3/030510
Full Text: [PDF 787 KB] (Downloads:791)
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In this paper, we consider the average-consensus problem with communication time delays and noisy links. We analyze two different cases of coupling topologies: fixed and switching topologies. By utilizing the stability theory of the stochastic differential equations, we analytically show that the average consensus could be achieved almost surely with the perturbation of noise and the communication time delays even if the time delay is time-varying. The theoretical results show that the multi-agent systems can tolerate relatively large time delays if the noise is weak, and it can tolerate relatively strong noise if the time delays are low. The simulation results show that systems with strong noise intensities yield slow convergence.

Novel loop-like solitons for generalized Vakhnenko equation

Zhang Min, Ma Yu-Lan, Li Bang-Qing
Chin. Phys. B, 2013, 22 (3): 030511 doi: 10.1088/1674-1056/22/3/030511
Full Text: [PDF 1313 KB] (Downloads:427)
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A nontraveling wave solution of a generalized Vakhnenko equation arising from the high-frequent wave motion in a relaxing medium is derived via the extended Riccati mapping method. The solution includes an arbitrary function of an independent variable. Based on the solution, two hyperbolic functions are chosen to construct new solitons. Novel single-loop-like and double-loop-like solitons are found for the equation.

Propagation of electromagnetic soliton in anisotropic biquadratic ferromagnetic medium

L. Kavitha, M. Saravanan, D. Gopi
Chin. Phys. B, 2013, 22 (3): 030512 doi: 10.1088/1674-1056/22/3/030512
Full Text: [PDF 1073 KB] (Downloads:753)
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The information storage technology based on anisotropic ferromagnets with sufficiently high magneto-optical effects has received much attention in recent years. The magneto-optical recording combines the merits of magnetic and optical techniques. We investigate the magneto-optical effects on a biquadratic ferromagnet and show that the dynamics of the system is governed by a perturbed nonlinear Schrödinger equation. The evolutions of amplitude and velocity of the soliton are found to be time independent, thereby admitting the lossless propagation of electromagnetic soliton in the medium, which may have potential applications in accordance with the soliton based optical communication systems. We also exploit the role of perturbation, which has a significant impact on the propagation of electromagnetic soliton.
RAPID COMMUNICATION

Average position in quantum walks with a U(2) coin Hot!

Li Min, Zhang Yong-Sheng, Guo Guang-Can
Chin. Phys. B, 2013, 22 (3): 030310 doi: 10.1088/1674-1056/22/3/030310
Full Text: [PDF 266 KB] (Downloads:316)
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We investigated discrete-time quantum walks with an arbitary unitary coin. Here we discover that the average position〈x〉=max(〈x〉)sin(α+γ), while the initial state is 1/√2(|0L〉+ i|0R〉). We verify the result, and obtain some symmetry properties of quantum walks with a U(2) coin with |0L〉 and |0R〉 as the initial state.

A single diffractive optical element implementing spectrum-splitting and beam-concentration functions simultaneously with high diffraction efficiency

Ye Jia-Sheng, Wang Jin-Ze, Huang Qing-Li, Dong Bi-Zhen, Zhang Yan, Yang Guo-Zhen
Chin. Phys. B, 2013, 22 (3): 034201 doi: 10.1088/1674-1056/22/3/034201
Full Text: [PDF 581 KB] (Downloads:448)
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In this paper, a novel method is proposed and employed to design a single diffractive optical element (DOE) for implementing spectrum-splitting and beam-concentration (SSBC) functions simultaneously. We develop an optimization algorithm, through which the SSBC DOE can be optimized within an arbitrary thickness range according to the limitations of the modern photolithography technology. Theoretical simulation results reveal that the designed SSBC DOE has a high optical focusing efficiency. It is expected that the designed SSBC DOE should have practical applications in high-efficiency solar cell systems.
ATOMIC AND MOLECULAR PHYSICS

New atomic data for Kr XXXV useful in fusion plasma

Sunny Aggarwal, Jagjit Singh, Man Mohan
Chin. Phys. B, 2013, 22 (3): 033201 doi: 10.1088/1674-1056/22/3/033201
Full Text: [PDF 177 KB] (Downloads:478)
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Energy levels and emission line wavelengths of high-Z materials are useful for impurity diagnostics due to its potential application in the next generation fusion devices. For this purpose, we have calculated the fine structural energies of the 67 levels belonging to the 1s2, 1s2l, 1s3l, 1s4l, 1s5l, and 1s6l configurations of Kr XXXV using GRASP (general purpose relativistic atomic structure package) code. Additionally, we have reported the transition probabilities, oscillator strengths, line strengths, and transition wavelengths for some electric dipole (E1) transitions among these levels. We predict new energy levels and radiative rates, which have not been reported experimentally or theoretically, forming the basis for future experimental work.

Linewidth of electromagnetically induced transparency under motional averaging in coated vapor cell

Xu Zhi-Xiang, Qu Wei-Zhi, Gao Ran, Hu Xin-Hua, Xiao Yan-Hong
Chin. Phys. B, 2013, 22 (3): 033202 doi: 10.1088/1674-1056/22/3/033202
Full Text: [PDF 3295 KB] (Downloads:1124)
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The linewidth of electromagnetically induced transparency (EIT) in a coated Rb vapor cell was studied under a magnetic field gradient. The nonlinear broadening of the EIT linewidth with the magnetic field gradient was observed. It was found that the motional averaging of the field gradient was more pronounced at higher laser intensities and larger beam sizes. In the same regime, there was a small linewidth decrease with the increasing magnetic field gradient. We have established a Monte–Carlo model, which gave results in good qualitative agreement with our experiment. Physics pictures for the above phenomena were also suggested. These results provide an understanding of the EIT linewidth behavior under the motional averaging, and should be useful for applications in quantum optics and metrology based on coated vapor cells.

High-intensity molecular harmonic generation without ionization

Wang Jun, Chen Gao, Guo Fu-Ming, Li Su-Yu, Chen Ji-Gen, Yang Yu-Jun
Chin. Phys. B, 2013, 22 (3): 033203 doi: 10.1088/1674-1056/22/3/033203
Full Text: [PDF 612 KB] (Downloads:461)
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We theoretically investigate the high-order harmonic generation from H2+ in an infrared laser field. Our numerical simulations show that there exists a highly efficient plateau structure in the molecular harmonic spectrum. Under the action of the infrared laser pulse, the bound electronic wave packet in a potential well has enough time to tunnel through the effective potential barrier, which is formed by the molecular potential and the infrared laser field, and then recombine with the neighboring nucleus emitting a harmonic photon. During the entire dynamic process, because the wave packet is mainly located in the effective potential, the diffusion effect is of no significance, and thus a highly efficient harmonic plateau can be achieved. Specifically, the cut-off frequency of the plateau is linearly scaled with the peak amplitude of the infrared laser electric field, which may open another route to examine the internuclear distance of the molecule. Furthermore, one may detect the molecular bond lengths using the harmonic plateau.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Switching the direction of spin accumulation in the spin Hall effect of light by adjusting the optical axis of an uniaxial crystal

Tang Ming, Zhou Xin-Xing, Xiao Zhi-Cheng, Luo Hai-Lu, Wen Shuang-Chun
Chin. Phys. B, 2013, 22 (3): 034101 doi: 10.1088/1674-1056/22/3/034101
Full Text: [PDF 744 KB] (Downloads:445)
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We theoretically and experimentally investigate a switchable spin Hall effect (SHE) of light in reflection near the Brewster angle at an air–uniaxial crystal interface. We find a large transverse spin splitting near the Brewster angle, whose sign can be altered by rotating the optical axis. As an analogy of the SHE in an electronic system, a switchable spin accumulation in the SHE of light is detected. We are able to switch the direction of the spin accumulation by adjusting the optical axis angle of the uniaxial crystal. These findings may give opportunities for photon spin manipulating and developing a new generation of nano-photonic devices.

Manipulating surface plasmon waves by transformation optics: Design examples of beam squeezer, bend, and omnidirectional absorber

Yu Zhen-Zhong, Feng Yi-Jun, Wang Zheng-Bin, Zhao Jun-Ming, Jiang Tian
Chin. Phys. B, 2013, 22 (3): 034102 doi: 10.1088/1674-1056/22/3/034102
Full Text: [PDF 2974 KB] (Downloads:986)
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We present several design examples of how to apply the transformation optics and curved space under coordinate transformation to manipulating the surface plasmon waves in a controlled manner. We demonstrate in detail the design procedure of the plasmonic wave squeezer, in-plane bend and omnidirectional absorber. We show that the approximation method of modifying only the dielectric material of a dielectric–metal surface of the plasmonic device could lead to acceptable performance, which facilitates the fabrication of the device. The functionality of the proposed plasmonic device is verified using three-dimensional full-wave electromagnetic simulations. Aiming at practical realization, we also show the design of plasmonic in-plane bend and omnidirectional absorber by an alternative transformation scheme, which results in simple device structure with a tapered isotropic dielectric cladding layer on the top of the metal surface that can be fabricated with the existing nanotechnology.

New formulas for normalizing photon-added (-subtracted) two-mode squeezed thermal states

Hu Li-Yun, Fan Hong-Yi, Zhang Zhi-Ming
Chin. Phys. B, 2013, 22 (3): 034202 doi: 10.1088/1674-1056/22/3/034202
Full Text: [PDF 236 KB] (Downloads:550)
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For the first time, we derive the compact forms of normalization factors for photon-added (-subtracted) two-mode squeezed thermal states by using the P-representation and the integration within an ordered product of operators (IWOP) technique. It is found that these two factors are related to the Jacobi polynomials. In addition, some new relations are presented for the Jacobi polynomials.

Dynamic thermal modeling and parameter identification for monolithic laser diode module

Li Jin-Yi, Du Zhen-Hui, Ma Yi-Wen, Xu Ke-Xin
Chin. Phys. B, 2013, 22 (3): 034203 doi: 10.1088/1674-1056/22/3/034203
Full Text: [PDF 311 KB] (Downloads:1001)
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We improve the thermal equivalent-circuit model of the laser diode module (LDM) to evaluate its thermal dynamic property and calculate the junction temperature of the laser diode with a high accuracy. The thermal parameters and the transient junction temperature of LDM are modeled and obtained according to the temperature of the thermistor integrated in the module. Our improved thermal model is verified indirectly by monitoring the emission wavelength of the laser diode against gas absorption lines, and several thermal parameters are obtained with the temperature uncertainty of 0.01 K in the thermal dynamic process.

Pulse collapse and blue-shifted enhanced supercontinuumin photonic crystal fiber

Liu Wen-Jun, Pang Li-Hui, Lin Xiang, Gao Ren-Xi, Song Xiao-Wei
Chin. Phys. B, 2013, 22 (3): 034204 doi: 10.1088/1674-1056/22/3/034204
Full Text: [PDF 1060 KB] (Downloads:469)
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The blue-shifted supercontinuum generation in a photonic crystal fiber pumped by high peak power femtosecond pulses with wavelength located in the anomalous dispersion region is investigated experimentally and numerically. The formation of a blue-shifted enhanced supercontinuum due to the pulse collapse is demonstrated. The process of the pulse collapse is measured by using the grating-eliminated no-nonsense observation of ultrafast incident laser light e-fields technique (GRENOUILLE). Numerical simulations in spectral and temporal domains are conducted. The data from numerical simulations are in good agreement with the experimental results. Our experimental results and numerical simulations show that the pulse collapse is the determining factor in the generation of blue-shifted supercontinuum.

Impacts of higher-order dispersions and saturable nonlinearities on modulation instability in negative-refractive metamaterials

Zhong Xian-Qiong, Cheng Ke, Xiang An-Ping
Chin. Phys. B, 2013, 22 (3): 034205 doi: 10.1088/1674-1056/22/3/034205
Full Text: [PDF 971 KB] (Downloads:520)
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On the basis of the standard linear stability analysis and Drude electromagnetic model, the impacts of higher-order dispersions and three kinds of typical saturable nonlinearities on modulation instability (MI) have been analyzed and calculated for negative-refractive metamaterials (MMs). Our results show that the MI gain spectra consist of only one spectral region instead of one or two regions in ordinary materials, which may be close to or far from the zero point. Particularly, the spectrum far from the zero point has a high cut-off frequency but a narrow spectral width, which is obviously beneficial to the generation of high-repetition-rate pulse trains. Moreover, MI characteristics here will vary with the normalized angular frequency which can be modified by adjusting the structures of negative-refractive MMs, signifying the controllability of bistable solitons and MI based applications. The effects of saturable nonlinearities are similar to those in ordinary materials.

Optical manipulation of gold nanoparticles using an optical nanofiber

Li Ying, Hu Yan-Jun
Chin. Phys. B, 2013, 22 (3): 034206 doi: 10.1088/1674-1056/22/3/034206
Full Text: [PDF 996 KB] (Downloads:507)
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Gold nanoparticles are gaining increasing attention due to their biological and medical applications. In this letter, we experimentally demonstrate an optical manipulation of 250-nm-diameter gold nanoparticles along an optical nanofiber (550 nm in diameter) injected by an 808-nm laser light. The nanoparticles situated in the evanescent optical field are trapped by optical gradient force and move along the direction of light propagation due to optical scattering force. The velocities reach as high as 132 μm/s at an optical power of 80 mW.

Infrared-induced temperature distributions of solid D2 ices

Bi Peng, Xie Duan, Lin Wei, Wang Kai, Liu Jiang-Ping, Tang Yong-Jian, Yang Xiang-Dong, Lei Hai-Le
Chin. Phys. B, 2013, 22 (3): 034401 doi: 10.1088/1674-1056/22/3/034401
Full Text: [PDF 1232 KB] (Downloads:602)
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A specific-wavelength infrared (IR) light (λ=3140 nm) was irradiated into a solid D2 ice prepared in a cylinder target cell. The temperature in the solid D2 ice oscillated periodically with a high amplitude when irradiated by the IR light. The temperature oscillation has been well explained based on the two-dimensional heat transfer theory plus the IR-irradiation effect. The transmission optical imaging reveals that such a temperature oscillation is favorable to recrystallize the solid D2 ice from multicrystal to quasi single crystal. This suggests an efficient method to layer the solid hydrogen-isotope ice for the inertial-confinement-fusion (ICF) experiments.

Mean and fluctuating velocity fields of a diamond turbulent jet

Xu Min-Yi, Zhang Jian-Peng, Mi Jian-Chun, Nathan G. J., Kalt P. A. M.
Chin. Phys. B, 2013, 22 (3): 034701 doi: 10.1088/1674-1056/22/3/034701
Full Text: [PDF 1892 KB] (Downloads:506)
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The present paper reports the first investigation on a turbulent jet issuing from a diamond orifice (hereafter termed ''diamond jet'') with an aspect ratio of 1.7. Velocity measurements were conducted in the transitional region, and the exit Reynolds number of the jet was 50000. For comparison, a round jet with identical normalized boundary conditions was also measured. It is shown that the diamond jet decays and spreads faster than the round jet does over the measured flow region. The axis-switching phenomenon is observed in the diamond jet. Although both jets display primary coherent structures in the near field, these structures are found to break down more rapidly in the diamond jet, due to the higher three-dimensionality of the flow. Moreover, the streamwise components of the Reynolds normal stress and all the shear stresses reach their maxima around the location of the maximal mean shear while the maxima of the lateral components of the Reynolds normal stresses occur around the centreline of the jet.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Effective ionization coefficients and electron drift velocities in gasmixtures of CF3I with N2 and CO2 obtained from Boltzmannequation analysis

Deng Yun-Kun, Xiao Deng-Ming
Chin. Phys. B, 2013, 22 (3): 035101 doi: 10.1088/1674-1056/22/3/035101
Full Text: [PDF 428 KB] (Downloads:1153)
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The electron swarm parameters including the density-normalized effective ionization coefficients (α-η)/N and the electron drift velocities Ve are calculated for the gas mixture of CF3I with N2 and CO2 by solving the Boltzmann equation in the condition of steady-state Townsend (SST) experiment. The overall density-reduced electric field strength is from 100 Td to 1000 Td (1 Td=10-17 V·cm2), while the CF3I content k in the gas mixture can be varied over the range from 0% to 100%. From the variation of (α-η)/N with the CF3I mixture ratio k, the limiting field strength (E/N)lim for each CF3I concentration is derived. It is found that for the mixtures with 70% CF3I, the values of (E/N)lim are essentially the same as that for pure SF6. Additionally, the global warming potential (GWP) and the liquefaction temperature of the gas mixtures are also taken into account to evaluate the possibility of applying in the gas insulation of power equipment.

Effect on Landau damping rates for non-Maxwellian distribution function consisting of two electron populations

M. N. S. Qureshi, S. Sehar, H. A. Shah, J. B. Cao
Chin. Phys. B, 2013, 22 (3): 035201 doi: 10.1088/1674-1056/22/3/035201
Full Text: [PDF 352 KB] (Downloads:699)
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In many physical situations where a laser or electron beam passes through a dense plasma, hot low-density electron populations can be generated, resulting in a particle distribution function consisting of a dense cold population and a small hot population. Presence of such low-density electron distributions can alter the wave damping rate. Kinetic model is employed to study the Landau damping of Langmuir waves when a small hot electron population is present in the dense cold electron population with non-Maxwellian distribution functions. Departure of plasma from Maxwellian distributions significantly alters the damping rates as compared to the Maxwellian plasma. Strong damping is found for highly non-Maxwellian distributions as well as plasmas with higher dense and hot electron population. Existence of weak damping is also established when the distribution contains broadened flat tops at the low energies or tends to be Maxwellian. These results may be applied in both experimental and space physics regimes.

Kadomtsev–Petviashvili equation for dust ion-acoustic solitons in pair-ion plasmas

Hafeez Ur-Rehman
Chin. Phys. B, 2013, 22 (3): 035202 doi: 10.1088/1674-1056/22/3/035202
Full Text: [PDF 387 KB] (Downloads:1057)
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Using the reductive perturbation method, we have derived the Kadomtsev–Petviashvili (KP) equation to study the nonlinear properties of electrostatic collisionless dust ion-acoustic solitons in the pair-ion (p-i) plasmas. We have chosen the fluid model for the positive ions, the negative ions, and a fraction of static charged (both positively and negatively) dust particles. Numerical solutions of these dust ion-acoustic solitons are plotted and their characteristics are discussed. It is found that only the amplitudes of the electrostatic dust ion-acoustic solitons vary when the dust is introduced in the pair-ion plasma. It is also noticed that the amplitude and the width of these solitons both vary when the thermal energy of the positive or negative ions is varied. It is shown that potential hump structures are formed when the temperature of the negative ions is higher than that of the positive ions, and potential dip structures are observed when the temperature of the positive ions supersedes that of the negative ions. As the pair-ion plasma mimics the electron–positron plasma, thus our results might be helpful in understanding the nonlinear dust ion acoustic solitary waves in super dense astronomical bodies.

Comparative investigation of resistance and ability to trigger high voltage discharge for single and multiple femtosecond filaments in air

Guo Kai-Min, Hao Zuo-Qiang, Lin Jing-Quan, Sun Chang-Kai, Gao Xun, Zhao Zhen-Ming
Chin. Phys. B, 2013, 22 (3): 035203 doi: 10.1088/1674-1056/22/3/035203
Full Text: [PDF 274 KB] (Downloads:394)
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A comparative investigation of resistance and ability to trigger high voltage (HV) discharge for single filament (SF) and multiple filaments (MF) has been carried out. The experimental results show that the trend of the breakdown threshold of the SF exactly follows that of its resistance, but this is not the case for the MF. The MF's resistance is much smaller than SF's. However, the MF shows a bit higher HV breakdown threshold than the SF. The underlying physics is that the measured resistance of the MF is collectively contributed by every filament in the MF while the HV breakdown threshold is determined by only one single discharging path.

Effect of pulsed bias on properties of ZrN/TiZrN films deposited by cathodic vacuum arc

Zhang Guo-Ping, Wang Xing-Quan, Lü Guo-Hua, Zhou Lan, Huang Jun, Chen Wei, Yang Si-Ze
Chin. Phys. B, 2013, 22 (3): 035204 doi: 10.1088/1674-1056/22/3/035204
Full Text: [PDF 835 KB] (Downloads:673)
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ZrN/TiZrN multilayer are deposited by cathodic vacuum arc method with different substrate bias (from 0 to -800 V), using Ti and Zr plasma flows in residual N2 atmosphere, combined with ion bombardment of sample surfaces. The effect of pulsed bias on structure and properties of films is investigated. Microstructure of the coating is analyzed by X-ray diffraction (XRD), and scanning electron microscopy (SEM). Meanwhile, the nanohardness, Young's modulus, and scratch tests are performed. The experimental results show that the films exhibit a nanoscale multilayer structure consisting of TiZrN and ZrN phases. Solid solutions are formed for component TiZrN films. The dominant preferred orientation of TiZrN films is (111) and (220). At pulsed bias of -200 V, the nanohardness and the adhesion strength of ZrN/TiZrN multilayer reach a maximum of 38 GPa, and 78 N, respectively. The ZrN/TiZrN multilayer demonstrates an enhanced nanohardness compared with binary TiN and ZrN films deposited under equivalent conditions.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Band structure characteristics of T-square fractal phononic crystals

Liu Xiao-Jian, Fan You-Hua
Chin. Phys. B, 2013, 22 (3): 036101 doi: 10.1088/1674-1056/22/3/036101
Full Text: [PDF 521 KB] (Downloads:553)
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The T-square fractal two-dimensional phononic crystal model is presented in this article. A comprehensive study is performed for the Bragg scattering and locally resonant fractal phononic crystal. We find that the band structures of the fractal and non-fractal phononic crystals at the same filling ratio are quite different through using the finite element method. The fractal design has important impact on the band structures of the two-dimensional phononic crystals.

Optical study of D–D neutron irradiation-induced defects in Co- and Cu-doped ZnO wafers

Wang Yun-Bo, Li Gong-Ping, Xu Nan-Nan, Pan Xiao-Dong
Chin. Phys. B, 2013, 22 (3): 036102 doi: 10.1088/1674-1056/22/3/036102
Full Text: [PDF 487 KB] (Downloads:488)
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Room-temperature photoluminescence and optical transmittance spectroscopy of Co-doped (1×1014,5×1016, and 1×1017 cm-2) and Cu-doped (5×1016 cm-2) ZnO wafers irradiated by D–D neutrons (fluence of 2.9×1010 cm-2) have been investigated. After irradiation, the Co or Cu metal and oxide clusters in doped ZnO wafers are dissolved, and the würtzite structure of ZnO substrate for each sample remains unchanged and keeps in high c-axis preferential orientation. The degree of irradiation-induced crystal disorder reflected from absorption band tail parameter (E0) is far greater for doped ZnO than undoped one. Under the same doping concentration, the Cu-doped ZnO wafer has much higher irradiation-induced disorder than the Co-doped one. Photoluminescence measurements indicate that the introduction rate of both zinc vacancy and zinc interstitial is much higher for the doped ZnO wafer with high doping level than the undoped one. In addition, both crystal lattice distortion and defect complexes are suggested to be formed in doped ZnO wafers. Consequently, the Co- or Cu-doped ZnO wafer (especially with high doping level) exhibits very low radiation hardness compared with the undoped one, and the Cu-doped ZnO wafer is much less radiation-hard than the Co-doped one.

Radiation damage effects on power VDMOS devices with composite SiO2–Si3N4 films

Gao Bo, Liu Gang, Wang Li-Xin, Han Zheng-Sheng, Song Li-Mei, Zhang Yan-Fei, Teng Rui, Wu Hai-Zhou
Chin. Phys. B, 2013, 22 (3): 036103 doi: 10.1088/1674-1056/22/3/036103
Full Text: [PDF 523 KB] (Downloads:536)
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Total dose effects and single event effects on radiation-hardened power vertical double-diffusion metal oxide semiconductor (VDMOS) devices with composite SiO2-–Si3N4 film gate are investigated. The relationships among the important electrical parameters of the samples with different thickness SiO2-–Si3N4 films, such as threshold voltage, breakdown voltage, and on-state resistance in accumulated dose, are discussed. The total dose experiment results show that the breakdown voltage and the on-state resistance barely change with the accumulated dose. However, the relationships between the threshold voltages of the samples and the accumulated dose are more complex, not only positive drift, but also negative drift. At the end of the total dose experiment, we select the group of samples which have the smaller threshold voltage shift to carry out the single event effect studies. We find that the samples with appropriate thickness ratio SiO2-–Si3N4 films have a good radiation-hardening ability. This method may be useful in solving both the SEGR and the total dose problems with the composite SiO2-–Si3N4 films.

A Dugdale–Barenblatt model for a strip with a semi-infinite crack embedded in decagonal quasicrystals

Li Wu, Xie Ling-Yun
Chin. Phys. B, 2013, 22 (3): 036201 doi: 10.1088/1674-1056/22/3/036201
Full Text: [PDF 253 KB] (Downloads:594)
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The present study is to determine the solution of a strip with a semi-infinite crack embedded in decagonal quasicrystals, which transforms a physically and mathematically daunting problem. Then cohesive forces are incorporated into a plastic strip in the elastic body for nonlinear deformation. By superposing the two linear elastic fields, one is evaluated with internal loadings and the other with cohesive forces, the problem is treated in Dugdale–Barenblatt manner. A simple but yet rigorous version of the complex analysis theory is employed here, which involves conformal mapping technique. The analytical approach leads to the establishment of a few equations, which allows the exact calculation of the size of cohesive force zone and the most important physical quantity in crack theory: stress intensity factor. The analytical results of the present study may be used as the basis of fracture theory of decagonal quasicrystals.

Site occupation of doping La3+ cations and phase transition in Na0.5Bi0.5TiO3–BaTiO3 solid solution

Liu Li-Ying, Wang Ru-Zhi, Zhu Man-Kang, Hou Yu-Dong
Chin. Phys. B, 2013, 22 (3): 036401 doi: 10.1088/1674-1056/22/3/036401
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Effects of La doping on the ferroelectric properties of 0.92Na0.5Bi0.5TiO3–0.08BaTiO3 (NBT–BT) solid solution have been studied both experimentally and theoretically. The experimental results show that an abnormal ferro-to-antiferroelectric phase transition is induced by La doping in NBT–BT. The first-principles calculations indicate that La3+ cations selectively substitute for the A site in NBT–BT as donors. Furthermore, the computed binding energy reveals that La cations is most likely to substitute for Ba2+ or Na+ to Bi3+ at A site as donors in NBT–BT, as supported by our Raman spectra. The ferro-to-antiferroelectric phase transition of La-doped NBT–BT is believed to originate from the lattice aberrance and redistribution of valence electrons, thus strengthening the bonding of A–O, enhancing the hybridization between the A cation d orbital and O 2p orbital, and resulting in the deflection of the polar direction of NBT–BT lattice.

Relation between Tolman length and isothermal compressibility for simple liquids

Wang Xiao-Song, Zhu Ru-Zeng
Chin. Phys. B, 2013, 22 (3): 036801 doi: 10.1088/1674-1056/22/3/036801
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Tolman length δ0 of the liquid with a plane surface has attracted an increasing theoretical attention in recent years, while the expression of Tolman length in terms of observable quantities is still not very clear. In 2001, Bartell gave a simple expression of Tolman length δ0 in terms of isothermal compressibility. However, this expression predicts that Tolman length is always negative, which is contrary to the results of molecular dynamics simulations (MDS) for simple liquids. In this paper, this contradiction is analyzed and the reason for the discrepancy in the sign is found. In addition, we introduce a new expression of Tolman length in terms of isothermal compressibility for simple fluids not near the critical points under some week restrictions. The Tolman length of simple liquids calculated by using this formula is consistent with that obtained using MDS regarding the sign.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Phase transition and thermodynamic properties of BiFeO3 from first-principles calculations

Li Qiang, Huang Duo-Hui, Cao Qi-Long, Wang Fan-Hou
Chin. Phys. B, 2013, 22 (3): 037101 doi: 10.1088/1674-1056/22/3/037101
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The first-principles projector-augmented wave method employing quasi-harmonic Debye model, is applied to investigate the thermodynamic properties and the phase transition between the trigonal R3c structure and the orthorhombic Pnma structure. It is found that at ambient temperature, the phase transition from the trigonal R3c phase to the orthorhombic Pnma phase is a first-order antiferromagnetic–nonmagnetic and insulator–metal transition, and occurs at 10.56 GPa, which is in good agreement with experimental data. With increasing temperature, the transition pressure decreases almost linearly. Moreover, the thermodynamic properties including Grüneisen parameter, heat capacity, entropy, and the dependences of thermal expansion coefficient on temperature and pressure are also obtained.

Ferromagnetism in ZnO with (Mn,Li) codoping

Ma Shi-Jia, Lu Peng-Fei, Yu Zhong-Yuan, Zhao Long, Li Qiong-Yao, Wu Cheng-Jie, Ding Lu
Chin. Phys. B, 2013, 22 (3): 037102 doi: 10.1088/1674-1056/22/3/037102
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First-principles calculations were performed to investigate the magnetic properties of Zn(Mn,Li)O based on the Perdew–Burke–Ernzerhof form of generalized gradient approximation. Antiferromagnetic (AFM) ordering is the ground state in Mn-doped ZnO system without the codopant of Li, while seven different geometrical configurations of Zn(Mn,Li)O prefer stable ferromagnetic (FM) ordering. We found that dopant Li can effectively change the magnetic coupling in the ZnMnO system. The Curie temperature (TC) of FM ordering depends on the geometric configuration, and the highest TC is about 1388 K. The FM stabilization is greatly affected by Mn–Mn distance rather than by the position of dopant Li. We propose that dopant Li mediates FM coupling through a double exchange interaction or an RKKY interaction when Li is located, respectively, near or far from Mn ions.

Abnormal lattice contraction of plutonium hydrides studied by first-principles calculations

Ao Bing-Yun, Shi Peng, Guo Yong, Gao Tao
Chin. Phys. B, 2013, 22 (3): 037103 doi: 10.1088/1674-1056/22/3/037103
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Pu can be loaded with H forming complicated continuous solid solutions and compounds, and causing remarkable electronic and structural changes. Full potential linearized augmented plane wave methods combining with Hubbard parameter U and the spin–orbit effects are employed to investigate the electronic and structural properties of stoichiometric and non-stoichiometric face-centered cubic Pu hydrides (PuHx, x=2, 2.25, 2.5, 2.75, 3). The decreasing trend with increasing x of the calculated lattice parameters is in reasonable agreement with the experimental findings. A comparative analysis of the electronic-structure results for a series of PuHx compositions reveals that the lattice contraction is resulted from the associated effects of the enhanced chemical bonding and the size effects involving the interstitial atoms. We find that the size effects are the driving force for the abnormal lattice contraction.

Optical absorption in asymmetric double quantum wells driven by two intense terahertz fields

Wu Hong-Wei, Mi Xian-Wu
Chin. Phys. B, 2013, 22 (3): 037104 doi: 10.1088/1674-1056/22/3/037104
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Optical absorption is investigated for asymmetric double quantum wells driven by a resonant terahertz field and a varied terahertz field both polarized along the growth direction. Rich nonlinear dynamics of the replica peak and the Autler–Townes splitting of various dressed states are systematically studied in undoped asymmetric double quantum wells by taking account of multiple factors, such as the frequency of the varied terahertz field and the strength of the resonant terahertz field. Each electron subband splits into two dressed states when the resonant terahertz field is applied in the absence of the varied terahertz field, the optical absorption spectrum shows the first order Autler–Townes splitting of the electron subbands. When a varied terahertz field is added into the resonant system, the replica peak and the second order Autler–Townes splitting of the dressed states near the band edge respectively emerge when the varied terahertz field is non-resonant and resonant with these dressed states. When the strength of the resonant terahertz field is increased, the first order Autler–Townes double peaks and the replica peak in the optical absorption spectrum shift with the shifts of the dressed states. The presented results have potential applications in electro-optical devices.

Analysis of resistive switching behaviors of vanadium oxide thin film

Wei Xiao-Ying, Hu Ming, Zhang Kai-Liang, Wang Fang, Zhao Jin-Shi, Miao Yin-Ping
Chin. Phys. B, 2013, 22 (3): 037201 doi: 10.1088/1674-1056/22/3/037201
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We demonstrated the polarization of resistive switching for Cu/VOx/Cu memory cell. Switching behaviors of Cu/VOx/Cu cell were tested by semiconductor device analyzer (Agilent B1500A), and the relative micro-analysis of I–V characteristics of VOx/Cu was characterized by conductive atomic force microscope (CAFM). The I–V test results indicated that both forming and the reversible resistive switching between low resistance state (LRS) and high resistance state (HRS) can be observed under either positive or negative sweep. The CAFM images for LRS and HRS directly exhibited evidences of the formation and rupture of filaments based on positive or negative voltage. Cu/VOx/Cu sandwiched structure exhibits a reversible resistive switching behavior and shows potential applications in the next generation nonvolatile memory field.

Tandem organic light-emitting diode with molybdenum tri-oxide thin film interconnector layer

Lu Fei-Ping, Wang Qian, Zhou Xiang
Chin. Phys. B, 2013, 22 (3): 037202 doi: 10.1088/1674-1056/22/1/037202
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A 10-nm thickness molybdenum tri-oxide (MoO3) thin film was used as the interconnector layer in tandem organic light-emitting devices (OLEDs). The tandem OLEDs with two identical emissive units consisting of N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (NPB)/tris(8-hydroxyquinoline) aluminum (Alq3) exhibited current efficiency–current density characteristics superior to the conventional single-unit devices. At 20 mA/cm2, the current efficiency of the tandem OLEDs using the interconnector layers of MoO3 thin film was about 4.0 cd/A, which is about twice of that of the corresponding conventional single-unit device (1.8 cd/A). The tandem OLED showed a higher power efficiency than the conventional single-unit device for luminance over 1200 cd/m2. The experimental results demonstrated that a MoO3 thin film with a proper thickness can be used as an effective interconnector layer in tandem OLEDs. Such an interconnector layer can be easily fabricated by simple thermal evaporation, greatly simplifying the device processing and fabrication processes required by previously reported interconnector layers. A possible explanation was proposed for the carrier generation of the MoO3 interconnector layer.

Simulation of near-infrared photodiode detectors based on β-FeSi2/4H-SiC heterojunction

Pu Hong-Bin, He Xin, Quan Ru-Dai, Cao Lin, Chen Zhi-Ming
Chin. Phys. B, 2013, 22 (3): 037301 doi: 10.1088/1674-1056/22/3/037301
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In this paper, we propose the near-infrared p-type β-FeSi2/n-type 4H-SiC heterojunction photodetector with semiconducting silicide (β-FeSi2) as the active region for the first time. Optoelectronic characteristics of the photodetector are simulated using a commercial simulator at room temperature. The results show that the photodetector has a good rectifying character and a good response to the near-infrared light. Interface states should be minimized to obtain a lower reverse leakage current. The response spectrum of the β-FeSi2/4H-SiC detector, which consists of a p-type β-FeSi2 absorption layer with a doping concentration of 1×1015 cm-3 and a thickness of 2.5 μm, has a peak of 755 mA/W at 1.42 μm. The illumination of the SiC side obtains a higher responsivity than that of the β-FeSi2 side. The results illustrate that the β-FeSi2/4H-SiC heterojunction can be used as a near-infrared photodetector compatible with near-infrared optically-activated SiC-based power switching devices.

Effect of microstructure on thermoelectric properties of CSD-grown Bi2Sr2Co2Oy thin films

Wang Shu-Fang, Yan Guo-Ying, Chen Shan-Shan, Bai Zi-Long, Wang Jiang-Long, Yu Wei, Fu Guang-Sheng
Chin. Phys. B, 2013, 22 (3): 037302 doi: 10.1088/1674-1056/22/3/037302
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Three Bi2Sr2Co2Oy thin films with different microstructures have been prepared by chemical solution deposition on LaAlO3(001) through varying the annealing temperature. With the decrease in the annealing temperature, both the size and c-axis alignment degree of grains in the film decrease as well, leading to an increase in the film resistivity. In addition, the decrease in the annealing temperature also results in a slight increase in the seebeck coefficient due to the enhanced energy filtering effect of small-grain film. The nanostructured Bi2Sr2Co2Oy film with the average grain size of about 100 nm shows a power factor comparable to that of the films with larger grains. Since the thermal conductivity of the nanostrcutured films can be depressed due to the enhanced phonon scattering by grain boundary, a higher figure of merit is expected in Bi2Sr2Co2Oy thin film with grains in nanometer size.

Dislocation-mediated creep process in nanocrystalline Cu

Mu Jun-Wei, Sun Shi-Cheng, Jiang Zhong-Hao, Lian Jian-She, Jiang Qing
Chin. Phys. B, 2013, 22 (3): 037303 doi: 10.1088/1674-1056/22/3/037303
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Nanocrystalline Cu with average grain sizes ranging from ~24.4 to 131.3 nm were prepared by electric brush-plating technique. Nanoindentation tests were performed within a wide strain rate range, and the creep process of nanocrystalline Cu during holding period and its relationship to dislocation and twin structures were examined. It was demonstrated that creep strain and creep strain rate are considerably significant for smaller grain size and higher loading strain rate, and are far higher than those predicted by the models of Cobble creep and grain boundary sliding. The analysis based on the calculations and experiments reveals that the significant creep deformation arises from the rapid absorption of high density dislocations stored in loading regime. Our experiments imply that stored dislocations during loading are highly unstable and dislocation activity can proceed and lead to significant post-loading plasticity.

Wave-vector filtering effect of electric–magnetic barrier in HgTe quantum wells

Zou Yong-Lian, Song Jun-Tao
Chin. Phys. B, 2013, 22 (3): 037304 doi: 10.1088/1674-1056/22/3/037304
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Because of helicity of electrons in HgTe quantum wells (QWs) with inverted band structure, the electrons cannot be confined by electric barriers since electrons can tunnel the barriers perfectly without backscattering in HgTe QWs. This behavior is similar to Dirac electrons in graphene. In this paper, we propose a scheme to confine carriers in HgTe QWs using an electric–magnetic barrier. We calculate the transmission of carriers in 2-dimensional HgTe QWs and find that the wave-vector filtering effect of local magnetic fields can confine the carriers. The confining effect will have potential application in nanodevices based on HgTe QWs.

Dynamic compensation temperature in kinetic spin-5/2 Ising model on hexagonal lattice

Ümüt Temizer, Ayşegül Özkılıç
Chin. Phys. B, 2013, 22 (3): 037501 doi: 10.1088/1674-1056/22/3/037501
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We present a study of the dynamic behavior of a two-sublattice spin-5/2 Ising model with bilinear and crystal-field interactions in the presence of a time-dependent oscillating external magnetic field on alternate layers of a hexagonal lattice by using the Glauber-type stochastic dynamics. The lattice is formed by alternate layers of spins σ=5/2 and S=5/2. We employ the Glauber transition rates to construct the mean-field dynamic equations. First, we investigate the time variations of the average sublattice magnetizations to find the phases in the system and then the thermal behavior of the dynamic sublattice magnetizations to characterize the nature (first- or second-order) of the phase transitions and to obtain the dynamic phase transition (DPT) points. We also study the thermal behavior of the dynamic total magnetization to find the dynamic compensation temperature and to determine the type of the dynamic compensation behavior. We present the dynamic phase diagrams, including the dynamic compensation temperatures, in nine different planes. The phase diagrams contain seven different fundamental phases, thirteen different mixed phases, in which the binary and ternary combination of fundamental phases and the compensation temperature or the L-type behavior strongly depend on the interaction parameters.

Dynamics of one-dimensional random quantum XY system with Dzyaloshinskii–Moriya interaction

Li Yin-Fang, Kong Xiang-Mu
Chin. Phys. B, 2013, 22 (3): 037502 doi: 10.1088/1674-1056/22/3/037502
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In this paper, the effects of random variables on the dynamics of the s=1/2 XY model with the Dzyaloshinskii–Moriya interaction are studied. By means of the recurrence relation method in the high-temperature limit, we calculate the spin autocorrelation functions as well as the corresponding spectral densities for the cases that the exchange couplings between spins or external magnetic fields satisfy the double-Gaussian distribution. It is found that when the standard deviation of random exchange coupling δj (or the standard deviation of random external field δB) is small, the dynamics of the system undergoes a crossover from a collective-mode behavior to a central-peak one. However, when δJ (or δB) is large, the crossover vanishes, and the system shows a central-peak behavior or the most disordered one. We also analyze the cases in which the exchange couplings or the external fields satisfy the bimodal and the Gaussian distributions. Our results show that for all the cases considered, the dynamics of the above system is similar to that of the one-dimensional random XY model.

Magnetic properties and magnetostriction of PrxNd1-xFe1.9 (0≤x≤1.0) alloys at low temperature Hot!

Wang Yong, Tang Shao-Long, Li Yu-Long, Xie Ren, Du You-Wei
Chin. Phys. B, 2013, 22 (3): 037503 doi: 10.1088/1674-1056/22/3/037503
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The crystal structure, magnetic and magnetostrictive properties of high-pressure synthesized PrxNd1-xFe1.9 (0≤x≤1.0) alloys were studied. The alloys exhibit single cubic Laves phase with MgCu2-type structure. The initial magnetization curve reveals that Pr0.2Nd0.8Fe1.9 has a minimum magnetocrystalline anisotropy at 5 K. The magnetostriction curve at 5 K shows that Pr0.2Nd0.8Fe1.9 has a very good low-field magnetostrictive property, and the magnetostriction of the PrxNd1-xFe1.9 alloy in high magnetic field is attributable mainly to Pr. The temperature dependence of the magnetostriction (λ||) at the field of 5 kOe shows that the substitution of Nd reduces the K1 remarkably, and the values of λ|| of Pr0.2Nd0.8Fe1.9 and Pr0.8Nd0.2Fe1.9 alloys are nearly five times larger than that of PrFe1.9 alloy below 50 K; the λ|| of Pr0.8Nd0.2Fe1.9 reaches up to 1082 ppm at 100 K, which makes it a potential candidate for application in this temperature range.

Defect types and room-temperature ferromagnetism in undoped rutile TiO2 single crystals

Li Dong-Xiang, Qin Xiu-Bo, Zheng Li-Rong, Li Yu-Xiao, Cao Xing-Zhong, Li Zhuo-Xin, Yang Jing, Wang Bao-Yi
Chin. Phys. B, 2013, 22 (3): 037504 doi: 10.1088/1674-1056/22/3/037504
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Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when magnetic field is applied parallel to the sample plane. By combining X-ray absorption near edge structure spectrum and positron annihilation lifetime spectroscopy, Ti3+–VO defect complexes (or clusters) have been identified in annealed crystals at high vacuum. We elucidate that the unpaired 3d electrons in Ti3+ ions provide the observed room-temperature ferromagnetism. Besides, excess oxygen ions in TiO2 lattice could induce a number of Ti vacancies which increase magnetic moments obviously.

Carbon materials with quasi-graphene layers: the dielectric, percolation properties and the electronic transport mechanism

Lu Ming-Ming, Yuan Jie, Wen Bo, Liu Jia, Cao Wen-Qiang, Cao Mao-Sheng
Chin. Phys. B, 2013, 22 (3): 037701 doi: 10.1088/1674-1056/22/3/037701
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We investigate the dielectric properties of multi-walled carbon nanotubes (MWCNTs) and graphite filling in SiO2 with the filling concentration of 2–20 wt.% in the frequency range of 102–107 Hz. MWCNTs and graphite have general electrical properties and percolation phenomena owing to their quasi-structure made up of graphene layers. Both permittivity ε and conductivity σ exhibit jumps around the percolation threshold. Variations of dielectric properties of the composites are in agreement with the percolation theory. All the percolation phenomena are determined by hopping and migrating electrons, which are attributed to the special electronic transport mechanism of the fillers in the composites. However, the twin-percolation phenomenon exists when the concentration of MWCNTs is between 5–10 wt.% and 15–20 wt.% in the MWCNTs/SiO2 composites, while in the graphite/SiO2 composites, there is only one percolation phenomenon in the graphite concentration of 10–15 wt.%. The unique twin-percolation phenomenon of MWCNTs/SiO2 is described and attributed to the electronic transfer mechanism, especially the network effect of MWCNTs in the composites. The formation of network plays an essential role in determining the second percolation threshold of MWCNTs/SiO2.

Evidence of GeO volatilization and its effect on the characteristics of HfO2 grown on Ge substrate

Fan Ji-Bin, Liu Hong-Xia, Fei Cheng-Xi, Ma Fei, Fan Xiao-Jiao, Hao Yue
Chin. Phys. B, 2013, 22 (3): 037702 doi: 10.1088/1674-1056/22/3/037702
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HfO2 films are deposited by atomic layer deposition (ALD) using tetrakis ethylmethylamino hafnium (TEMAH) as the hafnium precursor, while O3 or H2O is used as the oxygen precursor. After annealing at 500℃ in nitrogen, the thickness of Ge oxide's interfacial layer decreases, and the presence of GeO is observed at the H2O-based HfO2 interface due to GeO volatilization, while it is not observed for the O3-based HfO2. The difference is attributed to the residue hydroxyl groups or H2O molecules in H2O-based HfO2 hydrolyzing GeO2 and forming GeO, whereas GeO is only formed by the typical reaction mechanism between GeO2 and the Ge substrate for O3-based HfO2 after annealing. The volatilization of GeO deteriorates the characteristics of the high-κ films after annealing, which has effects on the variation of valence band offset and the C–V characteristics of HfO2/Ge after annealing. The results are confirmed by X-ray photoelectron spectroscopy (XPS) and electrical measurements.

Spectral and laser properties of Yb and Ho co-doped (YLa)2O3 transparent ceramic

Huang Dong-Dong, Yang Qiu-Hong, Wang Yong-Gang, Zhang Hao-Jia, Lu Shen-Zhou, Zou Yu-Wan, Wei Zhi-Yi
Chin. Phys. B, 2013, 22 (3): 037801 doi: 10.1088/1674-1056/22/3/037801
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Highly transparent Yb, Ho doped (YLa)2O3 ceramic was fabricated by conventional ceramic processing with nanopowders. The absorption and emission spectra of the ceramic were investigated. The energy transfer mechanism between Yb3+ and Ho3+ was also discussed. The strong emission band around 2 μm indicated that the Yb–Ho: (Y0.90La0.10)2O3 transparent ceramic is a promising gain medium for the generation of 2 μm laser emissions. The laser operation of Yb–Ho co-doped (YLa)2O3 ceramic at 2.1 μm is first reported.

Optical properties of InGaAsBi/GaAs strained quantum wells studied by temperature-dependent photoluminescence

Gu Yi, Zhang Yong-Gang, Song Yu-Xin, Ye Hong, Cao Yuan-Ying, Li Ai-Zhen, Wang Shu-Min
Chin. Phys. B, 2013, 22 (3): 037802 doi: 10.1088/1674-1056/22/3/037802
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The effect of bismuth on the optical properties of InGaAsBi/GaAs quantum well structures is investigated by using the temperature-dependent photoluminescence from 12 K to 450 K. The incorporation of bismuth in the InGaAsBi quantum well is confirmed and found to result in a red shift of photoluminescence wavelength of 27.3 meV at 300 K. The photoluminescence intensity is significantly enhanced by about 50 times at 12 K with respect to that of the InGaAs quantum well due to the surfactant effect of bismuth. The temperature-dependent integrated photoluminescence intensities of the two samples reveal different behaviors related to various non-radiative recombination processes. The incorporation of bismuth also induces alloy non-uniformity in the quantum well, leading to an increased photoluminescence linewidth.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Correlation between lithium storage and diffusion properties and electrochromic characteristics of WO3 thin films

Yu Peng-Fei, Cui Zhong-Hui, Fan Wu-Gang, Guo Xiang-Xin
Chin. Phys. B, 2013, 22 (3): 038101 doi: 10.1088/1674-1056/22/3/038101
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As essential electrochromic (EC) materials are related to energy savings in fenestration technology, tungsten oxide (WO3) films have been intensively studied recently. In order to achieve better understanding of the mechanism of EC properties, and thus facilitate optimization of device performance, clarification of correlation between the cation storage and transfer properties and the coloration performance is needed. In this study, transparent polycrystalline and amorphous WO3 thin films were deposited on SnO2:F-coated glass substrates by the pulsed laser deposition technique. Investigation into optical transmittance in wavelength range of 400–800 nm measured at the current density of 130 μA/cm2 with the applied potential ranging from 3.2 to 2.2 V indicates that the polycrystalline films have a larger optical modulation of ~30% at 600 nm and a larger coloration switch time of 95 s in the whole wavelength range compared with the amorphous films (~24% and 50 s). Meanwhile, under the same conditions, the polycrystalline films show a larger lithium storage capacity corresponding to a Li/W ratio of 0.5, a smaller lithium diffusion coefficient (2×10–12 cm2·–1 for Li/W=0.24) compared with the amorphous ones with the Li/W ratio of 0.29 and the coefficient of ~2.5×10–11 cm2· s–1 as Li/W=0.24. These results demonstrate that the large optical modulation relates to the large lithium storage capacity, and the fast coloration transition associates with the fast lithium diffusion.

Binary-component micelle and vesicle: Free energy and asymmetric distributions of amphiphiles between monolayers of vesicle

Zhang Qi-Yi, Xiang Xun
Chin. Phys. B, 2013, 22 (3): 038201 doi: 10.1088/1674-1056/22/3/038201
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The real-space two-dimensional self-consistent field theory (SCFT) is employed to study the free energies of micelles and vesicles constituted by binary amphiphilic diblock copolymer AB in homopolymer A. With increasing volume fraction of copolymer AB, there are morphological transitions from the circle micelles to oblate circle-like micelles, to compound structure with inverted micelles in the inner center and micelles outer layer, and to vesicles. Special attentions are paid to the role of the copolymer AB in controlling free energies of the micelles and vesicles, by examining the effect of length ratio of A/B with the fixed whole chain length of AB copolymer, the length effect of A or B block with the corresponding fixed length of B or A block, for one component of copolymer, and the effect of different amphiphile compositions for binary-component copolymer system. The quantity η is provided to describe the asymmetric density distribution of amphiphiles between the inner and outer monolayers of vesicles, and to quantify the relative asymmetric extent of the density distribution between two species of copolymers in binary component vesicles.

Analysis and modeling of resistive switching mechanisms oriented to resistive random-access memory

Huang Da, Wu Jun-Jie, Tang Yu-Hua
Chin. Phys. B, 2013, 22 (3): 038401 doi: 10.1088/1674-1056/22/3/038401
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With the progress of the semiconductor industry, the resistive random-access memory (RAM) has drawn increasing attention. The discovery of the memristor brings much attention to this study. Those researches focus on resistive switching characteristics of different materials and the analysis of resistive switching mechanisms. We discuss the resistive switching mechanisms of different materials in this paper and analyze the differences of those mechanisms from the view point of circuitry to establish their respective circuit models. Finally, simulations are present. We give the prospect of different materials used in resistive RAM on account of resistive switching mechanisms, which are applied to explain their resistive switchings.

Two-dimensional threshold voltage model of nanoscale silicon-on-insulator tunneling field-effect transistor

Li Yu-Chen, Zhang He-Ming, Zhang Yu-Ming, Hu Hui-Yong, Wang Bin, Lou Yong-Le, Zhou Chun-Yu
Chin. Phys. B, 2013, 22 (3): 038501 doi: 10.1088/1674-1056/22/3/038501
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The tunneling field-effect transistor (TFET) is a potential candidate for the post-CMOS era. In this paper, a threshold voltage model is developed for this new kind of device. First, two-dimensional (2D) models are used to describe the distributions of potential and electric field in the channel and two depletion regions. Then based on the physical definition of threshold voltage for the nanoscale TFET, the threshold voltage model is developed. The accuracy of the proposed model is verified by comparing the calculated results with the 2D device simulation data. It has been demonstrated that the effects of varying the device parameters can easily be investigated using the model presented in this paper. This threshold voltage model provides a valuable reference to the TFET device design, simulation, and fabrication.

Ballistic diffusion induced by non-Gaussian noise

Qin Li, Li Qiang
Chin. Phys. B, 2013, 22 (3): 038701 doi: 10.1088/1674-1056/22/3/038701
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In this letter, we have analyzed diffusive behavior of a Brownian particle subject to both internal Gaussian thermal and external non-Gaussian noise sources. We discuss two time correlation functions C(t) of the non-Gaussian stochastic process, and find that they depend on the parameter q, indicating the departure of the non-Gaussian noise from Gaussian behavior: for q≤1, C(t) is fitted very well by the first-order exponentially decaying curve and approaches zero in the long-time limit, whereas for q>1, C(t) can be approximated by a second-order exponentially decaying function and converges to a non-zero constant. Due to the properties of C(t), the particle exhibits a normal diffusion for q≤1, while for q>1 the non-Gaussian noise induces a ballistic diffusion, i.e., long-time mean square displacement of the free particle reads 〈[x(t)-〈x(t)〉]2〉∞t2.

Feasibility of similarity coefficient map in improving morphological evaluation of T2* weighted MRI for renal cancer

Wang Hao-Yu, Hu Jiani, Xie Yao-Qin, Chen Jie, Yu Amy, Wei Xin-Hua, Dai Yong-Ming, Li Meng, Bao Shang-Lian, E. M. Haacke
Chin. Phys. B, 2013, 22 (3): 038702 doi: 10.1088/1674-1056/22/3/038702
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The purpose of this paper is to investigate the feasibility of similarity coefficient map (SCM) in improving morphological evaluation of T2* weighted (T2*W) magnatic resonance imaging (MRI) for renal cancer. Simulation studies and in vivo 12-echo T2*W experiments for renal cancers were performed for this purpose. The results of the first simulation study suggest that SCM can reveal small structures which are hard to be distinguished from the background tissue in T2*W images and the corresponding T2* map. The capability of improving morphological evaluation is likely due to the improvement in signal to noise ratio (SNR) and carrier to noise ratio (CNR) by SCM technique. Compared with T2*W images, SCM can improve SNR by a factor ranging from 1.87 to 2.47. Compared with T2* maps, SCM can improve SNR by a factor ranging from 3.85 to 33.31. Compared with T2*W images, SCM can improve CNR by a factor raging from 2.09 to 2.43. Compared with T2* maps SCM can improve CNR by a factor raging from 1.94 to 8.14. For a given noise level, the improvements of SNR and CNR depend mainly on the original SNRs and CNRs in T2*W images, respectively. In vivo experiments confirmed the results of the first simulation study. The results of the second simulation study suggest that more echoes are used to generate SCM, and higher SNR and CNR can be achieved in SCM. In conclusion, SCM can provide improved morphological evaluation of T2*W MR images for renal cancer by unveiling fine structures which are ambiguous or invisible in the corresponding T2*W MR images and T2* maps. What is more, in practical application, for a fixed total sampling time, one should increase the number of echoes as much as possible to achieve SCMs with better SNR and CNR.

Finite-time consensus of heterogeneous multi-agent systems

Zhu Ya-Kun, Guan Xin-Ping, Luo Xiao-Yuan
Chin. Phys. B, 2013, 22 (3): 038901 doi: 10.1088/1674-1056/22/3/038901
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We investigate the finite-time consensus problem for the heterogeneous multi-agent systems composed of first-order and second-order agents. A novel continuous nonlinear distributed consensus protocol is constructed, and finite-time consensus criteria are obtained for the heterogeneous multi-agent systems. Compared with the existing results, the stationary and the kinetic consensuses of the heterogeneous multi-agent systems can be achieved in a finite time respectively. Moreover, the leader can be a first-order or a second-order integrator agent. Finally, some simulation examples are employed to verify the efficiency of the theoretical results.

Measuring causality by directional symbolic mutual information approach

Chen Gui, Xie Lei, Chu Jian
Chin. Phys. B, 2013, 22 (3): 038902 doi: 10.1088/1674-1056/22/3/038902
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We propose a novel measure to assess causality through the comparison of symbolic mutual information between the future of one random quantity and the past of the other. This provides a new perspective different from the conventional conceptions. Based on this point of view, a new causality index is derived that uses the definition of directional symbolic mutual information. This measure presents properties different from the time delayed mutual information since the symbolization captures the dynamic features of the analyzed time series. In addition to characterizing the direction and the amplitude of the information flow, it can also detect coupling delays. This method has the property of robustness, conceptual simplicity, and fast computational speed.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

New initial condition of the new agegraphic dark energy model

Li Yun-He, Zhang Jing-Fei, Zhang Xin
Chin. Phys. B, 2013, 22 (3): 039501 doi: 10.1088/1674-1056/22/3/039501
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The initial condition Ωde(zini)=n2(1+zini)–2/4 at zini=2000 widely used to solve the differential equation of the density of the new agegraphic dark energy (NADE) Ωde, makes the NADE model be a single-parameter dark-energy cosmological model. However, we find that this initial condition is only applicable in a flat universe with only dark energy and pressureless matter. In fact, in order to obtain more information from current observational data, such as the cosmic microwave background (CMB) and the baryon acoustic oscillations (BAO), we need to consider the contribution of radiation. For this situation, the initial condition mentioned above becomes invalid. To overcome this shortage, we investigate the evolutions of dark energy in the matter-dominated and the radiation-dominated epochs, and obtain a new initial condition Ωde(zini)=n2(1+zini)–2(1+√F(zini)2/4 at zini=2000, where F(z)≡Ωr0(1+z)/[Ωm0+Ωr0(1+z)] with Ωr0 and Ωm0 being the current density parameters of radiation and pressureless matter, respectively. This revised initial condition is applicable for the differential equation of Ωde obtained in the standard Friedmann–Robertson–Walker (FRW) universe with dark energy, pressureless matter, radiation, and even spatial curvature, and can still keep the NADE model being a single-parameter model. With the revised initial condition and the observational data of type Ia supernova (SNIa), CMB, and BAO, we finally constrain the NADE model. The results show that the single free parameter n of the NADE model can be constrained tightly.

Quantum nonthermal radiation and horizon surface gravity of an arbitrarily accelerating black hole with electric charge and magnetic charge

Xie Zhi-Kun, Pan Wei-Zhen, Yang Xue-Jun
Chin. Phys. B, 2013, 22 (3): 039701 doi: 10.1088/1674-1056/22/3/039701
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With a new tortoise coordinate transformation, we discussed the quantum nonthermal radiation characteristics near the event horizon by studying the Hamilton–Jacobi equation of a scalar particle in the curve space–time, and obtained the event horizon surface gravity and the Hawking temperature on the event horizon. The results showed that there is a crossing of particle energy near the event horizon. We derived the maximum overlap of the positive and negative energy levels. It was also found that the Hawking temperature of a black hole depends on not only the time, but also the angle. There is a problem of dimension in the usual tortoise coordinate, so the present results obtained by using a correct-dimension new tortoise coordinate transformation may be more reasonable.
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