Table of contents

01 April 2012, Volume 21 Issue 5 Previous issue    Next issue

GENERAL

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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(王肖肖), Sun Xian-Ting(孙现亭), Zhang Mei-Ling(张美玲), Han Yue-Lin(韩月林), and Jia Li-Qun(贾利群) Chin. Phys. B, 2012, 21 (5):  050201.  DOI: 10.1088/1674-1056/21/5/050201 Abstract ( 1570 )   PDF (93KB) ( 755 )   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.

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Mei conserved quantity directly induced by Lie symmetry in a nonconservative Hamilton system Fang Jian-Hui(方建会), Zhang Bin(张斌), Zhang Wei-Wei(张伟伟), and Xu Rui-Li(徐瑞莉) Chin. Phys. B, 2012, 21 (5):  050202.  DOI: 10.1088/1674-1056/21/5/050202 Abstract ( 1737 )   PDF (76KB) ( 675 )   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.

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Solving a class of burning disturbed problem with shock layers Ouyang Cheng(欧阳成), Chen Li-Hua(陈丽华), and Mo Jia-Qi(莫嘉琪) Chin. Phys. B, 2012, 21 (5):  050203.  DOI: 10.1088/1674-1056/21/5/050203 Abstract ( 1551 )   PDF (117KB) ( 646 )   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.

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Relevance vector machine technique for the inverse scattering problem Wang Fang-Fang(王芳芳) and Zhang Ye-Rong(张业荣) Chin. Phys. B, 2012, 21 (5):  050204.  DOI: 10.1088/1674-1056/21/5/050204 Abstract ( 1540 )   PDF (602KB) ( 721 )   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.

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Immunizations on small worlds of tree-based wireless sensor networks Li Qiao(李峤), Zhang Bai-Hai(张百海), Cui Ling-Guo(崔灵果), Fan Zhun(范衠), and Athanasios V. Vasilakos Chin. Phys. B, 2012, 21 (5):  050205.  DOI: 10.1088/1674-1056/21/5/050205 Abstract ( 1566 )   PDF (212KB) ( 709 )   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.

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Mechanism of micro-waviness induced KH2PO4 crystal laser damage and the corresponding vibration source Li Ming-Quan(李明全), Chen Ming-Jun(陈明君), An chen-Hui(安晨辉), Zhou Lian(周炼), Cheng Jian(程健), Xiao Yong(肖勇), and Jiang Wei(姜伟) Chin. Phys. B, 2012, 21 (5):  050301.  DOI: 10.1088/1674-1056/21/5/050301 Abstract ( 1396 )   PDF (2127KB) ( 914 )   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 μm-1 and 30-1 μm-1, especially between 90-1 μm-1 and 200-1 μm-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).

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Electromagnetic absorption properties of flowerlike cobalt composites at microwave frequencies Liu Tao(刘涛), Zhou Pei-Heng(周佩珩), Liang Di-Fei(梁迪飞), and Deng Long-Jiang(邓龙江) Chin. Phys. B, 2012, 21 (5):  050302.  DOI: 10.1088/1674-1056/21/5/050302 Abstract ( 1593 )   PDF (1174KB) ( 891 )   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.

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Entangled quantum heat engine based on two-qubit Heisenberg XY model He Ji-Zhou(何济洲), He Xian(何弦), and Zheng Jie(郑洁) Chin. Phys. B, 2012, 21 (5):  050303.  DOI: 10.1088/1674-1056/21/5/050303 Abstract ( 2029 )   PDF (344KB) ( 1227 )   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.

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Nonlocal quantum cloning via quantum dots trapped in distant cavities Yu Tao(于涛), Zhu Ai-Dong(朱爱东), and Zhang Shou(张寿) Chin. Phys. B, 2012, 21 (5):  050304.  DOI: 10.1088/1674-1056/21/5/050304 Abstract ( 1747 )   PDF (188KB) ( 605 )   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.

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Dynamic characteristics of resonant gyroscopes study based on the Mathieu equation approximate solution Fan Shang-Chun(樊尚春), Li Yan(李艳), Guo Zhan-She(郭占社), Li Jing(李晶), and Zhuang Hai-Han(庄海涵) Chin. Phys. B, 2012, 21 (5):  050401.  DOI: 10.1088/1674-1056/21/5/050401 Abstract ( 1514 )   PDF (974KB) ( 997 )   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.

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Simulation of pedestrian evacuation based on an improved dynamic parameter model Zhu Nuo(朱诺), Jia Bin(贾斌), Shao Chun-Fu(邵春福), and Yue Hao(岳昊) Chin. Phys. B, 2012, 21 (5):  050501.  DOI: 10.1088/1674-1056/21/5/050501 Abstract ( 1599 )   PDF (9840KB) ( 1322 )   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 $\alpha$, $\beta$, and $\gamma$ 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.

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Transport enhancement and efficiency optimization in two heat reservoir ratchets Zeng Chun-Hua(曾春华) and Wang Hua(王华) Chin. Phys. B, 2012, 21 (5):  050502.  DOI: 10.1088/1674-1056/21/5/050502 Abstract ( 1337 )   PDF (194KB) ( 872 )   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 $\delta$ and A. In other words, $\delta$ 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., $\delta$>0 and a lower amplitude value of the external driving force is necessary for efficiency optimization. (iii) The efficiency increases with $\delta$, and decreases with A. $\delta$ and A play opposite roles with respect to the efficiency, which indicates that δ enhances the efficiency of energy transformation while A weakens it.

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Effect of inertia mass on the stochastic resonance driven by a multiplicative dichotomous noise Li Peng(李鹏), Nie Lin-Ru(聂林如), Huang Qi-Rui(黄奇瑞), and Sun Xing-Xiu(孙兴修) Chin. Phys. B, 2012, 21 (5):  050503.  DOI: 10.1088/1674-1056/21/5/050503 Abstract ( 1561 )   PDF (241KB) ( 638 )   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.

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Dynamics of particles around a pseudo-Newtonian Kerr black hole with halos Wang Ying(王颖) and Wu Xin(伍歆) Chin. Phys. B, 2012, 21 (5):  050504.  DOI: 10.1088/1674-1056/21/5/050504 Abstract ( 1659 )   PDF (667KB) ( 900 )   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.

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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 Abstract ( 1259 )   PDF (482KB) ( 899 )   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.

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Image encryption based on a delayed fractional-order chaotic logistic system Wang Zhen(王震), Huang Xia(黄霞), Li Ning(李宁), and Song Xiao-Na(宋晓娜) Chin. Phys. B, 2012, 21 (5):  050506.  DOI: 10.1088/1674-1056/21/5/050506 Abstract ( 1609 )   PDF (4459KB) ( 1246 )   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.

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Parameter estimation for chaotic systems using the cuckoo search algorithm with an orthogonal learning method Li Xiang-Tao(李向涛) and Yin Ming-Hao(殷明浩) Chin. Phys. B, 2012, 21 (5):  050507.  DOI: 10.1088/1674-1056/21/5/050507 Abstract ( 1753 )   PDF (987KB) ( 2548 )   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.

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Pinning synchronization of time-varying delay coupled complex networks with time-varying delayed dynamical nodes Wang Shu-Guo(王树国) and Yao Hong-Xing(姚洪兴) Chin. Phys. B, 2012, 21 (5):  050508.  DOI: 10.1088/1674-1056/21/5/050508 Abstract ( 1749 )   PDF (219KB) ( 795 )   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.

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Synchronization of impulsively coupled complex networks Sun Wen(孙文), Chen Zhong(陈忠), and Chen Shi-Hua(陈士华) Chin. Phys. B, 2012, 21 (5):  050509.  DOI: 10.1088/1674-1056/21/5/050509 Abstract ( 1681 )   PDF (1507KB) ( 692 )   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.

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Solitons for the cubic–quintic nonlinear Schrödinger equation with varying coefficients Chen Yuan-Ming(陈元明), Ma Song-Hua(马松华), and Ma Zheng-Yi(马正义) Chin. Phys. B, 2012, 21 (5):  050510.  DOI: 10.1088/1674-1056/21/5/050510 Abstract ( 1768 )   PDF (4196KB) ( 1136 )   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.

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Chaotic behaviors of the (2+1)-dimensional generalized Breor–Kaup system Ma Song-Hua(马松华), Fang Jian-Ping(方建平), Ren Qing-Bao(任清褒), and Yang Zheng(杨征) Chin. Phys. B, 2012, 21 (5):  050511.  DOI: 10.1088/1674-1056/21/5/050511 Abstract ( 1414 )   PDF (502KB) ( 855 )   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.

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Nonautonomous bright solitons and soliton collisions in a nonlinear medium with an external potential Li Hua-Mei(李画眉), Ge Long(葛龙), and He Jun-Rong(何俊荣) Chin. Phys. B, 2012, 21 (5):  050512.  DOI: 10.1088/1674-1056/21/5/050512 Abstract ( 1527 )   PDF (5104KB) ( 1059 )   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

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Properties of a Si2N molecule under an external electric field Xu Guo-Liang(徐国亮), Xie Hui-Xiang(谢会香), Yuan Wei(袁伟), Zhang Xian-Zhou(张现周), and Liu Yu-Fang(刘玉芳) Chin. Phys. B, 2012, 21 (5):  053101.  DOI: 10.1088/1674-1056/21/5/053101 Abstract ( 1515 )   PDF (164KB) ( 673 )   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.

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Multiple-plateau structure and scaling relation in photoelectron spectra of high-order above-threshold ionization Wu Yan (吴艳), Ye Hui-Liang (叶会亮), Zhang Jing-Tao(张敬涛), and Guo Dong-Sheng (郭东升) Chin. Phys. B, 2012, 21 (5):  053201.  DOI: 10.1088/1674-1056/21/5/053201 Abstract ( 1563 )   PDF (1366KB) ( 630 )   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.

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Construction of embedded-atom-method interatomic potentials for alkaline metals (Li, Na, and K) by lattice inversion Yuan Xiao-Jian(袁晓俭), Chen Nan-Xian(陈难先), and Shen Jiang(申江) Chin. Phys. B, 2012, 21 (5):  053401.  DOI: 10.1088/1674-1056/21/5/053401 Abstract ( 1580 )   PDF (532KB) ( 1139 )   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.

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Resonance phenomena and threshold features in positron–helium scattering Yu Rong-Mei(于荣梅), Cheng Yong-Jun(程勇军), Wang Yang(王旸), and Zhou Ya-Jun(周雅君) Chin. Phys. B, 2012, 21 (5):  053402.  DOI: 10.1088/1674-1056/21/5/053402 Abstract ( 1452 )   PDF (192KB) ( 642 )   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.

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Coupled-channel optical calculation for positron–lithium scattering Liu Fang(刘芳), Cheng Yong-Jun(程勇军), and Zhou Ya-Jun(周雅君) Chin. Phys. B, 2012, 21 (5):  053403.  DOI: 10.1088/1674-1056/21/5/053403 Abstract ( 1406 )   PDF (158KB) ( 523 )   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.

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Peripheral collisions of highly charged ions with metal clusters Zhang Cheng-Jun(张成俊), Hu Bi-Tao(胡碧涛), and Luo Xian-Wen(罗先文) Chin. Phys. B, 2012, 21 (5):  053601.  DOI: 10.1088/1674-1056/21/5/053601 Abstract ( 1506 )   PDF (1088KB) ( 565 )   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

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Dual-band frequency selective surface with large band separation and stable performance Zhou Hang(周航), Qu Shao-Bo(屈绍波), Peng Wei-Dong(彭卫东), Lin Bao-Qin(林宝勤), Wang Jia-Fu(王甲富), Ma Hua(马华), Zhang Jie-Qiu(张介秋), Bai Peng(柏鹏), Wang Xu-Hua(王徐华), and Xu Zhuo(徐卓) Chin. Phys. B, 2012, 21 (5):  054101.  DOI: 10.1088/1674-1056/21/5/054101 Abstract ( 1566 )   PDF (949KB) ( 1601 )   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.

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Tunable frequency selective surface with a shorted ring slot Jia Hong-Yan(贾宏燕), Feng Xiao-Guo(冯晓国), and Sheng Cui-Xia(盛翠霞) Chin. Phys. B, 2012, 21 (5):  054102.  DOI: 10.1088/1674-1056/21/5/054102 Abstract ( 1501 )   PDF (584KB) ( 1164 )   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.

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Investigation of intense sheet electron beam transport using the macroscopic cold-fluid model and the single-particle orbit theory Han Ying(韩莹) and Ruan Cun-Jun(阮存军) Chin. Phys. B, 2012, 21 (5):  054103.  DOI: 10.1088/1674-1056/21/5/054103 Abstract ( 1371 )   PDF (264KB) ( 558 )   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.

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Characteristics of paraxial propagation of a super Lorentz–Gauss SLG01 mode in uniaxial crystal orthogonal to the optical axis Zhou Guo-Quan(周国泉) Chin. Phys. B, 2012, 21 (5):  054104.  DOI: 10.1088/1674-1056/21/5/054104 Abstract ( 1567 )   PDF (3908KB) ( 682 )   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.

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Propagation of Airy beams from right-handed material to left-handed material Lin Hui-Chuan(林惠川) and Pu Ji-Xiong(蒲继雄) Chin. Phys. B, 2012, 21 (5):  054201.  DOI: 10.1088/1674-1056/21/5/054201 Abstract ( 1539 )   PDF (2471KB) ( 844 )   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.

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Evolution of emergent C-points, L-lines, and C-lines in free space Yan Hong-Wei(闫红卫), He De(何德), and Lü Bai-Da(吕百达) Chin. Phys. B, 2012, 21 (5):  054202.  DOI: 10.1088/1674-1056/21/5/054202 Abstract ( 1458 )   PDF (910KB) ( 596 )   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.

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Characteristics of a partially coherent Gaussian Schell-model beam propagating in slanted atmospheric turbulence Li Ya-Qing(李亚清) and Wu Zhen-Sen(吴振森) Chin. Phys. B, 2012, 21 (5):  054203.  DOI: 10.1088/1674-1056/21/5/054203 Abstract ( 1794 )   PDF (363KB) ( 1071 )   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.

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Multiple scattering of light by water cloud droplets with external and internal mixing of black carbon aerosols Wang Hai-Hua(王海华) and Sun Xian-Ming(孙贤明) Chin. Phys. B, 2012, 21 (5):  054204.  DOI: 10.1088/1674-1056/21/5/054204 Abstract ( 1519 )   PDF (176KB) ( 774 )   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.

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Multi-wavelength laser active coherent combination Han Kai(韩凯), Xu Xiao-Jun(许晓军), and Liu Ze-Jin(刘泽金) Chin. Phys. B, 2012, 21 (5):  054205.  DOI: 10.1088/1674-1056/21/5/054205 Abstract ( 1504 )   PDF (1512KB) ( 604 )   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.

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Oscillation behaviour in the photon-number distribution of squeezed coherent states Wang Shuai(王帅), Zhang Xiao-Yan(张晓燕), and Fan Hong-Yi(范洪义) Chin. Phys. B, 2012, 21 (5):  054206.  DOI: 10.1088/1674-1056/21/5/054206 Abstract ( 1511 )   PDF (2651KB) ( 672 )   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.

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Orientation effects on the bandgap and dispersion behavior of 0.91Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 single crystals He Chong-Jun(赫崇君), Fu Xin-Duo(付信夺), Xu Feng(徐峰), Wang Ji-Ming(王吉明), Zhu Kong-Jun(朱孔军), Du Chao-Ling(杜朝玲), and Liu You-Wen(刘友文) Chin. Phys. B, 2012, 21 (5):  054207.  DOI: 10.1088/1674-1056/21/5/054207 Abstract ( 1520 )   PDF (271KB) ( 925 )   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, $\lambda$o, 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.

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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, and M. Hatami Chin. Phys. B, 2012, 21 (5):  054208.  DOI: 10.1088/1674-1056/21/5/054208 Abstract ( 1536 )   PDF (1621KB) ( 829 )   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.

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Dynamic control of retrieval contrast in a $\Lambda$-type atomic system Zhang Xiao-Hang(张晓航), Bao Qian-Qian(鲍倩倩), Zhang Yan(张岩), Su Ming-Che(苏铭彻), Cui Cui-Li(崔淬砺), and Wu Jin-Hui(吴金辉) Chin. Phys. B, 2012, 21 (5):  054209.  DOI: 10.1088/1674-1056/21/5/054209 Abstract ( 1395 )   PDF (228KB) ( 656 )   We propose an efficient scheme for optimizing the optical memory of a sequence of signal light pulses in a system of ultracold atoms in $\Lambda$ 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.

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Level crossing in a two-photon Jaynes–Cummings model Ren Xue-Zao(任学藻), Cong Hong-Lu(丛红璐), Liao Xu(廖旭), and Li Lei(黎雷) Chin. Phys. B, 2012, 21 (5):  054210.  DOI: 10.1088/1674-1056/21/5/054210 Abstract ( 1535 )   PDF (138KB) ( 648 )   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.

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Reflection-mode photoacoustic microscopy using a hollow focused ultrasound transducer for in vivo imaging of blood vessels Yuan Yi(袁毅) and Yang Si-Hua(杨思华) Chin. Phys. B, 2012, 21 (5):  054211.  DOI: 10.1088/1674-1056/21/5/054211 Abstract ( 1717 )   PDF (8815KB) ( 565 )   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.

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Effects of aligning pulse duration on the degree and the slope of nitrogen field-free alignment Wang Fei(王翡), Jiang Hong-Bing(蒋红兵), and Gong Qi-Huang(龚旗煌) Chin. Phys. B, 2012, 21 (5):  054212.  DOI: 10.1088/1674-1056/21/5/054212 Abstract ( 1584 )   PDF (335KB) ( 564 )   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.

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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(张秋琳), Zhang Jing(张静), Qiu Kang-Sheng(邱康生), Zhang Dong-Xiang(张东香), Feng Bao-Hua(冯宝华), and Zhang Jing-Yuan(张景园) Chin. Phys. B, 2012, 21 (5):  054213.  DOI: 10.1088/1674-1056/21/5/054213 Abstract ( 1450 )   PDF (199KB) ( 850 )   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.

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Generation of an isolated sub-30 attosecond pulse in a two-color laser field and a static electric field Zhang Gang-Tai(张刚台), Bai Ting-Ting(白婷婷), and Zhang Mei-Guang(张美光) Chin. Phys. B, 2012, 21 (5):  054214.  DOI: 10.1088/1674-1056/21/5/054214 Abstract ( 1827 )   PDF (525KB) ( 760 )   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.

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Effects of sea surface temperature, cloud radiative and microphysical processes, and diurnal variations on rainfall in equilibrium cloud-resolving model simulations Jiang Zhe(蒋哲), Li Xiao-Fan(李小凡), Zhou Yu-Shu(周玉淑), and Gao Shou-Ting(高守亭) Chin. Phys. B, 2012, 21 (5):  054215.  DOI: 10.1088/1674-1056/21/5/054215 Abstract ( 1574 )   PDF (154KB) ( 525 )   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.

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Mitigation of laser damage growth in fused silica by using a non-evaporative technique Jiang Yong(蒋勇), Liu Chun-Ming(刘春明), Luo Cheng-Si(罗成思), Yuan Xiao-Dong(袁晓东), Xiang Xia(向霞), Wang Hai-Jun(王海军), He Shao-Bo(贺少勃), LüHai-Bin(吕海兵), Ren Wei (任玮), Zheng Wan-Guo(郑万国), and Zu Xiao-Tao(祖小涛) Chin. Phys. B, 2012, 21 (5):  054216.  DOI: 10.1088/1674-1056/21/5/054216 Abstract ( 1437 )   PDF (3071KB) ( 894 )   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.

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Growth and spectroscopic characteristics of Nd-doped PbWO4 crystal Wang Qing-Guo(王庆国), Su Liang-Bi(苏良碧), Li Hong-Jun(李红军), Xiong Wei(熊巍), Yuan Hui(袁晖), Zheng Li-He(郑丽和), Xu Xiao-Dong(徐晓东), Wu Feng(吴锋), Tang Hui-Li(唐慧丽), Jiang Da-Peng(姜大朋), and Xu Jun(徐军) Chin. Phys. B, 2012, 21 (5):  054217.  DOI: 10.1088/1674-1056/21/5/054217 Abstract ( 1671 )   PDF (469KB) ( 814 )   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.

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Spontaneous emission from an atom in a photonic crystal with two coherent bands Huang Xian-Shan(黄仙山), Liu Hai-Lian(刘海莲), and Wang Dong(王东) Chin. Phys. B, 2012, 21 (5):  054218.  DOI: 10.1088/1674-1056/21/5/054218 Abstract ( 1442 )   PDF (160KB) ( 510 )   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(r0), 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.

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Design and fabrication of broadband rugate filter Zhang Jun-Chao(张俊超), Fang Ming(方明), Shao Yu-Chuan(邵宇川), Jin Yun-Xia(晋云霞), and He Hong-Bo(贺洪波) Chin. Phys. B, 2012, 21 (5):  054219.  DOI: 10.1088/1674-1056/21/5/054219 Abstract ( 1731 )   PDF (866KB) ( 1212 )   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.

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Generation of a mid-infrared broadband polarized supercontinuum in As2Se3 photonic crystal fibers Wang Xiao-Yan(王晓琰), Li Shu-Guang(李曙光), Liu Shuo(刘硕) Yin Guo-Bing(尹国冰), and Li Jian-She(李建设) Chin. Phys. B, 2012, 21 (5):  054220.  DOI: 10.1088/1674-1056/21/5/054220 Abstract ( 1549 )   PDF (1136KB) ( 1052 )   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.

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Acoustic characteristics of bubble bursting at the surface of a high-viscosity liquid Liu Xiao-Bo(刘晓波), Zhang Jian-Run(张建润), and Li Pu(李普) Chin. Phys. B, 2012, 21 (5):  054301.  DOI: 10.1088/1674-1056/21/5/054301 Abstract ( 1472 )   PDF (9083KB) ( 958 )   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.

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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 and Rania Fathy Chin. Phys. B, 2012, 21 (5):  054701.  DOI: 10.1088/1674-1056/21/5/054701 Abstract ( 1569 )   PDF (619KB) ( 1217 )   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 $\lambda$ except for $\lambda$=1. In addition, the imposition of fluid suction increases both the rate of heat and mass transfer, whereas fluid injection shows the opposite effect.

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Coupling effect of Brownian motion and laminar shear flow on colloid coagulation:a Brownian dynamics simulation study Xu Sheng-Hua(徐升华), Sun Zhi-Wei(孙祉伟), Li Xu(李旭), and Jin Tong Wang Chin. Phys. B, 2012, 21 (5):  054702.  DOI: 10.1088/1674-1056/21/5/054702 Abstract ( 1682 )   PDF (446KB) ( 793 )   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).

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Asymmetry of the water flux induced by the deformation of a nanotube He Jun-Xia(何俊霞), Lu Hang-Jun(陆杭军), Liu Yang(刘扬), Wu Feng-Min(吴锋民), Nie Xue-Chuan(聂雪川), Zhou Xiao-Yan(周晓艳), and Chen Yan-Yan(陈艳燕) Chin. Phys. B, 2012, 21 (5):  054703.  DOI: 10.1088/1674-1056/21/5/054703 Abstract ( 1436 )   PDF (2019KB) ( 728 )   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

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Improvement on the wave absorbing property of a lossy frequency selective surface absorber using a magnetic substrate Sun Liang-Kui(孙良奎), Cheng Hai-Feng(程海峰), Zhou Yong-Jiang(周永江), and Wang jun(王军) Chin. Phys. B, 2012, 21 (5):  055201.  DOI: 10.1088/1674-1056/21/5/055201 Abstract ( 1588 )   PDF (425KB) ( 1108 )   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.

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Effect of multicomponent dust grains in a cold quantum dusty plasma Yang Xiu-Feng(杨秀峰), Wang Shan-Jin(王善进), Chen Jian-Min(陈建敏), Shi Yu-Ren(石玉仁), Lin Mai-Mai(林麦麦), and Duan Wen-Shan(段文山) Chin. Phys. B, 2012, 21 (5):  055202.  DOI: 10.1088/1674-1056/21/5/055202 Abstract ( 1479 )   PDF (201KB) ( 825 )   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.

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A theoretical estimation of the pre-breakdown-heating time in the underwater discharge acoustic source Wang Yi-Bo(王一博), Wang Shang-Wu(王尚武), and Zeng Xin-Wu(曾新吾) Chin. Phys. B, 2012, 21 (5):  055203.  DOI: 10.1088/1674-1056/21/5/055203 Abstract ( 1460 )   PDF (1102KB) ( 1056 )   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.

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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 Abstract ( 1463 )   PDF (153KB) ( 1912 )   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.

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Using short pulses to enhance the production rate of vibrationally excited hydrogen molecules in hydrogen discharge Sun Ji-Zhong(孙继忠), Li Xian-Tao(李现涛), Bai Jing(白净), and Wang De-Zhen(王德真) Chin. Phys. B, 2012, 21 (5):  055205.  DOI: 10.1088/1674-1056/21/5/055205 Abstract ( 1405 )   PDF (700KB) ( 664 )   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.

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Radiation characteristics and implosion dynamics of tungsten wire array Z-pinches on the YANG accelerator Huang Xian-Bin(黄显宾), Yang Li-Bing(杨礼兵), Li Jing(李晶), Zhou Shao-Tong(周少彤), Ren Xiao-Dong(任晓东), Zhang Si-Qun(张思群), Dan Jia-Kun(但加坤), Cai Hong-Chun(蔡红春), Duan Shu-Chao(段书超) , Chen Guang-Hua(陈光华), Zhang Zheng-Wei(章征伟), Ouyang Kai(欧阳凯), Jun Li(李军), Zhang Zhao-Hui(张朝辉), Zhou Rong-Guo(周荣国), and Wang Gui-Lin(王贵林) Chin. Phys. B, 2012, 21 (5):  055206.  DOI: 10.1088/1674-1056/21/5/055206 Abstract ( 1523 )   PDF (17038KB) ( 2784 )   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.

RAPID COMMUNICATION

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Characterization of relativistic electrons generated by a cone guiding laser pulse Liu Hong-Jie(刘红杰), Gu Yu-Qiu(谷渝秋), Zhou Wei-Min(周维民), Yu Jin-Qing(余金清), Zhu Bin(朱斌), Wu Yu-Chi(吴玉迟), Shan Lian-Qiang(单连强), Wen Xian-Lun(温贤伦), Li Fang(李芳), Qian Feng(钱凤), Cao Lei-Feng(曹磊峰), Zhang Bao-Han(张保汉), and Zheng Zhi-Jian(郑志坚) Chin. Phys. B, 2012, 21 (5):  055207.  DOI: 10.1088/1674-1056/21/5/055207 Abstract ( 1622 )   PDF (4492KB) ( 935 )   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.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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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(徐立清), Hu Li-Qun(胡立群), Li Er-Zhong(李二众), Chen Kai-Yun(陈开云), Liu Zhi-Yuan(刘志远), Chen Ye-Bin(陈晔斌), Zhang Ji-Zong (张继宗), Zhou Rui-Jie(周瑞杰), Yang Mao(杨茂), Mao Song-Tao(毛松涛), and Duan Yan-Min(段艳敏) Chin. Phys. B, 2012, 21 (5):  055208.  DOI: 10.1088/1674-1056/21/5/055208 Abstract ( 1680 )   PDF (211KB) ( 608 )   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).

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Fracture characteristics of bulk metallic glass under high speed impact Sun Bao-Ru(孙宝茹), Zhan Zai-Ji(战再吉), Liang Bo(梁波), Zhang Rui-Jun(张瑞军), and Wang Wen-Kui(王文魁) Chin. Phys. B, 2012, 21 (5):  056101.  DOI: 10.1088/1674-1056/21/5/056101 Abstract ( 1579 )   PDF (3998KB) ( 1319 )   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.

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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(张孟), Feng Xiao-Juan(冯晓娟), Zhao Li-Xia(赵丽霞), Zhang Hong-Yu(张红雨), and Luo You-Hua(罗有华) Chin. Phys. B, 2012, 21 (5):  056102.  DOI: 10.1088/1674-1056/21/5/056102 Abstract ( 1541 )   PDF (985KB) ( 829 )   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.

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Effects of swift argon-ion irradiation on the proton-exchanged LiNbO3 crystal Huang Qing(黄庆), Liu Peng(刘鹏), Liu Tao(刘涛), Guo Sha-Sha(郭沙沙), and Wang Xue-Lin(王雪林) Chin. Phys. B, 2012, 21 (5):  056103.  DOI: 10.1088/1674-1056/21/5/056103 Abstract ( 1512 )   PDF (435KB) ( 607 )   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.

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A gate enhanced power U-shaped MOSFET integrated with a Schottky rectifier Wang Ying(王颖), Jiao Wen-Li(焦文利), Hu Hai-Fan (胡海帆), Liu Yun-Tao(刘云涛), and Cao Fei(曹菲) Chin. Phys. B, 2012, 21 (5):  056104.  DOI: 10.1088/1674-1056/21/5/056104 Abstract ( 1622 )   PDF (216KB) ( 606 )   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.

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First-principles investigation on the elastic stability and thermodynamic properties of Ti2SC Yang Ze-Jin(杨则金), Guo Yun-Dong(郭云东), Linghu Rong-Feng(令狐荣锋), Cheng Xin-Lu(程新路), and Yang Xiang-Dong(杨向东) Chin. Phys. B, 2012, 21 (5):  056301.  DOI: 10.1088/1674-1056/21/5/056301 Abstract ( 1657 )   PDF (519KB) ( 727 )   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 Grüneisen parameter show weak temperature dependence relative to the thermal expansion coefficient, entropy, and heat capacity, from which the pressure effects are clearly seen.

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Linear stability analysis on a spherical particle growing from a binary melt under the far-field flow Cao Bin(曹斌), Lin Xin(林鑫), Wang Meng(王猛), and Huang Wei-Dong(黄卫东) Chin. Phys. B, 2012, 21 (5):  056401.  DOI: 10.1088/1674-1056/21/5/056401 Abstract ( 1519 )   PDF (191KB) ( 571 )   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.

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Ab initio study of H and He migrations in β-phase Sc, Y, and Er hydrides Chen Ru-Cheng(陈汝承), Yang Li(杨莉), Dai Yun-Ya(代云雅), Zhu Zi-Qiang(朱自强), Peng Shu-Ming(彭述明), Long Xing-Gui(龙兴贵), Gao Fei(高飞), and Zu Xiao-Tao(祖小涛) Chin. Phys. B, 2012, 21 (5):  056601.  DOI: 10.1088/1674-1056/21/5/056601 Abstract ( 1597 )   PDF (1240KB) ( 600 )   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.

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Impact of back-gate bias on the hysteresis effect in partially depleted SOI MOSFETs Luo Jie-Xin(罗杰馨), Chen Jing(陈静), Zhou Jian-Hua(周建华), Wu Qing-Qing(伍青青), Chai Zhan(柴展), Yu Tao(余涛), and Wang Xi(王曦) Chin. Phys. B, 2012, 21 (5):  056602.  DOI: 10.1088/1674-1056/21/5/056602 Abstract ( 1479 )   PDF (268KB) ( 773 )   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.

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Stabilization variation of organic conductor surfaces induced by $\pi$-$\pi$ stacking interactions Dou Rui-Fen(窦瑞芬), Lin Feng(林峰), Liu Fu-Wei(刘富伟), Sun Yi(孙祎), Yang Ji-Yong(杨继勇), Lin Bing-Fa(林炳发), He Lin(何林), Xiong Chang-Min(熊昌民), and Nie Jia-Cai(聂家财) Chin. Phys. B, 2012, 21 (5):  056801.  DOI: 10.1088/1674-1056/21/5/056801 Abstract ( 1503 )   PDF (3670KB) ( 520 )   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 $\gamma$ 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 '$\pi$-atom model'.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Sudden birth and sudden death of thermal fidelity in a two-qubit system Qin Li-Guo(秦立国), Tian Li-Jun(田立君), Jiang Ying(姜颖), and Zhang Hong-Biao(张宏标) Chin. Phys. B, 2012, 21 (5):  057101.  DOI: 10.1088/1674-1056/21/5/057101 Abstract ( 1618 )   PDF (579KB) ( 550 )   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.

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First-principles study of mechanical stability and thermal properties of MNNi3 (M=Zn, Mg, Al) under pressure Zhai Hong-Cun(翟红村), Li Xiao-Feng(李晓凤), Du Jun-Yi(杜军毅), and Ji Guang-Fu(姬广富) Chin. Phys. B, 2012, 21 (5):  057102.  DOI: 10.1088/1674-1056/21/5/057102 Abstract ( 1482 )   PDF (178KB) ( 836 )   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.

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A k·p analytical model for valence band of biaxial strained Ge on (001) Si1-xGex Wang Guan-Yu(王冠宇), Zhang He-Ming(张鹤鸣), Gao Xiang(高翔), Wang Bin(王斌), and Zhou ChunYu(周春宇) Chin. Phys. B, 2012, 21 (5):  057103.  DOI: 10.1088/1674-1056/21/5/057103 Abstract ( 1638 )   PDF (673KB) ( 668 )   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.

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Electronic structures and optical properties of TiO2:Improved density-functional-theory investigation Gong Sai(龚赛) and Liu Bang-Gui(刘邦贵) Chin. Phys. B, 2012, 21 (5):  057104.  DOI: 10.1088/1674-1056/21/5/057104 Abstract ( 1657 )   PDF (497KB) ( 4373 )   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.

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The effect of Fe on the martensitic transformation of TaRu high-temperature shape memory alloys:A first-principles study Tan Chang-Long(谭昌龙), Tian Xiao-Hua (田晓华), and Cai Wei(蔡伟) Chin. Phys. B, 2012, 21 (5):  057105.  DOI: 10.1088/1674-1056/21/5/057105 Abstract ( 1634 )   PDF (201KB) ( 595 )   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.

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Implementation of LDA+DMFT with the pseudo-potential-plane-wave method Hot! Zhao Jian-Zhou(赵建洲), Zhuang Jia-Ning(庄嘉宁), Deng Xiao-Yu(邓小宇), Bi Yan(毕延), Cai Ling-Cang(蔡灵仓), Fang Zhong(方忠), and Dai Xi(戴希) Chin. Phys. B, 2012, 21 (5):  057106.  DOI: 10.1088/1674-1056/21/5/057106 Abstract ( 1697 )   PDF (1088KB) ( 1014 )   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.

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Optical Tamm state polaritons in a quantum well microcavity with gold layers Zhang Wei-Li (张伟利) and Rao Yun-Jiang(饶云江) Chin. Phys. B, 2012, 21 (5):  057107.  DOI: 10.1088/1674-1056/21/5/057107 Abstract ( 1615 )   PDF (685KB) ( 679 )   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.

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The optical phonon effect of quantum rod qubits Wang Cui-Tao(王翠桃), Wu Zhi-Yong(吴志永), Zhao Cui-Lan(赵翠兰), Ding Zhao-Hua(丁朝华), and Xiao Jing-Lin(肖景林) Chin. Phys. B, 2012, 21 (5):  057108.  DOI: 10.1088/1674-1056/21/5/057108 Abstract ( 1446 )   PDF (2049KB) ( 518 )   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.

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A possible mechanism for magnetar soft X-ray/$\gamma$-ray emission Gao Zhi-Fu(高志福), Peng Qiu-He(彭秋和), Wang Na(王娜), and Chou Chih-Kang(邹志刚) Chin. Phys. B, 2012, 21 (5):  057109.  DOI: 10.1088/1674-1056/21/5/057109 Abstract ( 1298 )   PDF (206KB) ( 546 )   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/$\gamma$-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.

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The effect of spin-orbit coupling on magnetoresistance in nonmagnetic organic semiconductors Zhao Jun-Qing(赵俊卿), Ding Meng(丁猛), Zhang Tian-You(张天佑), Zhang Ning-Yu(张宁玉), Pang Yan-Tao(庞岩涛), Ji Yan-Ju(季燕菊), Chen Ying(陈莹), Wang Feng-Xiang(王凤翔), and Fu Gang(付刚) Chin. Phys. B, 2012, 21 (5):  057110.  DOI: 10.1088/1674-1056/21/5/057110 Abstract ( 1745 )   PDF (242KB) ( 1003 )   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.

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Breakdown voltage analysis of Al0.25Ga0.75N/GaN high electron mobility transistors with partial silicon doping in the AlGaN layer Duan Bao-Xing(段宝兴) and Yang Yin-Tang(杨银堂) Chin. Phys. B, 2012, 21 (5):  057201.  DOI: 10.1088/1674-1056/21/5/057201 Abstract ( 1482 )   PDF (562KB) ( 1527 )   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.

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Electric field distribution and effective nonlinear AC and DC responses of graded cylindrical composites Ding Xia(丁霞), Jia Yan-Xia(贾艳霞), and Wei En-Bo(魏恩泊) Chin. Phys. B, 2012, 21 (5):  057202.  DOI: 10.1088/1674-1056/21/5/057202 Abstract ( 1565 )   PDF (176KB) ( 703 )   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.

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Improving lithographic masks with the assistance of indentations Guo Ying-Nan(郭英楠), Li Xu-Feng(李旭峰), Pan Shi(潘石), Wang Qiao(王乔), Wang Shuo(王硕), and Wu Yong-Kuan(吴永宽) Chin. Phys. B, 2012, 21 (5):  057301.  DOI: 10.1088/1674-1056/21/5/057301 Abstract ( 1531 )   PDF (1634KB) ( 686 )   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.

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Plasmons in a free-standing nanorod with a two-dimensional parabolic quantum well caused by surface states Song Ya-Feng(宋亚峰), Lü Yan-Wu(吕燕伍), Wen Wei(文伟), Liu Xiang-Lin(刘祥林), Yang Shao-Yan(杨少延), Zhu Qin-Sheng(朱勤生), and Wang Zhan-Guo(王占国) Chin. Phys. B, 2012, 21 (5):  057302.  DOI: 10.1088/1674-1056/21/5/057302 Abstract ( 1341 )   PDF (4654KB) ( 573 )   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.

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Graphene films grown on sapphire substrates via solid source molecular beam epitaxy Tang Jun(唐军), Kang Chao-Yang(康朝阳), Li Li-Min(李利民), Liu Zhong-Liang(刘忠良), Yan Wen-Sheng(闫文盛), Wei Shi-Qiang(韦世强), and Xu Peng-Shou(徐彭寿) Chin. Phys. B, 2012, 21 (5):  057303.  DOI: 10.1088/1674-1056/21/5/057303 Abstract ( 1757 )   PDF (1089KB) ( 925 )   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.

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A threshold voltage analytical model for high-k gate dielectric MOSFETs with fully overlapped lightly doped drain structures Ma Fei(马飞), Liu Hong-Xia(刘红侠), Kuang Qian-Wei(匡潜玮), and Fan Ji-Bin(樊继斌) Chin. Phys. B, 2012, 21 (5):  057304.  DOI: 10.1088/1674-1056/21/5/057304 Abstract ( 1725 )   PDF (180KB) ( 2204 )   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.

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The influence and explanation of fringing-induced barrier lowering on sub-100 nm MOSFETs with high-k gate dielectrics Ma Fei(马飞), Liu Hong-Xia(刘红侠), Kuang Qian-Wei(匡潜玮), and Fan Ji-Bin(樊继斌) Chin. Phys. B, 2012, 21 (5):  057305.  DOI: 10.1088/1674-1056/21/5/057305 Abstract ( 1654 )   PDF (245KB) ( 1108 )   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.

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Dispersion relation of dust acoustic waves in metallic multi-walled carbon nanotubes Ali Fathalian and Shahram Nikjo Chin. Phys. B, 2012, 21 (5):  057306.  DOI: 10.1088/1674-1056/21/5/057306 Abstract ( 1584 )   PDF (122KB) ( 815 )   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.

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Vortex lines in a ferromagnetic spin-triplet superconductor Zhao Li(赵力), Yang Jie(杨捷), Xie Qun-Ying(谢群英), Tian Miao(田苗), and Duan Yi-Shi(段一士) Chin. Phys. B, 2012, 21 (5):  057401.  DOI: 10.1088/1674-1056/21/5/057401 Abstract ( 1460 )   PDF (225KB) ( 708 )   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 $\delta$ 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 $\phi$-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 $\delta$ -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.

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Interfacial spin Hall current in a Josephson junction with Rashba spin–orbit coupling Yang Zhi-Hong(杨志红), Yang Yong-Hong(杨永宏), and Wang Jun(汪军) Chin. Phys. B, 2012, 21 (5):  057402.  DOI: 10.1088/1674-1056/21/5/057402 Abstract ( 1470 )   PDF (196KB) ( 546 )   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.

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The crystal structure, magnetism, and colossal magnetoresistance of Y2CrS4 Liu Rong-Deng(刘荣灯), Liu Yun-Tao(刘蕴韬), He Lun-Hua(何伦华), Wang Zhi-Cui(王志翠), Chen Dong-Feng(陈东风), and Wang Fang-Wei(王芳卫) Chin. Phys. B, 2012, 21 (5):  057501.  DOI: 10.1088/1674-1056/21/5/057501 Abstract ( 1491 )   PDF (930KB) ( 723 )   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$\times$104% in the semiconducting compound of Y2CrS4.

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Growth and photoluminescence properties of inclined ZnO and ZnCoO thin films on SrTiO3(110) substrates Bai Hong-Liang(白洪亮), Liu Guo-Lei(刘国磊), He Shu-Min(贺树敏), Yan Shi-Shen(颜世申), Zhu Da-Peng(朱大鹏), Guo Hong-Yu(郭红雨), Ji Zi-Wu(冀子武), Yang Feng-Fan(杨丰帆), Chen Yan-Xue(陈延学), and Mei Liang-Mo(梅良模) Chin. Phys. B, 2012, 21 (5):  057801.  DOI: 10.1088/1674-1056/21/5/057801 Abstract ( 1544 )   PDF (309KB) ( 812 )   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[1$\bar{1}$0] and ZnCoO[1$\bar{1}$1]//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.

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Electric potential distribution near nanocone arrays on metal substrates Huang Xiao-Jing(黄晓菁) and You Rong-Yi(游荣义) Chin. Phys. B, 2012, 21 (5):  057802.  DOI: 10.1088/1674-1056/21/5/057802 Abstract ( 1434 )   PDF (1591KB) ( 865 )   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.

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Optical and fast nondestructive identification of the ages of leaded ancient pottery Wu Fang-Yuan (吴方媛) and Yang Xiang-Bo(杨湘波) Chin. Phys. B, 2012, 21 (5):  057803.  DOI: 10.1088/1674-1056/21/5/057803 Abstract ( 1426 )   PDF (3389KB) ( 478 )   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.

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Field emission properties of capped carbon nanotubes doped by alkali metals:a theoretical investigation Jin Lei(靳磊), Fu Hong-Gang(付宏刚), Xie Ying(谢颖), and Yu Hai-Tao(于海涛) Chin. Phys. B, 2012, 21 (5):  057901.  DOI: 10.1088/1674-1056/21/5/057901 Abstract ( 1535 )   PDF (4413KB) ( 720 )   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

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Growth and annealing study of hydrogen-doped single diamond crystals under high pressure and high temperature Li Yong(李勇), Jia Xiao-Peng(贾晓鹏), Hu Mei-Hua(胡美华), Liu Xiao-Bing(刘晓兵), Yan Bing-Min(颜丙敏), Zhou Zhen-Xiang(周振翔), Zhang Zhuang-Fei(张壮飞), and Ma Hong-An(马红安) Chin. Phys. B, 2012, 21 (5):  058101.  DOI: 10.1088/1674-1056/21/5/058101 Abstract ( 1700 )   PDF (3185KB) ( 928 )   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.

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The light-enhanced NO2 sensing properties of porous silicon gas sensors at room temperature Chen Hui-Qing(陈慧卿), Hu Ming(胡明), Zeng Jing(曾晶), and Wang Wei-Dan(王巍丹) Chin. Phys. B, 2012, 21 (5):  058201.  DOI: 10.1088/1674-1056/21/5/058201 Abstract ( 1749 )   PDF (917KB) ( 1740 )   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.

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Analysis and design of the taper in metal-grating periodic slow-wave structures for rectangular Cerenkov masers Chen Ye(陈晔), Zhao Ding(赵鼎), Wang Yong(王勇), and Shu Wen(舒雯) Chin. Phys. B, 2012, 21 (5):  058401.  DOI: 10.1088/1674-1056/21/5/058401 Abstract ( 1685 )   PDF (1156KB) ( 860 )   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.

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Physical modeling based on hydrodynamic simulation for the design of InGaAs/InP double heterojunction bipolar transistors Ge Ji(葛霁), Liu Hong-Gang(刘洪刚), Su Yong-Bo(苏永波), Cao Yu-Xiong(曹玉雄), and Jin Zhi(金智) Chin. Phys. B, 2012, 21 (5):  058501.  DOI: 10.1088/1674-1056/21/5/058501 Abstract ( 1551 )   PDF (187KB) ( 1069 )   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.

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Effects of microwave pulse-width damage on a bipolar transistor Ma Zhen-Yang(马振洋), Chai Chang-Chun(柴常春), Ren Xing-Rong(任兴荣), Yang Yin-Tang(杨银堂), Chen Bin(陈斌), and Zhao Ying-Bo(赵颖博) Chin. Phys. B, 2012, 21 (5):  058502.  DOI: 10.1088/1674-1056/21/5/058502 Abstract ( 1606 )   PDF (1579KB) ( 1387 )   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 $\tau$ 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.

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Highly efficient blue fluorescent OLEDs with doped double emitting layers based on p–n heterojunctions Su Yue-Ju(苏跃举), Wu Xiao-Ming(吴晓明), Hua Yu-Lin(华玉林), Shen Li-Ying(申利莹), Jiao Zhi-Qiang(焦志强), Dong Mu-Sen(董木森), and Yin Shou-Gen(印寿根) Chin. Phys. B, 2012, 21 (5):  058503.  DOI: 10.1088/1674-1056/21/5/058503 Abstract ( 1831 )   PDF (165KB) ( 1484 )   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) $N$,$N^\prime$-bis(naphthalen-1-yl)-$N$,$N^\prime$-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.

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Performance improvement of InGaN blue light-emitting diodes with several kinds of electron-blocking layers Chen Jun(陈峻), Fan Guang-Han(范广涵), Zhang Yun-Yan(张运炎), Pang Wei(庞玮), Zheng Shu-Wen(郑树文), and Yao Guang-Rui(姚光锐) Chin. Phys. B, 2012, 21 (5):  058504.  DOI: 10.1088/1674-1056/21/5/058504 Abstract ( 1680 )   PDF (475KB) ( 829 )   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.

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Transient optical modulation properties in the terahertz metamaterial of split ring resonators Zhou Qing-Li(周庆莉), Shi Yu-Lei(施宇蕾), Wang Ai-Hua(王爱华), Li Lei(李磊), and Zhang Cun-Lin(张存林) Chin. Phys. B, 2012, 21 (5):  058701.  DOI: 10.1088/1674-1056/21/5/058701 Abstract ( 1708 )   PDF (2795KB) ( 718 )   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.

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Preparing Cu2ZnSnS4 films using the co-electro-deposition method with ionic liquids Chen Yong-Sheng(陈永生), Wang Ying-Jun(王英君), Li Rui(李瑞), Gu Jin-Hua(谷锦华), Lu Jing-Xiao(卢景霄), and Yang Shi-E(杨仕娥) Chin. Phys. B, 2012, 21 (5):  058801.  DOI: 10.1088/1674-1056/21/5/058801 Abstract ( 1949 )   PDF (12057KB) ( 8030 )   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.