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Chin. Phys. B  
  Chin. Phys. B--2012, Vol.21, No.5
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GENERAL

Mei symmetry and Mei conserved quantity of the Appell equation in a dynamical system of relative motion with non-Chetaev nonholonomic constraints

Wang Xiao-Xiao,Sun Xian-Ting,Zhang Mei-Ling,Han Yue-Lin,Jia Li-Qun
Chin. Phys. B 2012, 21 (5): 050201;  doi: 10.1088/1674-1056/21/5/050201
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The Mei symmetry and the Mei conserved quantity of Appell equations in a dynamical system of relative motion with non-Chetaev nonholonomic constraints are studied. The differential equations of motion of the Appell equation for the system, the definition and the criterion of the Mei symmetry, and the expression of the Mei conserved quantity deduced directly from the Mei symmetry for the system are obtained. An example is given to illustrate the application of the results.

Mei conserved quantity directly induced by Lie symmetry in a nonconservative Hamilton system

Fang Jian-Hui,Zhang Bin,Zhang Wei-Wei,Xu Rui-Li
Chin. Phys. B 2012, 21 (5): 050202;  doi: 10.1088/1674-1056/21/5/050202
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In this paper, we investigate whether the Lie symmetry can induce the Mei conserved quantity directly in a nonconservative Hamilton system and a theorem is presented. The condition under which the Lie symmetry of the system directly induces the Mei conserved quantity is given. Meanwhile, an example is discussed to illustrate the application of the results. The present results have shown that the Lie symmetry of a nonconservative Hamilton system can also induce the Mei conserved quantity directly.

Solving a class of burning disturbed problem with shock layers

Ouyang Cheng,Chen Li-Hua,Mo Jia-Qi
Chin. Phys. B 2012, 21 (5): 050203;  doi: 10.1088/1674-1056/21/5/050203
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A class of combustion problem with shock layers is considered. A modified perturbation method is presented. Using this simple and valid technique, we construct the boundary and the shock layers solution to the problem, and the asymptotic behavior of the solution is discussed. The modifying perturbation method is shown to be a valid method.

Relevance vector machine technique for the inverse scattering problem

Wang Fang-Fang,Zhang Ye-Rong
Chin. Phys. B 2012, 21 (5): 050204;  doi: 10.1088/1674-1056/21/5/050204
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A novel method based on the relevance vector machine (RVM) for the inverse scattering problem is presented in this paper. The nonlinearity and the ill-posedness inherent in this problem are simultaneously considered. The nonlinearity is embodied in the relation between the scattered field and the target property, which can be obtained through the RVM training process. Besides, rather than utilizing regularization, the ill-posed nature of the inversion is naturally accounted for because the RVM can produce a probabilistic output. Simulation results reveal that the proposed RVM-based approach can provide comparative performances in terms of accuracy, convergence, robustness, generalization, and improved performance in terms of sparse property in comparison with the support vector machine (SVM) based approach.

Immunizations on small worlds of tree-based wireless sensor networks

Li Qiao,Zhang Bai-Hai,Cui Ling-Guo,Fan Zhun,Athanasios V. Vasilakos
Chin. Phys. B 2012, 21 (5): 050205;  doi: 10.1088/1674-1056/21/5/050205
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The sensor virus is a serious threat, as an attacker can simply send a single packet to compromise the entire sensor network. Epidemics become drastic with link additions among sensors when the small world phenomena occur. Two immunization strategies, uniform immunization and temporary immunization, are conducted on small worlds of tree-based wireless sensor networks to combat the sensor viruses. With the former strategy, the infection extends exponentially, although the immunization effectively reduces the contagion speed. With the latter strategy, recurrent contagion oscillations occur in the small world when the spatial--temporal dynamics of the epidemic are considered. The oscillations come from the small-world structure and the temporary immunization. Mathematical analyses on the small world of the Cayley tree are presented to reveal the epidemic dynamics with the two immunization strategies.

Mechanism of micro-waviness induced KH2PO4 crystal laser damage and the corresponding vibration source

Li Ming-Quan,Chen Ming-Jun,An chen-Hui,Zhou Lian,Cheng Jian,Xiao Yong,Jiang Wei
Chin. Phys. B 2012, 21 (5): 050301;  doi: 10.1088/1674-1056/21/5/050301
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The low laser induced damage threshold of the KH2PO4 crystal seriously restricts the output power of inertial confinement fusion. The micro-waviness on the KH2PO4 surface processed by single point diamond turning has a significant influence on the damage threshold. In this paper, the influence of micro-waviness on the damage threshold of the KH2PO4 crystal and the chief sources introducing the micro-waviness are analysed based on the combination of the Fourier modal theory and the power spectrum density method. Research results indicate that among the sub-wavinesses with different characteristic spatial frequencies there exists the most dangerous frequency which greatly reduces the damage threshold, although it may not occupy the largest proportion in the original surface. The experimental damage threshold is basically consistent with the theoretical calculation. For the processing parameters used, the leading frequency of micro-waviness which causes the damage threshold to decrease is between 350-1 μ-1 and 30-1 μ-1, especially between 90-1 μ-1 and 200-1 μ-1. Based on the classification study of the time frequencies of micro-waviness, we find that the axial vibration of the spindle is the chief source introducing the micro-waviness, nearly all the leading frequencies are related to the practical spindle frequency (about 6.68 Hz, 400 r/min) and a special middle frequency (between 1.029 Hz and 1.143 Hz).

Electromagnetic absorption properties of flowerlike cobalt composites at microwave frequencies

Liu Tao,Zhou Pei-Heng,Liang Di-Fei,Deng Long-Jiang
Chin. Phys. B 2012, 21 (5): 050302;  doi: 10.1088/1674-1056/21/5/050302
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In this work, we report the electromagnetic absorption (EMA) properties of composites consisting of micrometer-sized cobalt with flowerlike architecture synthesized by a facile hydrothermal reduction method. Compared with the conventional spherical Co-paraffin composites, the flowerlike Co-paraffin composites are favorable with respect to EMA performance in the low frequency region, ascribing interfacial polarization loss and Ohmic loss to the improvement in the impedance match.

Entangled quantum heat engine based on two-qubit Heisenberg XY model

He Ji-Zhou,He Xian,Zheng Jie
Chin. Phys. B 2012, 21 (5): 050303;  doi: 10.1088/1674-1056/21/5/050303
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Based on a two-qubit isotropic Heisenberg XY model under a constant external magnetic field, we construct a four-level entangled quantum heat engine (QHE). The expressions for the heat transferred, the work, and the efficiency are derived. Moreover, the influence of the entanglement on the thermodynamic quantities is investigated analytically and numerically. Several interesting features of the variations of the heat transferred, the work, and the efficiency with the concurrences of the thermal entanglement of two different thermal equilibrium states in zero and nonzero magnetic fields are obtained.

Nonlocal quantum cloning via quantum dots trapped in distant cavities

Yu Tao,Zhu Ai-Dong,Zhang Shou
Chin. Phys. B 2012, 21 (5): 050304;  doi: 10.1088/1674-1056/21/5/050304
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A scheme for implementing nonlocal quantum cloning via quantum dots trapped in cavities is proposed. By modulating the parameters of the system, the optimal 1→2 universal quantum cloning machine, 1→2 phase-covariant cloning machine, and 1→3 economical phase-covariant cloning machine are constructed. The present scheme, which is attainable with current technology, saves two qubits compared with previous cloning machines.

Dynamic characteristics of resonant gyroscopes study based on the Mathieu equation approximate solution

Fan Shang-Chun,Li Yan,Guo Zhan-She,Li Jing,Zhuang Hai-Han
Chin. Phys. B 2012, 21 (5): 050401;  doi: 10.1088/1674-1056/21/5/050401
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Dynamic characteristics of the resonant gyroscope are studied based on the Mathieu equation approximate solution in this paper. The Mathieu equation is used to analyze the parametric resonant characteristics and the approximate output of the resonant gyroscope. The method of small parameter perturbation is used to analyze the approximate solution of the Mathieu equation. The theoretical analysis and the numerical simulations show that the approximate solution of the Mathieu equation is close to the dynamic output characteristics of the resonant gyroscope. The experimental analysis shows that the theoretical curve and the experimental data processing results coincide perfectly, which means that the approximate solution of the Mathieu equation can present the dynamic output characteristic of the resonant gyroscope. The theoretical approach and the experimental results of the Mathieu equation approximate solution are obtained, which provides a reference for the robust design of the resonant gyroscope.

Simulation of pedestrian evacuation based on an improved dynamic parameter model

Zhu Nuo,Jia Bin,Shao Chun-Fu,Yue Hao
Chin. Phys. B 2012, 21 (5): 050501;  doi: 10.1088/1674-1056/21/5/050501
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An improved dynamic parameter model is presented based on cellular automata. The dynamic parameters, including direction parameter, empty parameter, and cognition parameter, are formulated to simplify tactically the process of making decisions for pedestrians. The improved model reflects the judgement of pedestrians on surrounding conditions and the action of choosing or decision. According to the two-dimensional cellular automaton Moore neighborhood we establish the pedestrian moving rule, and carry out corresponding simulations of pedestrian evacuation. The improved model considers the impact of pedestrian density near exits on the evacuation process. Simulated and experimental results demonstrate that the improvement makes sense due to the fact that except for the spatial distance to exits, people also choose an exit according to the pedestrian density around exits. The impact factors α, β, and γ are introduced to describe transition payoff, and their optimal values are determined through simulation. Moreover, the effects of pedestrian distribution, pedestrian density, and the width of exits on the evacuation time are discussed. The optimal exit layout, i.e., the optimal position and width, is offered. The comparison between the simulated results obtained with the improved model and that from a previous model and experiments indicates that the improved model can reproduce experimental results well. Thus, it has great significance for further study, and important instructional meaning for pedestrian evacuation so as to reduce the number of casualties.

Transport enhancement and efficiency optimization in two heat reservoir ratchets

Zeng Chun-Hua,Wang Hua
Chin. Phys. B 2012, 21 (5): 050502;  doi: 10.1088/1674-1056/21/5/050502
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We study a Brownian motor moving in a sawtooth potential in the presence of an external driving force and two heat reservoirs. Based on the corresponding Fokker--Planck equation, the analytical expressions of the current and efficiency in the quasi-steady-state limit are obtained. The effects of temperature difference and the amplitude of the external driving force on the current and efficiency are discussed, respectively. The following is our findings. (i) The current increases with both δ and A. In other words, δ and A enhance the transport of the Brownian motor. (ii) The competition between the temperature difference and the amplitude of the external driving force can lead to efficiency optimization. The efficiency is a peaked function of temperature, i.e., δ>0 and a lower amplitude value of the external driving force is necessary for efficiency optimization. (iii) The efficiency increases with δ, and decreases with A. δ and A play opposite roles with respect to the efficiency, which indicates that δ enhances the efficiency of energy transformation while A weakens it.

Effect of inertia mass on the stochastic resonance driven by a multiplicative dichotomous noise

Li Peng,Nie Lin-Ru,Huang Qi-Rui,Sun Xing-Xiu
Chin. Phys. B 2012, 21 (5): 050503;  doi: 10.1088/1674-1056/21/5/050503
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A stochastic system driven by dichotomous noise and periodic signal is investigated in the under-damped case. The exact expressions of output signal amplitude and signal-to-noise ratio (SNR) of the system are derived. Numerical results indicate that the inertial mass greatly affects the output signal amplitude and the SNR. Regardless of whether the noise is symmetric or asymmetric, the inertial mass can influence the phenomenon of stochastic resonance (SR) of the system, leading to two types of resonance phenomenon:one is coherence-resonance-like of the SNR with inertial mass, the other is the SR of the SNR with noise intensity.

Dynamics of particles around a pseudo-Newtonian Kerr black hole with halos

Wang Ying,Wu Xin
Chin. Phys. B 2012, 21 (5): 050504;  doi: 10.1088/1674-1056/21/5/050504
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The regular and chaotic dynamics of test particles in a superposed field between a pseudo-Newtonian Kerr black hole and quadrupolar halos is detailed. In particular, the dependence of dynamics on the quadrupolar parameter of the halos and the spin angular momentum of the rotating black hole is studied. It is found that the small quadrupolar moment, in contrast with the spin angular momentum, does not have a great effect on the stability and radii of the innermost stable circular orbits of these test particles. In addition, chaos mainly occurs for small absolute values of the rotating parameters, and does not exist for the maximum counter-rotating case under some certain initial conditions and parameters. This means that the rotating parameters of the black hole weaken the chaotic properties. It is also found that the counter-rotating system is more unstable than the co-rotating one. Furthermore, chaos is absent for small absolute values of the quadrupoles, and the onset of chaos is easier for the prolate halos than for the oblate ones.

Generalized synchronization between different chaotic maps via dead-beat control

Grassi G
Chin. Phys. B 2012, 21 (5): 050505;  doi: 10.1088/1674-1056/21/5/050505
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This paper presents a new scheme to achieve generalized synchronization (GS) between different discrete-time chaotic (hyperchaotic) systems. The approach is based on a theorem, which assures that GS is achieved when a structural condition on the considered class of response systems is satisfied. The method presents some useful features:it enables exact GS to be achieved in finite time (i.e., dead-beat synchronization); it is rigorous, systematic, and straightforward in checking GS; it can be applied to a wide class of chaotic maps. Some examples of GS, including the Grassi-Miller map and a recently introduced minimal 2-D quadratic map, are illustrated.

Image encryption based on a delayed fractional-order chaotic logistic system

Wang Zhen,Huang Xia,Li Ning,Song Xiao-Na
Chin. Phys. B 2012, 21 (5): 050506;  doi: 10.1088/1674-1056/21/5/050506
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A new image encryption scheme is proposed based on a delayed fractional-order chaotic logistic system. In the process of generating a key stream, the time-varying delay and fractional derivative are embedded in the proposed scheme to improve the security. Such a scheme is described in detail with security analyses including correlation analysis, information entropy analysis, run statistic analysis, mean-variance gray value analysis, and key sensitivity analysis. Experimental results show that the newly proposed image encryption scheme possesses high security.

Parameter estimation for chaotic systems using the cuckoo search algorithm with an orthogonal learning method

Li Xiang-Tao,Yin Ming-Hao
Chin. Phys. B 2012, 21 (5): 050507;  doi: 10.1088/1674-1056/21/5/050507
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We study the parameter estimation of a nonlinear chaotic system, which can be essentially formulated as a multi-dimensional optimization problem. In this paper, an orthogonal learning cuckoo search algorithm is used to estimate the parameters of chaotic systems. This algorithm can combine the stochastic exploration of the cuckoo search and the exploitation capability of the orthogonal learning strategy. Experiments are conducted on the Lorenz system and the Chen system. The proposed algorithm is used to estimate the parameters for these two systems. Simulation results and comparisons demonstrate that the proposed algorithm is better or at least comparable to the particle swarm optimization and the genetic algorithm when considering the quality of the solutions obtained.

Pinning synchronization of time-varying delay coupled complex networks with time-varying delayed dynamical nodes

Wang Shu-Guo,Yao Hong-Xing
Chin. Phys. B 2012, 21 (5): 050508;  doi: 10.1088/1674-1056/21/5/050508
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This paper deals with the pinning synchronization of nonlinearly coupled complex networks with time-varying coupling delays and time-varying delays in the dynamical nodes. We control a part of the nodes of the complex networks by using adaptive feedback controllers and adjusting the time-varying coupling strengths. Based on the Lyapunov--Krasovskii stability theory for functional differential equations and a linear matrix inequality (LMI), some sufficient conditions for the synchronization are derived. A numerical simulation example is also provided to verify the correctness and the effectiveness of the proposed scheme.

Synchronization of impulsively coupled complex networks

Sun Wen,Chen Zhong,Chen Shi-Hua
Chin. Phys. B 2012, 21 (5): 050509;  doi: 10.1088/1674-1056/21/5/050509
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We investigate the synchronization of complex networks, which are impulsively coupled only at discrete instants. Based on the comparison theory of impulsive differential systems, a distributed impulsive control scheme is proposed for complex dynamical networks to achieve synchronization. The proposed scheme not only takes into account the influence of all nodes to network synchronization, which depends on the weight of each node in the network, but also provides us with a flexible method to select the synchronized state of the network. In addition, it is unnecessary for the impulsive coupling matrix to be symmetrical. Finally, the proposed control scheme is applied to a chaotic Lorenz network and Chua's circuit network. Numerical simulations are used to illustrate the validity of this control scheme.

Solitons for the cubic–quintic nonlinear Schrödinger equation with varying coefficients

Chen Yuan-Ming,Ma Song-Hua,Ma Zheng-Yi
Chin. Phys. B 2012, 21 (5): 050510;  doi: 10.1088/1674-1056/21/5/050510
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In this paper, by means of similarity transfomations, we obtain explicit solutions to the cubic--quintic nonlinear Schrödinger equation with varying coefficients, which involve four free functions of space. Four types of free functions are chosen to exhibit the corresponding nonlinear wave propagations.

Chaotic behaviors of the (2+1)-dimensional generalized Breor–Kaup system

Ma Song-Hua,Fang Jian-Ping,Ren Qing-Bao,Yang Zheng
Chin. Phys. B 2012, 21 (5): 050511;  doi: 10.1088/1674-1056/21/5/050511
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With the help of the Maple symbolic computation system and the projective equation approach, a new family of variable separation solutions with arbitrary functions for the (2+1)-dimensional generalized Breor--Kaup (GBK) system is derived. Based on the derived solitary wave solution, some chaotic behaviors of the GBK system are investigated.

Nonautonomous bright solitons and soliton collisions in a nonlinear medium with an external potential

Li Hua-Mei,Ge Long,He Jun-Rong
Chin. Phys. B 2012, 21 (5): 050512;  doi: 10.1088/1674-1056/21/5/050512
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We present exact bright multi-soliton solutions of a generalized nonautonomous nonlinear Schrödinger equation with time-and space-dependent distributed coefficients and an external potential which describes a pulse propagating in nonlinear media when its transverse and longitudinal directions are nonuniformly distributed. Such solutions exist in certain constraint conditions on the coefficients depicting dispersion, nonlinearity, and gain (loss). Various shapes of bright solitons and interesting interactions between two solitons are observed. Physical applications of interest to the field and stability of the solitons are discussed.
ATOMIC AND MOLECULAR PHYSICS

Properties of a Si2N molecule under an external electric field

Xu Guo-Liang,Xie Hui-Xiang,Yuan Wei,Zhang Xian-Zhou,Liu Yu-Fang
Chin. Phys. B 2012, 21 (5): 053101;  doi: 10.1088/1674-1056/21/5/053101
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In the present work, we adopt the ccsd/6-31g(d) method to optimize the ground state structure and calculate the vibrational frequency of the Si2N molecule. The calculated frequencies accord satisfactorily with the experimental values, which helps confirm the ground state structure of the molecule. In order to find how the external electric field affects the Si2N molecule, we use the density functional method B3P86/6-31g(d) to optimize the ground state structure and the time-dependent density functional theory TDDFT/6-31g(d) to study the absorption spectra, the excitation energies, the oscillator strengths, and the dipole moments of the Si2N molecule under different external electric fields. It is found that the absorption spectra, the excitation energies, the oscillator strengths, and the dipole moments of the Si2N molecule are affected by the external electric field. One of the valuable results is that the absorption spectra of the yellow and the blue-violet light of the Si2N molecule each have a red shift under the electric field. The luminescence mechanism in the visible light region of the Si2N molecule is also investigated and compared with the experimental data.

Multiple-plateau structure and scaling relation in photoelectron spectra of high-order above-threshold ionization

Wu Yan,Ye Hui-Liang,Zhang Jing-Tao,Guo Dong-Sheng
Chin. Phys. B 2012, 21 (5): 053201;  doi: 10.1088/1674-1056/21/5/053201
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By developing a full quantum scattering theory of high-order above-threshold ionization, we study the energy spectra and the angular distributions of photoelectrons from atoms with intense laser fields shining on them. We find that real rescattering can occur many times, and even infinite times. The photoelectrons from the rescattering process form a broad plateau in the kinetic-energy spectrum. We further disclose a multiple-plateau structure formed by the high-energy photoelectrons, which absorb many photons during the rescattering process. Moreover, we find that both the angular distributions and the kinetic-energy spectra of photoelectrons obey the same scaling law as that for directly emitted photoelectrons.

Construction of embedded-atom-method interatomic potentials for alkaline metals (Li, Na, and K) by lattice inversion

Yuan Xiao-Jian,Chen Nan-Xian,Shen Jiang
Chin. Phys. B 2012, 21 (5): 053401;  doi: 10.1088/1674-1056/21/5/053401
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The lattice-inversion embedded-atom-method interatomic potential developed previously by us is extended to alkaline metals including Li, Na, and K. It is found that considering interatomic interactions between neighboring atoms of an appropriate distance is a matter of great significance in constructing accurate embedded-atom-method interatomic potentials, especially for the prediction of surface energy. The lattice-inversion embedded-atom-method interatomic potentials for Li, Na, and K are successfully constructed by taking the fourth-neighbor atoms into consideration. These angular-independent potentials markedly promote the accuracy of predicted surface energies, which agree well with experimental results. In addition, the predicted structural stability, elastic constants, formation and migration energies of vacancy, and activation energy of vacancy diffusion are in good agreement with available experimental data and first-principles calculations, and the equilibrium condition is satisfied.

Resonance phenomena and threshold features in positron–helium scattering

Yu Rong-Mei,Cheng Yong-Jun,Wang Yang,Zhou Ya-Jun
Chin. Phys. B 2012, 21 (5): 053402;  doi: 10.1088/1674-1056/21/5/053402
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Investigations of resonances and threshold behaviors in positron--helium scattering have been made using the momentum-space coupled-channels optical method. The positronium formation channels are considered via an equivalent-local complex potential. The s-wave resonances and the Wigner cusp feature at the positronium (n=1) formation threshold are compared with the previous reports. The p-and the d-wave resonances and a Wigner cusp feature at the positronium (n=2) formation threshold are reported for the first time.

Coupled-channel optical calculation for positron–lithium scattering

Liu Fang,Cheng Yong-Jun,Zhou Ya-Jun
Chin. Phys. B 2012, 21 (5): 053403;  doi: 10.1088/1674-1056/21/5/053403
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Positron scattering with atomic lithium is investigated by using a coupled-channel optical method. The ionization continuum and positronium formation channels are taken into account via a complex equivalent-local optical potential. The positronium formation cross sections and the ionization cross sections, as well as the total scattering cross sections, are reported at energies above 3 eV and compared with available experimental and theoretical data.

Peripheral collisions of highly charged ions with metal clusters

Zhang Cheng-Jun,Hu Bi-Tao,Luo Xian-Wen
Chin. Phys. B 2012, 21 (5): 053601;  doi: 10.1088/1674-1056/21/5/053601
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Within the framework of the dynamical classical over-barrier model, the soft collisions between slow highly charged ions (SHCIs) Ar17+ and the large copper clusters under large impact parameters have been studied in this paper. We present the dominant mechanism of the electron transfer between SHCIs and a large metal cluster by computational simulation. The evolution of the occupation of projectile ions, KLx satellite lines, X-ray yields, Auger electron spectrum and scattering angles are provided.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Dual-band frequency selective surface with large band separation and stable performance

Zhou Hang,Qu Shao-Bo,Peng Wei-Dong,Lin Bao-Qin,Wang Jia-Fu,Ma Hua,Zhang Jie-Qiu,Bai Peng,Wang Xu-Hua,Xu Zhuo
Chin. Phys. B 2012, 21 (5): 054101;  doi: 10.1088/1674-1056/21/5/054101
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A new technique of designing a dual-band frequency selective surface with large band separation is presented. This technique is based on a delicately designed topology of L-and Ku-band microwave filters. The two band-pass responses are generated by a capacitively-loaded square-loop frequency selective surface and an aperture-coupled frequency selective surface, respectively. A Faraday cage is located between the two frequency selective surface structures to eliminate undesired couplings. Based on this technique, a dual-band frequency selective surface with large band separation is designed, which possesses large band separation, high selectivity, and stable performance under various incident angles and different polarizations.

Tunable frequency selective surface with a shorted ring slot

Jia Hong-Yan,Feng Xiao-Guo,Sheng Cui-Xia
Chin. Phys. B 2012, 21 (5): 054102;  doi: 10.1088/1674-1056/21/5/054102
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In order to realize the tunable performance of a frequency selective surface (FSS), a new unit cell is designed in this paper by properly adding two metal shorts to the ring slot. Based on the spectral-domain method, the frequency responses of the FSS structure with two shorts per slot ring are analysed for both the horizontal and the vertical polarizations at the normal incidence. It is demonstrated that the presence of the metal shorts does not affect the resonant frequency of the horizontally polarized wave but doubles the resonant frequency of the vertically polarized wave. Therefore based on the analysis of the novel transmission properties, a new approach to adjusting the resonant frequency by rotating the FSS screen 90? is presented in this paper.

Investigation of intense sheet electron beam transport using the macroscopic cold-fluid model and the single-particle orbit theory

Han Ying,Ruan Cun-Jun
Chin. Phys. B 2012, 21 (5): 054103;  doi: 10.1088/1674-1056/21/5/054103
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The focusing and the stable transport of an intense elliptic sheet electron beam in a uniform magnetic field are investigated thoroughly by using the macroscopic cold-fluid model and the single-particle orbit theory. The results indicate that the envelopes and the tilted angles of the sheet electron beam obtained by the two theories are consistent. The single-particle orbit theory is more accurate due to its treatment of the space-charge fields in a rectangular drift tube. The macroscopic cold-fluid model describes the collective transport process in order to provide detailed information about the beam dynamics, such as beam shape, density, and velocity profile. The tilt of the elliptic sheet beam in a uniform magnetic field is carefully studied and demonstrated. The results presented in this paper provide two complete theories for systemically discussing the transport of the sheet beam and are useful for understanding and guiding the practical engineering design of electron optics systems in high power vacuum electronic devices.

Characteristics of paraxial propagation of a super Lorentz–Gauss SLG01 mode in uniaxial crystal orthogonal to the optical axis

Zhou Guo-Quan
Chin. Phys. B 2012, 21 (5): 054104;  doi: 10.1088/1674-1056/21/5/054104
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Analytical propagation expression of a super Lorentz--Gauss (SLG)01 mode in uniaxial crystal orthogonal to the optical axis is derived. The SLG01 mode propagating in uniaxial crystal orthogonal to the optical axis mainly depends on the ratio of the extraordinary refractive index to the ordinary refractive index. The SLG01 mode propagating in uniaxial crystals becomes an astigmatic beam. The beam spot of the SLG01 mode in the uniaxial crystal is elongated in the x-or y-direction, which is determined by the ratio of the extraordinary refractive index to the ordinary refractive index. With the increase of the deviation of the ratio of the extraordinary refractive index to the ordinary refractive index from unity, the elongation of the beam spot also augments. In different observation planes, the phase distribution of an SLG01 mode in the uniaxial crystal takes on different shapes. With the variation of the ratio of the extraordinary refractive index to the ordinary refractive index, the phase distribution is elongated in one transversal direction and is contracted in the other perpendicular direction. This research is beneficial to the practical applications of an SLG mode.

Propagation of Airy beams from right-handed material to left-handed material

Lin Hui-Chuan,Pu Ji-Xiong
Chin. Phys. B 2012, 21 (5): 054201;  doi: 10.1088/1674-1056/21/5/054201
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Based on the ABCD matrix formalism, the propagation property of an Airy beam from right-handed material (RHM) to left-handed material (LHM) is investigated. The result shows that when the Airy beam propagates in the LHM, the intensity self-bending due to its propagation in the RHM can be compensated. In particular, if the propagation distance in the RHM is equal to that in the LHM and the refractive index of the LHM is nL =-1, the transverse intensity distribution of the Airy beam can return to its original state.

Evolution of emergent C-points, L-lines, and C-lines in free space

Yan Hong-Wei,He De,Lü Bai-Da
Chin. Phys. B 2012, 21 (5): 054202;  doi: 10.1088/1674-1056/21/5/054202
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Polarization singularities, which emerge from the incoherent superposition of two vector electric fields with the same frequency, and their evolution in free space are studied analytically and illustrated by numerical examples. It is shown that there exist C-points, L-lines, in particular, C-lines in incoherently superimposed two-dimensional wavefields. Usually, the C-lines are unstable and disappear during the free-space propagation. The motion, pair creation--annihilation process of the emergent C-points, as well as the distortion of the L-lines may take place, and the degree of polarization of the emergent C-points varies upon propagation and may be less than 1.

Characteristics of a partially coherent Gaussian Schell-model beam propagating in slanted atmospheric turbulence

Li Ya-Qing,Wu Zhen-Sen
Chin. Phys. B 2012, 21 (5): 054203;  doi: 10.1088/1674-1056/21/5/054203
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On the basis of the extended Huygens--Fresnel principle and the model of the refractive-index structure constant in the atmospheric turbulence proposed by the International Telecommunication Union-Radio Communication Sector, the characteristics of the partially coherent Gaussian Schell-model (GSM) beams propagating in slanted atmospheric turbulence are studied. Using the cross-spectral density function (CSDF), we derive the expressions for the effective beam radius, the spreading angle, and the average intensity. The variance of the angle-of-arrival fluctuation and the wander effect of the GSM beam in the turbulence are calculated numerically. The influences of the coherence degree, the propagation distance, the propagation height, and the waist radius on the propagation characteristics of the partially coherent beams are discussed and compared with those of the fully coherent Gaussian beams.

Multiple scattering of light by water cloud droplets with external and internal mixing of black carbon aerosols

Wang Hai-Hua,Sun Xian-Ming
Chin. Phys. B 2012, 21 (5): 054204;  doi: 10.1088/1674-1056/21/5/054204
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The mixture of water cloud droplets with black carbon impurities is modeled by external and internal mixing models. The internal mixing model is modeled with a two-layered sphere (water cloud droplets containing black carbon (BC) inclusions), and the single scattering and absorption characteristics are calculated at the visible wavelength of 0.55 μm by using the Lorenz--Mie theory. The external mixing model is developed assuming that the same amount of BC particles are mixed with the water droplets externally. The multiple scattering characteristics are computed by using the Monte Carlo method. The results show that when the size of the BC aerosol is small, the reflection intensity of the internal mixing model is bigger than that of the external mixing model. However, if the size of the BC aerosol is big, the absorption of the internal mixing model will be larger than that of the external mixing model.

Multi-wavelength laser active coherent combination

Han Kai,Xu Xiao-Jun,Liu Ze-Jin
Chin. Phys. B 2012, 21 (5): 054205;  doi: 10.1088/1674-1056/21/5/054205
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A seed laser oscillating at different frequencies is proved to have the potential to mitigate the stimulated Brillouin scattering (SBS) effect in a fiber amplifier, which may increase the emission power of a coherent beam combination (CBC) system greatly. In this study, a basic mathematical model describing the multi-wavelength CBC is proposed on the fundamentals of CBC. A useful method for estimating the combination effect and analysing the feasibility and the validity of the multi-wavelength coherent combination is provided. In the numerical analysis, accordant results with four-wavelength four-channel CBC experiments are obtained. Through calculations of some examples with certain spectra, the unanticipated excellent combination effect with a few frequencies involved is explained, and the dependence of the combination effect on the variance of the amplifier chain length and the channel number is clarified.

Oscillation behaviour in the photon-number distribution of squeezed coherent states

Wang Shuai,Zhang Xiao-Yan,Fan Hong-Yi
Chin. Phys. B 2012, 21 (5): 054206;  doi: 10.1088/1674-1056/21/5/054206
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From the normally ordered form of the density operator of a squeezed coherent state (SCS), we directly derive the compact expression of the SCS's photon-number distribution (PND). Besides the known oscillation characteristics, we find that the PND is a periodic function with a period of π and extremely sensitive to phase. If the squeezing is strong enough, and the compound phase which is relevant to the complex squeezing and displacement parameters are assigned appropriate values, different oscillation behaviours in PND for even and odd photon numbers appear, respectively.

Orientation effects on the bandgap and dispersion behavior of 0.91Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 single crystals

He Chong-Jun,Fu Xin-Duo,Xu Feng,Wang Ji-Ming,Zhu Kong-Jun,Du Chao-Ling,Liu You-Wen
Chin. Phys. B 2012, 21 (5): 054207;  doi: 10.1088/1674-1056/21/5/054207
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0.91Pb(Zn1/3Nb2/3)O3--0.09PbTiO3 (PZN--9%PT) single crystals with different orientations are investigated by using a spectroscopic ellipsometer, and the refractive indices and the extinction coefficients are obtained. The Sellmeier dispersion equations for the refractive indices are obtained by the least square fitting, which can be used to calculate the refractive indices in a low absorption wavelength range. Average Sellmeier oscillator parameters Eo, λo, So, and Ed are calculated by fitting with the single-term oscillator equation, which are related directly to the electronic energy band structure. The optical energy bandgaps are obtained from the absorption coefficient spectra. Our results show that the optical properties of [001] and [111] poled crystals are very similar, but quite different from those of the [011] poled crystal.

Quantum phase distribution and the number–phase Wigner function of the generalized squeezed vacuum states associated with solvable quantum systems

G. R. Honarasa,M. K. Tavassoly,M. Hatami
Chin. Phys. B 2012, 21 (5): 054208;  doi: 10.1088/1674-1056/21/5/054208
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The quantum phase properties of the generalized squeezed vacuum states associated with solvable quantum systems are studied by using the Pegg--Barnett formalism. Then, two nonclassical features, i.e., squeezing in the number and phase operators, as well as the number--phase Wigner function of the generalized squeezed states are investigated. Due to some actual physical situations, the present approach is applied to two classes of generalized squeezed states:solvable quantum systems with discrete spectra and nonlinear squeezed states with particular nonlinear functions. Finally, the time evolution of the nonclassical properties of the considered systems has been numerically investigated.

Dynamic control of retrieval contrast in a Λ-type atomic system

Zhang Xiao-Hang,Bao Qian-Qian,Zhang Yan,Su Ming-Che,Cui Cui-Li,Wu Jin-Hui
Chin. Phys. B 2012, 21 (5): 054209;  doi: 10.1088/1674-1056/21/5/054209
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We propose an efficient scheme for optimizing the optical memory of a sequence of signal light pulses in a system of ultracold atoms in Λ configuration. The memory procedure consists of write-in, storage, and retrieval phases. By applying a weak microwave field in the storage stage, additional phase-dependent terms are included, and the contrast of the output signal pulses can be dynamically controlled (enhanced or suppressed) through manipulating the relative phase φ between optical and microwave fields. Our numerical analysis shows that the contrast is enhanced to the most extent when φ=1.5π. In addition, the contrast is in proportion to the Rabi frequency of the microwave field with a certain relative phase.

Level crossing in a two-photon Jaynes–Cummings model

Ren Xue-Zao,Cong Hong-Lu,Liao Xu,Li Lei
Chin. Phys. B 2012, 21 (5): 054210;  doi: 10.1088/1674-1056/21/5/054210
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In this paper, the energy spectrum of the two-photon Jaynes--Cummings model (TPJCM) is calculated exactly in the non-rotating wave approximation (non-RWA), and we study the level-crossing problem by means of fidelity. A narrow peak of the fidelity is observed at the level-crossing point, which does not appear at the avoided-crossing point. Therefore fidelity is perfectly suited for detecting the level-crossing point in the energy spectrum.

Reflection-mode photoacoustic microscopy using a hollow focused ultrasound transducer for in vivo imaging of blood vessels

Yuan Yi,Yang Si-Hua
Chin. Phys. B 2012, 21 (5): 054211;  doi: 10.1088/1674-1056/21/5/054211
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A reflection-mode photoacoustic microscope using a hollow focused ultrasound transducer is developed for high-resolution in vivo imaging. A confocal structure of the laser and the ultrasound is used to improve the system resolution. The axial and lateral resolutions of the system are measured to be ~ 32 μm and ~ 58 μm, respectively. Ex vivo and in vivo modes are tested to validate the imaging capability of the photoacoustic microscope. The adjacent vein and artery can be seen clearly from the reconstructed photoacoustic images. The results demonstrate that the reflection-mode photoacoustic microscope can be used for high-resolution imaging of micro-blood vessels, which would be of great benefit for monitoring the neovascularization in tumor angiogenesis.

Effects of aligning pulse duration on the degree and the slope of nitrogen field-free alignment

Wang Fei,Jiang Hong-Bing,Gong Qi-Huang
Chin. Phys. B 2012, 21 (5): 054212;  doi: 10.1088/1674-1056/21/5/054212
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Through theoretical analysis, we show how aligning pulse durations affect the degree and the time-rate slope of nitrogen field-free alignment at a fixed pulse intensity. It is found that both the degree and the slope first increase, then saturate, and finally decrease with the increasing pump duration. The optimal durations for the maximum degree and the maximum slope of the alignment are found to be different. Additionally, they are found to mainly depend on the molecular rotational period, and are affected by the temperature and the aligning pump intensities. The mechanism of molecular alignment is also discussed.

Generation of broadly tunable picosecond mid-infrared laser and sensitive detection of a mid-infrared signal by parametric frequency up-conversion in MgO:LiNbO3 optical parametric amplifiers Hot!

Zhang Qiu-Lin,Zhang Jing,Qiu Kang-Sheng,Zhang Dong-Xiang,Feng Bao-Hua,Zhang Jing-Yuan
Chin. Phys. B 2012, 21 (5): 054213;  doi: 10.1088/1674-1056/21/5/054213
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Picosecond optical parametric generation and amplification in the near-infrared region within 1.361--1.656 μm and the mid-infrared region within 2.976--4.875 μm is constructed on the basis of bulk MgO:LiNbO3 crystals pumped at 1.064 μm. The maximum pulse energy reaches 1.3 mJ at 1.464 μm and 0.47 mJ at 3.894 μm, corresponding to a pump-to-idler photon conversion efficiency of 25%. By seeding the hard-to-measure mid-infrared radiation as the idler in the optical parametric amplification and measuring the amplified and frequency up-converted signal in the near-infrared or even visible region, one can measure very week mid-infrared radiation with ordinary detectors, which are insensitive to mid-infrared radiation, with a very high gain. A maximum gain factor of about 7× 107 is achieved at the mid-infrared wavelength of 3.374 μm and the corresponding energy detection limit is as low as about 390 aJ per pulse.

Generation of an isolated sub-30 attosecond pulse in a two-color laser field and a static electric field

Zhang Gang-Tai,Bai Ting-Ting,Zhang Mei-Guang
Chin. Phys. B 2012, 21 (5): 054214;  doi: 10.1088/1674-1056/21/5/054214
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We theoretically investigate high-order harmonic generation (HHG) from a helium ion model in a two-color laser field, which is synthesized by a fundamental pulse and its second harmonic pulse. It is shown that a supercontinuum spectrum can be generated in the two-color field. However, the spectral intensity is very low, limiting the application of the generated attosecond (as) pulse. By adding a static electric field to the synthesized two-color field, not only is the ionization yield of electrons contributing to the harmonic emission remarkably increased, but also the quantum paths of the HHG can be significantly modulated. As a result, the extension and enhancement of the supercontinuum spectrum are achieved, producing an intense isolated 26-as pulse with a bandwidth of about 170.5 eV. In particular, we also analyse the influence of the laser parameters on the ultrabroad supercontinuum spectrum and isolated sub-30-as pulse generation.

Effects of sea surface temperature, cloud radiative and microphysical processes, and diurnal variations on rainfall in equilibrium cloud-resolving model simulations

Jiang Zhe,Li Xiao-Fan,Zhou Yu-Shu,Gao Shou-Ting
Chin. Phys. B 2012, 21 (5): 054215;  doi: 10.1088/1674-1056/21/5/054215
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The effects of sea surface temperature (SST), cloud radiative and microphysical processes, and diurnal variations on rainfall statistics are documented with grid data from the two-dimensional equilibrium cloud-resolving model simulations. For a rain rate of higher than 3 mm·h-1, water vapor convergence prevails. The rainfall amount decreases with the decrease of SST from 29℃ to 27℃, the inclusion of diurnal variation of SST, or the exclusion of microphysical effects of ice clouds and radiative effects of water clouds, which are primarily associated with the decreases in water vapor convergence. However, the amount of rainfall increases with the increase of SST from 29℃ to 31℃, the exclusion of diurnal variation of solar zenith angle, and the exclusion of the radiative effects of ice clouds, which are primarily related to increases in water vapor convergence. For a rain rate of less than 3 mm·h-1, water vapor divergence prevails. Unlike rainfall statistics for rain rates of higher than 3 mm·h-1, the decrease of SST from 29℃ to 27℃ and the exclusion of radiative effects of water clouds in the presence of radiative effects of ice clouds increase the rainfall amount, which corresponds to the suppression in water vapor divergence. The exclusion of microphysical effects of ice clouds decreases the amount of rainfall, which corresponds to the enhancement in water vapor divergence. The amount of rainfall is less sensitive to the increase of SST from 29℃ to 31℃ and to the radiative effects of water clouds in the absence of the radiative effects of ice clouds.

Mitigation of laser damage growth in fused silica by using a non-evaporative technique

Jiang Yong,Liu Chun-Ming,Luo Cheng-Si,Yuan Xiao-Dong,Xiang Xia,Wang Hai-Jun,He Shao-Bo,Lü Hai-Bing,Ren Wei,Zheng Wan-Guo,Zu Xiao-Tao
Chin. Phys. B 2012, 21 (5): 054216;  doi: 10.1088/1674-1056/21/5/054216
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A non-evaporative technique is used to mitigate damage sites with lateral sizes in a range from 50 μm to 400 μm and depths smaller than 100 μm. The influence of the pulse frequency of a CO2 laser on the mitigation effect is studied. It is found that a more symmetrical and smooth mitigation crater can be obtained by increasing the laser pulse frequency form 0.1 to 20 kHz. Furthermore, the sizes of laser-affected and distorted zones decrease with the increase of the laser pulse frequency, leading to less degradation of the wave-front quality of the conditioned sample. The energy density of the CO2 laser beam is introduced for selecting the mitigation parameters. The damage sites can be successfully mitigated by increasing the energy density in a ramped way. Finally, the laser-induced damage threshold (LIDT) of the mitigated site is tested using 355 nm laser beam with a small spot (0.23 mm2) and a large spot (3.14 mm2), separately. It is shown that the non-evaporative mitigation technique is a successful method to stop damage re-initiation since the average LIDTs of mitigated sites tested with small or large laser spots are higher than that of pristine material.

Growth and spectroscopic characteristics of Nd-doped PbWO4 crystal

Wang Qing-Guo,Su Liang-Bi,Li Hong-Jun,Xiong Wei,Yuan Hui,Zheng Li-He,Xu Xiao-Dong,Wu Feng,Tang Hui-Li,Jiang Da-Peng,Xu Jun
Chin. Phys. B 2012, 21 (5): 054217;  doi: 10.1088/1674-1056/21/5/054217
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Nd-doped PbWO4 crystals are grown by using the modified Bridgman method. The spectroscopic properties of the crystals are investigated. The changes of the absorption band at 350 nm are discussed for samples annealed at 740℃ and 1040℃. The radiative lifetime of the 4F3/2 level is calculated by using the Judd--Ofelt theory according to the absorption spectrum of 0.5 at.% Nd-doped PbWO4 crystal. The spontaneous Raman scattering properties of the crystals are analysed.

Spontaneous emission from an atom in a photonic crystal with two coherent bands

Huang Xian-Shan,Liu Hai-Lian,Wang Dong
Chin. Phys. B 2012, 21 (5): 054218;  doi: 10.1088/1674-1056/21/5/054218
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The dynamic and the radiative properties of an excited three-level atom embedded in an anisotropic photonic crystal with two coherent bands are investigated. The relative position of the atom in a Wigner--Seitz cell is described with a position-dependent parameter θ(r 0), which is used as the coherent parameter for the two bands. The result shows that the dynamic properties of the atomic system are not only determined by atomic transition frequencies, but also affected by the gap width and the coherence of the two bands. In addition, the spontaneous emission spectrum of the atomic transition in free space is discussed. The center and the intensity of the spectrum can be obviously manipulated via the coherent parameter.

Design and fabrication of broadband rugate filter

Zhang Jun-Chao,Fang Ming,Shao Yu-Chuan,Jin Yun-Xia,He Hong-Bo
Chin. Phys. B 2012, 21 (5): 054219;  doi: 10.1088/1674-1056/21/5/054219
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The design and the deposition of a rugate filter for broadband applications are discussed. The bandwidth is extended by increasing the rugate period continuously with depth. The width and the smoothness of the reflection band with the distribution of the periods are investigated. The improvement of the steepness of the stopband edges and the suppression of the side lobes in the transmission zone are realized by adding two apodized rugate structures with fixed periods at the external broadband rugate filter interfaces. The rapidly alternating deposition technology is used to fabricate a rugate filter sample. The measured transmission spectrum with a reflection bandwidth of approximately 505 nm is close to that of the designed broadband rugate filter except a transmittance peak in the stopband. Based on the analysis of the cross-sectional scanning electron microscopic image of the sample, it is found that the transmission peak is most likely to be caused by the instability of the deposition rate.

Generation of a mid-infrared broadband polarized supercontinuum in As2Se3 photonic crystal fibers

Wang Xiao-Yan,Li Shu-Guang,Liu Shuo,Yin Guo-Bing,Li Jian-She
Chin. Phys. B 2012, 21 (5): 054220;  doi: 10.1088/1674-1056/21/5/054220
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A simplified structure of birefringent chalcogenide As2Se3 photonic crystal fiber (PCF) is designed. Properties of birefringence, polarization extinction ratio, chromatic dispersion, nonlinear coefficient, and transmission are studied by using the multipole method, the finite-difference beam propagation method, and the adaptive split-step Fourier method. Considering that the zero dispersion wavelength of our proposed fiber is about 4 μm, we have analysed the mechanism of spectral broadening in PCFs with different pitches in detail, with femtosecond pulses at a wavelength of 4 μm as the pump pulses. Especially, mid-infrared broadband polarized supercontinuums are obtained in a 3-cm PCF with an optimal pitch of 2 μm. Their spectral width at-20 dB reaches up to 12 μm. In the birefringent PCF, we find that the supercontinuum generation changes with the pump alignment angle. Research results show that no coupling between eigenpolarization modes are observed at the maximum average power (i.e., 37 mW), which indicates that the polarization state is well maintained.

Acoustic characteristics of bubble bursting at the surface of a high-viscosity liquid

Liu Xiao-Bo,Zhang Jian-Run,Li Pu
Chin. Phys. B 2012, 21 (5): 054301;  doi: 10.1088/1674-1056/21/5/054301
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An acoustic pressure model of bubble bursting is proposed. An experiment studying the acoustic characteristics of the bursting bubble at the surface of a high-viscosity liquid is reported. It is found that the sudden bursting of a bubble at the high-viscosity liquid surface generates N-shape wave at first, then it transforms into a jet wave. The fundamental frequency of the acoustic signal caused by the bursting bubble decreases linearly as the bubble size increases. The results of the investigation can be used to understand the acoustic characteristics of bubble bursting.

Effects of variable properties on MHD heat and mass transfer flow near a stagnation point towards a stretching sheet in a porous medium with thermal radiation

A. M. Salem,Rania Fathy
Chin. Phys. B 2012, 21 (5): 054701;  doi: 10.1088/1674-1056/21/5/054701
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The effect of variable viscosity and thermal conductivity on steady magnetohydrodynamic (MHD) heat and mass transfer flow of viscous and incompressible fluid near a stagnation point towards a permeable stretching sheet embedded in a porous medium are presented, taking into account thermal radiation and internal heat genberation/absorbtion. The stretching velocity and the ambient fluid velocity are assumed to vary linearly with the distance from the stagnation point. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing fundamental equations are first transformed into a system of ordinary differential equations using a scaling group of transformations and are solved numerically by using the fourth-order Rung--Kutta method with the shooting technique. A comparison with previously published work has been carried out and the results are found to be in good agreement. The results are analyzed for the effect of different physical parameters, such as the variable viscosity and thermal conductivity, the ratio of free stream velocity to stretching velocity, the magnetic field, the porosity, the radiation and suction/injection on the flow, and the heat and mass transfer characteristics. The results indicate that the inclusion of variable viscosity and thermal conductivity into the fluids of light and medium molecular weight is able to change the boundary-layer behavior for all values of the velocity ratio parameter λ except for λ=1. In addition, the imposition of fluid suction increases both the rate of heat and mass transfer, whereas fluid injection shows the opposite effect.

Coupling effect of Brownian motion and laminar shear flow on colloid coagulation:a Brownian dynamics simulation study

Xu Sheng-Hua,Sun Zhi-Wei,Li Xu,Tong Wang
Chin. Phys. B 2012, 21 (5): 054702;  doi: 10.1088/1674-1056/21/5/054702
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Simultaneous orthokinetic and perikinetic coagulations (SOPCs) are studied for small and large Peclet numbers (Pe) using Brownian dynamics simulation. The results demonstrate that the contributions of the Brownian motion and the shear flow to the overall coagulation rate are basically not additive. At the early stages of coagulation with small Peclet numbers, the ratio of overall coagulation rate to the rate of pure  perikinetic coagulation is proportional to  Pe-1/2, while with high Peclet numbers, the ratio of overall coagulation rate to the rate of pure orthokinetic coagulation is proportional to  Pe-1/2.Moreover, our results show that the aggregation rate generally changes with time for the SOPC, which is different from that for pure perikinetic and pure orthokinetic coagulations. By comparing the SOPC with pure perikinetic and pure orthokinetic coagulations, we show that the redistribution of particles due to Brownian motion can play a very important role in the SOPC. In addition, the effects of redistribution in the directions perpendicular and parallel to the shear flow direction are different. This perspective explains the behavior of coagulation due to the joint effects of the Brownian motion (perikinetic) and the fluid motion (orthokinetic).

Asymmetry of the water flux induced by the deformation of a nanotube

He Jun-Xia,Lu Hang-Jun,Liu Yang,Wu Feng-Min,Nie Xue-Chuan,Zhou Xiao-Yan,Chen Yan-Yan
Chin. Phys. B 2012, 21 (5): 054703;  doi: 10.1088/1674-1056/21/5/054703
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The behavior of nano-confined water is expected to be fundamentally different from the behavior of bulk water. At the nanoscale, it is still unclear whether water flows more easily along the convergent direction or the divergent one, and whether a hourglass shape is more convenient than a funnel shape for water molecules to pass through a nanotube. Here, we present an approach to explore these questions by changing the deformation position of a carbon nanotube. The results of our molecular dynamics simulation indicate that the water flux through the nanotube changes significantly when the deformation position moves away from the middle region of the tube. Different from the macroscopic level, we find water flux asymmetry (water flows more easily along the convergent direction than along the divergent one), which plays a key role in a nano water pump driven by a ratchet-like mechanism. We explore the mechanism and calculate the water flux by means of the Fokker--Planck equation and find that our theoretical results are well consistent with the simulation results. Furthermore, the simulation results demonstrate that the effect of deformation location on the water flux will be reduced when the diameter of the nanochannel increases. These findings are helpful for devising water transporters or filters based on carbon nanotubes and understanding the molecular mechanism of biological channels.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Improvement on the wave absorbing property of a lossy frequency selective surface absorber using a magnetic substrate

Sun Liang-Kui,Cheng Hai-Feng,Zhou Yong-Jiang,Wang Jun
Chin. Phys. B 2012, 21 (5): 055201;  doi: 10.1088/1674-1056/21/5/055201
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An equivalent-circuit model is used to analyse the improvement of the wave absorbing performance of the lossy frequency selective surface (FSS) absorber by using a magnetic substrate, showing that it is possible to widen the wave absorbing bandwidth. Three pieces of magnetic substrates are prepared. According to the complex permittivity and permeability, the reflectivity of the corresponding absorber is calculated by the finite difference time-domain (FDTD) method, and the bandwidth of the reflectivity below-10 dB is optimized by genetic algorithm. The calculated results indicate that the wave absorbing performance is significantly improved by increasing the complex permeability of the substrate; the reflectivity bandwidth below-10 dB of the single layer FSS absorber can reach 3.6--18 GHz with a thickness of 5 mm, which is wider than that with a dielectric substrate. The density of the FSS absorber is only 0.92 g/cm3. Additionally, the absorption band can be further widened by inserting a second lossy FSS. Finally, a double layer lossy FSS absorber with a magnetic substrate is fabricated based on the design result. The experimental result is consistent with the design one.

Effect of multicomponent dust grains in a cold quantum dusty plasma

Yang Xiu-Feng,Wang Shan-Jin,Chen Jian-Min,Shi Yu-Ren,Lin Mai-Mai,Duan Wen-Shan
Chin. Phys. B 2012, 21 (5): 055202;  doi: 10.1088/1674-1056/21/5/055202
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By employing the quantum hydrodynamic model for electron--ion--dust plasma, we derive a dispersion relation of the quantum dusty plasma. The effects of the dust size distribution on the dispersion relation in a cold quantum dusty plasma are studied. Both analytical and numerical results are given to compare the differences between the dusty plasma by considering the dust size distribution and the mono-sized dusty plasma. It is shown that many system parameters can significantly influence the dispersion relation of the quantum dusty plasma.

A theoretical estimation of the pre-breakdown-heating time in the underwater discharge acoustic source

Wang Yi-Bo,Wang Shang-Wu,Zeng Xin-Wu
Chin. Phys. B 2012, 21 (5): 055203;  doi: 10.1088/1674-1056/21/5/055203
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One of the common characteristics of the electrothermal breakdown in an underwater discharge acoustic source (UDAS) is the existence of a pre-breakdown-heating phase. In our experiment, two phenomena were observed:(1) the breakdown time that takes on high randomicity and obeys a ''double-peak'' stochastic distribution; (2) the higher salt concentration that reduces the residual voltage and causes 100% non-breakdown. The mechanism of electrothermal breakdown is analysed. To specify the end of the pre-breakdown-heating phase, a ''border boiling'' assumption is proposed, in which the breakdown time is assumed to be the time needed to heat the border water around the initial arc to 773 K. Based on this 'border boiling' assumption, the numerical simulation is performed to evaluate the effects of two heating mechanisms:the Joule heating from the ionic current, and the radiation heating from the initial arc. The simulation results verify the theoretical explanations to these two experiment phenomena:(1) the stochastic distribution of the radius of the initial arc results in the randomicity of the breakdown time; (2) the difference in efficiency between the radiation heating and the Joule heating determines that, in the case of higher salt concentration, more energy will be consumed in the pre-breakdown-heating phase.

Analytical evaluation of the plasma dispersion function for a Fermi–Dirac distribution

B.A. Mamedov
Chin. Phys. B 2012, 21 (5): 055204;  doi: 10.1088/1674-1056/21/5/055204
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An efficient method for the analytic evaluation of the plasma dispersion function for the Fermi--Dirac distribution is proposed. The new method has been developed using the binomial expansion theorem and the Gamma functions. The general formulas obtained for the plasma dispersion function are utilized for the evaluation of the response function. The resulting series present better convergence rates. Several acceleration techniques are combined to further improve the efficiency. The obtained results for the plasma dispersion function are in good agreement with the known numerical data.

Using short pulses to enhance the production rate of vibrationally excited hydrogen molecules in hydrogen discharge

Sun Ji-Zhong,Li Xian-Tao,Bai Jing,Wang De-Zhen
Chin. Phys. B 2012, 21 (5): 055205;  doi: 10.1088/1674-1056/21/5/055205
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Hydrogen discharges driven by the combined radio-frequency (rf)/short pulse sources are investigated using the particle-in-cell method. The simulation results show that the discharge driven additionally by the short pulse can enhance the electron density and modulate the electron energy to provide a better condition for negative hydrogen ion production than the discharge driven by the rf-only source.

Radiation characteristics and implosion dynamics of tungsten wire array Z-pinches on the YANG accelerator

Huang Xian-Bin,Yang Li-Bing,Li Jing,Zhou Shao-Tong,Ren Xiao-Dong,Zhang Si-Qun,Dan Jia-Kun,Cai Hong-Chun,Duan Shu-Chao,Chen Guang-Hua,Zhang Zheng-Wei,Ouyang Kai,Li Jun,Zhang Zhao-Hui,Zhou Rong-Guo,Wang Gui-Lin
Chin. Phys. B 2012, 21 (5): 055206;  doi: 10.1088/1674-1056/21/5/055206
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We investigated the radiation characteristics and implosion dynamics of low-wire-number cylindrical tungsten wire array Z-pinches on the YANG accelerator with a peak current 0.8--1.1 MA and a rising time ~ 90 ns. The arrays are made up of (8--32)× 5 μm wires 6/10 mm in diameter and 15 mm in height. The highest X-ray power obtained in the experiments was about 0.37 TW with the total radiation energy ~ 13 kJ and the energy conversion efficiency ~ 9% (24× 5 μm wires, 6 mm in diameter). Most of the X-ray emissions from tungsten Z-pinch plasmas were distributed in the spectral band of 100--600 eV, peaked at 250 and 375 eV. The dominant wavelengths of the wire ablation and the magneto-Rayleigh--Taylor instability were found and analyzed through measuring the time-gated self-emission and laser interferometric images. Through analyzing the implosion trajectories obtained by an optical streak camera, the run-in velocities of the Z-pinch plasmas at the end of the implosion phase were determined to be about (1.3--2.1)× 107 cm/s.

Identification of m=2 competent mode of complex magneto-hydro-dynamics activities during internal soft disruption based on singular value decomposition and tomography of soft-X-ray emission on the HT-7 tokamak

Xu Li-Qing,Hu Li-Qun,Li Er-Zhong,Chen Kai-Yun,Liu Zhi-Yuan,Chen Ye-Bin,Zhang Ji-Zong,Zhou Rui-Jie,Yang Mao,Mao Song-Tao,Duan Yan-Min
Chin. Phys. B 2012, 21 (5): 055208;  doi: 10.1088/1674-1056/21/5/055208
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In this paper, the singular value decomposition (SVD) method as a filter is applied before the tomographic inversion of soft-X-ray emission. Series of 'filtered' signals including specific chronos and topos are obtained. (Here, chronos and topos are the decomposed spatial vectors and the decomposed temporal vectors, respectively). Given specific magnetic flux function with coupling m=1 and m=2 modes, the line-integrated soft-X-ray signals at all chords have been obtained. Then m=1 and m=2 modes have been identified by tomography of simulated 'filtered' signals extracted by the SVD method. Finaly, using the experimental line-integrated soft-X-ray signals,m=2 competent mode of complex magnetohydrodynamics(MHD) activities during internal soft disruption is observed. This result demonstrates that m=2 mode plays an important role in internal disruption (Here, m is the poloidal mode number).
RAPID COMMUNICATION

Characterization of relativistic electrons generated by a cone guiding laser pulse

Liu Hong-Jie,Gu Yu-Qiu,Zhou Wei-Min,Yu Jin-Qing,Zhu Bin,Wu Yu-Chi,Shan Lian-Qiang,Wen Xian-Lun,Li Fang,Qian Feng,Cao Lei-Feng,Zhang Bao-Han,Zheng Zhi-Jian
Chin. Phys. B 2012, 21 (5): 055207;  doi: 10.1088/1674-1056/21/5/055207
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We demonstrated the interaction of a gold cone target with a femto second (fs) laser pulse above the relativistic intensity of 1.37× 1018 μm 2W/cm2. Relativistic electrons with energy above 2 MeV were observed. A 25%--40% increase of the electron temperature is achieved compared to the case when a plane gold target is used. The electron temperature increase results from the guiding of the laser beam at the tip and the intense quasistatic magnetic field in the cone geometry. The behavior of the relativistic electrons is verified in our 2D-PIC simulations.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Fracture characteristics of bulk metallic glass under high speed impact

Sun Bao-Ru,Zhan Zai-Ji,Liang Bo,Zhang Rui-Jun,Wang Wen-Kui
Chin. Phys. B 2012, 21 (5): 056101;  doi: 10.1088/1674-1056/21/5/056101
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High speed impact experiments of rectangular plate-shaped Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) were performed using a two-stage light gas gun. Under spherical shock waves with impact velocities ranging from 0.503 km/s to 4.917 km/s, obvious traces of laminated spallation at the back (free) surface and melting (liquid droplets) at the impact point were observed. The angles about 0?, 17?, 36?, and 90? to the shocking direction were shown in the internal samples because of the interaction between the compressive shock waves and the rarefaction waves. The compressive normal stress was found to induce the consequent temperature rise in the core of the shear band.

High stability of the goldalloy fullerenes:A density functional theory investigation of M12@Au20 (M=Na, Al, Ag, Sc, Y, La, Lu, and Au) clusters Hot!

Zhang Meng,Feng Xiao-Juan,Zhao Li-Xia,Zhang Hong-Yu,Luo You-Hua
Chin. Phys. B 2012, 21 (5): 056102;  doi: 10.1088/1674-1056/21/5/056102
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Discovering highly stable metal fullerenes such as the celebrated C60 is interesting in cluster science as they have potential applications as building blocks in new nanostructures. We here investigated the structural and electronic properties of the fullerenes M12@Au20 (M=Na, Al, Ag, Sc, Y, La, Lu, and Au), using a first-principles investigation with the density functional theory. It is found that these compound clusters possess a similar cage structure to the icosahedral Au32 fullerene. La12@Au20 is found to be particularly stable among these clusters. The binding energy of La12@Au20 is 3.43 eV per atom, 1.05 eV larger than that in Au32. The highest occupied molecular orbital--lowest unoccupied molecular orbital (HOMO--LUMO) gap of La12@Au20 is only 0.31 eV, suggesting that it should be relatively chemically reactive.

Effects of swift argon-ion irradiation on the proton-exchanged LiNbO3 crystal

Huang Qing,Liu Peng,Liu Tao,Guo Sha-Sha,Wang Xue-Lin
Chin. Phys. B 2012, 21 (5): 056103;  doi: 10.1088/1674-1056/21/5/056103
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A proton-exchanged LiNbO3 crystal was subjected to 70-MeV argon-ion irradiation. The lattice damage was investigated by the Rutherford backscattering and channeling technique. It was found that the lattice disorder induced by the proton exchange process was partially recovered and the proton-exchanged layer was broadened. It indicated that the lithium ions underneath the initial proton-exchanged layer migrated to the surface during the swift argon-ion irradiation and supplemented the lack of lithium ions in the initial proton-exchanged layer. This effect was ascribed to the great electronic energy deposition and relaxation. The swift argon-ion irradiation induced an increase in extraordinary refractive index and formed another waveguide structure beneath the proton-exchanged waveguide.

A gate enhanced power U-shaped MOSFET integrated with a Schottky rectifier

Wang Ying,Jiao Wen-Li,Hu Hai-Fan,Liu Yun-Tao,Cao Fei
Chin. Phys. B 2012, 21 (5): 056104;  doi: 10.1088/1674-1056/21/5/056104
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An accumulation gate enhanced power U-shaped metal-oxide-semiconductor field-effect-transistor (UMOSFET) integrated with a Schottky rectifier is proposed. In this device, a Schottky rectifier is integrated into each cell of the accumulation gate enhanced power UMOSFET. Specific on-resistances of 7.7 mΩ·mm2 and 6.5 mΩ·mm2 for the gate bias voltages of 5 V and 10 V are achieved, respectively, and the breakdown voltage is 61 V. The numerical simulation shows a 25% reduction in the reverse recovery time and about three orders of magnitude reduction in the leakage current as compared with the accumulation gate enhanced power UMOSFET.

First-principles investigation on the elastic stability and thermodynamic properties of Ti2SC

Yang Ze-Jin,Guo Yun-Dong,Linghu Rong-Feng,Cheng Xin-Lu,Yang Xiang-Dong
Chin. Phys. B 2012, 21 (5): 056301;  doi: 10.1088/1674-1056/21/5/056301
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Using Vanderbilt-type plane-wave ultrasoft pseudopotentials within the generalized gradient approximation (GGA) in the frame of density functional theory (DFT), we have investigated the crystal structures, elastic, and thermodynamic properties for Ti2SC under high temperature and high pressure. The calculated pressure dependence of the lattice volume is in excellent agreement with the experimental results. The calculated structural parameter of the Ti atom experienced a subtle increase with applied pressures and the increase suspended under higher pressures. The elastic constants calculations demonstrated that the crystal lattice is still stable up to 200 GPa. Investigations on the elastic properties show that the c axis is stiffer than the a axis, which is consistent with the larger longitudinal elastic constants (C33, C11) relative to transverse ones (C44, C12, C13). Study on Poisson's ratio confirmed that the higher ionic or weaker covalent contribution in intra-atomic bonding for Ti2SC should be assumed and the nature of ionic increased with pressure. The ratio (B/G) of bulk (B) and shear (G) moduli as well as B/C44 demonstrated the brittleness of Ti2SC at ambient conditions and the brittleness decreased with pressure. Moreover, the isothermal and adiabatic bulk moduli displayed opposite temperature dependence under different pressures. Again, we observed that the Debye temperature and Gr黱eisen parameter show weak temperature dependence relative to the thermal expansion coefficient, entropy, and heat capacity, from which the pressure effects are clearly seen.

Linear stability analysis on a spherical particle growing from a binary melt under the far-field flow

Cao Bin,Lin Xin,Wang Meng,Huang Wei-Dong
Chin. Phys. B 2012, 21 (5): 056401;  doi: 10.1088/1674-1056/21/5/056401
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The solutions of temperature and solute fields around a spherical crystal growing from a binary melt under the far-field flow are obtained. Based on the results, a linear stability analysis on the spherical interface growing from the binary melt under the far-field flow is performed. It is found that the constitutional supercooling effect ahead of the spherical crystal interface under the far-field flow is enhanced compared with that without the flow. The growth rate of the perturbation amplitude at the up-wind side of the spherical crystal interface is larger than that at the down-wind side. The critical stability radius of the crystal interface decreases with the increasing far-field flow velocity. Under the far-field flow, the whole spherical interface becomes more unstable compared with that without the flow.

Ab initio study of H and He migrations in β-phase Sc, Y, and Er hydrides

Chen Ru-Cheng,Yang Li,Dai Yun-Ya,Zhu Zi-Qiang,Peng Shu-Ming,Long Xing-Gui,Gao Fei,Zu Xiao-Tao
Chin. Phys. B 2012, 21 (5): 056601;  doi: 10.1088/1674-1056/21/5/056601
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Ab initio calculations based on the density functional theory have been performed to investigate the migrations of hydrogen (H) and helium (He) atoms in β -phase scandium (Sc), yttrium (Y), and erbium (Er) hydrides with three different ratios of H to metal. The results show that the migration mechanisms of H and He atoms mainly depend on the crystal structures of hydrides, but their energy barriers are affected by the host-lattice in metal hydrides. The formation energies of octahedral-occupancy H (Hoct) and tetrahedral vacancy (Vmtet) pairs are almost the same (about 1.2 eV). It is of interest to note that the migration barriers of H increase with increasing host-lattice atomic number. In addition, the results show that the favorable migration mechanism of He depends slightly on the Vmtet in the Sc hydride, but strongly on that in the Y and Er hydrides, which may account for different behaviours of initial He release from ScT2 and ErT2.

Impact of back-gate bias on the hysteresis effect in partially depleted SOI MOSFETs

Luo Jie-Xin,Chen Jing,Zhou Jian-Hua,Wu Qing-Qing,Chai Zhan,Yu Tao,Wang Xi
Chin. Phys. B 2012, 21 (5): 056602;  doi: 10.1088/1674-1056/21/5/056602
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The hysteresis effect in the output characteristics, originating from the floating body effect, has been measured in partially depleted (PD) silicon-on-insulator (SOI) MOSFETs at different back-gate biases. ID hysteresis has been developed to clarify the hysteresis characteristics. The fabricated devices show the positive and negative peaks in the ID hysteresis. The experimental results show that the ID hysteresis is sensitive to the back gate bias in 0.13-μm PD SOI MOSFETs and does not vary monotonously with the back-gate bias. Based on the steady-state Shockley--Read--Hall (SRH) recombination theory, we have successfully interpreted the impact of the back-gate bias on the hysteresis effect in PD SOI MOSFETs.

Stabilization variation of organic conductor surfaces induced by π–π stacking interactions

Dou Rui-Fen,Lin Feng,Liu Fu-Wei,Sun Yi,Yang Ji-Yong,Lin Bing-Fa,He Lin,Xiong Chang-Min,Nie Jia-Cai
Chin. Phys. B 2012, 21 (5): 056801;  doi: 10.1088/1674-1056/21/5/056801
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The structures and stabilization of three crystal surfaces of TCNQ-based charge transfer complexes (CTCs) including PrQ(TCNQ)2, MPM(TCNQ)2, and MEM(TCNQ)2, have been investigated by scanning tunneling microscopy (STM). The three bulk-truncated surfaces are all ac-surface, which are terminated with TCNQ molecular arrays. On the ac-surface of PrQ(TCNQ)2, the TCNQ molecules form a tetramer structure with a wavelike row behavior and a γ angle of about 18° between adjacent molecules. Moreover, the dimer structures are resolved on both ac-surfaces of MPM(TCNQ)2 and MEM(TCNQ)2. In addition, the tetramer structure is the most stable structure, while the dimer structures are unstable and easily subject to the STM tip disturbance, which results in changeable unit cells. The main reasons for the surface stabilization variation among the three ac-surfaces are provided by using the 'π-atom model'.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Sudden birth and sudden death of thermal fidelity in a two-qubit system

Qin Li-Guo,Tian Li-Jun,Jiang Ying,Zhang Hong-Biao
Chin. Phys. B 2012, 21 (5): 057101;  doi: 10.1088/1674-1056/21/5/057101
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We study the energy level crossing and the thermal fidelity in a two-qubit system with the presence of a transverse inhomogeneous magnetic field. With the help of contour plots, we clearly identify the ground states of the system in different regions of parameter space, and discuss the corresponding energy level crossing. The fidelity between the ground state of the system and the state of the system at temperature T is calculated. The result shows that the fidelity is very sensitive to the magnetic field anisotropic factor, indicating that this factor may be used as a controller of the fidelity. The influence of the Yangian transition operators on the fidelity of the system is discussed. We find that the Yangian operators can change the fidelity dramatically and give rise to sudden birth and sudden death phenomena of the thermal fidelity. This makes the corresponding Yangian operators possible candidates for switchers to turn the fidelity on and off.

First-principles study of mechanical stability and thermal properties of MNNi3 (M=Zn, Mg, Al) under pressure

Zhai Hong-Cun,Li Xiao-Feng,Du Jun-Yi,Ji Guang-Fu
Chin. Phys. B 2012, 21 (5): 057102;  doi: 10.1088/1674-1056/21/5/057102
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The mechanical stability, elastic, and thermodynamic properties of the anti-perovskite superconductors MNNi3 (M=Zn, Mg, Al) are investigated by means of the first-principles calculations. The calculated structural parameters and elastic properties of MNNi3 are in good agreement with the experimental and the other theoretical results. From the elastic constants under high pressure, we predict that ZnNNi3, MgNNi3, and AlNNi3 are not stable at the pressures above 61.2 GPa, 113.3 GPa, and 122.4 GPa, respectively. By employing the Debye model, the thermodynamic properties, such as the heat capacity and the thermal expansion coefficient, under pressures and at finite temperatures are also obtained successfully.

A k·p analytical model for valence band of biaxial strained Ge on (001) Si1-xGex

Wang Guan-Yu,Zhang He-Ming,Gao Xiang,Wang Bin,Zhou Chun-Yu
Chin. Phys. B 2012, 21 (5): 057103;  doi: 10.1088/1674-1056/21/5/057103
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In this paper, the dispersion relationship is derived by using the k·p method with the help of the perturbation theory, and we obtain the analytical expression in connection with the deformation potential. The calculation of the valence band of the biaxial strained Ge/(001)Si1-xGex is then performed. The results show that the first valence band edge moves up as Ge fraction x decreases, while the second valence band edge moves down. The band structures in the strained Ge/ (001)Si0.4Ge0.6 exhibit significant changes with x decreasing in the relaxed Ge along the [0, 0, k] and the [k, 0, 0] directions. Furthermore, we employ a pseudo-potential total energy package (CASTEP) approach to calculate the band structure with the Ge fraction ranging from x=0.6 to 1. Our analytical results of the splitting energy accord with the CASTEP-extracted results. The quantitative results obtained in this work can provide some theoretical references to the understanding of the strained Ge materials and the conduction channel design related to stress and orientation in the strained Ge pMOSFET.

Electronic structures and optical properties of TiO2:Improved density-functional-theory investigation

Gong Sai,Liu Bang-Gui
Chin. Phys. B 2012, 21 (5): 057104;  doi: 10.1088/1674-1056/21/5/057104
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TiO2 has been recently used to realize high-temperature ferromagnetic semiconductors. In fact, it has been widely used for a long time as white pigment and sunscreen because of its whiteness, high refractive index, and excellent optical properties. However, its electronic structures and the related properties have not been satisfactorily understood. Here, we use Tran and Blaha's modified Becke-Johnson (TB-mBJ) exchange potential (plus a local density approximation correlation potential) within the density functional theory to investigate electronic structures and optical properties of rutile and anatase TiO2. Our comparative calculations show that the energy gaps obtained from mBJ method agree better with the experimental results than that obtained from local density approximation (LDA) and generalized gradient approximation (GGA), in contrast with substantially overestimated values from many-body perturbation (GW) calculations. As for optical dielectric functions (both real and imaginary parts), refractive index, and extinction coefficients as functions of photon energy, our mBJ calculated results are in excellent agreement with the experimental curves. Our further analysis reveals that these excellent improvements are achieved because mBJ potential describes accurately the energy levels of Ti 3d states. These results should be helpful to understand the high temperature ferromagnetism in doped TiO2. This approach can be used as a standard to understand electronic structures and the related properties of such materials as TiO2.

The effect of Fe on the martensitic transformation of TaRu high-temperature shape memory alloys:A first-principles study

Tan Chang-Long,Tian Xiao-Hua,Cai Wei
Chin. Phys. B 2012, 21 (5): 057105;  doi: 10.1088/1674-1056/21/5/057105
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The effect of Fe on the martensitic transformation of TaRu high-temperature shape memory alloys has been investigated using first-principles calculations. The site preference of Fe in TaRu alloys has been clarified for the first time, and the results show that Fe is predicted to occupy Ru sites. The addition of Fe increases the stability of the Ta50Ru50-xFex β phase, leading to a significant decrease in the β to β′ martensitic transformation temperature. In addition, the mechanism of the Fe alloying effect is explained on the basis of the electronic structure.

Implementation of LDA+DMFT with the pseudo-potential-plane-wave method Hot!

Zhao Jian-Zhou,Zhuang Jia-Ning,Deng Xiao-Yu,Bi Yan,Cai Ling-Cang,Fang Zhong,Dai Xi
Chin. Phys. B 2012, 21 (5): 057106;  doi: 10.1088/1674-1056/21/5/057106
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We propose an efficient implementation of combining dynamical mean field theory (DMFT) with electronic structural calculation based on the local density approximation (LDA). The pseudo-potential-plane-wave method is used in the LDA part, which enables it to be applied to large systems. The full loop self consistency of the charge density has been reached in our implementation, which allows us to compute the total energy related properties. The procedure of LDA+DMFT is introduced in detail with a complete flow chart. We have also applied our code to study the electronic structure of several typical strong correlated materials, including cerium, americium and NiO. Our results fit quite well with both the experimental data and previous studies.

Optical Tamm state polaritons in a quantum well microcavity with gold layers

Zhang Wei-Li,Rao Yun-Jiang
Chin. Phys. B 2012, 21 (5): 057107;  doi: 10.1088/1674-1056/21/5/057107
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A new type of cavity polariton, the optical Tamm state (OTS) polariton, is proposed to be realized by sandwiching a quantum well (QW) between a gold layer and a distributed Bragg reflector (DBR). It is shown that OTS polaritons can be generated from the strong couplings between the QW excitons and the free OTSs. In addition, if a second gold layer is introduced into the bottom of the DBR, two independent free OTSs can interact strongly with the QW excitons to produce extra OTS polaritons.

The optical phonon effect of quantum rod qubits

Wang Cui-Tao,Wu Zhi-Yong,Zhao Cui-Lan,Ding Zhao-Hua,Xiao Jing-Lin
Chin. Phys. B 2012, 21 (5): 057108;  doi: 10.1088/1674-1056/21/5/057108
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The Hamiltonian of a quantum rod with an ellipsoidal boundary is given by using a coordinate transformation in which the ellipsoidal boundary is changed into a spherical one. Under the condition of strong electron--longitudinal optical phonon coupling in the rod, we obtain both the electron eigenfunctions and the eigenenergies of the ground and first-excited state by using the Pekar-type variational method. This quantum rod system may be used as a two-level qubit. When the electron is in the superposition state of the ground and first-excited states, the probability density of the electron oscillates in the rod with a certain period. It is found that the oscillation period is an increasing function of the ellipsoid aspect ratio and the transverse and longitudinal effective confinement lengths of the quantum rod, whereas it is a decreasing function of the electron--phonon coupling strength.

A possible mechanism for magnetar soft X-ray/γ-ray emission

Gao Zhi-Fu,Peng Qiu-He,Wang Na,Chou Chih-Kang
Chin. Phys. B 2012, 21 (5): 057109;  doi: 10.1088/1674-1056/21/5/057109
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Once the energies of electrons near the Fermi surface obviously exceed the threshold energy of the inverse β decay, electron capture (EC) dominates inside the magnetar. Since the maximal binding energy of the 3P2 neutron Cooper pair is only about 0.048 MeV, the outgoing high-energy neutrons (Ek(n)>60 MeV) created by the EC can easily destroy the 3P2 neutron Cooper pairs through the interaction of nuclear force. In the anisotropic neutron superfluid, each 3P2 neutron Cooper pair has magnetic energy 2μnB in the applied magnetic field B, where μn=0.966× 10-23 erg·G-1 is the absolute value of the neutron abnormal magnetic moment. While being destroyed by the high-energy EC neutrons, the magnetic moments of the 3P2 Cooper pairs are no longer arranged in the paramagnetic direction, and the magnetic energy is released. This released energy can be transformed into thermal energy. Only a small fraction of the generated thermal energy is transported from the interior to the surface by conduction, and then it is radiated in the form of thermal photons from the surface. After highly efficient modulation within the star's magnetosphere, the thermal surface emission is shaped into a spectrum of soft X-rays/γ-rays with the observed characteristics of magnetars. By introducing related parameters, we calculate the theoretical luminosities of magnetars. The calculation results agree well with the observed parameters of magnetars.

The effect of spin-orbit coupling on magnetoresistance in nonmagnetic organic semiconductors

Zhao Jun-Qing,Ding Meng,Zhang Tian-You,Zhang Ning-Yu,Pang Yan-Tao,Ji Yan-Ju,Chen Ying,Wang Feng-Xiang,Fu Gang
Chin. Phys. B 2012, 21 (5): 057110;  doi: 10.1088/1674-1056/21/5/057110
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We investigated the effect of spin-orbit coupling on magnetoresistance in nonmagnetic organic semiconductors. A Lorentz-type magnetoresistance is obtained from spin-orbit coupling-dependent spin precession under the condition of a space-charge-limited current. The magnetoresistance depends on the initial spin orientation of the electron with respect to the hole in electron--hole pairs, and the increasing spin-orbit coupling slows down the change in magnetoresistance with magnetic field. The field dependence, the sign and the saturation value of the magnetoresistance are composite effects of recombination and dissociation rate constants of singlet and triplet electron--hole pairs. The simulated magnetoresistance shows good consistency with the experimental results.

Breakdown voltage analysis of Al0.25Ga0.75N/GaN high electron mobility transistors with partial silicon doping in the AlGaN layer

Duan Bao-Xing,Yang Yin-Tang
Chin. Phys. B 2012, 21 (5): 057201;  doi: 10.1088/1674-1056/21/5/057201
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In this paper, two-dimensional electron gas (2DEG) regions in AlGaN/GaN high electron mobility transistors (HEMTs) are realized by doping partial silicon into the AlGaN layer for the first time. A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge. The high electric field near the gate for the complete silicon doping structure is effectively decreased, which makes the surface electric field uniform. The high electric field peak near the drain results from the potential difference between the surface and the depletion regions. Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer. The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain. The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field.

Electric field distribution and effective nonlinear AC and DC responses of graded cylindrical composites

Ding Xia,Jia Yan-Xia,Wei En-Bo
Chin. Phys. B 2012, 21 (5): 057202;  doi: 10.1088/1674-1056/21/5/057202
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The perturbation method is used to study the localization of electric field distribution and the effective nonlinear response of graded composites under an external alternating-current (AC) and direct-current (DC) electric field Eapp = E0 (1+sin ωt). The dielectric profile of the cylindrical inclusions is modeled by function εi (r) = Ck rk (r ≤ a), where r is the radius of the cylindrical inclusion, and Ck, k, a are parameters. In the dilute limit, the local potentials and the effective nonlinear responses at all harmonics are derived. Meanwhile, the general effective nonlinear responses are also derived and compared with the effective nonlinear responses at harmonics under the AC and DC external field. It is found that the effective nonlinear AC and DC responses at harmonics can be calculated by those of the general effective nonlinear of the graded composites under the external DC electric field. Moreover, the obtained local electrical fields show that the electrical field distribution in the cylindrical inclusions is controllable, and the maximum of the electric field inside the cylinder is at its center.

Improving lithographic masks with the assistance of indentations

Guo Ying-Nan,Li Xu-Feng,Pan Shi,Wang Qiao,Wang Shuo,Wu Yong-Kuan
Chin. Phys. B 2012, 21 (5): 057301;  doi: 10.1088/1674-1056/21/5/057301
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Indentations etched on the output surface of a metallic mask are proposed to produce fine lithographic patterns with a resolution of 500 nm using the finite-difference time domain (FDTD) method. Such a designed mask is capable of enhancing near field lithography (NFL) resolution more than three times compared with the structure without indentations. The simulation results show that the interference disturbance between the adjacent lithographic channels can be eliminated efficiently by employing the indentations. As a straightforward consequence, the channel-to-channel interspaces can be shortened significantly, maintaining a uniform field distribution and high contrast.

Plasmons in a free-standing nanorod with a two-dimensional parabolic quantum well caused by surface states

Song Ya-Feng,Lü Yan-Wu,Wen Wei,Liu Xiang-Lin,Yang Shao-Yan,Zhu Qin-Sheng,Wang Zhan-Guo
Chin. Phys. B 2012, 21 (5): 057302;  doi: 10.1088/1674-1056/21/5/057302
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The collective charge density excitations in a free-standing nanorod with a two-dimensional parabolic quantum well are investigated within the framework of Bohm--Pine's random-phase approximation in the two-subband model. The new simplified analytical expressions of the Coulomb interaction matrix elements and dielectric functions are derived and numerically discussed. In addition, the electron density and temperature dependences of dispersion features are also investigated. We find that in the two-dimensional parabolic quantum well, the intrasubband upper branch is coupled with the intersubband mode, which is quite different from other quasi-one-dimensional systems like a cylindrical quantum wire with an infinite rectangular potential. In addition, we also find that higher temperature results in the intersubband mode (with an energy of 12 meV (~ 3 THz)) becoming totally damped, which agrees well with the experimental results of Raman scattering in the literature. These interesting properties may provide useful references to the design of free-standing nanorod based devices.

Graphene films grown on sapphire substrates via solid source molecular beam epitaxy

Tang Jun,Kang Chao-Yang,Li Li-Min,Liu Zhong-Liang,Yan Wen-Sheng,Wei Shi-Qiang,Xu Peng-Shou
Chin. Phys. B 2012, 21 (5): 057303;  doi: 10.1088/1674-1056/21/5/057303
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A method for growing graphene on a sapphire substrate by depositing an SiC buffer layer and then annealing at high temperature in solid source molecular beam epitaxy (SSMBE) equipment was presented. The structural and electronic properties of the samples were characterized by reflection high energy diffraction (RHEED), X-ray diffraction Φ scans, Raman spectroscopy, and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The results of the RHEED and Φ scan, as well as the Raman spectra, showed that an epitaxial hexagonal α-SiC layer was grown on the sapphire substrate. The results of the Raman and NEXAFS spectra revealed that the graphene films with the AB Bernal stacking structure were formed on the sapphire substrate after annealing. The layer number of the graphene was between four and five, and the thickness of the unreacted SiC layer was about 1--1.5 nm.

A threshold voltage analytical model for high-k gate dielectric MOSFETs with fully overlapped lightly doped drain structures

Ma Fei,Liu Hong-Xia,Kuang Qian-Wei,Fan Ji-Bin
Chin. Phys. B 2012, 21 (5): 057304;  doi: 10.1088/1674-1056/21/5/057304
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We investigate the influence of voltage drop across the lightly doped drain (LDD) region and the built-in potential on MOSFETs, and develop a threshold voltage model for high-k gate dielectric MOSFETs with fully overlapped LDD structures by solving the two-dimensional Poisson's equation in the silicon and gate dielectric layers. The model can predict the fringing-induced barrier lowering effect and the short channel effect. It is also valid for non-LDD MOSFETs. Based on this model, the relationship between threshold voltage roll-off and three parameters, channel length, drain voltage and gate dielectric permittivity, is investigated. Compared with the non-LDD MOSFET, the LDD MOSFET depends slightly on channel length, drain voltage, and gate dielectric permittivity. The model is verified at the end of the paper.

The influence and explanation of fringing-induced barrier lowering on sub-100 nm MOSFETs with high-k gate dielectrics

Ma Fei,Liu Hong-Xia,Kuang Qian-Wei,Fan Ji-Bin
Chin. Phys. B 2012, 21 (5): 057305;  doi: 10.1088/1674-1056/21/5/057305
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The fringing-induced barrier lowering (FIBL) effect of sub-100 nm MOSFETs with high-k gate dielectrics is investigated using a two-dimensional device simulator. An equivalent capacitance theory is proposed to explain the physics mechanism of the FIBL effect. The FIBL effect is enhanced and the short channel performance is degraded with increasing capacitance. Based on equivalent capacitance theory, the influences of channel length, junction depth, gate/lightly doped drain (LDD) overlap length, spacer material and spacer width on FIBL is thoroughly investigated. A stack gate dielectric is presented to suppress the FIBL effect.

Dispersion relation of dust acoustic waves in metallic multi-walled carbon nanotubes

Ali Fathalian,Shahram Nikjo
Chin. Phys. B 2012, 21 (5): 057306;  doi: 10.1088/1674-1056/21/5/057306
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In this paper, a charged multi-walled carbon nanotube (MWCNT), which is surrounded by charged nanoparticles, is modeled as a cylindrical shell of electron--ion--dust plasma. By employing classical electrodynamics formulations and the linearized hydrodynamic model, the dispersion relation of the dust acoustic wave oscillations in the composed system is investigated. We obtain a new low-frequency electrostatic excitation in the MWCNT, i.e. dust acoustic wave oscillations.

Vortex lines in a ferromagnetic spin-triplet superconductor

Zhao Li,Yang Jie,Xie Qun-Ying,Tian Miao,Duan Yi-Shi
Chin. Phys. B 2012, 21 (5): 057401;  doi: 10.1088/1674-1056/21/5/057401
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Based on Duan's topological current theory, we show that in a ferromagnetic spin-triplet superconductor there is a topological defect of string structures which can be interpreted as vortex lines. Such defects are different from the Abrikosov vortices in one-component condensate systems. We investigate the inner topological structure of the vortex lines. The topological charge density, velocity, and topological current of the vortex lines can all be expressed in terms of δ function, which indicates that the vortices can only arise from the zero points of an order parameter field. The topological charges of vortex lines are quantized in terms of the Hopf indices and Brouwer degrees of φ-mapping. The divergence of the self-induced magnetic field can be rigorously determined by the corresponding order parameter fields and its expression also takes the form of a δ-like function. Finally, based on the implicit function theorem and the Taylor expansion, we conduct detailed studies on the bifurcation of vortex topological current and find different directions of the bifurcation.

Interfacial spin Hall current in a Josephson junction with Rashba spin–orbit coupling

Yang Zhi-Hong,Yang Yong-Hong,Wang Jun
Chin. Phys. B 2012, 21 (5): 057402;  doi: 10.1088/1674-1056/21/5/057402
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We theoretically investigate the spin transport properties of the Cooper pairs in a conventional Josephson junction with Rashba spin--orbit coupling considered in one of the superconducting leads. It is found that an angle-resolved spin supercurrent flows through the junction and a nonzero interfacial spin Hall current driven by the superconducting phase difference also appears at the interface. The physical origin of this is that the Rashba spin--orbit coupling can induce a triplet order parameter in the s-wave superconductor. The interfacial spin Hall current dependences on the system parameters are also discussed.

The crystal structure, magnetism, and colossal magnetoresistance of Y2CrS4

Liu Rong-Deng,Liu Yun-Tao,He Lun-Hua,Wang Zhi-Cui,Chen Dong-Feng,Wang Fang-Wei
Chin. Phys. B 2012, 21 (5): 057501;  doi: 10.1088/1674-1056/21/5/057501
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Ternary yttrium chromium sulfide, Y2CrS4, prepared by the solid-state reaction of Y2S3, Cr, and S, was found to exhibit an antiferromagnetic transition at about 64 K. The X-ray diffraction pattern at 300 K was refined with space group Pca21, and the structure parameters were determined to be a=12.51 Å, b=7.53 Å, and c=12.49 Å. We investigated the magnetotransport properties, and observed negative colossal magnetoresistance reaching up to 2.5? 104% in the semiconducting compound of Y2CrS4.

Growth and photoluminescence properties of inclined ZnO and ZnCoO thin films on SrTiO3(110) substrates

Bai Hong-Liang,Liu Guo-Lei,He Shu-Min,Yan Shi-Shen,Zhu Da-Peng,Guo Hong-Yu,Ji Zi-Wu,Yang Feng-Fan,Chen Yan-Xue,Mei Liang-Mo
Chin. Phys. B 2012, 21 (5): 057801;  doi: 10.1088/1674-1056/21/5/057801
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ZnO thin film growth prefers different orientations on the etched and unetched SrTiO3(STO)(110) substrates. Inclined ZnO and cobalt-doped ZnO (ZnCoO) thin films are grown on unetched STO(110) substrates using oxygen plasma assisted molecular beam epitaxy, with the c-axis 42° inclined from the normal STO(110) surface. The growth geometries are ZnCoO[100]//STO[110] and ZnCoO[111]//STO[001]. The low temperature photoluminescence spectra of the inclined ZnO and ZnCoO films are dominated by D0X emissions associated with A0X emissions, and the characteristic emissions for the 2E(2G)→4A2(4F) transition of Co2+ dopants and the relevant phonon-participated emissions are observed in the ZnCoO film, indicating the incorporation of Co2+ ions at the lattice positions of the Zn2+ ions. The c-axis inclined ZnCoO film shows ferromagnetic properties at room temperature.

Electric potential distribution near nanocone arrays on metal substrates

Huang Xiao-Jing,You Rong-Yi
Chin. Phys. B 2012, 21 (5): 057802;  doi: 10.1088/1674-1056/21/5/057802
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Based on the nanostructured surface model, where conical nanoparticle arrays grow out symmetrically from a plane metal substrate, a theoretical model of the local electric potential near nanocones is built when a uniform external electric field is applied. In terms of this model, the electric potential distribution near the nanocone arrays is obtained and given by a curved surface using a numerical computation method. The computational results show that the electric potential distribution near the nanocone arrays exhibit an obvious geometrical symmetry. These results could serve as a basis for explaining many abnormal phenomena, such as the abnormal infrared effects (AIREs) which are found on nanostructured metal surfaces, as well as a reference for investigating the applications of nanomaterials, such as nanoelectrodes and nanosensors.

Optical and fast nondestructive identification of the ages of leaded ancient pottery

Wu Fang-Yuan,Yang Xiang-Bo
Chin. Phys. B 2012, 21 (5): 057803;  doi: 10.1088/1674-1056/21/5/057803
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In this paper, based on the one-dimensional (1D) optical superlattice model, we calculate the average reflectivities (ARs) of leaded ancient pottery (AP) made within the last 2000 years, and find that for incident light with a suitable wavelength, the AR of the leaded AP increases monotonously with the increase in the layer number of the silvery glaze (SG) media. Based on this property, we propose an optical nondestructive method for identifying the age of leaded AP by detecting the AR. By using the exhaust algorithm and the discriminant function of variance, we obtain the optimal wavelength range of the incident light to identify the ages of the leaded AP. It is found that in the visible light band, if we choose green light with a wavelength range of 540--540.1 nm as the incident light, leaded AP made within the last 2000 years can be identified swiftly and precisely by detecting the ARs. This will be useful for designing optical instruments for the fast nondestructive identification of the ages of leaded AP.

Field emission properties of capped carbon nanotubes doped by alkali metals:a theoretical investigation

Jin Lei,Fu Hong-Gang,Xie Ying,Yu Hai-Tao
Chin. Phys. B 2012, 21 (5): 057901;  doi: 10.1088/1674-1056/21/5/057901
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The electronic structures and field emission properties of capped CNT55 systems with or without alkali metal atom adsorption were systematically investigated by density functional theory calculation. The results indicate that the adsorption of alkali metal on the center site of a CNT tip is energetically favorable. In addition, the adsorption energies increase with the introduction of the electric field. The excessive negative charges on CNT tips make electron emittance much easier and result in a decrease in work function. Furthermore, the inducing effect by positively charged alkali metal atoms can be reasonably considered as the dominant reason for the improvement in field emission properties.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Growth and annealing study of hydrogen-doped single diamond crystals under high pressure and high temperature

Li Yong,Jia Xiao-Peng,Hu Mei-Hua,Liu Xiao-Bing,Yan Bing-Min,Zhou Zhen-Xiang,Zhang Zhuang-Fei,Ma Hong-An
Chin. Phys. B 2012, 21 (5): 058101;  doi: 10.1088/1674-1056/21/5/058101
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A series of diamond crystals doped with hydrogen is successfully synthesized using LiH as the hydrogen source in a catalyst-carbon system at a pressure of 6.0 GPa and temperature ranging from 1255℃ to 1350℃. It is shown that the high temperature plays a key role in the incorporation of hydrogen atoms during diamond crystallization. Fourier transform infrared micro-spectroscopy reveals that most of the hydrogen atoms in the synthesized diamond are incorporated into the crystal structure as sp3--CH2-symmetric (2850 cm-1) and sp3 CH2-antisymmetric vibrations (2920 cm-1). The intensities of these peaks increase gradually with an increase in the content of the hydrogen source in the catalyst. The incorporation of hydrogen impurity leads to a significant shift towards higher frequencies of the Raman peak from 1332.06 cm-1 to 1333.05 cm-1 and gives rise to some compressive stress in the diamond crystal lattice. Furthermore, hydrogen to carbon bonds are evident in the annealed diamond, indicating that the bonds that remain throughout the annealing process and the vibration frequencies centred at 2850 and 2920 cm-1 have no observable shift. Therefore, we suggest that the sp3 C--H bond is rather stable in diamond crystals.

The light-enhanced NO2 sensing properties of porous silicon gas sensors at room temperature

Chen Hui-Qing,Hu Ming,Zeng Jing,Wang Wei-Dan
Chin. Phys. B 2012, 21 (5): 058201;  doi: 10.1088/1674-1056/21/5/058201
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The NO2 gas sensing behavior of porous silicon (PS) is studied at room temperature with and without ultraviolet (UV) light radiation. The PS layer is fabricated by electrochemical etching in an HF-based solution on a p+-type silicon substrate. Then, Pt electrodes are deposited on the surface of the PS to obtain the PS gas sensor. The NO2 sensing properties of the PS with different porosities are investigated under UV light radiation at room temperature. The measurement results show that the PS gas sensor has a much higher response sensitivity and faster response--recovery characteristics than NO2 under the illumination. The sensitivity of the PS sample with the largest porosity to 1 ppm NO2 is 9.9 with UV light radiation, while it is 2.4 without UV light radiation. We find that the ability to absorb UV light is enhanced with the increase in porosity. The PS sample with the highest porosity has a larger change than the other samples. Therefore, the effect of UV radiation on the NO2 sensing properties of PS is closely related to the porosity.

Analysis and design of the taper in metal-grating periodic slow-wave structures for rectangular Cerenkov masers

Chen Ye,Zhao Ding,Wang Yong,Shu Wen
Chin. Phys. B 2012, 21 (5): 058401;  doi: 10.1088/1674-1056/21/5/058401
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The hybrid-mode dispersion equation of the metal-grating periodic slow-wave structure for a rectangular Cerenkov maser is derived by using the Borgnis function and field-matching methods. An equivalent-circuit model for the taper of the groove depth that matches the smooth waveguide to the metal-grating structure is proposed. By using the equivalent-circuit method, as well as the Ansoft high frequency structure simulator (HFSS) code, an appropriate electromagnetic mode for beam-wave interaction is selected and the equivalent-circuit analysis on the taper is given. The calculated results show that a cumulative reflection coefficient of 0.025 for the beam-wave interaction structure at a working frequency of 78.1 GHz can be reached by designing the exponential taper with a TEz10 rectangular waveguide mode as the input and the desired TEx10 mode as the output. It is worth pointing out that by using the equivalent-circuit method, the complex field-matching problems from the traditional field-theory method for taper design can be avoided, so the taper analysis process is markedly simplified.

Physical modeling based on hydrodynamic simulation for the design of InGaAs/InP double heterojunction bipolar transistors

Ge Ji,Liu Hong-Gang,Su Yong-Bo,Cao Yu-Xiong,Jin Zhi
Chin. Phys. B 2012, 21 (5): 058501;  doi: 10.1088/1674-1056/21/5/058501
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A physical model for scaling and optimizing InGaAs/InP double heterojunction bipolar transistors (DHBTs) based on hydrodynamic simulation is developed. The model is based on the hydrodynamic equation, which can accurately describe non-equilibrium conditions such as quasi-ballistic transport in the thin base and the velocity overshoot effect in the depleted collector. In addition, the model accounts for several physical effects such as bandgap narrowing, variable effective mass, and doping-dependent mobility at high fields. Good agreement between the measured and simulated values of cutoff frequency, ft, and maximum oscillation frequency, fmax, are achieved for lateral and vertical device scalings. It is shown that the model in this paper is appropriate for downscaling and designing InGaAs/InP DHBTs.

Effects of microwave pulse-width damage on a bipolar transistor

Ma Zhen-Yang,Chai Chang-Chun,Ren Xing-Rong,Yang Yin-Tang,Chen Bin,Zhao Ying-Bo
Chin. Phys. B 2012, 21 (5): 058502;  doi: 10.1088/1674-1056/21/5/058502
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This paper presents a theoretical study of the pulse-width effects on the damage process of a typical bipolar transistor caused by high power microwaves (HPMs) through the injection approach. The dependences of the microwave damage power, P, and the absorbed energy, E, required to cause the device failure on the pulse width τ are obtained in the nanosecond region by utilizing the curve fitting method. A comparison of the microwave pulse damage data and the existing dc pulse damage data for the same transistor is carried out. By means of a two-dimensional simulator, ISE-TCAD, the internal damage processes of the device caused by microwave voltage signals and dc pulse voltage signals are analyzed comparatively. The simulation results suggest that the temperature-rising positions of the device induced by the microwaves in the negative and positive half periods are different, while only one hot spot exists under the injection of dc pulses. The results demonstrate that the microwave damage power threshold and the absorbed energy must exceed the dc pulse power threshold and the absorbed energy, respectively. The dc pulse damage data may be useful as a lower bound for microwave pulse damage data.

Highly efficient blue fluorescent OLEDs with doped double emitting layers based on p–n heterojunctions

Su Yue-Ju,Wu Xiao-Ming,Hua Yu-Lin,Shen Li-Ying,Jiao Zhi-Qiang,Dong Mu-Sen,Yin Shou-Gen
Chin. Phys. B 2012, 21 (5): 058503;  doi: 10.1088/1674-1056/21/5/058503
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We fabricate a kind of novel efficient blue fluorescent organic light emitting device (OLED) based on p--n heterojunctions composed of hole transporting layer (HTL) N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (NPB) and electron transporting layer (ETL) 4,7-diphnenyl-1,10-phenanthroline (BPhen), into which a new blue material, DNCA (a derivation of N6, N6, N12, N12-tetrap-tolylchrysene-6,12-diamine), is partially doped simultaneously, and double emitting layers are configured. With a turn-on voltage of 2.6 V at 1 cd/m2, this type of OLED presents a maximum luminance efficiency (ηmax) of 8.83 cd/A at 5.818 mA/cm2 and a maximum luminance of over 40000 cd/m2. Meanwhile, the Commission Internationale De L'Eclairage (CIE) coordinates of this device change slightly from (0.13, 0.27) to (0.13, 0.23) as the driving voltage increases from 3 V to 11 V. This improvement in the electroluminescent characteristics is attributed mainly to the ideal p--n heterojunction which can confine and distribute excitons evenly on two sides of the heterojunction interface so as to improve the carrier combination rate and expand the light-emitting region.

Performance improvement of InGaN blue light-emitting diodes with several kinds of electron-blocking layers

Chen Jun,Fan Guang-Han,Zhang Yun-Yan,Pang Wei,Zheng Shu-Wen,Yao Guang-Rui
Chin. Phys. B 2012, 21 (5): 058504;  doi: 10.1088/1674-1056/21/5/058504
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The performance of InGaN blue light-emitting diodes (LEDs) with different kinds of electron-blocking layers is investigated numerically. We compare the simulated emission spectra, electron and hole concentrations, energy band diagrams, electrostatic fields, and internal quantum efficiencies of the LEDs. The LED using AlGaN with gradually increasing Al content from 0% to 20% as the electron-blocking layer (EBL) has a strong spectrum intensity, mitigates efficiency droop, and possesses higher output power compared with the LEDs with the other three types of EBLs. These advantages could be because of the lower electron leakage current and more effective hole injection. The optical performance of the specifically designed LED is also improved in the case of large injection current.

Transient optical modulation properties in the terahertz metamaterial of split ring resonators

Zhou Qing-Li,Shi Yu-Lei,Wang Ai-Hua,Li Lei,Zhang Cun-Lin
Chin. Phys. B 2012, 21 (5): 058701;  doi: 10.1088/1674-1056/21/5/058701
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The ultrafast optical modulation properties of split ring resonators are characterized by utilizing optical pump--terahertz probe spectroscopy. The experimental results show that when the terahertz electric vector is perpendicular to the gap of the split ring resonator, resonant absorption can be quenched significantly under high pump excitation. However, when the terahertz electric vector is parallel to the gap, the resonant absorption is less sensitive to pump excitation due to the structural properties of the metamaterial. Our numerical simulations also demonstrate that the pump pulse significantly influences the split ring resonator current by generating carriers in the substrate.

Preparing Cu2ZnSnS4 films using the co-electro-deposition method with ionic liquids

Chen Yong-Sheng,Wang Ying-Jun,Li Rui,Gu Jin-Hua,Lu Jing-Xiao,Yang Shi-E
Chin. Phys. B 2012, 21 (5): 058801;  doi: 10.1088/1674-1056/21/5/058801
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Cu2ZnSnS4 (CZTS) films are successfully prepared by co-electrodeposition in aqueous ionic solution and sulfurized in elemental sulfur vapor ambient at 400℃ for 30 min using nitrogen as the protective gas. It is found that the CZTS film synthesized at Cu/(Zn+Sn)=0.71 has a kesterite structure, a bandgap of about 1.51 eV, and an absorption coefficient of the order of 104 cm-1. This indicates that the co-electrodeposition method with aqueous ionic solution is a viable process for the growth of CZTS films for application in photovoltaic devices.
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