Chin. Phys. B

Multi-symplectic scheme for the coupled Schrödinger–Boussinesq equations

Huang Lang-Yang (黄浪扬), Jiao Yan-Dong (焦艳东), Liang De-Min (梁德民)

Chin. Phys. B, 2013, 22 (7): 070201. DOI: 10.1088/1674-1056/22/7/070201

Abstract ( 902 )

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In this paper, a multi-symplectic Hamiltonian formulation is presented for the coupled Schrödinger–Boussinesq equations (CSBE). Then, a multi-symplectic scheme of the CSBE is derived. The discrete conservation laws of the Langmuir plasmon number and total perturbed number density are also proved. Numerical experiments show that the multi-symplectic scheme simulates the solitary waves for a long time, and preserves the conservation laws well.

Decoherence dynamics of a charge qubit coupled to the noise bath

Yang Qin-Ying (杨芹英), Liang Bao-Long (梁宝龙), Wang Ji-Suo (王继锁)

Chin. Phys. B, 2013, 22 (7): 070301. DOI: 10.1088/1674-1056/22/7/070301

Abstract ( 655 )

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By virtue of the canonical quantization method, we present a quantization scheme about a charge qubit based on the superconducting quantum interference device (SQUID), taking the self-inductance of the loop into account. Under the reasonable short-time approximation, we study the effect of decoherence in the Ohmic case by employing the response function and the norm. It is confirmed that the decoherence time which depends on the parameters of circuit components, coupling strength, and temperature, can be as low as several picoseconds, so that there is enough time to record information.

Non-Markovian decoherent quantum walks

Xue Peng (薛鹏), Zhang Yong-Sheng (张永生)

Chin. Phys. B, 2013, 22 (7): 070302. DOI: 10.1088/1674-1056/22/7/070302

Abstract ( 585 )

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Quantum walk acts obviously different from its classical counterpart, but the decoherence will lessen and close the gap between them. To understand this process, it is necessary to investigate the evolution of the quantum walk under different situations of decoherence. In this article, we study a non-Markovian decoherent quantum walk on a line. In the short time regime, the behavior of the walk deviates from both idea quantum walks and classical random walks. The position variance as a measure of the quantum-walk collapses and revivals for a short time and tends to have a linear relation with time, that is the walker's behavior shows a diffusive spread in the long time limit, which is caused by the non-Markovian dephasing affecting on quantum correlations between the quantum walker and his coin. We also study both quantum discord and measurement-induced disturbance as measures of quantum correlations and observe that both collapse and revival in the short time regime and tend to be zero in the long time limit. Therefore, the quantum walk with a non-Markovian decoherence tends to diffusive spreading behavior in the long time limit, while in the short time regime, it oscillates between a ballistic and diffusive spreading behavior, and the quantum correlation collapses and revivals due to the memory effect.

Relativistic solutions for diatomic molecules subject to pseudoharmonic oscillator in arbitrary dimensions

Sami Ortakaya

Chin. Phys. B, 2013, 22 (7): 070303. DOI: 10.1088/1674-1056/22/7/070303

Abstract ( 705 )

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The exact solutions of the N-dimensional Klein-Gordon equation in the presence of an exactly solvable potential of V(r) = D_e(r/r_e-r_e/r)² type have been obtained. The N dimensional Klein-Gordon equation has been reduced to a first-order differential equation via Laplace transformation. The exact bound state energy eigenvalues and corresponding wave functions for CH, H₂, and HCl molecules interacting with pseudoharmonic oscillator potential in the arbitrary N dimensions have been determined. Bound state eigenfunctions used in applications related to molecular spectroscopy are obtained in terms of confluent hypergeometric functions.

Absorption cross section of black holes with a global monopole

Huang Hai (黄海), Wang Yong-Jiu (王永久), Chen Ju-Hua (陈菊华)

Chin. Phys. B, 2013, 22 (7): 070401. DOI: 10.1088/1674-1056/22/7/070401

Abstract ( 719 )

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We study the absorption problem for a massless scalar field propagating in general static spherically-symmetric black holes with a global monopole. The expression of absorption cross section is provided by using a partial-wave method, which permits us to make an elegant and powerful resummation of the absorption cross section and to extract the physical information encoded in the sum over the partial-wave contributions.

Robust finite-time stabilization of unified chaotic complex systems with certain and uncertain parameters

Liu Ping (刘平)

Chin. Phys. B, 2013, 22 (7): 070501. DOI: 10.1088/1674-1056/22/7/070501

Abstract ( 765 )

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This paper deals with the finite-time stabilization of the unified chaotic complex systems with known and unknown parameters. Based on the finite-time stability theory, the nonlinear control laws are presented to achieve finite-time chaos control of the determined and uncertain unified chaotic complex systems, respectively. The two controllers are simple and one of the uncertain unified chaotic complex systems is robust. For the design of finite-time controller on uncertain unified chaotic complex systems, only part of all unknown parameters are required to be bounded. Simulation results for the chaotic complex Lorenz, Lü and Chen systems are presented to validate the design and the analysis.

Phase synchronization and synchronization frequency of two-coupled van der Pol oscillators with delayed coupling

Hossein Gholizade-Narm, Asad Azemi, Morteza Khademi

Chin. Phys. B, 2013, 22 (7): 070502. DOI: 10.1088/1674-1056/22/7/070502

Abstract ( 819 )

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In this paper, phase synchronization and the frequency of two synchronized van der Pol oscillators with delay coupling are studied. The dynamics of such a system are obtained using the describing function method, and the necessary conditions for phase synchronization are also achieved. Finding the vicinity of the synchronization frequency is the major advantage of the describing function method over other traditional methods. The equations obtained based on this method justify the phenomenon of the synchronization of coupled oscillators on a frequency either higher, between, or lower than the highest,in between, or lowest natural frequency of the aggregate oscillators. Several numerical examples simulate the different cases versus the various synchronization frequency delays.

Adaptive function projective synchronization of uncertain complex dynamical networks with disturbance

Wang Shu-Guo (王树国), Zheng Song (郑松)

Chin. Phys. B, 2013, 22 (7): 070503. DOI: 10.1088/1674-1056/22/7/070503

Abstract ( 719 )

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We investigate the problem of function projective synchronization (FPS) in drive-response dynamical networks with non-identical nodes, an adaptive controller is proposed for the FPS of complex dynamical networks with uncertain parameters and disturbance. Not only unknown parameters of the networks are estimated by the adaptive laws obtained from the Lyapunov stability theory and Taylor expansions but also unknown bounded disturbances can be simultaneously conquered by the proposed control. Finally, a numerical simulation is provided to illustrate the feasibility and effectiveness of the obtained result.

Generalized projective synchronization of two coupled complex networks with different sizes

Li Ke-Zan (李科赞), He En (何恩), Zeng Zhao-Rong (曾朝蓉), Chi K. Tse (谢智刚)

Chin. Phys. B, 2013, 22 (7): 070504. DOI: 10.1088/1674-1056/22/7/070504

Abstract ( 652 )

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We investigate a new generalized projective synchronization (GPS) between two complex dynamical networks of different sizes. To the best of our knowledge, most current studies on the projective synchronization have dealt with coupled networks with the same size. By generalized projective synchronization, we mean that the states of nodes in each network can realize complete synchronization, and the states of pair nodes from both networks can achieve projective synchronization. By using the stability theory of dynamical system, several sufficient conditions for guaranteeing the existence of the generalized projective synchronization under feedback control and adaptive control are obtained. As an example, we use Chua's circuits to demonstrate the effectiveness of our proposed approach.

Normal thermal conduction in lattice models with asymmetric harmonic interparticle interactions ^Hot!

Zhong Yi (钟毅), Zhang Yong (张勇), Wang Jiao (王矫), Zhao Hong (赵鸿)

Chin. Phys. B, 2013, 22 (7): 070505. DOI: 10.1088/1674-1056/22/7/070505

Abstract ( 719 )

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We study the thermal conduction behaviors of one-dimensional lattice models with asymmetric harmonic interparticle interactions. Normal thermal conductivity independent of the system size is observed when the lattice chains are long enough. Because only the harmonic interactions are involved, the result confirms without ambiguity that asymmetry plays a key role in resulting in normal thermal conduction in one-dimensional momentum conserving lattices. Both equilibrium and nonequilibrium simulations are performed to support the conclusion.

Leader–following consensus control for networked multi-teleoperator systems with interval time-varying communication delays

M. J. Park, S. M. Lee, J. W. Son, O. M. Kwon, E. J. Cha

Chin. Phys. B, 2013, 22 (7): 070506. DOI: 10.1088/1674-1056/22/7/070506

Abstract ( 684 )

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We study the leader–following consensus stability and stabilization of networked multi-teleoperator systems with interval time-varying communication delays. By the construction of a suitable Lyapunov–Krasovskii functional and the utilization of the reciprocally convex approach, novel delay-dependent consensus stability and stabilization conditions for the systems are established in terms of linear matrix inequalities (LMIs), which can be easily solved by various effective optimization algorithms. One illustrative example is given to illustrate the effectiveness of the proposed methods.

Time-dependent Ginzburg–Landau equation for lattice hydrodynamic model describing pedestrian flow

Ge Hong-Xia (葛红霞), Cheng Rong-Jun (程荣军), Lo Siu-Ming (卢兆明)

Chin. Phys. B, 2013, 22 (7): 070507. DOI: 10.1088/1674-1056/22/7/070507

Abstract ( 727 )

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A thermodynamic theory is formulated to describe the phase transition and critical phenomena in pedestrian flow. Based on the extended lattice hydrodynamic pedestrian model taking the interaction of the next-nearest-neighbor persons into account, the time-dependent Ginzburg-Landau (TDGL) equation is derived to describe the pedestrian flow near the critical point through the nonlinear analysis method. And the corresponding two solutions, the uniform and the kink solutions, are given. The coexisting curve, spinodal line, and critical point are obtained by the first and second derivatives of the thermodynamic potential.

Classical trajectory Monte Carlo investigation for Lorentz ionization of H (1s)

He Bin (何斌), Wang Jian-Guo (王建国), Liu Chun-Lei (刘春雷)

Chin. Phys. B, 2013, 22 (7): 073101. DOI: 10.1088/1674-1056/22/7/073101

Abstract ( 784 )

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Lorentz ionization of H(1s) is investigated by classical trajectory Monte Carlo (CTMC) simulation. The effect of the transverse magnetic field on the considered process is analyzed in terms of the time evolution of interactions in the system, total electron energy, and electron trajectories. A classical mechanism for the ionization is found, where the variation of the kinetic energy of the nuclei is found to be important in the process. Compared with the results of tunneling ionization, the classical mechanism becomes more and more important with the increase of the velocity of the H-atom or the strength of the magnetic field.

Stark spectra of Rydberg states in atomic cesium in the vicinity of n=18

Dong Hui-Jie (董慧杰), Wang Ting (王婷), Li Chang-Yong (李昌勇), Zhao Jian-Ming (赵建明), Zhang Lin-Jie (张临杰)

Chin. Phys. B, 2013, 22 (7): 073201. DOI: 10.1088/1674-1056/22/7/073201

Abstract ( 957 )

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The Stark structures in a cesium atom around n=18 are numerically calculated. The results manifest that the components of 20D states with a small azimuthal quantum number |m| shift upward a lot, and that with a large |m| shift downward a little within 1100 V/cm. All components of P states shift downward. Experimental work has been performed in an ultracold atomic cesium. Atoms initially in 6P_3/2 state are excited to high-n Rydberg states by a polarization light perpendicular to field, and Stark spectra with |m|=1/2,3/2,5/2 are simultaneously observed with a large linewidth for the first time. The observed spectra are analyzed in detail. The relative transition probability is calculated. The experimental results are in good agreement with our numerical computation.

Intercombination transitions of the carbon-like isoelectronic sequence

Liu Hao (刘浩), Jiang Gang (蒋刚), Hu Feng (胡峰), Wang Chuan-Ke (王传珂), Wang Zhe-Bin (王哲斌), Yang Jia-Min (杨家敏)

Chin. Phys. B, 2013, 22 (7): 073202. DOI: 10.1088/1674-1056/22/7/073202

Abstract ( 701 )

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Energy levels, wavelengths, transition rates, oscillator strengths, and lifetimes between the 2s²2p^{2 3}P₁, 2s²2p^{2 3}P₂, and 2s2p^{3 5}S₂ levels of ions in the carbon-like (C-like) isoelectronic sequence (nuclear charges Z=7-92) are calculated in the valence and core-valence limits using the multiconfiguration Dirac-Fock method. The Breit interaction, quantum electrodynamics (QED), and finite nuclear mass effects are taken into account in subsequent relativistic configuration-interaction calculations. The calculated energies and transition rates are compared with the critically evaluated experimental values and other recent calculated results. Our calculated data are in good agreement with these data.

TDDFT study of excitation of water molecules with short laser pulses

Wang Zhi-Ping (王志萍), Wu Ya-Min (吴亚敏), Zhang Xiu-Mei (张秀梅), Lu Chao (鲁超)

Chin. Phys. B, 2013, 22 (7): 073301. DOI: 10.1088/1674-1056/22/7/073301

Abstract ( 771 )

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We explore the excitation of water molecules subject to short and intense laser pulses in the frame of time-dependent density function theory (TDDFT) at the level of the time-dependent local-density approximation (TDLDA), applied to valence electrons, coupled non-adiabatically to molecular dynamics (MD) of ions. We first study the optical absorption spectra of the water molecule as an observable in the “linear” domain and results are in good agreement with experiments. We then explore the influence of the laser frequency on the excitation. It is found that when the laser frequency is off-resonant or highly above the resonant region, the excitations are weak whereas for the resonant frequency case, the ionization is enhanced and and bond lengths are enlarged. Furthermore, a direct coupling of ions with the laser pulse with the off-resonant frequency is found when investigating the OH bond lengths. We finally study the effect of laser intensity on the excitation of H₂O and it is found that ionization increases when the laser intensity varies from low to high and we observe stable vibrations to Coulomb fragmentation when the ionization is up to typically two more charge unit.

Global analysis of the Comet-tail system of ¹²C¹⁶O⁺

Shao Xu-Ping (邵旭萍), Zhao Min (赵敏), Yang Xiao-Hua (杨晓华)

Chin. Phys. B, 2013, 22 (7): 073302. DOI: 10.1088/1674-1056/22/7/073302

Abstract ( 800 )

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A global analysis of the ro-vibrational spectra of 19 bands in the comet-tail (A²Π_i-X²Σ⁺) system of the ¹²C¹⁶O⁺ cation is presented, and the precise molecular constants of the vibrational levels involved are obtained via a weighted nonlinear least-squares fitting procedure. Furthermore, the resultant precise equilibrium molecular constants enable us to achieve accurate Rydberg-Klein-Rees (RKR) potential curves for both the A and X states, yielding the accurate Franck-Condon factor and band origin of each band in this system.

Manifestation of external field effect in time-resolved photo-dissociation dynamics of LiF

Meng Qing-Tian (孟庆田), A. J. C. Varandas

Chin. Phys. B, 2013, 22 (7): 073303. DOI: 10.1088/1674-1056/22/7/073303

Abstract ( 665 )

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The photo-dissociation dynamics of LiF is investigated with newly constructed accurate ab initio potential energy curves (PECs) using the time-dependent quantum wave packet method. The oscillations and decay of the wave packet on the adiabats as a function of time are given, which can be compared with the femtosecond transition-state (FTS) spectroscopy. The photo-absorption spectra and the kinetic-energy distribution of the dissociation fragments, which can exhibit the vibration-level structure and the dispersion of the wave packet, respectively, are also obtained. The investigation shows a blue shift of the band center for the photo-absorption spectrum and multiple peaks in the kinetic-energy spectrum with increasing laser intensity, which can be attributed to external field effects. By analyzing the oscillations of the wave packet evolving on the upper adiabat, an approximate inversion scheme is devised to roughly deduce its shape.

Imprints of molecular orbitals using photoelectron angular distribution by strong laser pulses of circular polarization

Ren Xiang-He (任向河), Zhang Jing-Tao (张敬涛), Wu Yan (吴艳), Ma Hui (马慧), Xu Yu-Long (许玉龙)

Chin. Phys. B, 2013, 22 (7): 073304. DOI: 10.1088/1674-1056/22/7/073304

Abstract ( 752 )

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We theoretically investigate the strong-field ionization of H₂⁺ molecules in four different electronic states by calculating photoelectron angular distributions in circularly polarized fields. We find that the structure of photoelectron angular distribution depends on the molecular orbital as well as the energy of photoelectron. The location of main lobes changes with the symmetric property of the molecular orbital. Generally, for molecules with bonding electronic states, the photoelectron's angular distribution shows a rotation of π/2 with respect to the molecular axis, while for molecules with antibonding electronic states, no rotation occurs. We use an interference scenario to interpret these phenomena. We also find that, due to the interference effect, a new pair of jets appears in the waist of the main lobes, and the main lobes or jets of photoelectron's angular distribution are split into two parts if the photoelectron energy is sufficiently high.

Photodetachment of hydrogen negative ion inside a circular microcavity

Wang De-Hua (王德华), Liu Sheng (刘声), Li Shao-Sheng (李绍晟), Wang Yi-Hao (王一豪)

Chin. Phys. B, 2013, 22 (7): 073401. DOI: 10.1088/1674-1056/22/7/073401

Abstract ( 817 )

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The photodetachment of hydrogen negative ion inside a circular microcavity is studied based on the semiclassical closed orbit theory. The closed orbit of the photo-detached electron in a circular microcavity is investigated and the photodetachment cross section of this system is calculated. The calculation result suggests that oscillating structure appears in the photodetachment cross section, which is caused by the interference effects of the returning electron waves with the outgoing waves traveling along the closed orbits. Besides, our study suggests that the photodetachment cross section of the negative ions depends on the laser polarization sensitively. In order to show the correspondence between the cross section and the closed orbits of detached electron clearly, we calculate the Fourier transformation of the cross section and find that each peak corresponds to the length of one closed orbit. We hope that our results will be useful for understanding the photodetachment process of negative ions or the electron transport in a microcavity.

Ionization cross sections for electron scattering from metastable rare-gas atoms (Ne^* and Ar^*)

Zhang Yong-Zhi (张永志), Zhou Ya-Jun (周雅君)

Chin. Phys. B, 2013, 22 (7): 073402. DOI: 10.1088/1674-1056/22/7/073402

Abstract ( 640 )

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The optical-model approach has been used to investigate the electron-impact ionization of metastable rare-gas atoms. A complex equivalent-local polarization potential is obtained to describe the ionization continuum channels. We have calculated the cross sections for collisional ionization of the metastable atoms Ne^* and Ar^* by electrons in the energy range from threshold to 200 eV. The present results are in agreement with the available experimental measurements and other theoretical calculations.

Triple differential cross section for single ionization of H₂ by electron impact

Wang Yuan-Cheng (王远成), Liu Jun-Bo (刘俊伯), Ma Jia (马佳), Liu De-Jun (刘德军), Zhou Ya-Jun (周雅君)

Chin. Phys. B, 2013, 22 (7): 073403. DOI: 10.1088/1674-1056/22/7/073403

Abstract ( 639 )

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The triple differential cross section (TDCS) for the (e, 2e) ionization of hydrogen molecule is calculated using the molecule distorted-wave Born approximation (MDWBA). Distorted waves are obtained by solving momentum-space coupled-channel Lippmann-Schwinger equations, including the ground state and the lowest-lying electronic state of b³Σ_u. TDCS at the incident energy 100 eV in coplanar asymmetric geometry are reported. The present calculations are compared with the available experimental measurements and the theoretical results.

Computer study of the water–ammonia clusters formation and their dielectric properties

Alexander Galashev

Chin. Phys. B, 2013, 22 (7): 073601. DOI: 10.1088/1674-1056/22/7/073601

Abstract ( 649 )

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The absorption of one to six ammonia molecules by the (H₂O)₅₀ cluster is studied by the method of molecular dynamics under near-atmospheric conditions. The capture of NH₃ molecules by a water cluster produces an increase in the integrated intensity of IR absorbance, substantially decreases emission power in the frequency range of 0 ≤ ω ≤ 3500 cm^-1, and transforms a continuous reflectance spectrum into a banded one. Adsorption of ammonia molecules by water clusters greatly diminishes the number of electrons that are active with respect to electromagnetic radiation. The present results are also compared with the experimental findings wherever available.

Nanoscale guiding for cold atoms based on surface plasmons alongtips of metallic wedges

Wang Zheng-Ling (王正岭), Tang Wei-Min (唐伟民), Zhou Ming (周明), Gao Chuan-Yu (高传玉)

Chin. Phys. B, 2013, 22 (7): 073701. DOI: 10.1088/1674-1056/22/7/073701

Abstract ( 656 )

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We propose a novel scheme to guide neutral cold atoms in a nanoscale region based on surface plasmons (SPs) of one pair and two pairs of tips of metallic wedges with locally enhanced light intensity and sub-optical wavelength resolution. We analyze the near-field intensity distribution of the tip of the metallic wedge by the FDTD method, and study the total intensity as well as the total potential of optical potentials and van der Waals potentials for ⁸⁷Rb atoms in the light field of one pair and two pairs of tips of metallic wedges. It shows that the total potentials of one pair and two pairs of tips of metallic wedges can generate a gravito-optical trap and a dark closed trap for nanoscale guiding of neutral cold atoms. Guided atoms can be cooled with efficient intensity-gradient Sisyphus cooling by blue-detuned light field. This provides an important step towards the generation of hybrid systems consisting of isolated atoms and solid devices.

Experiment research on residual magnetization of rare earth permanent magnet for cryogenic undulator

He Yong-Zhou (何永周)

Chin. Phys. B, 2013, 22 (7): 074101. DOI: 10.1088/1674-1056/22/7/074101

Abstract ( 650 )

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The magnetic properties of commercial polycrystalline Nd₂Fe₁₄B (N50M, N45H, N40SH, N35EH) and Sm₂Co₁₇ (XG30/20, XG26/25, XG22/20) magnets at cryogenic temperatures were tested by using a comprehensive physical properties measurement system (PPMS). The results show that spin tilt temperature T_st of Nd₂Fe₁₄B magnets is closely related to intrinsic coercivity H_ci, N50M and N45H with smaller H_ci show a residual magnetization jump at 235 K and 225 K, respectively. For Sm₂Co₁₇ magnets, in 50-300 K, with temperature decreasing, residual magnetization M_rc shows a nearly linear increase, while in 10-50 K, M_rc has little change. The research results provide a reference for cryogenic undulators and other high-precision cryogenic devices.

Three-dimensional simulation of long-wavelength free-electron lasers with helical wiggler and ion-channel guiding

F. Jafari Bahman, B. Maraghechi

Chin. Phys. B, 2013, 22 (7): 074102. DOI: 10.1088/1674-1056/22/7/074102

Abstract ( 711 )

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A three-dimensional simulation of a steady-state amplifier model of a long-wavelength free-electron laser (FEL) with realizable helical wiggler and ion-channel guiding is presented. The set of coupled nonlinear differential equations for electron orbits and fields of TE₁₁ mode in a cylindrical waveguide are solved numerically by Runge-Kutta algorithm with averages calculated by the Gaussian quadrature technique. Self-fields and space-charge effects are neglected, and the electron beam is assumed to be cold and slippage is ignored. The parameters correspond to the Compton regime. Evolution of the radiation power and growth rate along the wiggler is studied. Ion-channel density is chosen to obtain optimum efficiency. Simulations are preformed for the FEL operating in the neighborhood of 35 GHz and 16.5 GHz for the electron beam energies of 250 keV and 400 keV, respectively. The result of the saturated efficiency was found to be in good agreement with the simple estimation based on the phase-trapping model.

Defect solitons supported by parity-time symmetric defect in superlattices

Hu Su-Mei (胡素梅), Hu Wei (胡巍)

Chin. Phys. B, 2013, 22 (7): 074201. DOI: 10.1088/1674-1056/22/7/074201

Abstract ( 703 )

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The existence and stability of defect solitons supported by parity-time (PT) symmetric defects in superlattices are investigated. In the semi-infinite gap, in-phase solitons are found to exist stably for positive defects, zero defects, and negative defects. In the first gap, out-of-phase solitons are stable for positive defects or zero defects, whereas in-phase solitons are stable for negative defects. For both the in-phase and out-of-phase solitons with the positive defect and in-phase solitons with negative defect in the first gap, there exists a cutoff point of the propagation constant below which the defect solitons vanish. The value of the cutoff point depends on the depth of defect and the imaginary parts of the PT symmetric defect potentials. The influence of the imaginary part of the PT symmetric defect potentials on soliton stability is revealed.

Preparing quantum vortex states with odd Schrödinger cat states through a coupled waveguide system

Tang Hui-Qin (唐慧琴), Li Shao-Xin (李绍新), Zhu Kai-Cheng (朱开成), Tang Ying (唐英), Zheng Xiao-Juan (郑小娟)

Chin. Phys. B, 2013, 22 (7): 074202. DOI: 10.1088/1674-1056/22/7/074202

Abstract ( 807 )

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A scheme is proposed for preparing a quantum vortex state with a coupled waveguide, in which a single-mode odd cat state with weak intensity and a single-mode coherent state are inserted in the input ports, respectively. The analytical wavefunction of the resulting state in the quadrature space is derived, and the vortex structure of output state is analyzed. It is found that the obtained states, which may carry a vortex with topological charge index one, are entangled and nonclassical, depending only on the scaled propagation time and the weak intensity of the input odd cat state instead of the displacement parameter of the input coherent state. The phase distribution, however, in the quadrature space, depends on the displacement parameter of the input coherent state.

Two-dimensional atom localization via probe absorption in a four-level atomic system

Wang Zhi-Ping (王志平), Ge Qiang (葛强), Ruan Yu-Hua (阮于华), Yu Ben-Li (俞本立)

Chin. Phys. B, 2013, 22 (7): 074203. DOI: 10.1088/1674-1056/22/7/074203

Abstract ( 732 )

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We have investigated the two-dimensional (2D) atom localization via probe absorption in a coherently driven four-level atomic system by means of a radio-frequency field driving a hyperfine transition. It is found that the detecting probability and precision of 2D atom localization can be significantly improved via adjusting the system parameters. As a result, our scheme may be helpful in laser cooling or the atom nano-lithography via atom localization.

Supercontinuum generated in all-normal dispersion photonic crystal fibers with picosecond pump pulses

Li Pan (李磐), Shi Lei (时雷), Mao Qing-He (毛庆和)

Chin. Phys. B, 2013, 22 (7): 074204. DOI: 10.1088/1674-1056/22/7/074204

Abstract ( 739 )

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The supercontinuum (SC) generations in all-normal dispersion (ANDi) photonic-crystal fiber (PCF) pumped by high power picosecond pulses are investigated in this paper. Our results show that an octave SC may be achieved by pumping the ANDi PCF with picosecond pump pulses. However, the PCF length required may have to be lengthened to several tens of centimeters, which is much longer than that with femtosecond pump pulses. The relatively long PCF gives rise to much higher Raman gain and stronger Raman frequency shift compared to those with femtosecond pump pulses, which in turn not only cause a distorted temporal waveform and an un-flatted spectrum, but also severely degrade the coherence of the generated SC.

Picosecond supercontinuum generation seeded by a weak continuous wave

Li Ying (李荧), Hou Jing (侯静), Leng Jin-Yong (冷进勇), Wang Wen-Liang (王文亮), Jiang Zong-Fu (姜宗福)

Chin. Phys. B, 2013, 22 (7): 074205. DOI: 10.1088/1674-1056/22/7/074205

Abstract ( 735 )

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We experimentally investigate the spectral details of picosecond supercontinuum pumped at 1064 nm and seeded by a weak continuous wave (～20000 times weaker than the pulse peak power) at several power levels in photonic crystal fibers. Seeding at different wavelengths leads to different spectral details, and the effects to the bandwidth of supercontinuum are also distinct. Spectra can be widened when seeded a continuous wave at 1070 nm, and be narrowed for ～100 nm when seeded at 1080 nm. The influence is enhanced with increasing seeded average power.

Numerical analysis of photonic crystal fiber with chalcogenide core tellurite cladding composite microstructure

Liu Shuo (刘硕), Li Shu-Guang (李曙光)

Chin. Phys. B, 2013, 22 (7): 074206. DOI: 10.1088/1674-1056/22/7/074206

Abstract ( 686 )

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Kinds of photonic crystal fibers with chalcogenide core tellurite cladding composite microstructure are proposed. The multi-core photonic crystal fiber can reach the higher nonlinearity coefficient and the larger effective mode area. The small single-core photonic crystal fiber has a very high nonlinearity coefficient. At the wavelength λ=0.8 μm, the nonlinearity coefficient can reach 31.37053 W^-1·m^-1, at the wavelength λ=1.55 μm, the nonlinearity coefficient is 11.19686 W^-1·m^-1.

Effect of water temperature on pulse duration and energy of stimulated Brillouin scattering

Zhang Lei (张磊), Zhang Dong (张东), Li Jin-Zeng (李金增)

Chin. Phys. B, 2013, 22 (7): 074207. DOI: 10.1088/1674-1056/22/7/074207

Abstract ( 799 )

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The water temperature has a strong effect on the kinematic viscosity, which is inversely proportional to the phonon lifetime and the gain coefficient. The higher the temperature is, the smaller the kinematic viscosity is, and the larger the phonon lifetime is. At a low pump power and a short focal length, we can derive a single-peak stimulated Brillouin scattering (SBS) pulse. The duration of this single-peak SBS pulse depends mainly on the phonon lifetime of water. With the raise of the water temperature, the duration of such a single-peak SBS pulse will become longer, and the SBS energy will become higher for the gain coefficient, which is related to the phonon lifetime. Therefore, varying the medium temperature can lead to the changes of SBS pulse duration and SBS energy.

Broadband tunable optical amplification based on modulation instability characteristic of high-birefringence photonic crystal fibers

Wang He-Lin (王河林), Yang Ai-Jun (杨爱军), Leng Yu-Xin (冷雨欣)

Chin. Phys. B, 2013, 22 (7): 074208. DOI: 10.1088/1674-1056/22/7/074208

Abstract ( 752 )

PDF (858KB) ( 486 )

A novel high-birefringence photonic crystal fiber (HB-PCF) with two zero-dispersion wavelengths (ZDWs) is designed, and an extraordinarily high modal birefringence of 1.56×10^-2 is obtained at pump wavelength λ_p=1850 nm. With the designed HB-PCF, the effect of the pump parameters on the modulation instability (MI) in the anomalous dispersion region close to the second ZDWs of the HB-PCF is comprehensively studied in this work. A broadband and tunable optical amplification is achieved by controlling the pump power and the pump wavelength based on the combined operation of Raman effect and cross phase modulation. By optimizing the pump parameters, the amplification bandwidth along the fiber slow axis reaches 152 nm for the pump power P_p=280 W and the pump wavelength λ_p=1675 nm, while the gain bandwidth along the fiber fast axis is 165 nm for the pump power P_p=600 W and the pump wavelength λ_p=1818 nm.

Stabilization of optical solitons in chirped PT-symmetric lattices

Li Chun-Yan (李春艳), Huang Chang-Ming (黄长明), Dong Liang-Wei (董亮伟)

Chin. Phys. B, 2013, 22 (7): 074209. DOI: 10.1088/1674-1056/22/7/074209

Abstract ( 938 )

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We investigate the stability properties of optical solitons in a chirped PT-symmetric lattice whose frequency changes in the transverse direction. Linear-stability analysis together with the direct propagation simulations demonstrates that the chirped lattice can improve the stability of optical solitons dramatically. The instability of fundamental solitons can be completely suppressed if the chirp rate exceeds a critical value. A broad stability area of dipole solitons appears if the lattice appropriately chirped. Thus, we propose an effective way to suppress the instability of solitons in PT-symmetric potentials.

Deformed soliton, breather, and rogue wave solutions of an inhomogeneous nonlinear Schrödinger equation

Tao Yong-Sheng (陶勇胜), He Jing-Song (贺劲松), K. Porsezian

Chin. Phys. B, 2013, 22 (7): 074210. DOI: 10.1088/1674-1056/22/7/074210

Abstract ( 858 )

PDF (707KB) ( 843 )

We use the 1-fold Darboux transformation (DT) of an inhomogeneous nonlinear Schrödinger equation (INLSE) to construct the deformed-soliton, breather, and rogue wave solutions explicitly. Furthermore, the obtained first-order deformed rogue wave solution, which is derived from the deformed breather solution through the Taylor expansion, is different from the known rogue wave solution of the nonlinear Schrödinger equation (NLSE). The effect of inhomogeneity is fully reflected in the variable height of the deformed soliton and the curved background of the deformed breather and rogue wave. By suitably adjusting the physical parameter, we show that a desired shape of the rogue wave can be generated. In particular, the newly constructed rogue wave can be reduced to the corresponding rogue wave of the nonlinear Schrödinger equation under a suitable parametric condition.

Theoretical study on the photonic band gap in one-dimensional photonic crystals with graded multilayer structure

Fan Chun-Zhen (范春珍), Wang Jun-Qiao (王俊俏), He Jin-Na (何金娜), Ding Pei (丁佩), Liang Er-Jun (梁二军)

Chin. Phys. B, 2013, 22 (7): 074211. DOI: 10.1088/1674-1056/22/7/074211

Abstract ( 822 )

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We theoretically investigate the photonic band gap in one-dimensional photonic crystals with a graded multilayer structure. The proposed structure is constituted of the alternating composite layer (metallic nanoparticles embedded in TiO₂ film) and the air layer. Regarding the multilayer as a series of capacitance, effective optical properties are derived. The dispersion relation is obtained with the solution of the transfer matrix equation. With a graded structure in the composite layer, numerical results show that the position and width of the photonic band gap can be effectively modulated by varying the number of the graded composite layers, the volume fraction of nanoparticles and the external stimuli.

Sphere-cone-polynomial special window with good aberration characteristic

Wang Chao (王超), Zhang Xin (张新), Qu He-meng (曲贺盟), Wang Ling-jie (王灵杰), Wang Yu (王钰)

Chin. Phys. B, 2013, 22 (7): 074212. DOI: 10.1088/1674-1056/22/7/074212

Abstract ( 740 )

PDF (299KB) ( 519 )

Optical windows with external surfaces shaped to satisfy operational environment needs are known as special windows. A novel special window, sphere-cone-polynomial (SCP) window, is proposed. The formulas of this window shape are given. An SCP MgF₂ window with a fineness ratio of 1.33 is designed as an example. The field-of-regard (FOR) angle is ±75°. From the window system simulation results obtained with the calculated fluid dynamics (CFD) and optical design software, we find that compared to the conventional window forms, the SCP shape can not only introduce relatively less drag in the airflow, but also have the minimal effect on imaging. So the SCP window optical system can achieve a high image quality across a super wide FOR without adding extra aberration correctors. The tolerance analysis results show that the optical performance can be maintained with a reasonable fabricating tolerance to manufacturing errors.

Numerical analysis of a photonic crystal fiber based on two polarized modes for biosensing applications

Qin Wei (秦伟), Li Shu-Guang (李曙光), Xue Jian-Rong (薛建荣), Xin Xu-Jun (辛旭军), Zhang Lei (张磊)

Chin. Phys. B, 2013, 22 (7): 074213. DOI: 10.1088/1674-1056/22/7/074213

Abstract ( 872 )

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This paper presents a theoretical study on a photonic crystal fiber plasmonic refractive index biosensor. The proposed photonic crystal fiber sensor introduces the concept of simultaneous detection with the linearly polarized and radially polarized modes because the sensing performance of the sensor based on both modes is relatively high, which will be useful for selecting the modes to make the detection accurately. The sharp single resonant peaks of linearly polarized mode and radially polarized mode, which are stronger and more sensitive to the variation of analyte refractive index than that of any other polarized mode in this kind of photonic crystal fiber. For linearly polarized mode and radially polarized mode, the maximum sensitivities of 10448.5 nm per refractive index unit and 8230.7 nm per refractive index unit can be obtained, as well as 949.8 and 791.4 for figure of merits in the sensing range of 1.33-1.45, respectively. Compared with the conventional Au-metalized surface plasmon resonance sensors, our device is better and can be applied as a biosensor.

Influence of laser linewidth on performance of Brillouin optical time domain reflectometry

Hao Yun-Qi (郝蕴琦), Ye Qing (叶青), Pan Zheng-Qing (潘政清), Cai Hai-Wen (蔡海文), Qu Rong-Hui (瞿荣辉)

Chin. Phys. B, 2013, 22 (7): 074214. DOI: 10.1088/1674-1056/22/7/074214

Abstract ( 856 )

PDF (341KB) ( 1074 )

The effects of optical sources with different laser linewidths on Brillouin optical time domain reflectometry (BOTDR) are investigated numerically and experimentally. Simulation results show that the spectral linewidth of spontaneous Brillouin scattering remains almost constant when the laser linewidth is less than 1 MHz at the same pulse width; otherwise, it increases sharply. A comparison between a fiber laser (FL) with 4-kHz linewidth at 3 dB and a distributed feedback (DFB) laser with 3-MHz linewidth is made experimentally. When a constant laser power is launched into the sensing fiber, the fitting linewidths of the beat signals (backscattered Brillouin light and local oscillator (LO)) is about 5 MHz wider for the DFB laser than for the FL and the intensity of the beat signal is about a half. Furthermore, the frequency fluctuation in the long sensing fiber is lower for the FL source, yielding about 2 MHz less than that of the DFB laser, indicating higher temperature/strain resolution. The experimental results are in good agreement with the numerical simulations.

Tunable band gaps in acoustic metamaterials with periodic arrays of resonant shunted piezos

Chen Sheng-Bing (陈圣兵), Wen Ji-Hong (温激鸿), Wang Gang (王刚), Wen Xi-Sen (温熙森)

Chin. Phys. B, 2013, 22 (7): 074301. DOI: 10.1088/1674-1056/22/7/074301

Abstract ( 801 )

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Periodic arrays of resonant shunted piezoelectric patches are employed to control the wave propagation in a two-dimensional (2D) acoustic metamaterial. The performance is characterized by the finite element method. More importantly, we propose an approach to solving the conventional issue of nonlinear eigenvalue problem, and give a convenient solution to the dispersion properties of 2D metamaterials with periodic arrays of resonant shunts in this article. Based on this modeling method, the dispersion relations of a 2D metamaterial with periodic arrays of resonant shunted piezos are calculated. The results show that the internal resonances of the shunting system split the dispersion curves, thereby forming a locally resonant band gap. However, unlike the conventional locally resonant gap, the vibrations in this locally resonant gap are unable to be completely localized in oscillators consisting of shunting inductors and piezo-patches.

Oblique incidence properties of locally resonant sonic materials with resonance and Bragg scattering effects

Yuan Bo (袁博), Wen Ji-Hong (温激鸿), Wen Xi-Sen (温熙森)

Chin. Phys. B, 2013, 22 (7): 074302. DOI: 10.1088/1674-1056/22/7/074302

Abstract ( 781 )

PDF (843KB) ( 541 )

A locally resonant sonic material (LRSM) is an elastic matrix containing a periodic arrangement of identical local resonators (LRs), which can reflect strongly near their natural frequencies, where the wavelength in the matrix is still much larger than the structural periodicity. Due to the periodic arrangement, an LRSM can also display a Bragg scattering effect, which is a characteristic of phononic crystals. A specific LRSM which possesses both local resonance and Bragg scattering effects is presented. Via the layered-multiple-scattering theory, the complex band structure and the transmittance of such LRSM are discussed in detail. Through the analysis of the refraction behavior at the boundary of the composite, we find that the transmittance performance of an LRSM for oblique incidence depends on the refraction of its boundary and the transmission behaviors of different wave modes inside the composite. As a result, it is better to use some low-speed materials (compared with the speed of waves in surrounding medium) as the matrix of LRSM for designing sound blocking materials in underwater applications, since their acoustic properties are more robust to the incident angle. Finally, a gap-coupled LRSM with a broad sub-wavelength transmission gap is studied, whose acoustic performance is insensitive to the angle of incidence.

Effects of size and arrangement of virtual transducer on photoacoustic tomography

Wang Shao-Hua (王少华), Tao Chao (陶超), Liu Xiao-Jun (刘晓峻)

Chin. Phys. B, 2013, 22 (7): 074303. DOI: 10.1088/1674-1056/22/7/074303

Abstract ( 802 )

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In this paper, we investigate the effects of the relative size and arrangement of the virtual transducer on the image quality in limited-view photoacoustic tomography. A virtual transducer refers to the acoustic scatterers used to reflect photoacoustic waves and improve the images reconstructed from incomplete PA signal. Size and spatial arrangement determine the performance of the virtual transducer. In this study, the scatterers utilized as virtual transducers are arranged in different manners, such as on a straight line or on an arc line. We find that virtual transducers with a big distributing angle can provide more significant image improvement than with a small distributing angle, which is similar to the true transducers. We also change the size of virtual transducer and study its influence on image quality. It is found that the bigger scatterers provide better images than the smaller ones. Especially, when the size of scatterers is reduced to the wavelength of photoacoustic wave, the image quality observably decreases, owing to the strong diffraction effect. Thus, it is suggested that the size of the acoustical scatterers should be much larger than the photoacoustic wavelength. The simulations are conducted, and the results could be helpful for the application and further study of virtual transducer theory in limited-view photoacoustic tomography.

Determining the thermophysical properties of Al-doped ZnO nanoparticles by the photoacoustic technique

T. A. El-Brolossy, O. Saber, S. S. Ibrahim

Chin. Phys. B, 2013, 22 (7): 074401. DOI: 10.1088/1674-1056/22/7/074401

Abstract ( 783 )

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Thermal conductivity and specific heat capacity of undoped and Al-doped (1-10 at.%) ZnO nanoparticles prepared using solvent thermal method are determined by measuring both thermal diffusivity and thermal effusivity of a pressed powder compact of the prepared nanoparticles using laser-induced photoacoustic technique. The impact of Al doping versus microstructure of the samples on such thermal parameters has been investigated. The results reveal an obvious enhancement in the specific heat capacity when decreasing the particle size, while the effect of Al doping on the specific heat capacity is minor. The measured thermal conductivities are about one order of magnitude smaller than that of the bulk ZnO due to several nested reducing heat transfer mechanisms. The results also show that Al doping significantly influences the thermal resistance. Using a simple thermal impedance model, the added thermal resistance due to Al dopant has been estimated.

Uniqueness, reciprocity theorem, and plane waves in thermoelastic diffusion with fractional order derivative

Rajneesh Kumar, Vandana Gupta

Chin. Phys. B, 2013, 22 (7): 074601. DOI: 10.1088/1674-1056/22/7/074601

Abstract ( 937 )

PDF (2527KB) ( 1947 )

In this work, a theory of thermoelasticity with diffusion is taken into consideration by using the methodology of fractional calculus. The governing equations for particle motion in a homogeneous anisotropic fractional order generalized thermoelastic diffusive medium are presented. Uniqueness and reciprocity theorems are proved. The plane wave propagation in the homogeneous transversely isotropic thermoelastic diffusive medium with fractional order derivative is studied. For the two-dimensional problem, there exist a quasi-longitudinal wave, a quasi-transverse wave, a quasi-mass diffusion wave, and a quasi-thermal wave. From the obtained results, the different characteristics of waves, like phase velocity, attenuation coefficient, specific loss, and penetration depth, are computed numerically and presented graphically. Some special cases are also discussed.

Casson fluid flow and heat transfer over a nonlinearly stretching surface

Swati Mukhopadhyay

Chin. Phys. B, 2013, 22 (7): 074701. DOI: 10.1088/1674-1056/22/7/074701

Abstract ( 1139 )

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A boundary layer analysis is presented for non-Newtonian fluid flow and heat transfer over a nonlinearly stretching surface. The Casson fluid model is used to characterize the non-Newtonian fluid behavior. By using suitable transformations, the governing partial differential equations corresponding to the momentum and energy equations are converted into non-linear ordinary differential equations. Numerical solutions of these equations are obtained with the shooting method. The effect of increasing the Casson parameter is to suppress the velocity field. However the temperature is enhanced with the increasing Casson parameter.

Effects of rotation and magnetic field on nonlinear peristaltic flow of second-order fluid in an asymmetric channel through a porous medium

A. M. Abd-Alla, S. M. Abo-Dahab, H. D. El-Shahrany

Chin. Phys. B, 2013, 22 (7): 074702. DOI: 10.1088/1674-1056/22/7/074702

Abstract ( 682 )

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In this paper, the effects of both rotation and magnetic field of the peristaltic transport of second-order fluid through a porous medium in a channel are studied analytically and computed numerically. The material was represented by the constitutive equations for a second-order fluid. Closed-form solutions under the consideration of long wavelength and low Reynolds number is presented. The analytical expressions for the pressure gradient, pressure rise, friction force, stream function, shear stress, and velocity are obtained in the physical domain. The effects of the non-dimensional wave amplitude, porosity, magnetic field, rotation, and the dimensionless time-mean flow in the wave frame are analyzed theoretically and computed numerically. Numerical results are given and illustrated graphically in each case considered. Comparison was made with the results obtained in the presence and absence of rotation, magnetic field, and porosity. The results indicate that the effects of the non-dimensional wave amplitude, porosity, magnetic field, rotation, and the dimensionless time-mean flow are very pronounced in the phenomena.

Extraction and verification of coherent structures in near-wall turbulence

Hu Hai-Bao (胡海豹), Du Peng (杜鹏), Huang Su-He (黄苏和), Wang Ying (王鹰)

Chin. Phys. B, 2013, 22 (7): 074703. DOI: 10.1088/1674-1056/22/7/074703

Abstract ( 658 )

PDF (690KB) ( 547 )

According to the characteristics of coherent structures in near-wall turbulence, an accurate extraction and verification method is developed based on wavelet transform (WT) and correlation analysis in this paper. At first, the fluid field of a turbulent boundary layer is measured precisely in a gravitational low-speed water tunnel. On the basis of the distribution of the coherent structures, velocity data of three test points are selected and analyzed, whose dimensionless heights are 20.8, 33.5, and 42.6. According to the frequency range of power spectrum density (PSD), coherent and incoherent structures are both extracted from the original signals using continuous and orthogonal wavelet transforms. To confirm the validity of the extracted signals, the probability density function (PDF) of each extracted signal is calculated. The result demonstrates that the incoherent structures obey the Gaussian distribution, while the coherent structures deviate from the Gaussian distribution. The PDFs of the coherent structures and the original signals are similar, which shows that the coherent structures make most contributions to the turbulence. For further verification, a correlation parameter between coherent and incoherent structures is defined, which evidently proves the validity of the extraction method in this paper.

An improved element-free Galerkin method for solving generalized fifth-order Korteweg-de Vries equation

Feng Zhao (冯昭), Wang Xiao-Dong (王晓东), Ouyang Jie (欧阳洁)

Chin. Phys. B, 2013, 22 (7): 074704. DOI: 10.1088/1674-1056/22/7/074704

Abstract ( 875 )

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In this paper, an improved element-free Galerkin (IEFG) method is proposed to solve the generalized fifth-order Korteweg-de Vries (gfKdV) equation. When the traditional element-free Galerkin (EFG) method is used to solve such an equation, unstable or even wrong numerical solutions may be obtained due to the violation of the consistency conditions of the moving least-squares (MLS) shape functions. To solve this problem, the EFG method is improved by employing the improved moving least-squares (IMLS) approximation based on the shifted polynomial basis functions. The effectiveness of the IEFG method for the gfKdV equation is investigated by using some numerical examples. Meanwhile, the motion of single solitary wave and the interaction of two solitons are simulated using the IEFG method.

Heat transfer in boundary layer stagnation-point flow towards a shrinking sheet with non-uniform heat flux

Krishnendu Bhattacharyya

Chin. Phys. B, 2013, 22 (7): 074705. DOI: 10.1088/1674-1056/22/7/074705

Abstract ( 867 )

PDF (558KB) ( 1441 )

In this paper, the effect of non-uniform heat flux on heat transfer in boundary layer stagnation-point flow over a shrinking sheet is studied. The variable boundary heat fluxes are considered of two types: direct power-law variation with the distance along the sheet and inverse power-law variation with the distance. The governing partial differential equations (PDEs) are transformed into non linear self-similar ordinary differential equations (ODEs) by similarity transformations,and then those are solved using very efficient shooting method. The direct variation and inverse variation of heat flux along the sheet have completely different effects on the temperature distribution. Moreover, the heat transfer characteristics in the presence of non-uniform heat flux for several values of physical parameters are also found to be interesting.

Diffusion dynamics in external noise-activated non-equilibrium open system reservoir coupling environment

Wang Chun-Yang (王春阳)

Chin. Phys. B, 2013, 22 (7): 074706. DOI: 10.1088/1674-1056/22/7/074706

Abstract ( 621 )

PDF (287KB) ( 482 )

The diffusion process in an external noise-activated non-equilibrium open system-reservoir coupling environment is studied by analytically solving the generalized Langevin equation. The dynamical property of the system near the barrier top is investigated in detail by numerically calculating the quantities such as mean diffusion path, invariance, barrier passing probability, and so on. It is found that, comparing with the unfavorable effect of internal fluctuations, the external noise activation is sometimes beneficial to the diffusion process. An optimal strength of external activation or correlation time of the internal fluctuation is expected for the diffusing particle to have a maximal probability to escape from the potential well.

Cylindrical and spherical Gardner solitons and double layers in a dusty electronegative nonthermal plasma with two-temperature electrons

T. Akhter, M. M. Hossain, A. A. Mamun

Chin. Phys. B, 2013, 22 (7): 075201. DOI: 10.1088/1674-1056/22/7/075201

Abstract ( 598 )

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A precise theoretical investigation has been made on the cylindrical and spherical (nonplanar) Gardner solitons (GSs) and double layers (DLs) in a dusty electronegative plasma (composed of inertial positive and negative ions, Maxwellian cold electrons, non-thermal hot electrons, and negatively charged static dust). The reductive perturbation method has been used in derivation of the modified Gardner (MG) equation describing the nonlinear propagation of the dust ion-acoustic (DIA) waves. The MG equation admits solitary waves (SWs) and DLs solutions for σ around its critical value σ_c (where σ_c is the value of σ corresponding to the vanishing of the nonlinear coefficient of the Korteweg de-Vries (K-dV) equation). The nonplanar SWs and DLs solutions are numerically analyzed and the parametric regimes for the existence of the positive as well as negative SWs and negative DLs are obtained. The basic features of nonplanar DIA SWs and DLs, which are found to be different from planar ones, are also identified. The implications of our results to different space and laboratory dusty plasma situations, are discussed.

Blockage effects on viscous fluid flow and heat transfer past a magnetic obstacle in a duct

Zhang Xi-Dong (张喜东), Huang Hu-Lin (黄护林)

Chin. Phys. B, 2013, 22 (7): 075202. DOI: 10.1088/1674-1056/22/7/075202

Abstract ( 827 )

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The effect of the lateral walls on the fluid flow and heat transfer is investigated when the fluid passes a magnetic obstacle in present paper. The blockage ratio β that represents the ratio between the width of external magnet M_y and the spanwise width L_y is employed to depict the effect. The finite volume method (FVM) based on the PISO algorithm is applied for the blockage ratios of 0.2, 0.3, and 0.4. The results show that, the value of Strouhal number St increases as the blockage ratio β increases, and for small β, the variation of St is very small when the interaction parameter and Reynolds number are increasing. Moreover, the cross-stream mixing induced by the magnetic obstacle can enhance the wall-heat transfer and the maximum value of the overall heat transfer increment is about 50.5%.

Effect of shear equilibrium flow in Tokamak plasma on resistive wall modes

Li Li (李莉), Liu Yue (刘悦)

Chin. Phys. B, 2013, 22 (7): 075203. DOI: 10.1088/1674-1056/22/7/075203

Abstract ( 723 )

PDF (644KB) ( 424 )

A code named LARWM with non-ideal magnetohydrodynamic equations in cylindrical model is used to describe the instability in Tokamak plasma surrounded by a conducting wall with finite resistivity. We mainly take three factors related to the shear equilibrium plasma flow into consideration to study the stabilizing effect of the shear flow on the resistive wall modes (RWMs). The three factors are the velocity amplitude of flow, the shear rate of flow on plasma surface, and the inertial energy of equilibrium plasma flow. In addition, a local shear plasma flow is also calculated by the LARWM code. Consequently, it is found that the inertial energy of the shear equilibrium plasma flow has an important role in the stabilization of the RWMs.

Spectral modulation and supercontinuum generation assisted by infrared femtosecond plasma grating

Liu Zuo-Ye (刘作业), Sun Shao-Hua (孙少华), Shi Yan-Chao (史彦超), Ding Peng-Ji (丁鹏基), Liu Qing-Cao (刘情操), Liu Xiao-Liang (刘小亮), Ding Bao-Wei (丁宝卫), Hu Bi-Tao (胡碧涛)

Chin. Phys. B, 2013, 22 (7): 075204. DOI: 10.1088/1674-1056/22/7/075204

Abstract ( 723 )

PDF (516KB) ( 642 )

Spectral modulation and supercontinuum generation of a probe pulse is investigated by using the plasma grating induced by the interference of two infrared femtosecond laser pulses. The dependences of the supercontinuum generation from the probe pulse on the time delay, the relative polarization angle between the probe pulse and the two-pump pulses, and the input probe pulse energy are investigated. The far-field spatial profiles of the three pulses are measured with different time delays and relative polarization angle, and the core energy of the probe pulse as functions of the time delay and relative polarization angle are also shown.

Dispersion relation and growth rate for a corrugated channel free-electron laser with a helical wiggler pump

A. Hasanbeigi, H. Mehdiank

Chin. Phys. B, 2013, 22 (7): 075205. DOI: 10.1088/1674-1056/22/7/075205

Abstract ( 738 )

PDF (327KB) ( 578 )

The effects of corrugated ion channels on electron trajectories and spatial growth rate for a free-electron laser with a one-dimensional helical wiggler have been investigated. Analysis of the steady-state electron trajectories is performed by solving equations of motion. Our results show that the presence of corrugated channel shifts the resonance frequency to smaller values of ion channel frequency. The sixth-order dispersion equation describing the coupling between the electrostatic beam mode and the electromagnetic mode has also been derived. The characteristic of dispersion relation is analyzed in detail by numerical solution. Results show that the growth rate of instability in the presence of corrugated ion channels can be greatly enhanced relative to the case of an uniform ion channel.

Preferred orientations of encapsulated C₆₀ molecules inside single wall carbon nanotubes

Yao Zhen (姚震), Liu Ran (刘然), Ma Feng-Xian (马凤仙), Lu Shuang-Chen (路双臣), Tian Fu-Bo (田夫波), Duan De-Fang (段德芳), Cui Tian (崔田), Liu Bing-Bing (刘冰冰)

Chin. Phys. B, 2013, 22 (7): 076101. DOI: 10.1088/1674-1056/22/7/076101

Abstract ( 616 )

PDF (1462KB) ( 468 )

A systematical study of the orientational behavior of C₆₀ molecules in single wall carbon nanotubes (SWCNTs) with different chirality and diameter has been performed by using a model of an infinite long nanotube filled with two C₆₀ (denoted as C₆₀-1 and C₆₀-2) molecules. We studied the preferred orientation of the C₆₀-1 molecule when the neighboring C₆₀-2 molecule was fixed at the pentagon, double-bond, and hexagon orientations respectively. Our results showed that the C₆₀-1 molecule prefers the pentagon (hexagon) orientation when the tube diameter is smaller (larger) than 1.31 nm (1.36 nm). For the tube diameter in between, the preferred molecular orientation of C₆₀-1 changes from pentagon to hexagon with the increasing tube diameter when the neighboring C₆₀-2 molecule is fixed at the pentagon or double-bond orientation. A novel vertex orientation for the C₆₀-1 molecule has been found when the C₆₀-2 molecule is fixed at the hexagon orientation.

Growth and characterization of straight InAs/GaAs nanowireheterostructures on Si substrate

Yan Xin (颜鑫), Zhang Xia (张霞), Li Jun-Shuai (李军帅), Lü Xiao-Long (吕晓龙), Ren Xiao-Min (任晓敏), Huang Yong-Qing (黄永清)

Chin. Phys. B, 2013, 22 (7): 076102. DOI: 10.1088/1674-1056/22/7/076102

Abstract ( 653 )

PDF (1455KB) ( 649 )

Vertical InAs/GaAs nanowire (NW) heterostructures with a straight InAs segment have been successfully fabricated on Si (111) substrate by using AlGaAs/GaAs buffer layers coupled with a composition grading InGaAs segment. Both the GaAs and InAs segments are not limited by the misfit strain induced critical diameter. The low growth rate of InAs NWs is attributed to the AlGaAs/GaAs buffer layers which dramatically decrease the adatom diffusion contribution to the InAs NW growth. The crystal structure of InAs NW can be tuned from zincblende to wurtzite by controlling its diameter as well as the length of GaAs NWs. This work helps to open up a road for the integration of high-quality III-V NW heterostructures with Si.

Effect of Nano-SiO₂ films on electron radiation induced conductivity of polyimide

Yue Long (岳龙), Wu Yi-Yong (吴宜勇), Sun Cheng-Yue (孙承月), Shi Ya-Ping (石亚平), Xiao Jing-Dong (肖景东), He Shi-Yu (何世禹)

Chin. Phys. B, 2013, 22 (7): 076103. DOI: 10.1088/1674-1056/22/7/076103

Abstract ( 818 )

PDF (596KB) ( 784 )

The radiation induced conductivity (RIC) behaviors in nano-SiO₂ deposited polyimide (PI) were investigated using in situ measurement technique. The results indicate that, by comparison with the case of virgin polyimide, the RIC in nano-SiO₂/polyimide shows low steady state values. Moreover, the steady state RIC is a power function of the dose rate with a power index of 0.659, lower than that of 0.76 in the virgin polyimide. The interfacial barrier and trapping effects are the main reasons for the change. Meanwhile, both of the interfacial effects also result in a unipolar carrier transportation mechanism in nano-SiO₂ deposited PI from the dipolar one in the virgin PI. The mechanisms of the RIC behaviors are discussed in the paper.

Towards understanding carbon trapping mechanism in copper by investigating the carbon-vacancy interaction

Zhou Hong-Bo (周洪波), Jin Shuo (金硕)

Chin. Phys. B, 2013, 22 (7): 076104. DOI: 10.1088/1674-1056/22/7/076104

Abstract ( 676 )

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We propose a vacancy trapping mechanism for carbon-vacancy (C-V) complex formation in copper (Cu) according to the first-principles calculations of the energetics and kinetics of C-V interaction. Vacancy reduces charge density in its vicinity to induce C nucleation. A monovacancy is capable of trapping as many as four C atoms to form C_nV (n=1, 2, 3, 4) complexes. Single C atom prefers to interact with neighboring Cu at vacancy with a trapping energy of-0.21 eV. With multiple C atoms added, they are preferred to bind with each other to form covalent-like bonds despite of the metallic Cu environment. For the C_nV complexes, C₂V is the major one due to its lowest average trapping energy (1.31 eV). Kinetically, the formation of the C_nV complexes can be ascribed to the vacancy mechanism due to the lower activation energy barrier and the larger diffusion coefficient of vacancy than those of the interstitial C.

Theoretical demonstration of hybrid focusing points ofsonic crystal flat lenses and possible applications

Serkan Alagoz, Baris Baykant Alagoz

Chin. Phys. B, 2013, 22 (7): 076201. DOI: 10.1088/1674-1056/22/7/076201

Abstract ( 618 )

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We demonstrate the hybrid focusing points of sonic crystals for a multi-source array applied to flat sonic crystal lenses. The contributions of different point source couples form hybrid focusing points. Ray-trace analyses are conducted for acoustic flat lenses with multi-source configurations. The finite-difference time-domain (FDTD) simulation of flat lenses with multi-source configurations demonstrates the establishment of pure and hybrid focusing points in a pyramidal constellation. The number of focusing points in the pyramidal constellation depends on the number of point sources. We propose an acoustic device for fine-tuning the location of a far-field hybrid focusing point and discuss its benefits for acoustic energy focusing application.

Study of lattice thermal conductivity of alpha-zirconium by molecular dynamics simulation

Wu Tian-Yu (武天宇), Lai Wen-Sheng (赖文生), Fu Bao-Qin (付宝勤)

Chin. Phys. B, 2013, 22 (7): 076601. DOI: 10.1088/1674-1056/22/7/076601

Abstract ( 707 )

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The non-equilibrium molecular dynamics method is adapted to calculate the phonon thermal conductivity of alphazirconium.By exchanging velocities of atoms in different regions, the stable heat flux and the temperature gradient are established to calculate the thermal conductivity. The phonon thermal conductivities under different conditions, such as different heat exchange frequencies, different temperatures, different crystallographic orientations, and crossing grain boundary (GB), are studied in detail with considering the finite size effect. It turns out that the phonon thermal conductivity decreases with the increase of temperature, and displays anisotropies along different crystallographic orientations. The phonon thermal conductivity in [0001] direction (close-packed plane) is largest, while the values in other two directions of [2110] and [0110] are relatively close. In the region near GB, there is a sharp temperature drop, and the phonon thermal conductivity is about one-tenth of that of the single crystal at 550 K, suggesting that the GB may act as a thermal barrier in the crystal.

Interfacial characteristics of Al/Al₂O₃/ZnO/n-GaAs MOS capacitor

Liu Chen (刘琛), Zhang Yu-Ming (张玉明), Zhang Yi-Men (张义门), Lü Hong-Liang (吕红亮)

Chin. Phys. B, 2013, 22 (7): 076701. DOI: 10.1088/1674-1056/22/7/076701

Abstract ( 613 )

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The interfacial characteristics of Al/Al₂O₃/ZnO/n-GaAs metal-oxide-semiconductor (MOS) capacitor are investigated. The results measured by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) show that the presence of ZnO can effectively suppress the formations of oxides at the interface between the GaAs and gate dielectric and gain smooth interface. The ZnO-passivated GaAs MOS capacitor exhibits a very small hysteresis and frequency dispersion. Using the Terman method, the interface trap density is extracted from C-V curves. It is found that the ZnO layer can effectively improve the interface quality.

Penetrating view of nano-structures in Aleochara verna spermatheca and flagellum by hard X-ray microscopy

Zhang Kai (张凯), Li Dee (李德娥), Hong You-Li (洪友丽), Zhu Pei-Ping (朱佩平), Yuan Qing-Xi (袁清习), Huang Wan-Xia (黄万霞), Gao Kun (高昆), Zhou Hong-Zhang (周红章), Wu Zi-Yu (吴自玉)

Chin. Phys. B, 2013, 22 (7): 076801. DOI: 10.1088/1674-1056/22/7/076801

Abstract ( 719 )

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A penetrating view of the three-dimensional nano-structure of female spermatheca and male flagellum in the species Aleochara verna is obtained with 100-nm resolution using a hard X-ray microscope, which provides a fast noninvasive imaging technology for insect morphology. Through introducing Zernike phase contrast and heavy metal staining, images taken at 8 keV displayed sufficient contrast for observing nanoscale fine structures, such as the spermatheca cochleate duct and the subapex of the flagellum, which have some implications for the study of the sperm transfer process and genital evolution in insects. This work shows that both the spatial resolution and the contrast characteristic of hard X-ray microscope are quite promising for insect morphology studies, in particularly, provide an attractive alternative to destructive techniques for internal soft tissues.

Scanning tunneling microscopy study of molecular growth structures of Gd@C₈₂ on Cu(111) ^Hot!

Chen Jian (陈建), Qin Zhi-Hui (秦志辉), Pan Jin-Bo (潘金波), Lu Shuang-Zan (卢双赞), Du Shi-Xuan (杜世萱), Gao Hong-Jun (高鸿钧), Cao Geng-Yu (曹更玉)

Chin. Phys. B, 2013, 22 (7): 076802. DOI: 10.1088/1674-1056/22/7/076802

Abstract ( 787 )

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The coverage and temperature-dependent nucleation behaviors of the Gd@C₈₂ metallofullerenes on Cu(111) have been studied by low-temperature scanning tunneling microscopy (LT-STM) in detail. Upon molecular deposition at low temperature, Gd@C₈₂ molecules preferentially decorate the steps and nucleate into single layer islands with increasing coverage. Further annealing treatment leads some of the Gd@C₈₂ molecules to assemble into bright and dim patches, which are correlated to the adsorption induced substrate reconstruction. Upon sufficient thermal activation, Gd@C₈₂ molecules sink into the Cu(111) surface one-copper-layer-deep, forming hexagonal close-packed molecular islands with intra-molecular details observed as striped patterns. By considering the commensurability between the Gd@C₈₂ nearest-neighbor distance and the lattice of the underlying Cu(111), we clearly identified two kinds of in-plane molecular arrangements as (√19×19)R23.4° and (19×19)R36.6° with respect to Cu(111). Within the assembled Gd@C₈₂ molecular, island molecules with dim-bright contrast are spatially distributed, which may be modulated by the preexisted species on Cu(111).

Effects of prestrained InGaN interlayer on the emission properties of InGaN/GaN multiple quantum wells in a laser diode structure

Cao Wen-Yu (曹文彧), He Yong-Fa (贺永发), Chen Zhao (陈钊), Yang Wei (杨薇), Du Wei-Min (杜为民), Hu Xiao-Dong (胡晓东)

Chin. Phys. B, 2013, 22 (7): 076803. DOI: 10.1088/1674-1056/22/7/076803

Abstract ( 906 )

PDF (286KB) ( 916 )

The electroluminescence (EL) and photoluminescence (PL) spectra of InGaN/GaN multiple quantum wells (MQWs) with a prestrained InGaN interlayer in a laser diode structure are investigated. When the injection current increases from 5 mA to 50 mA, the blueshift of the EL emission peak is 1 meV for the prestrained sample and 23 meV for a control sample with the conventional structure. Also, the internal quantum efficiency and the EL intensity at the injection current of 20 mA are increased by 71% and 65% respectively by inserting the prestrained InGaN interlayer. The reduced blueshift and the enhanced emission are attributed mainly to the reduced quantum-confined Stark effect (QCSE) in the prestrained sample. Such attributions are supported by the theoretical simulation results, which reveal the smaller piezoelectric field and the enhanced overlap of electron and hole wave functions in the prestrained sample. Therefore, the prestrained InGaN interlayer contributes to strain relaxation in the MQW layer and enhancement of light emission due to the reduction of QCSE.

Significant photoelectrical response of epitaxial graphene grown on Si-terminated 6H-SiC

Hao Xin (郝昕), Chen Yuan-Fu (陈远富), Wang Ze-Gao (王泽高), Liu Jing-Bo (刘竞博), He Jia-Rui (贺加瑞), Li Yan-Rong (李言荣)

Chin. Phys. B, 2013, 22 (7): 076804. DOI: 10.1088/1674-1056/22/7/076804

Abstract ( 639 )

PDF (1419KB) ( 682 )

Photoelectrical response characteristics of epitaxial graphene (EG) films on Si-and C-terminated 6H-SiC, and transferred chemical vapor deposition (CVD) graphene films on Si-terminated 6H-SiC have been investigated. The results show that upon illumination of xenon lamp, the photocurrent of EG grown on Si-terminated SiC significantly increases by 147.6%, while the photocurrents of EG grown on C-terminated SiC, and transferred CVD graphene on Si-terminated SiC slightly decrease by 0.5% and 2.7%, respectively. The interfacial buffer layer between EG and Si-terminated 6H-SiC is responsible for the significant photoelectrical response of EG. Strong photoelectrical response makes it promising for optoelectronic applications.

Density-functional theory study of the effect of pressure on the elastic properties of CaB₆

Han Han (韩晗)

Chin. Phys. B, 2013, 22 (7): 077101. DOI: 10.1088/1674-1056/22/7/077101

Abstract ( 833 )

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Under a high pressure, long believed single-phase material CaB₆ is latterly discovered to have a new phase tI56. Based on the density-functional theory, the pressure effects on the structural and elastic properties of CaB₆ are obtained. The calculated bulk, shear, and Young's moduli of the recently synthesized high pressure phase tI56-CaB₆ are larger than those of the low pressure phase. Moreover, the high pressure phase of CaB₆ has ductile behaviors, and its ductility increases with the increase of pressure. On the contrary, the calculated results indicate that the low pressure phase of CaB₆ is brittle. The calculated Debye temperature indicates that the thermal conductivity of CaB₆ is not very good. Furthermore, based on the Christoffel equation, the slowness surface of the acoustic waves is obtained.

Directly extracting both threshold voltage and series resistance from conductance-voltage curve for AlGaN/GaN Schottky diode

Lü Yuan-Jie (吕元杰), Feng Zhi-Hong (冯志红), Gu Guo-Dong (顾国栋), Dun Shao-Bo (敦少博), Yin Jia-Yun (尹甲运), Han Ting-Ting (韩婷婷), Sheng Bai-Cheng (盛百城), Cai Shu-Jun (蔡树军), Liu Bo (刘波), Lin Zhao-Jun (林兆军)

Chin. Phys. B, 2013, 22 (7): 077102. DOI: 10.1088/1674-1056/22/7/077102

Abstract ( 903 )

PDF (270KB) ( 1502 )

An Ni/Au Schottky contact on an AlGaN/GaN heterostructure has been prepared. By using the peak-conductance model, the threshold voltage and the series resistance of the AlGaN/GaN diode are simultaneously extracted from the conductance-voltage (G-V) curve and found to be in good agreement with the ones gotten by using the capacitance-voltage (C-V) curve integration and the plot of dV/zd(lnI) versus current I. Thus, a method of directly and simultaneously extracting both the threshold voltage and the series resistance from the conductance-voltage curve for the AlGaN/GaN Schottky diode is developed.

First-principles study on the effect of high In doping on the conductivity of ZnO

Hou Qing-Yu (侯清玉), Li Ji-Jun (李继军), Ying Chun (迎春), Zhao Chun-Wang (赵春旺), Zhao Er-Jun (赵二俊), Zhang Yue (张跃)

Chin. Phys. B, 2013, 22 (7): 077103. DOI: 10.1088/1674-1056/22/7/077103

Abstract ( 792 )

PDF (437KB) ( 712 )

Based on the density functional theory (DFT), using first-principles plane-wave ultrasoft pseudopotential method, the models of the unit cell of pure ZnO and two highly In-doped supercells of Zn_0.9375In_0.0625O and Zn_0.875In_0.125O are constructed, and the geometry optimizations of the three models are carried out. The total density of states (DOS) and the band structures (BS) are also calculated. The calculation results show that in the range of high doping concentration, when the doping concentration is hihger than a specific value, the conductivity decreases with the increase of the doping concentration of In in ZnO, which is in consistence with the change trend of the experimental results.

A comparison of the transport properties of bilayer graphene, monolayer graphene, and two-dimensional electron gas

Sun Li-Feng (孙立风), Dong Li-Min (董利民), Wu Zhi-Fang (吴志芳), Fang Chao (房超)

Chin. Phys. B, 2013, 22 (7): 077201. DOI: 10.1088/1674-1056/22/7/077201

Abstract ( 875 )

PDF (376KB) ( 751 )

We studied and compared the transport properties of charge carriers in the bilayer graphene, the monolayer graphene, and the conventional semiconductors (the two-dimensional electron gas (2DEG)). It is elucidated that the normal incidence transmission in the bilayer graphene is identical to that in the 2DEG but totally different from that in the monolayer graphene. However, the resonant peaks appear in the non-normal incidence transmission profile for a high barrier in the bilayer graphene, which do not occur in the 2DEG. Furthermore, there are tunneling and forbidden regions in the transmission spectrum for each material, and the division of the two regions has been given in the work. The tunneling region covers a wide range of the incident energy for the two graphene systems, but only exists under specific conditions for the 2DEG. The counterparts of the transmission in the conductance profile are also given for the three materials, which may be used as high-performance devices based on the bilayer graphene.

Rainbow trapping based on long-range plasmonic Bragg gratings at telecom frequencies

Chen Lin (陈林), Zhang Tian (张天), Li Xun

Chin. Phys. B, 2013, 22 (7): 077301. DOI: 10.1088/1674-1056/22/7/077301

Abstract ( 760 )

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The group velocity of long-range surface plasmon polaritons (LRSPPs) in a wide frequency bandwidth at infrared frequencies is significantly reduced by dielectric gratings of graded thickness on both sides of a thin metal film. This structure can reduce the propagation loss of slow surface plasmons in “rainbow trapping” systems based on plasmonic Bragg gratings. Compared with dielectric gratings of graded thickness on a single side of a metal film, the proposed structure is able to guide slow light with a much longer propagation distance for the same group index factor. Finite-difference time-domain simulation results show that slow LRSPPs with the group velocity of c/14.5 and the propagation distance of 10.4 μm are achieved in dielectric gratings of uniform thickness on both sides of a thin metal film at 1.62 μm.

Low-cost, high performance surface plasmon resonance-compatible films characterized by surface plasmon resonance technique

Li Song-Quan (李松权), Ye Hong-An (叶红安), Liu Chun-Yu (柳春郁), Dou Yin-Feng (窦寅丰), Huang Yan (黄妍)

Chin. Phys. B, 2013, 22 (7): 077302. DOI: 10.1088/1674-1056/22/7/077302

Abstract ( 618 )

PDF (2008KB) ( 860 )

A new analytical method based on the surface plasmon resonance (SPR) technique is presented, with which SPR curves for both wavelength and angular modulations can be obtained simultaneously via only a single scan of the incident angle. Using this method, the SPR responses of TiO₂-coated Cu films are characterized in the wavelength range from 600 nm to 900 nm. For the first time, we determine the effective optical constants and the thicknesses of TiO₂-coated Cu films using the SPR curves of wavelength modulation. The sensitivities of prism-based SPR refractive index sensors using TiO₂-coated Cu films are investigated theoretically for both wavelength and angular modulations, the results show that in the case of sensitivity with wavelength modulation, TiO₂-coated Cu films are not as good as the Au film, however, they are more suitable than the Au film for SPR refractive index sensors with angular modulation because a higher sensitivity can be achieved.

Color-stable, reduced efficiency roll-off hybrid white organic light emitting diodes with ultra high brightness

Liu Bai-Quan (刘佰全), Tao Hong (陶洪), Su Yue-Ju (苏跃举), Gao Dong-Yu (高栋雨), Lan Lin-Feng (兰林锋), Zou Jian-Hua (邹建华), Peng Jun-Biao (彭俊彪)

Chin. Phys. B, 2013, 22 (7): 077303. DOI: 10.1088/1674-1056/22/7/077303

Abstract ( 746 )

PDF (558KB) ( 787 )

High-brightness and color-stable two-wavelength hybrid white organic light emitting diodes (HWOLEDs) with the configuration of indium tin oxide (ITO)/N, N, N', N'-tetrakis(4-methoxyphenyl)-benzidine (MeO-TPD): tetrafluoro-tetracyanoqino dimethane (F4-TCNQ)/N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB)/4,4-N,N-dicarbazolebiphenyl (CBP): iridium (III) diazine complexes (MPPZ)₂Ir(acac)/NPB/2-methyl-9,10-di(2-naphthyl)anthracene (MADN): p-bis(p-N,N-di-phenyl-aminostyryl)benzene (DSA-ph)/bis(10-hydroxybenzo[h] quinolinato)beryllium complex (Bebq₂)/LiF/Al have been fabricated and characterized. The optimal brightness of the device is 69932 cd/m² at a voltage of 13 V, and the Commission Internationale de l'Eclairage (CIE) chromaticity coordinates are almost constant during a large voltage change of 6-12 V. Furthermore, a current efficiency of 15.3 cd/A at an illumination-relevant brightness of 1000 cd/m² is obtained, which rolls off slightly to 13.0 cd/A at an ultra high brightness of 50000 cd/m². We attribute this great performance to wisely selecting an appropriate spacer together with effectively utilizing the combinations of exciton-harvested orange-phosphorescence/blue-fluorescence in the device. Undoubtedly, this is one of the most exciting results in two-wavelength HWOLEDs up to now.

Contact effect in the dynamic electron transport of two-probe mesoscopic conductor

Quan Jun (全军), Xiao Shi-Fa (肖世发), Tian Ying (田英)

Chin. Phys. B, 2013, 22 (7): 077304. DOI: 10.1088/1674-1056/22/7/077304

Abstract ( 818 )

PDF (304KB) ( 380 )

Based on the self-consistent electron dynamic transport theory for multi-probe mesoscopic systems, we calculate the distribution of internal potential, charge density, and ac conductance of a two-probe mesoscopic conductor with wide trapezoid reservoirs, and study the contact effect. The results show that including the contact effect can make a significant difference to the frequency-dependent electron transport properties. In the nonzero frequency case, the internal potential and the charge density are complex with extremely small imaginary parts. Importantly, the imaginary part of the charge density gives rise to a real ac conductance (admittance), which corresponds to the charge-relaxation resistance.

Electron mobility limited by surface and interface roughness scatterings in Al_xGa_1-xN/GaN quantum wells

Wang Jian-Xia (王建霞), Yang Shao-Yan (杨少延), Wang Jun (王俊), Liu Gui-Peng (刘贵鹏), Li Zhi-Wei (李志伟), Li Hui-Jie (李辉杰), Jin Dong-Dong (金东东), Liu Xiang-Lin (刘祥林), Zhu Qin-Sheng (朱勤生), Wang Zhan-Guo (王占国)

Chin. Phys. B, 2013, 22 (7): 077305. DOI: 10.1088/1674-1056/22/7/077305

Abstract ( 834 )

PDF (419KB) ( 669 )

The electron mobility limited by the interface and surface roughness scatterings of the two-dimensional electron gas in Al_xGa_1-xN/GaN quantum wells is studied. The newly proposed surface roughness scattering in the AlGaN/GaN quantum wells becomes effective when an electric field exists in the Al_xGa_1-xN barrier. For the AlGaN/GaN potential well, the ground subband energy is governed by the spontaneous and the piezoelectric polarization fields which are determined by the barrier and the well thicknesses. The thickness fluctuation of the AlGaN barrier and the GaN well due to the roughnesses cause the local fluctuation of the ground subband energy, which will reduce the 2DEG mobility.

Effect of Si-doped In_0.49Ga_0.51P barrier layer on the device performance of In_0.4Ga_0.6As MOSFETs grown onsemi-insulating GaAs substrate

Chang Hu-Dong (常虎东), Sun Bing (孙兵), Xue Bai-Qing (薛百清), Liu Gui-Ming (刘桂明), Zhao Wei (赵威), Wang Sheng-Kai (王盛凯), Liu Hong-Gang (刘洪刚)

Chin. Phys. B, 2013, 22 (7): 077306. DOI: 10.1088/1674-1056/22/7/077306

Abstract ( 791 )

PDF (503KB) ( 655 )

In_0.4Ga_0.6As channel metal-oxide-semiconductor field-effect transistors (MOSFETs) with and without Si-doped In_0.49Ga_0.51P barrier layer grown on semi-insulating GaAs substrates have been investigated for the first time. Compared with the In_0.4Ga_0.6As MOSFETs without In_0.49Ga_0.51P barrier layer, In_0.4Ga_0.6As MOSFETs with In_0.49Ga_0.51P barrier layer show higher drive current, higher transconductance, lower gate leakage current, lower subthreshold swing, and higher effective channel mobility. These In_0.4Ga_0.6As MOSFETs (gate length 2 μm) with In_0.49Ga_0.51P barrier layer exhibit a high drive current of 117 mA/mm, a high transconductance of 71.9 mS/mm, and a maximum effective channel mobility of 1266 cm²/(V·s).

Ultraviolet emissions realized in ZnO via avalanche multiplication process

Yu Ji (于吉), Shan Chong-Xin (单崇新), Shen He (申赫), Zhang Xiang-Wei (张祥伟), Wang Shuang-Peng (王双鹏), Shen De-Zhen (申德振)

Chin. Phys. B, 2013, 22 (7): 077307. DOI: 10.1088/1674-1056/22/7/077307

Abstract ( 849 )

PDF (500KB) ( 457 )

Au/MgO/ZnO/MgO/Au structures have been designed and constructed in this study. Under a bias voltage, a carrier avalanche multiplication will occur via an impact ionization process in the MgO layer. The generated holes will be drifted into the ZnO layer, and recombine radiatively with the electrons in the ZnO layer, thus obvious emissions at around 387 nm coming from the near-band-edge emission of ZnO will be observed. The results reported in this paper demonstrate the ultraviolet (UV) emission realized via a carrier multiplication process, thus may provide an alternative route to efficient UV emissions by bypassing the challenging p-type doping issues of ZnO.

Bipolar resistive switching based on bis(8-hydroxyquinoline) cadmium complex：Mechanism and non-volatile memory application

Wang Ying (王颖), Yang Ting (杨汀), Xie Ji-Peng (谢吉鹏), Lü Wen-Li (吕文理), Fan Guo-Ying (范国莹), Liu Su (刘肃)

Chin. Phys. B, 2013, 22 (7): 077308. DOI: 10.1088/1674-1056/22/7/077308

Abstract ( 793 )

PDF (644KB) ( 684 )

Stable and persistent bipolar resistive switching was observed in an organic diode with the structure of indium-tin oxide (ITO)/bis(8-hydroxyquinoline) cadmium (Cdq₂)/Al. Aggregate formation and electric field driven trapping and detrapping of charge carriers in the aggregate states that lie in the energy gap of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the organic molecule were proposed as the mechanism of the observed bipolar resistive switching, which was solidly supported by the results of AFM investigations. Repeatedly set, read, and reset measurements demonstrated that the device is potentially applicable in non-volatile memories.

A dual-gate and dielectric-inserted lateral trench insulated gate bipolar transistor on a silicon-on-insulator substrate

Fu Qiang (付强), Zhang Bo (张波), Luo Xiao-Rong (罗小蓉), Li Zhao-Ji (李肇基)

Chin. Phys. B, 2013, 22 (7): 077309. DOI: 10.1088/1674-1056/22/7/077309

Abstract ( 651 )

PDF (585KB) ( 636 )

In this paper, a novel dual-gate & dielectric-inserted lateral trench insulated gate bipolar transistor (DGDI LTIGBT) structure which features the double extended trench gate and dielectric-inserted in the drift region is proposed and discussed. The device can not only decrease the specific on-resistance R_on,sp but also simultaneously improve the temperature performance. Simulation results show that the proposed LTIGBT achieves an ultra-low on-state voltage drop of 1.31 V at 700 A·cm^-2 with a small half-cell pitch of 10.5 μm, a specific on-resistance R_on,sp of 187 mΩ·mm², and a high breakdown voltage of 250 V. The on-state voltage drop of the DGDI LTIGBT is 18% less than that of the DI LTIGBT and 30.3% less than that of the conventional LTIGBT. The proposed LTIGBT exhibits a good positive temperature coefficient for safety paralleling to handling larger currents and enhances the short-circuit capability while maintaining a low self-heating effect. Furthermore, it also shows a better tradeoff between the specific on-resistance and the turnoff loss, although it has a longer turnoff delay time.

Confined states and spin polarization on a topological insulator thin film modulated by an electric potential

Liu Yi-Man (刘一曼), Shao Huai-Hua (邵怀华), Zhou Xiao-Ying (周小英), Zhou Guang-Hui (周光辉)

Chin. Phys. B, 2013, 22 (7): 077310. DOI: 10.1088/1674-1056/22/7/077310

Abstract ( 759 )

PDF (849KB) ( 685 )

We study the electronic structure and spin polarization for surface states of a three-dimensional topological insulator (TI) thin film modulated by an electrical potential well. By routinely solving the low energy surface Dirac equation for the system, we demonstrated that there exist confined surface states in which the electron density is nearly localized inside the well and is exponentially decayed outside in real space, and their subband dispersions are quasilinear with respect to the propagating wavevector. Interestingly, the top and bottom surface confined states with the same density distribution have opposite spin polarizations due to the hybridization between the two surfaces. Along with the mathematical analysis, we provide an intuitive, topological understanding of the effect.

Strong flux pinning enhancement in YBa₂Cu₃O_7-x films by embedded BaZrO₃ and BaTiO₃ nanoparticles

Ding Fa-Zhu (丁发柱), Gu Hong-Wei (古宏伟), Zhang Teng (张腾), Wang Hong-Yan (王洪艳), Qu Fei (屈飞), Qiu Qing-Quan (邱清泉), Dai Shao-Tao (戴少涛), Peng Xing-Yu (彭星煜)

Chin. Phys. B, 2013, 22 (7): 077401. DOI: 10.1088/1674-1056/22/7/077401

Abstract ( 713 )

PDF (1636KB) ( 896 )

YBa₂Cu₃O_7-x (YBCO) films with embedded BaZrO₃ and BaTiO₃ nanoparitcles were fabricated by metalorganic deposition using trifluoroacetates (TFA-MOD). Both X-ray diffraction and transmission electron microscopy revealed that these BaZrO₃ and BaTiO₃ nanoparitcles had random orientations and were distributed stochastically in the YBCO matrix. The unique combined microstructure enhanced the critical current density (J_c) of the BaZrO₃/BaTiO₃ doped-YBCO films while keeping the critical transition temperature (T_c) close to that in the pure YBCO films. These results indicated that the BaZrO₃ and BaTiO₃ nanoparitcles provide strong flux pinning in YBCO films.

Magnetization of Gd diffused Yba₂Cu₃O_7-x superconductor：Experiment and theory

F. Inanira, Ş. Yildizb, K. Ozturkc, S. Celebic

Chin. Phys. B, 2013, 22 (7): 077402. DOI: 10.1088/1674-1056/22/7/077402

Abstract ( 610 )

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The magnetization of Gd diffused YBa₂Cu₃O_7-x is measured by a vibrating sample magnetometer (VSM) at selected temperatures (5, 25, 50, 77 K). The experimental results for the magnetization are analyzed in the critical state framework involving Kim-Anderson field dependence J_c(H) = J_c0/(1+|H>|/H₀)ⁿ of critical current density and equilibrium magnetization M_eq. It is found that the inclusion of the equilibrium magnetization becomes more important at higher temperatures. At 77 K, the shape of the isothermal M-H hysteresis curve is governed by the equilibrium magnetization. Some superconducting parameters are determined by fitting the calculated curves to the experimental data.

Spin-1 Blume–Capel model with longitudinal random crystaland transverse magnetic fields：a mean-field approach

Erhan Albayrak

Chin. Phys. B, 2013, 22 (7): 077501. DOI: 10.1088/1674-1056/22/7/077501

Abstract ( 672 )

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The spin-1 Blume-Capel model with transverse Ω and longitudinal external magnetic fields h in addition to a longitudinal random crystal field D is studied in the mean-field approximation. It is assumed that the crystal field is either turned on with probability p or turned off with probability 1-p on the sites of a square lattice. Then the phase diagrams are calculated on the reduced temperature-crystal field planes for given values of γ=Ω/J and p at zero h. Thus, the effect of changing γ and p are illustrated on the phase diagrams in a great detail and interesting results are observed.

R-site cation randomness effect in thec A-site ordered Y_0.5La_0.5BaMn₂O₆ compound

Gao Qing-Qing (高庆庆), Li Jing-Bo (李静波), Li Guan-Nan (李冠男), Rao Guang-Hui (饶光辉), Luo Jun (骆军), Liu Guang-Yao (刘广耀), Liang Jing-Kui (梁敬魁)

Chin. Phys. B, 2013, 22 (7): 077502. DOI: 10.1088/1674-1056/22/7/077502

Abstract ( 836 )

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The R/Ba-ordered and R-site mixed compound Y_0.5La_0.5BaMn₂O₆ has been synthesized in which (Y, La) and Ba are regularly arranged while Y and La randomly occupy the R-site. Y_0.5La_0.5BaMn₂O₆ has a tetragonal unit cell with a space group of P4/mmm. A structural transition between tetragonal and orthorhombic is observed at about 325 K by X-ray powder diffraction (XRD). Thermal magnetic measurement shows the occurrence of an antiferromagnetic transition at the temperature T_N～190 K. Anomalies in magnetization, resistivity and lattice parameters observed around 340 K indicate a charge/orbital order transition accompanying the structural phase transition. R-site randomness effect is discussed to interpret the different properties of Y_0.5La_0.5BaMn₂O₆ between NdBaMn₂O₆ and SmBaMn₂O₆.

Topology-like dynamical behavior of magnetization reversal inexchange-bias systems

Su Yuan-Chang (苏垣昌), Zhang Li-Juan (张丽娟), Yang Xin (杨鑫), Pan Jing (潘靖), Hu Jing-Guo (胡经国)

Chin. Phys. B, 2013, 22 (7): 077503. DOI: 10.1088/1674-1056/22/7/077503

Abstract ( 678 )

PDF (348KB) ( 407 )

In an exchange-bias system, the barriers with intrinsic potential energy may be asymmetric due to unidirectional anisotropy. Base on Stoner-Wohlfarth model, we show that the asymmetric barriers may lead to four kinds of dynamical process underlying the hysteresis-loop measurement. These kinds of dynamical process are different in a topology-like property, which can be controlled by the orientation of the external field. In our study, a new analysis approach has been proposed to reveal the dynamical behaviors of magnetization reversal. With this approach, coercivity, exchange-bias field, and asymmetry of hysteresis loop can be quantitatively obtained.

Frequency dependence of magnetoelectric effect in magnetostrictive-piezoelectric heterostructure

Yu Guo-Liang (郁国良), Li Yuan-Xun (李元勋), Zeng Yu-Qin (曾玉琴), Li Jie (李颉), Zuo Lin (左林), Li Qiang (李强), Zhang Huai-Wu (张怀武)

Chin. Phys. B, 2013, 22 (7): 077504. DOI: 10.1088/1674-1056/22/7/077504

Abstract ( 683 )

PDF (371KB) ( 770 )

The frequency dependence of the magnetoelectric effect in a magnetostrictive-piezoelectric heterostructure is theoretically studied by solving combined magnetic, elastic, and electric equations with boundary conditions. Both the mechanical coupling coefficient and the losses of the magnetostrictive and piezoelectric phases are taken into account. The numerical result indicates that the magnetoelectric coefficient and the resonance frequency are determined by the mechanical coupling coefficient, losses, and geometric parameters. Moreover, at the electromechanical resonance frequency, the module of the magnetoelectric coefficient is mostly contributed by the imaginary part. The relationship between the real and the imaginary parts of the magnetoelectric coefficient fit well to the Cole-Cole circle. The magnetostrictive-piezoelectric heterostructure has a great potential application as miniature and no-secondary coil solid-state transformers.

Tunable characteristics of bending resonance frequency in magnetoelectric laminated composites

Chen Lei (陈蕾), Li Ping (李平), Wen Yu-Mei (文玉梅), Zhu Yong (朱永)

Chin. Phys. B, 2013, 22 (7): 077505. DOI: 10.1088/1674-1056/22/7/077505

Abstract ( 735 )

PDF (333KB) ( 630 )

As magnetoelectric (ME) effect in the piezoelectric/magnetostrictive laminated composites is mediated by mechanical deformation, the ME effect is significantly enhanced in the vicinity of resonance frequency. The bending resonance frequency (f_r) of bilayered Terfenol-D/PZT (MP) laminated composites is studied, and our analysis predicts that (i) the bending resonance frequency of MP laminated composite can be tuned by an applied dc magnetic bias (H_dc) due to Δ E effect; (ii) the bending resonance frequency of the MP laminated composite can be controlled by incorporating FeCuNbSiB layers with different thicknesses. The experimental results show that with H_dc increasing from 0 Oe (1 Oe=79.5775 A/m) to 700 Oe, the bending resonance frequency can be shifted in a range of 32.68 kHz ≤qslant f_r ≤qslant 33.96 kHz. In addition, with the thickness of FeCuNbSiB layer increasing from 0 μm to 90 μm, the bending resonance frequency of the MP laminated composite gradually increases from 33.66 kHz to 39.18 kHz. This study offers the means by adjusting the strength of dc magnetic bias or the thicknesses of FeCuNbSiB layer to tune the bending resonance frequency for ME composite, which plays a guiding role in the ME composites design for real applications.

Martensitic transformation & related magnetic effects in Ni-Mn-based ferro magnetic shape memory alloys

Wang Dun-Hui (王敦辉), Han Zhi-Da (韩志达), Xuan Hai-Cheng (轩海成), Ma Sheng-Can (马胜灿), Chen Shui-Yuan (陈水源), Zhang Cheng-Liang (张成亮), Du You-Wei (都有为)

Chin. Phys. B, 2013, 22 (7): 077506. DOI: 10.1088/1674-1056/22/7/077506

Abstract ( 944 )

PDF (772KB) ( 2069 )

Ferromagnetic shape memory alloys, which undergo the martensitic transformation, are famous multifunctional materials. They exhibit many interesting magnetic properties around the martensitic transformation temperature due to the strong coupling between magnetism and structure. Tuning magnetic phase transition and optimizing the magnetic effects in these alloys are of great importance. In this paper, the regulation of martensitic transformation and the investigation of some related magnetic effects in Ni-Mn-based alloys are reviewed based on our recent research results.

Progress in bulk MgCu₂-type rare-earth iron magnetostrictive compounds

Ren Wei-Jun (任卫军), Zhang Zhi-Dong (张志东)

Chin. Phys. B, 2013, 22 (7): 077507. DOI: 10.1088/1674-1056/22/7/077507

Abstract ( 603 )

PDF (1077KB) ( 1638 )

Studies of bulk MgCu₂-type rare-earth iron compounds with Laves phase are reviewed. The relationship between magnetostriction and structural distortion and the consequent crystallographic method for measuring magnetostriction are introduced at first. Then we review recent progress in understanding bulk magnetostrictive Laves phase materials, especially the magnetostriction and the minimization of the anisotropy of the light rare-earth Pr-and Sm-based compounds. Finally, a summary and outlook for this kind of compounds are presented.

Critical exponents of ferroelectric transitions in modulated SrTiO₃：Consequences of quantum fluctuations and quenched disorder

Wang Jing-Xue (王景雪), Liu Mei-Feng (刘美风), Yan Zhi-Bo (颜志波), Liu Jun-Ming (刘俊明)

Chin. Phys. B, 2013, 22 (7): 077701. DOI: 10.1088/1674-1056/22/7/077701

Abstract ( 684 )

PDF (526KB) ( 955 )

The ferroelectric transitions of several SrTiO₃-based ferroelectrics are investigated experimentally and theoretically, with special attention to the critical scaling exponents associated with the phase transitions, in order to understand the competition among quantum fluctuations (QFs), quenched disorder, and ferroelectric ordering. Two representative systems with sufficiently strong QFs and quenched disorders in competition with the ferroelectric ordering are investigated. We start from non-stoichiometric SrTiO₃ (STO) with the Sr/Ti ratio deviating slightly from one, which is believed to maintain strong QFs. Then, we address Ba/Ca co-doped Sr_1-x(Ca_0.6389Ba_0.3611)_xTiO₃ (SCBT) with the averaged Sr-site ionic radius identical to the Sr²⁺ ionic radius, which is believed to offer remarkable quenched disorder associated with the Sr-site ionic mismatch. The critical exponents associated with polarization P and dielectric susceptibility ε, respectively, as functions of temperature T close to the critical point T_c, are evaluated. It is revealed that both non-stoichiometric SrTiO₃ and SCBT exhibit much bigger critical exponents than the Landau mean-field theory predictions. These critical exponents then decrease gradually with increasing doping level or deviation of Sr/Ti ratio from one. A transverse Ising model applicable to the Sr-site doped STO (e.g., Sr_1-xCa_xTiO₃) at low level is used to explain the observed experimental data. It is suggested that the serious deviation of these critical exponents from the Landau theory predictions in these STO-based systems is ascribed to the significant QFs and quenched disorder by partially suppressing the long-range spatial correlation of electric dipoles around the transitions. The present work thus sheds light on our understanding of the critical behaviors of ferroelectric transitions in STO in the presence of quantum fluctuations and quenched disorder, whose effects have been demonstrated to be remarkable.

Photoluminescence properties of Ce³⁺ and Mn²⁺-activated Ba₉Sc₂Si₆O₂₄ phosphor for white light emitting diodes

Bian Liu (边柳), Wang Ting (王婷), Song Zhen (宋振), Liu Zhao-Hui (刘朝晖), Li Jia-Xu (李嘉旭), Liu Quan-Lin (刘泉林)

Chin. Phys. B, 2013, 22 (7): 077801. DOI: 10.1088/1674-1056/22/7/077801

Abstract ( 954 )

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A single-phased silicate compound (Ba_1-xCe_x)₉₍Sc_1-yMn_y)₂Si₆O₂₄ was prepared by solid-state reaction at high temperature. From powder X-ray diffraction (XRD) analysis, the formation of Ba₉Sc₂Si₆O₂₄ with R3 space group was confirmed. In the photoluminescence spectra under ultraviolet (UV) ray excitation, the Ba₉Sc₂Si₆O₂₄:Ce³⁺, Mn²⁺ phosphor emits two distinctive color light bands: a blue one originating from Ce³⁺ and a red one caused by Mn²⁺. The energy transfer process from Ce³⁺ to Mn²⁺ was confirmed, the critical radius as well as the transfer efficiency was calculated, and the energy transfer mechanism was discussed. In addition, the decay-time testing indicates that the energy transfer efficiencies from Ce(1) to Mn²⁺ and Ce(2) to Mn²⁺ are different. The emission chromaticity of Ba₉Sc₂Si₆O₂₄:Ce³⁺, Mn²⁺ phosphor could be tuned from blue to red by altering the Ce³⁺/Mn²⁺ concentration ratio.

A 1550-nm linearly tunable CW single-mode external cavity diode laser based on a single-cavity all-dielectric thin-film Fabry–Pérot filter

Xiao Xiao (肖啸), Lu Yuan-Fu (鲁远甫), Yu Feng-Qi (于峰崎), Jin Lei (金雷)

Chin. Phys. B, 2013, 22 (7): 077802. DOI: 10.1088/1674-1056/22/7/077802

Abstract ( 1489 )

PDF (687KB) ( 809 )

A 1550-nm linearly tunable CW single-mode external cavity diode laser (ECDL) based on a single-cavity all-dielectric thin-film Fabry–Pérot filter (s-AFPF) is proposed and realized in this paper. Its internal optical components as well as their operation mechanisms are introduced first, and then its longitudinal mode output characteristic is theoretically analyzed. Afterwards, we set up the experimental platform for the output characteristic measurement of this tunable ECDL; under different experimental conditions, we execute accurate and real-time measurements for the output central wavelength, output optical power, output longitudinal mode distribution, and the line-width of the tunable ECDL in its tuning process. By summing up the optimal experimental condition from the measured data, we obtain the optimal tunable relevant parameters ECDL of the tunable ECDL has a linear mode-hop-free wavelength tuning region of 1547.203 nm-1552.426 nm, a stable output optical power in the range of 40 μW-50 μW, and a stable output longitudinal mode distribution of a single longitudinal mode with a line-width in the range of 100 MHz-150 MHz. This tunable ECDL can be used in environmental gas monitoring, atomic and molecular laser spectroscopy research, precise measurements, and so on.

Photo-induced absorption in pump probe spectroscopy of single-walled carbon nanotubes

Zhu Zi-Peng (朱子鹏)

Chin. Phys. B, 2013, 22 (7): 077803. DOI: 10.1088/1674-1056/22/7/077803

Abstract ( 788 )

PDF (436KB) ( 1189 )

Femtosecond pump probe spectroscopy is employed to study the photo-induced absorption feature in single-walled carbon nanotube transient spectrum. The two advantages of the experiment, a chirality enriched sample and tuning the pump wavelength to the resonance of a specific nanotube species, greatly facilitate the identification of the photo-induced absorption signal of one tube species. It is found that a photo-induced absorption feature is located at one radial breathing mode to the blue side of the E₁₁ state. This finding prompts a new explanation for the origin of the photo-induced absorption: the transition from the ground state to a phonon coupled state near the E_ii state. The explanation suggests a superposition mechanism of the photo-bleach and photo-induced absorption signals, which may serve as a key to the interpretation of the complex pump probe transient spectrum of carbon nanotubes. The finding shed some light on the understanding of the complex non-radiative relaxation process and the electronic structure of single-walled carbon nanotubes.

A steady solution of the gasar eutectic growth in directional solidification

Li Xiang-Ming (李向明), Li Wen-Qiong (李文琼), Jin Qing-Lin (金青林), Zhou Rong (周荣)

Chin. Phys. B, 2013, 22 (7): 078101. DOI: 10.1088/1674-1056/22/7/078101

Abstract ( 733 )

PDF (326KB) ( 452 )

This paper presents the general mathematical model on gasar eutectic growth in directional solidification. Using multiple scale expansion and matching method, we obtain the global steady solution of gasar eutectic growth as the Peclet number ε«1, where ε is defined as the ratio of half an inter-pore spacing and solutal diffusion length. We also give the interfacial shape and predict the porosity of gasar eutectic growth. Results show that porosity is mainly determined by external pressure above metal melt and independent of pulling velocity. Our predicted results are in agreement with experimental data.

Influences of high-temperature annealing on atomic layer deposited Al₂O₃/4H-SiC

Wang Yi-Yu (王弋宇), Shen Hua-Jun (申华军), Bai Yun (白云), Tang Yi-Dan (汤益丹), Liu Ke-An (刘可安), Li Cheng-Zhan (李诚瞻), Liu Xin-Yu (刘新宇)

Chin. Phys. B, 2013, 22 (7): 078102. DOI: 10.1088/1674-1056/22/7/078102

Abstract ( 634 )

PDF (643KB) ( 1725 )

High-temperature annealing of atomic layer deposition (ALD) of Al₂O₃ films on 4H-SiC in O₂ atmosphere is studied with temperature ranging from 800℃ to 1000℃. It is observed that the surface morphology of Al₂O₃ films annealed at 800℃ and 900℃ is pretty good, while the surface of the sample annealed at 1000℃ becomes bumpy. Grazing incidence X-ray diffraction (GIXRD) measurements demonstrate that the as-grown films are amorphous and begin to crystallize at 900℃. Furthermore, C-V measurements exhibit improved interface characterization after annealing, especially for samples annealed at 900℃ and 1000℃. It is indicated that high-temperature annealing in O₂ atmosphere can improve the interface of Al₂O₃/SiC and annealing at 900℃ would be an optimum condition for surface morphology, dielectric quality, and interface states.

Densification and lithium ion conductivity of garnet-type Li_7-xLa₃Zr_2-xTa_xO₁₂ (x=0.25) solid electrolytes

Cao Yang (曹阳), Li Yi-Qiu (李忆秋), Guo Xiang-Xin (郭向欣)

Chin. Phys. B, 2013, 22 (7): 078201. DOI: 10.1088/1674-1056/22/7/078201

Abstract ( 927 )

PDF (547KB) ( 2343 )

The garnet-type Li₇La₃Zr₂O₁₂ ceramic is one of promising solid electrolytes for all-solid-state secondary lithium batteries. However, it faces problem of volatilization of lithium during sintering, which may cause low density and deterioration of ionic conductivity. In this work, the effects of sintering temperature and addition on the density as well as the lithium ion conductivity of Li_7-xLa₃Zr_2-xTa_xO₁₂ (LLZTO, x=0.25) ceramics prepared by solid state reaction have been studied. It is found that optimization of the sintering temperature leads to a minor increase in the ceramic density, yielding an optimum ionic conductivity of 2.9×10^-4 S·cm^-1 at 25℃. Introduction of Li₃PO₄ addition in an appropriate concentration can obviously increase the density, leading to an optimum ionic conductivity of 7.2×10^-4 S·cm^-1 at 25℃. This value is superior to the conductivity data in most recent reports on the LLZTO ceramics.

Stochastic asymptotical synchronization of chaotic Markovian jumping fuzzy cellular neural networks with mixed delays and Wiener process based on sampled-data control

M. Kalpana, P. Balasubramaniam

Chin. Phys. B, 2013, 22 (7): 078401. DOI: 10.1088/1674-1056/22/7/078401

Abstract ( 546 )

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We investigate the stochastic asymptotical synchronization of chaotic Markovian jumping fuzzy cellular neural networks (MJFCNNs) with discrete unbounded distributed delays, and Wiener process based on sampled-data control using linear matrix inequality (LMI) approach. Lyapunov-Krasovskii functional (LKF) combining with the input delay approach as well as the free-weighting matrix approach is employed to derive several sufficient criteria in terms of LMIs to ensure the delayed MJFCNNs with the Wiener process is stochastic asymptotical synchronous. Restrictions (e.g., time derivative is smaller than one) are removed to obtain a proposed sampled-data controller. Finally, a numerical example is provided to demonstrate the reliability of the derived results.

Advantages of InGaN/GaN multiple quantum well solar cells with stepped-thickness quantum wells ^Hot!

Chen Xin (陈鑫), Zhao Bi-Jun (赵璧君), Ren Zhi-Wei (任志伟), Tong Jin-Hui (童金辉), Wang Xing-Fu (王幸福), Zhuo Xiang-Jing (卓祥景), Zhang Jun (章俊), Li Dan-Wei (李丹伟), Yi Han-Xiang (易翰翔), Li Shu-Ti (李述体)

Chin. Phys. B, 2013, 22 (7): 078402. DOI: 10.1088/1674-1056/22/7/078402

Abstract ( 940 )

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InGaN/GaN multiple quantum well (MQW) solar cells with stepped-thickness quantum wells (SQW) are designed and grown by metal-organic chemical vapor deposition. The stepped-thickness quantum wells structure, in which the well thickness becomes smaller and smaller along the growth direction, reveals better crystalline quality and better spectral overlap with the solar spectrum. Consequently, the short-circuit current density (J_sc) and conversion efficiency of the solar cell are enhanced by 27.12% and 56.41% compared with the conventional structure under illumination of AM1.5G (100 mW/cm²). In addition, approaches to further promote the performance of InGaN/GaN multiple quantum well solar cells are discussed and presented.

Lead zirconate titanate behaviors in LDMOS

Zhai Ya-Hong (翟亚红), Li Wei (李威), Li Ping (李平), Li Jun-Hong (李俊宏), Hu Bin (胡滨), Huo Wei-Rong (霍伟荣), Fan Xue (范雪), Wang Gang (王刚)

Chin. Phys. B, 2013, 22 (7): 078501. DOI: 10.1088/1674-1056/22/7/078501

Abstract ( 582 )

PDF (439KB) ( 481 )

The behaviors of lead zirconate titanate (PZT) deposited as the dielectric for high-voltage devices are investigated experimentally and theoretically. The devices demonstrate not only high breakdown voltages above 350 V, but also excellent memory behaviors. A drain current-gate voltage (I_D-V_G) memory window of about 2.2 V is obtained at the sweep voltages of ± 10 V for the 350-V laterally diffused metal oxide semiconductor (LDMOS). The retention time of about 270 s is recorded for the LDMOS through a controlled I_D-V_G measurement. The LDMOS with memory behaviors has potential to be applied in future power conversion circuits to boost the performance of the energy conversion system.

Image reconstruction based on total-variation minimization and alternating direction method in linear scan computed tomography

Zhang Han-Ming (张瀚铭), Wang Lin-Yuan (王林元), Yan Bin (闫镔), Li Lei (李磊), Xi Xiao-Qi (席晓琦), Lu Li-Zhong (陆利忠)

Chin. Phys. B, 2013, 22 (7): 078701. DOI: 10.1088/1674-1056/22/7/078701

Abstract ( 1086 )

PDF (586KB) ( 1292 )

Linear scan computed tomography (LCT) is of great benefit to online industrial scanning and security inspection due to its characteristics of straight-line source trajectory and high scanning speed. However, in practical applications of LCT, there are challenges to image reconstruction due to limited-angle and insufficient data. In this paper, a new reconstruction algorithm based on total-variation (TV) minimization is developed to reconstruct images from limited-angle and insufficient data in LCT. The main idea of our approach is to reformulate a TV problem as a linear equality constrained problem where the objective function is separable, and then minimize its augmented Lagrangian function by using alternating direction method (ADM) to solve subproblems. The proposed method is robust and efficient in the task of reconstruction by showing the convergence of ADM. The numerical simulations and real data reconstructions show that the proposed reconstruction method brings reasonable performance and outperforms some previous ones when applied to an LCT imaging problem.

Light scattering effect of submicro-textured Ag/Al composite films prepared at lower substrate temperatures

Tang Ping-Lin (唐平林), Wu Yong-Gang (吴永刚), Tong Guang-De (童广德), Xia Zi-Huan (夏子奂), Liu Ren-Chen (刘仁臣), Liang Zhao-Ming (梁钊铭), Zhou Jian (周建)

Chin. Phys. B, 2013, 22 (7): 078801. DOI: 10.1088/1674-1056/22/7/078801

Abstract ( 582 )

PDF (604KB) ( 491 )

We present a new and practical approach for preparing submicro-textured silver and aluminum (Ag/Al) double-structured layers at low substrate temperatures. By increasing the deposition temperature of the Al layers to 270℃, the surface texturing of silver and aluminum double-structured layers was performed. The highly submicro-textured silver and aluminum double-structured layers were prepared by thermal evaporation on quartz glasses and their surface microstructure, light scattering properties, and thermal stability were investigated. Results showed that the highly submicro-textured Ag/Al composite films prepared at low substrate temperatures used as back reflectors not only can enhance the light scattering and have good thermal stability, but also have good adhesion properties. In addition, their fabrication is low cost and readily carried out.

SPICE modeling of flux-controlled unipolar memristive devices

Fang Xu-Dong (方旭东), Tang Yu-Hua (唐玉华), Wu Jun-Jie (吴俊杰), Zhu Xuan (朱玄), Zhou Jing (周静), Huang Da (黄达)

Chin. Phys. B, 2013, 22 (7): 078901. DOI: 10.1088/1674-1056/22/7/078901

Abstract ( 797 )

PDF (508KB) ( 748 )

Unipolar memristive devices are an important kind of resistive switching devices. However, few circuit models of them have been proposed. In this paper, we propose the SPICE modeling of flux-controlled unipolar memristive devices based on the memristance versus state map. Using our model, the flux thresholds, ON and OFF resistance, compliance current can easily be set as model parameters. We simulate the model in HSPICE using model parameters abstracted from real devices, and the simulation results show that our model caters to the real device data very well, thus demonstrating that our model is correct. Using the same modeling methodology, the SPICE model of charge-controlled unipolar memristive devices could also be developed. The proposed model could be used to model resistive memory cells, logical gates as well as synapses in artificial neural networks.

Evolution of IPv6 Internet topology with unusual sudden changes

Ai Jun (艾均), Zhao Hai (赵海), Kathleen M. Carleyb, Su Zhan (苏湛), Li Hui (李辉)

Chin. Phys. B, 2013, 22 (7): 078902. DOI: 10.1088/1674-1056/22/7/078902

Abstract ( 833 )

PDF (1631KB) ( 829 )

The evolution of Internet topology is not always smooth but sometimes with unusual sudden changes. Consequently, identifying patterns of unusual topology evolution is critical for Internet topology modeling and simulation. We analyze IPv6 Internet topology evolution in IP-level graph to demonstrate how it changes in uncommon ways to restructure the Internet. After evaluating the changes of average degree, average path length, and some other metrics over time, we find that in the case of a large-scale growing the Internet becomes more robust; whereas in a top-bottom connection enhancement the Internet maintains its efficiency with links largely decreased.

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