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    2014年, 第23卷, 第10期 刊出日期:2014-10-15 上一期    下一期
    New interaction solutions of the Kadomtsev-Petviashvili equation
    刘希忠, 俞军, 任博, 杨建荣
    2014 (10):  100201-100201.  doi: 10.1088/1674-1056/23/10/100201
    摘要 ( 182 )   PDF(221KB) ( 702 )  
    The residual symmetry relating to the truncated Painlevé expansion of the Kadomtsev-Petviashvili (KP) equation is nonlocal, which is localized in this paper by introducing multiple new dependent variables. By using the standard Lie group approach, new symmetry reduction solutions for the KP equation are obtained based on the general form of Lie point symmetry for the prolonged system. In this way, the interaction solutions between solitons and background waves are obtained, which are hard to find by other traditional methods.
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    Transmission time in the reflectionless complex potential
    殷澄, 王贤平, 单鸣雷, 韩庆邦, 朱昌平
    2014 (10):  100301-100301.  doi: 10.1088/1674-1056/23/10/100301
    摘要 ( 121 )   PDF(507KB) ( 513 )  
    A phase time definition directly obtained from the Schrödinger equation is used to investigate the time delay of a particle scattered by complex reflectionless potential. The artifacts introduced by truncating in the numerical simulation are clarified. The time delay of the transmitted wave packet is found to be equal to the reflection time of the truncated potential. Both time delays are the same as the traversal time in the free space, but shorter than the time taken by a classical particle to pass the same potential.
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    Relative ordering of square-norm distance correlations in open quantum systems
    吴韬, 宋学科, 叶柳
    2014 (10):  100302-100302.  doi: 10.1088/1674-1056/23/10/100302
    摘要 ( 177 )   PDF(412KB) ( 376 )  
    We investigate the square-norm distance correlation dynamics of the Bell-diagonal states under different local decoherence channels, including phase flip, bit flip, and bit-phase flip channels by employing the geometric discord (GD) and its modified geometric discord (MGD), as the measures of the square-norm distance correlations. Moreover, an explicit comparison between them is made in detail. The results show that there is no distinct dominant relative ordering between them. Furthermore, we obtain that the GD just gradually deceases to zero, while MGD initially has a large freezing interval, and then suddenly changes in evolution. The longer the freezing interval, the less the MGD is. Interestingly, it is shown that the dynamic behaviors of the two geometric discords under the three noisy environments for the Werner-type initial states are the same.
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    Hybrid double-dot qubit measurement with a quantum point contact
    严蕾, 殷雯, 王芳卫
    2014 (10):  100303-100303.  doi: 10.1088/1674-1056/23/10/100303
    摘要 ( 208 )   PDF(705KB) ( 535 )  
    We present the measurement of a hybrid double-dot qubit using a quantum point contact (QPC). To study the dynamics, we derive the rate equations of the entire system. Numerical results show that QPC current can directly reflect the evolution of the qubit. By adjusting Coulomb interaction, energy mismatch, and QPC tunneling rate, the efficiency and dephasing time can be improved. In addition, the initial state with a hybrid triplet state is superior to that with the purely triplet states on the efficiency. Moreover, the decoherence time is estimated on the magnitude of a microsecond, long enough to implement quantum operations.
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    Security of biased BB84 quantum key distribution with finite resource
    赵良圆, 李宏伟, 银振强, 陈巍, 尤娟, 韩正甫
    2014 (10):  100304-100304.  doi: 10.1088/1674-1056/23/10/100304
    摘要 ( 200 )   PDF(394KB) ( 504 )  
    In the original BB84 quantum key distribution protocol, the states are prepared and measured randomly, which lose the unmatched detection results. To improve the sifting efficiency, biased bases selection BB84 protocol is proposed. Meanwhile, a practical quantum key distribution protocol can only transmit a finite number of signals, resulting in keys of finite length. The previous techniques for finite-key analysis focus mainly on the statistical fluctuations of the error rates and yields of the qubits. However, the prior choice probabilities of the two bases also have fluctuations by taking into account the finite-size effect. In this paper, we discuss the security of biased decoy state BB84 protocol with finite resources by considering all of the statistical fluctuations. The results can be directly used in the experimental realizations.
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    Excitations of optomechanically driven Bose–Einstein condensates in a cavity: Photodetection measurements
    Neha Aggarwal, Sonam Mahajan, Aranya B. Bhattacherjee, Man Mohan
    2014 (10):  100305-100305.  doi: 10.1088/1674-1056/23/10/100305
    摘要 ( 139 )   PDF(523KB) ( 387 )  
    We present a detailed study to analyze the Dicke quantum phase transition within the thermodynamic limit for an optomechanically driven Bose-Einstein condensate in a cavity. The photodetection-based quantum optical measurements have been performed to study the dynamics and excitations of this optomechanical Dicke system. For this, we discuss the eigenvalue analysis, fluorescence spectrum and the homodyne spectrum of the system. It has been shown that the normal phase is negligibly affected by the mechanical mode of the mirror while it has a significant effect in the superradiant phase. We have observed that the eigenvalues and the spectra both exhibit distinct features that can be identified with the photonic, atomic and phononic branches. In the fluorescence spectra, we further observe an asymmetric coherent energy exchange between the three degrees of freedom of the system in the superradiant phase arising as a result of optomechanical interaction and Bloch-Siegert shift.
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    Relativistic symmetries of Deng–Fan and Eckart potentials with Coulomb-like and Yukawa-like tensor interactions
    Akpan N. Ikot, S. Zarrinkamar, B. H. Yazarloo, H. Hassanabadi
    2014 (10):  100306-100306.  doi: 10.1088/1674-1056/23/10/100306
    摘要 ( 171 )   PDF(1002KB) ( 476 )  
    Relativistic symmetries of the Dirac equation under spin and pseudo-spin symmetries are investigated and a combination of Deng-Fan and Eckart potentials with Coulomb-like and Yukawa-like tensor interaction terms are considered. The energy equation is obtained by using the Nikiforov-Uvarov method and the corresponding wave functions are expressed in terms of the hypergeometric functions. The effects of the Coulomb and Yukawa tensor interactions are numerically discussed as well.
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    A full quantum network scheme
    马海强, 韦克金, 杨建会, 李瑞雪, 朱武
    2014 (10):  100307-100307.  doi: 10.1088/1674-1056/23/10/100307
    摘要 ( 238 )   PDF(281KB) ( 412 )  
    We present a full quantum network scheme using a modified BB84 protocol. Unlike other quantum network schemes, it allows quantum keys to be distributed between two arbitrary users with the help of an intermediary detecting user. Moreover, it has good expansibility and prevents all potential attacks using loopholes in a detector, so it is more practical to apply. Because the fiber birefringence effects are automatically compensated, the scheme is distinctly stable in principle and in experiment. The simple components for every user make our scheme easier for many applications. The experimental results demonstrate the stability and feasibility of this scheme.
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    Thermodynamics of a two-dimensional charged black holein the geometric framework
    韩亦文, 洪云
    2014 (10):  100401-100401.  doi: 10.1088/1674-1056/23/10/100401
    摘要 ( 140 )   PDF(183KB) ( 333 )  
    In this paper, we study the thermodynamic features of a two-dimensional charged black hole. Weinhold curvature and Ruppeiner curvature are explored as information geometry, respectively. Moreover, based on the Legendre invariant proposed by Hernando Quevedo, the geometro-thermodynamics behavior of this black hole is investigated.
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    Generalized projective synchronization of the fractional-order chaotic system using adaptive fuzzy sliding mode control
    王立明, 唐永光, 柴永泉, 吴峰
    2014 (10):  100501-100501.  doi: 10.1088/1674-1056/23/10/100501
    摘要 ( 207 )   PDF(1342KB) ( 532 )  
    An adaptive fuzzy sliding mode strategy is developed for the generalized projective synchronization of a fractional-order chaotic system, where the slave system is not necessarily known in advance. Based on the designed adaptive update laws and the linear feedback method, the adaptive fuzzy sliding controllers are proposed via the fuzzy design, and the strength of the designed controllers can be adaptively adjusted according to the external disturbances. Based on the Lyapunov stability theorem, the stability and the robustness of the controlled system are proved theoretically. Numerical simulations further support the theoretical results of the paper and demonstrate the efficiency of the proposed method. Moreover, it is revealed that the proposed method allows us to manipulate arbitrarily the response dynamics of the slave system by adjusting the desired scaling factor λi and the desired translating factor ηi, which may be used in a channel-independent chaotic secure communication.
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    Periodic solitons in dispersion decreasingfibers with a cosine profile
    贾仁需, 闫宏丽, 刘文军, 雷鸣
    2014 (10):  100502-100502.  doi: 10.1088/1674-1056/23/10/100502
    摘要 ( 193 )   PDF(1840KB) ( 379 )  
    Periodic solitons are studied in dispersion decreasing fibers with a cosine profile. The variable-coefficient nonlinear Schrödinger equation, which can be used to describe the propagation of solitons, is investigated analytically. Analytic soliton solutions for this equation are derived with the Hirota's bilinear method. Using the soliton solutions, we obtain periodic solitons, and analyze the soliton characteristics. Influences of physical parameters on periodic solitons are discussed. The presented results can be used in optical communication systems and fiber lasers.
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    Drift coefficients of motor proteins moving along sidesteps
    2014 (10):  100503-100503.  doi: 10.1088/1674-1056/23/10/100503
    摘要 ( 110 )   PDF(210KB) ( 318 )  
    In the paper, we investigate two motor proteins moving along the sidesteps: a motor protein moving along a two-dimensional sidestep and another protein moving along a three-dimensional sidestep. The drift coefficients (or stationary average velocities) of these two motor proteins are calculated. We believe that our investigation of the motor proteins moving along the sidesteps in the present paper can benefit the investigation of the transport of the motor proteins to some extent.
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    Finite-time sliding mode synchronization of chaotic systems
    倪骏康, 刘崇新, 刘凯, 刘凌
    2014 (10):  100504-100504.  doi: 10.1088/1674-1056/23/10/100504
    摘要 ( 375 )   PDF(1085KB) ( 629 )  
    A new finite-time sliding mode control approach is presented for synchronizing two different topological structure chaotic systems. With the help of the Lyapunov method, the convergence property of the proposed control strategy is discussed in a rigorous manner. Furthermore, it is mathematically proved that our control strategy has a faster convergence speed than the conventional finite-time sliding mode control scheme. In addition, the proposed control strategy can ensure the finite-time synchronization between the master and the slave chaotic systems under internal uncertainties and external disturbances. Simulation results are provided to show the speediness and robustness of the proposed scheme. It is worth noticing that the proposed control scheme is applicable for secure communications.
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    Theoretical study of γ-aminobutyric acid conformers: Intramolecular interactions and ionization energies
    王克栋, 王美婷, 孟举
    2014 (10):  103101-103101.  doi: 10.1088/1674-1056/23/10/103101
    摘要 ( 190 )   PDF(413KB) ( 312 )  
    Allowing for all combinations of internal single-bond rotamers, 1,296 unique trial structures of γ-Aminobutyric acid (GABA) are obtained. All of these structures are optimized at the M06-2X level of theory and a total of 68 local minimal conformers are found. The nine low-lying conformers are used for further studies. According to the calculated relative Gibbs free energies at M06-2X level of theory, we find that the dispersion is important for the relative energy of GABA. The intramolecular hydrogen bonds and hyperconjugative interaction and their effects on the conformational stability are studied. The results show that both of them have great influence on the conformers. The vertical ionization energies (VIE) are calculated and match the experimental data well. The results show that the neutral GABA in the gas phase is a multi-conformer system and at least four conformations exist.
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    Nonlinear spectroscopy of barium in parallel electric and magnetic fields
    杨海峰, 高伟, 成红, 刘红平
    2014 (10):  103201-103201.  doi: 10.1088/1674-1056/23/10/103201
    摘要 ( 173 )   PDF(379KB) ( 709 )  
    We report on the experimental spectral observations of barium in parallel electric and magnetic fields. The laser pulse is linearly polarized along or perpendicular to the fields, leading to the states m=0 and the states m=±1 populated, respectively, by one photon excitation. By sweeping the electric field, we observe the linear and nonlinear splitting of the diamagnetic spectrum as the electric field increases. The spectral anticrossing is induced by the atomic core effect. The Stark spectrum also shows an obvious nonlinear quadratic behavior when the applied magnetic field varies strongly. All spectra are well explained by the full quantum calculation after taking the quantum defect effects of the channel ns up to nf into account.
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    Time-dependent approach to the double-channel dissociation of the NaCs molecule induced by pulsed lasers
    张彩霞, 牛余全, 孟庆田
    2014 (10):  103301-103301.  doi: 10.1088/1674-1056/23/10/103301
    摘要 ( 182 )   PDF(360KB) ( 411 )  
    The dynamics of the double-channel dissociation of the NaCs molecule is investigated by using the time-dependent wave packet (TDWP) method with the “split operator-Fourier transform” scheme. At a given wavelength and intensity of laser pulse, the population of each state changing with time is obtained. The photo-absorption spectra and kinetic-energy distribution of the dissociation fragments, which exhibit vibration-level structure and dispersion of the wave packet, respectively, are also obtained. The results show that by increasing the laser intensity, one can find not only the band center shift of the photo-absorption spectrum, but also the change of the fragment energy. The appearance of the diffusive band in the photo-absorption spectrum and the multiple peaks in the kinetic-energy spectrum can be attributed to the effects of the predissociation limit and the external field.
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    Nonsequential double ionization of diatomic molecules by elliptically polarized laser pulses
    童爱红, 刘丹, 冯国强
    2014 (10):  103302-103302.  doi: 10.1088/1674-1056/23/10/103302
    摘要 ( 141 )   PDF(930KB) ( 434 )  
    Using the classical ensemble method, we investigate nonsequential double ionization (NSDI) of diatomic molecules by elliptically polarized laser pulses. The results show that the ellipticity of the laser field has a strong suppression effect on NSDI probabilities both in parallel and perpendicular alignments. The double ionization (DI) channel is commonly dominated by NSDI, and the NSDI channel changes with ellipticity. As ellipticity increases, more and more NSDIs occur through recollision excitation with subsequent field ionization (RESI). Moreover, like the case of linear polarization, the two electrons involved in NSDI for perpendicularly aligned molecules are more likely to emit into the opposite hemispheres as compared to the case of parallel alignment. Additionally, this alignment effect increases as ellipticity increases.
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    Optical and magneto-optical properties of periodic Co double layer film
    夏文斌, 高锦龙, 张绍银, 陈乐易, 唐妍梅, 唐少龙, 都有为
    2014 (10):  103303-103303.  doi: 10.1088/1674-1056/23/10/103303
    摘要 ( 180 )   PDF(694KB) ( 418 )  
    Co double layer film (CoDLF) consisting of a disk-array layer and an antidot-array layer, both with square order, was investigated. Both the reflectivity and Kerr spectra of CoDLF show anisotropic effects when the azimuthal angle of incident light changes. From the simulation result of surface plasmon polaritons (SPPs), we attribute the reflectivity minima and Kerr angle maxima in the spectra mainly to the excitation of different diffractional orders' SPPs. More interestingly, the Kerr angle changes sign at specific wavelengths. We attribute these phenomena to the excitation of SPPs and localized surface plasmons (LSPs), and the interaction between them.
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    Interferences in photo-detached electron spectra froma non-collinear tri-atomic anion
    A. Afaq, K. Farooq, M. A. Khan, 衣学喜
    2014 (10):  103304-103304.  doi: 10.1088/1674-1056/23/10/103304
    摘要 ( 155 )   PDF(1853KB) ( 452 )  
    The electron flux oscillations in photo-detachment of a non-collinear tri-atomic anion have been studied by taking each atom of the system as a coherent source of detached-electron wave. These electron waves traversing along three different trajectories result in a quantum interference. An analytical expression of detached-electron flux is evaluated for various detached-electron energies and for different geometrical shapes of the system. The results show that the electron flux distributions exhibit molecular shape-induced oscillatory structures. These oscillations are explained using the semi-classical closed-orbit theory; the outgoing electron waves produced from one center are propagated in the vicinity of the sources at other centers. It is also observed that in a particular case our non-collinear tri-atomic system reduces to the collinear tri-atomic system recently published.
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    Universal form of the power spectrum of the aero-optical aberration caused by the supersonic turbulent boundary layer
    高穹, 易仕和, 姜宗福
    2014 (10):  104201-104201.  doi: 10.1088/1674-1056/23/10/104201
    摘要 ( 163 )   PDF(362KB) ( 388 )  
    Based on the measurement of one-dimensional (1D) optical path difference (OPD) of the supersonic turbulent boundary layer, an analytical form for the power spectrum of the two-dimensional (2D) OPD is obtained with its structure function and under the locally homogeneous isotropic assumption. The universality of this spectrum is argued, and its validity is checked by the comparison with experimental result. The potential applications of this model in theoretical and numerical studies are emphasized. Another contribution of this work is around the application of correlation function to analyzing the statistics of OPD. Based on our results and other results published elsewhere, we show that the OPD is often not stationary, and one should be cautious about using this tool.
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    Analysis of detection limit to time-resolved coherent anti-Stokes Raman scattering nanoscopy
    刘伟, 刘双龙, 陈丹妮, 牛憨笨
    2014 (10):  104202-104202.  doi: 10.1088/1674-1056/23/10/104202
    摘要 ( 203 )   PDF(268KB) ( 445 )  
    In the implementation of CARS nanoscopy, signal strength decreases with focal volume size decreasing. A crucial problem that remains to be solved is whether the reduced signal generated in the suppressed focal volume can be detected. Here reported is a theoretical analysis of detection limit (DL) to time-resolved CARS (T-CARS) nanoscopy based on our proposed additional probe-beam-induced phonon depletion (APIPD) method for the low concentration samples. In order to acquire a detailed shot-noise limited signal-to-noise (SNR) and the involved parameters to evaluate DL, the T-CARS process is described with full quantum theory to estimate the extreme power density levels of the pump and Stokes beams determined by saturation behavior of coherent phonons, which are both actually on the order of ~ 1019 W/cm2. When the pump and Stokes intensities reach such values and the total intensity of the excitation beams arrives at a maximum tolerable by most biological samples in a certain suppressed focal volume (40-nm suppressed focal scale in APIPD method), the DL correspondingly varies with exposure time, for example, DL values are 103 and 102 when exposure times are 20 ms and 200 ms respectively.
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    Scattering properties of polluted dust in 1.6-μm wavelength
    范萌, 陈良富, 李莘莘, 陶金花, 苏林, 邹铭敏
    2014 (10):  104203-104203.  doi: 10.1088/1674-1056/23/10/104203
    摘要 ( 183 )   PDF(2242KB) ( 378 )  
    Three typical polluted dust particles (i.e., single coated dust, two-sphere/spheroid system, and coated dust with aggregate) including internal and semi-external mixtures are modeled, and their scattering properties at 1.6-μm wavelength are calculated by using the generalized multi-sphere Mie-solution (GMM) method. We investigate the influences of particle size, morphology, and chemical composition on the scattering parameters of polluted dust particles. The analysis results demonstrate that the single scattering albedo of coated dust is much smaller than that of pure dust, especially for the spheroidal black carbon (BC) coated dust. When a dust particle semi-mixes with another aerosol particle to form a two-sphere/spheroid system, its scattering properties are much more sensitive to the size and species of monomers than the monomer shape. If an aggregated BC attaches to the coated dust, the scattering properties of whole particle mainly depend on the host particle (coated dust).
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    Measurement-induced disturbance between two atoms in Tavis–Cummings model with dipole–dipole interaction
    张国锋, 王骁, 吕广宏
    2014 (10):  104204-104204.  doi: 10.1088/1674-1056/23/10/104204
    摘要 ( 150 )   PDF(743KB) ( 418 )  
    Quantum correlation, measured by measurement-induced disturbance (MID), between two two-level atoms is investigated in detail in Tavis-Cummings model with dipole-dipole interaction (DDI). We find that MID can be determined only by the dipole-dipole interaction between the two atoms when the cavity and atoms are at resonance. Moreover, DDI will have different effects on MID for two different kinds of initial states.
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    Phase control of group-velocity-based biexciton coherence ina multiple quantum well nanostructure
    Seyyed Hossein Asadpour, H. Rahimpour Soleimani
    2014 (10):  104205-104205.  doi: 10.1088/1674-1056/23/10/104205
    摘要 ( 148 )   PDF(410KB) ( 372 )  
    A double cascade-type four-level multiple-quantum-well-based exciton-biexciton transitions are proposed. The study is carried out on a 4.8-nm ZnSe single-quantum well which is embedded into ZnMgSSe cladding layers and pseudomorphically grown by molecular beam epitaxy on a (0 0 1) GaAs substrate. It is displayed that the exciton spin relaxation and relative phases between applied fields can influence the transient and steady-state behaviors of absorption, dispersion, and group velocity of two weak probe and signal fields. Also, transient behaviors of electron population of different levels are discussed. It is found that the probe or signal amplification occurs in the absence of population inversion.
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    227-W output all-fiberized Tm-doped fiber laser at 1908 nm
    胡震岳, 闫平, 肖起榕, 柳强, 巩马理
    2014 (10):  104206-104206.  doi: 10.1088/1674-1056/23/10/104206
    摘要 ( 341 )   PDF(457KB) ( 745 )  
    In this paper, we report that a diode-pumped thulium-doped double clad silica fiber laser can provide powers of up to 227 W at 1908 nm, corresponding to a slope efficiency of 54.3%, and an optical-to-optical efficiency of 51.2%. The output power, to the best of our knowledge, is the highest output at 1908 nm. The beam quality M2 factor is about 1.56. Also discussed in this paper is the dependence of the laser performance on fiber length.
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    Material growth and device fabrication of terahertz quantum-cascade laser based on bound-to-continuum structure
    尹嵘, 万文坚, 张真真, 谭智勇, 曹俊诚
    2014 (10):  104207-104207.  doi: 10.1088/1674-1056/23/10/104207
    摘要 ( 232 )   PDF(345KB) ( 575 )  
    The terahertz quantum-cascade laser (THz QCL) based on bound-to-continuum structure is demonstrated. The X-ray diffraction measurement of the material shows a high crystalline quality of the active region. A THz QCL device was fabricated with semi-insulating surface-plasmon waveguide. The test device is lasing at about 3 THz and operating up to 60 K. It shows a single frequency property under different drive currents and temperatures. At 9 K, the maximum output power is greater than 2 mW with a threshold current density of 159 A/cm2.
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    Nonlinear polarization rotation-induced pulse shaping in a stretched-pulse ytterbium-doped fiber laser
    白东碧, 李文雪, 杨康文, 沈旭玲, 陈修亮, 曾和平
    2014 (10):  104208-104208.  doi: 10.1088/1674-1056/23/10/104208
    摘要 ( 215 )   PDF(1977KB) ( 624 )  
    We report on controllable pulse shaping in a Yb-doped stretched-pulse fiber laser followed by a high-power chirped pulse amplifier. We demonstrate that the pulses after an extra-cavity grating pair change their intensity profile from Lorentz to Gaussian and then to sech2 shapes by adjusting the intra-cavity polarization through a quarter-wave plate inside the fiber laser cavity. The laser pulses with different pulse shapes exhibit pulse-to-pulse amplitude fluctuation of ~ 1.02%, while the sech2-shaped pulse train is provided with a more stable free-running repetition rate as a result of the stronger self-phase modulation in the fiber laser cavity than Lorentz-and Gaussian-shaped pulse trains.
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    Resonant cavity-enhanced quantum dot field-effect transistor as a single-photon detector
    董宇, 王广龙, 王红培, 倪海桥, 陈建辉, 高凤岐, 乔中涛, 杨晓红, 牛智川
    2014 (10):  104209-104209.  doi: 10.1088/1674-1056/23/10/104209
    摘要 ( 159 )   PDF(542KB) ( 536 )  
    A resonant cavity-enhanced (RCE) quantum dot (QD) field-effect transistor (RCEQDFET) is designed for single-photon detection in this paper. Adding distributed Bragg reflection (DBR) mirrors to the single-photon detector (SPD), we improve the light absorption efficiency of the SPD. The effects of the reflectivity of the mirrors, the thickness and light absorption coefficient of the absorbing layer on the detector's light absorption efficiency are investigated, and the resonant cavity is determined by using the air/semiconductor interface as the mirror on the top. Through analyzing the relationship between the refractive index of AlxGa1-xAs and Al component, we choose AlAs/Al0.15Ga0.85As as the material of the mirror on the bottom. The pairs of AlAs/Al0.15Ga0.85As film are further determined to be 21 by calculating the reflectivity of the mirror. The detector is fabricated from semiconductor heterostructures grown by molecular beam epitaxy. The reflection spectrum, photoluminescence (PL) spectrum, photocurrent response, and channel current of the detector are tested and the results show that the RCEQDFET-SPD designed in this paper has better performances in photonic response and wavelength selection.
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    Carrier-envelope phase effects on high-harmonic generation driven by mid-infrared laser field
    刁寒虎, 郑颖辉, 钟悦, 曾志男, 葛晓春, 李闯, 李儒新, 徐至展
    2014 (10):  104210-104210.  doi: 10.1088/1674-1056/23/10/104210
    摘要 ( 206 )   PDF(884KB) ( 768 )  
    The influence of the carrier-envelope phase on high-harmonic generation is investigated, both experimentally and theoretically, for three different interaction gas media, driven by mid-infrared, few-cycle and CEP-stabilized laser pulses. Different patterns of harmonic spectra with varying CEP for the three interaction gas media are observed. Furthermore, in comparing our experiment results to the previous works driven by near-infrared laser pulses, different phenomena are found. Through numerical simulation, we find that for the two different kinds of driving fields, i.e. mid-infrared and near-infrared laser pulses, different kinds of electron trajectories contribute to the generation of high harmonics.
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    Wavelength-dependence of double optical gating for attosecond pulse generation
    田佳, 黎敏, 于济洲, 邓勇开, 刘运全
    2014 (10):  104211-104211.  doi: 10.1088/1674-1056/23/10/104211
    摘要 ( 147 )   PDF(311KB) ( 414 )  
    Both polarization gating (PG) and double optical gating (DOG) are productive methods to generate single attosecond (as) pulses. In this paper, considering the ground-state depletion effect, we investigate the wavelength-dependence of the DOG method in order to optimize the generation of single attosecond pulses for the future application. By calculating the ionization probabilities of the leading edge of the pulse at different driving laser wavelengths, we obtain the upper limit of duration for the driving laser pulse for the DOG setup. We find that the upper limit duration increases with the increase of laser wavelength. We further describe the technical method of choosing and calculating the thickness values of optical components for the DOG setup.
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    Code synchronization based on lumped time-delay compensation scheme with a linearly chirped fiber Bragg grating in all-optical analog-to-digital conversion
    王涛, 康哲, 苑金辉, 田野, 颜玢玢, 桑新柱, 余重秀
    2014 (10):  104212-104212.  doi: 10.1088/1674-1056/23/10/104212
    摘要 ( 161 )   PDF(445KB) ( 437 )  
    We propose a novel lumped time-delay compensation scheme for all-optical analog-to-digital conversion based on soliton self-frequency shift and optical interconnection techniques. A linearly chirped fiber Bragg grating is optimally designed and used to compensate for the entire time-delays of the quantized pulses precisely. Simulation results show that the compensated coding pulses are well synchronized with a time difference less than 3.3 ps, which can support a maximum sampling rate of 151.52 GSa/s. The proposed scheme can efficiently reduce the structure complexity and cost of all-optical analog-to-digital conversion compared to the previous schemes with multiple optical time-delay lines.
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    Higher-order solitons in amplitude-disordered waveguide arrays
    刘海东, 金洪震, 董亮伟
    2014 (10):  104213-104213.  doi: 10.1088/1674-1056/23/10/104213
    摘要 ( 165 )   PDF(3338KB) ( 403 )  
    We investigate the existence and stability of different families of spatial solitons in optical waveguide arrays whose amplitudes obey a disordered distribution. The competition between focusing nonlinearity and linearly disordered refractive index modulation results in the formation of spatial localized nonlinear states. Solitons originating from Anderson modes with few nodes are robust during propagation. While multi-peaked solitons with in-phase neighboring components are completely unstable, multipole-mode solitons whose neighboring components are out-of-phase can propagate stably in wide parameter regions provided that their power exceeds a critical value. Our findings, thus, provide the first example of stable higher-order nonlinear states in disordered systems.
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    Nonlinear modes in rotating double well potential with parity-time symmetry
    庞玮, 付神贺, 吴剑雄, 黎永耀, 麦志杰
    2014 (10):  104214-104214.  doi: 10.1088/1674-1056/23/10/104214
    摘要 ( 161 )   PDF(422KB) ( 453 )  
    We investigate the nonlinear modes in a rotating double well potential with PT symmetry. Focus on the existence and stability of the nonlinear PT modes in this system, we found that five types of PT modes can stably exist by given certain parameter settings. The multistable area between these modes are studied numerically and the bistable and tristable areas are delimited. With different input trial wavefunctions, five types of solitary wave modes are identified. We found that the rotating of the potential can significantly affect the power flow of the fundamental harmonic mode, whose effect is absent for the other modes.
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    Description and reconstruction of one-dimensional photoniccrystal by digital signal processing theory
    张娟, 付文鹏, 张荣军, 王阳
    2014 (10):  104215-104215.  doi: 10.1088/1674-1056/23/10/104215
    摘要 ( 140 )   PDF(736KB) ( 377 )  
    A method of describing one-dimensional photonic crystals (1DPCs) based on Z-domain digital signal processing theory is presented. The analytical expression of the target band gap spectrum in the digital domain is obtained by the autocorrelation of its impulse response. The feasibility of this method is verified by reconstructing two simple 1DPC structures with a target photonic band gap obtained by the traditional transfer matrix method. This method provides an effective approach to function-guided designs of interference-based band gap structures for photonic applications.
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    Theory study on a photonic-assisted radio frequency phase shifter with direct current voltage control
    李晶, 宁提纲, 裴丽, 简伟, 油海东, 温晓东, 陈宏尧, 张婵, 郑晶晶
    2014 (10):  104216-104216.  doi: 10.1088/1674-1056/23/10/104216
    摘要 ( 154 )   PDF(550KB) ( 360 )  
    A photonic-assisted radio frequency phase shifter with direct current voltage control is proposed using a polymer-based integrated Mach-Zehnder modulator. A closed-form expression of radio frequency (RF) signal power and phase is given. Theoretical calculation reveals that by carefully setting the bias voltages, RF signal power variation lower than 1-dB and phase accuracy less than 3° can be achieved and are not degraded by perturbation of modulation index once the bias voltage drift is kept within -3% ~ 3%.
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    Improved partial response maximum likelihood method combining modulation code for signal waveform modulation multi-level disc
    王鹤群, 裴京, 潘龙法
    2014 (10):  104217-104217.  doi: 10.1088/1674-1056/23/10/104217
    摘要 ( 188 )   PDF(453KB) ( 353 )  
    In this paper, we describe an improved adaptive partial response maximum likelihood (PRML) method combining modulation code for signal waveform modulation multi-level disc. This improved adaptive PRML method employs partial response equalizer and adaptive viterbi detector combining modulation code. Compared with the traditional adaptive PRML detector, the improved PRML detector additionally employs illogical sequence detector and corrector. Illogical sequence detector and corrector can avoid the appearance of illogical sequences effectively, which do not follow the law of modulation code for signal waveform modulation multi-level disc, and obtain the correct sequences. We implement the improved PRML detector using a DSP and an FPGA chip. The experimental results show good performance. The higher efficient and lower complexity can be obtained by using the improved PRML method than by using the previous PRML method. Meanwhile, resource utilization of the improved PRML detector is not changed, but the bit error rate (BER) is reduced by more than 20%.
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    Designing of a polarization beam splitter for the wavelength of1310 nm on dual-core photonic crystal fiber with high birefringence and double-zero dispersion
    鲍亚杰, 李曙光, 张婉, 安国文, 范振凯
    2014 (10):  104218-104218.  doi: 10.1088/1674-1056/23/10/104218
    摘要 ( 280 )   PDF(1140KB) ( 790 )  
    We have proposed a novel kind of photonic crystal fiber which contains two asymmetric cores. The birefringence and the dispersion are numerically analyzed based on finite element method when the size of the air holes and the pitch of two adjacent air holes are changed. It is shown that the proposed photonic crystal fiber has high birefringence up to the order of 10-2 and double-zero dispersion points are at the wavelengths of 1310 nm and 800 nm, simultaneously. At the same time, the normalized power and the extinction ratios of the proposed photonic crystal fiber have been simulated. It is demonstrated that, at the wavelength of 1310 nm, the x-polarized mode and the y-polarized mode are separated when the propagation distance is 2.481 mm.
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    Highly sensitive fiber refractive index sensor based on side-core holey structure
    韩雅, 夏历, 刘德明
    2014 (10):  104219-104219.  doi: 10.1088/1674-1056/23/10/104219
    摘要 ( 226 )   PDF(797KB) ( 550 )  
    We propose a side-core holey fiber (SCHF)-based surface plasmon resonance (SPR) sensor to achieve high refractive index (RI) sensitivity. The SCHF structure can facilitate analyte filling and enhance the overlapping area of the core mode and surface plasmon polariton (SPP) mode. The coupling properties of the sensor are analyzed by numerical simulation. The maximum sensitivity of 5000 nm/RIU in an RI range of 1.33-1.44, and the average sensitivity of 9295 nm/RIU in an RI range from 1.44 to 1.54 can be obtained.
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    Passive polarization rotator based on silica photonic crystal fiber for 1.31-μm and 1.55-μm bands via adjusting the fiber length
    陈雷, 张伟刚, 王丽, 白志勇, 张珊珊, 王标, 严铁毅, Jonathan Sieg
    2014 (10):  104220-104220.  doi: 10.1088/1674-1056/23/10/104220
    摘要 ( 233 )   PDF(4108KB) ( 451 )  
    A new polarization rotator based on the silica photonic crystal fiber is proposed. The proposed polarization rotator photonic crystal fiber (PR-PCF) possesses a triangle jigsaw-shape core region. The full-vector finite-element method is used to analyze the phenomenon of polarization conversion between the quasi-TE and quasi-TM modes. Numerical simulations show that the wavelengths of 1.31 μm and 1.55 μm are converted with a nearly 100% polarization conversion ratio with their matched coupling length and has a relatively strong realistic fabrication tolerance-100 nm on the y axis and 50 nm on the x axis. The full vectorial finite difference beam propagation method is used to confirm the performance of the proposed PR-PCF.
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    Influence of mode competition on beam quality of fiber amplifier
    肖起榕, 闫平, 孙骏逸, 陈霄, 任海翠, 巩马理
    2014 (10):  104221-104221.  doi: 10.1088/1674-1056/23/10/104221
    摘要 ( 191 )   PDF(462KB) ( 682 )  
    Theoretical and experimental studies of the influence of the mode competition on the output beam quality of fiber amplifiers are presented. Rate equations and modal decomposition method are used in the theoretical model. In the experiment, the output beam-quality factor of a fiber amplifier, which is based on a Yb-doped double-clad large mode area fiber as a function of the seed beam quality and the pump power of the amplifier, is measured. The experimental results are consistent with the theoretical analysis.
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    Laser frequency stabilization and shifting by usingmodulation transfer spectroscopy
    程冰, 王兆英, 吴彬, 许翱鹏, 王启宇, 徐云飞, 林强
    2014 (10):  104222-104222.  doi: 10.1088/1674-1056/23/10/104222
    摘要 ( 276 )   PDF(933KB) ( 2566 )  
    The stabilizing and shifting of laser frequency are very important for the interaction between the laser and atoms. The modulation transfer spectroscopy for the 87Rb atom with D2 line transition F=2→F'=3 is used for stabilizing and shifting the frequency of the external cavity grating feedback diode laser. The resonant phase modulator with electro–optical effect is used to generate frequency sideband to lock the laser frequency. In the locking scheme, circularly polarized pump-and probe-beams are used. By optimizing the temperature of the vapor, the pump-and probe-beam intensity, the laser linewidth of 280 kHz is obtained. Furthermore, the magnetic field generated by a solenoid is added into the system. Therefore the system can achieve the frequency locking at any point in a range of hundreds of megahertz frequency shifting with very low power loss.
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    Er3+ ion concentration effect on transient and steady-state behaviorin Er3+ :YAG crystal
    Asadpour Seyyed Hossein, Rahimpour Soleimani H
    2014 (10):  104223-104223.  doi: 10.1088/1674-1056/23/10/104223
    摘要 ( 235 )   PDF(368KB) ( 356 )  
    The effect of Er3+ ion concentration on transient and steady-state behavior in 45-nm Er3+ :YAG crystal is investigated. It is shown that by changing the signal field, the coherent field and the concentration of Er3+ ions in the crystal, the absorption, dispersion, and group index of the weak probe field can be adjusted. Also, it is found that the probe absorption occurs in the presence of population inversion and probe amplification is obtained in the absence of population inversion.
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    Preparation and characterization of nanosized GdxBi0.95-x VO4:0.05Eu3+ solid solution as red phosphor
    易娟, 邱建备, 王宇岸, 周大成
    2014 (10):  104224-104224.  doi: 10.1088/1674-1056/23/10/104224
    摘要 ( 254 )   PDF(1605KB) ( 1457 )  
    A complete solid solutions with monophasic zircon-type structure of vanadates of formula GdxBi0.95-xVO4:0.05Eu3+ (x=0-0.95) are synthesized by combined method of co-precipitation and hydrothermal synthesis. Their microstructures and morphologies are characterized by X-ray powder diffraction and transmission electronic microscope, and the results show that each of all the samples has a monophasic zircon-type structure. The absorption spectrum of the prepared phosphor shows a blue-shift of the fundamental absorption band edge with increasing the gadolinium content. Under UV-light and visible-light excitation, all the prepared phosphors show the typical luminescence properties of Eu3+ in the zircon-type structure. The emission intensity of GdxBi0.95-xVO4:0.05Eu3+ (x=0.55) is strongest in all samples under UV-light and visible-light excitations. Finally, the mechanisms of luminescence of Eu3+ in the GdxBi0.95-xVO4:0.05Eu3+ (x=0-0.95) solid solutions are analyzed and discussed.
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    Multi-crack imaging using nonclassical nonlinear acoustic method
    张略, 张盈, 刘晓宙, 龚秀芬
    2014 (10):  104301-104301.  doi: 10.1088/1674-1056/23/10/104301
    摘要 ( 349 )   PDF(404KB) ( 607 )  
    Solid materials with cracks exhibit the nonclassical nonlinear acoustical behavior. The micro-defects in solid materials can be detected by nonlinear elastic wave spectroscopy (NEWS) method with a time-reversal (TR) mirror. While defects lie in viscoelastic solid material with different distances from one another, the nonlinear and hysteretic stress-strain relation is established with Preisach-Mayergoyz (PM) model in crack zone. Pulse inversion (PI) and TR methods are used in numerical simulation and defect locations can be determined from images obtained by the maximum value. Since false-positive defects might appear and degrade the imaging when the defects are located quite closely, the maximum value imaging with a time window is introduced to analyze how defects affect each other and how the fake one occurs. Furthermore, NEWS-TR-NEWS method is put forward to improve NEWS-TR scheme, with another forward propagation (NEWS) added to the existing phases (NEWS and TR). In the added phase, scanner locations are determined by locations of all defects imaged in previous phases, so that whether an imaged defect is real can be deduced. NEWS-TR-NEWS method is proved to be effective to distinguish real defects from the false-positive ones. Moreover, it is also helpful to detect the crack that is weaker than others during imaging procedure.
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    Investigation on the relationship between overpressure and sub-harmonic response from encapsulated microbubbles
    吴军, 范庭波, 许迪, 章东
    2014 (10):  104302-104302.  doi: 10.1088/1674-1056/23/10/104302
    摘要 ( 208 )   PDF(302KB) ( 310 )  
    Sub-harmonic component generated from microbubbles is proven to be potentially used in noninvasive blood pressure measurement. Both theoretical and experimental studies are performed in the present work to investigate the dependence of the sub-harmonic generation on the overpressure with different excitation pressure amplitudes and pulse lengths. With 4-MHz ultrasound excitation at an applied acoustic pressure amplitude of 0.24 MPa, the measured sub-harmonic amplitude exhibits a decreasing change as overpressure increases; while non-monotonic change is observed for the applied acoustic pressures of 0.36 MPa and 0.48 MPa, and the peak position in the curve of the sub-harmonic response versus the overpressure shifts toward higher overpressure as the excitation pressure amplitude increases. Furthermore, the exciting pulse with long duration could lead to a better sensitivity of the sub-harmonic response to overpressure. The measured results are explained by the numerical simulations based on the Marmottant model. The numerical simulations qualitatively accord with the measured results. This work might provide a preliminary proof for the optimization of the noninvasive blood pressure measurement through using sub-harmonic generation from microbubbles.
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    Conductivity reconstruction algorithms and numerical simulations for magneto-acousto-electrical tomography with piston transducer in scan mode
    郭亮, 刘国强, 夏慧, 刘宇, 陆敏华
    2014 (10):  104303-104303.  doi: 10.1088/1674-1056/23/10/104303
    摘要 ( 178 )   PDF(720KB) ( 437 )  
    Conductivities tomography with the interactions of magnetic field, electrical field, and ultrasound field is presented in this paper. We utilize a beam of ultrasound in scanning mode instead of the traditional ultrasound field generated by point source. Many formulae for the reconstruction of conductivities are derived from the voltage signals detected by two electrodes arranged somewhere on tissue's surface. In a forward problem, the numerical solutions of ultrasound fields generated by the piston transducer are calculated using the angular spectrum method and its Green's function is designed approximately in far fields. In an inverse problems, the magneto-acousto-electrical voltage signals are proved to satisfy the wave equations if the voltage signals are extended to the whole region from the boundary locations of transducers. Thus the time-reversal method is applied to reconstructing the curl of the reciprocal current density. In addition, a least square iteration method of recovering conductivities from reciprocal current densities is discussed.
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    Acoustic anechoic layers with singly periodic arrayof scatterers: Computational methods, absorptionmechanisms, and optimal design
    杨海滨, 李岳, 赵宏刚, 温激鸿, 温熙森
    2014 (10):  104304-104304.  doi: 10.1088/1674-1056/23/10/104304
    摘要 ( 159 )   PDF(490KB) ( 433 )  
    The acoustic properties of anechoic layers with a singly periodic array of cylindrical scatterers are investigated. A method combined plane wave expansion and finite element analysis is extended for out-of-plane incidence. The reflection characteristics of the anechoic layers with cavities and locally resonant scatterers are discussed. The backing is a steel plate followed by an air half space. Under this approximate zero transmission backing condition, the reflection reduction is induced by the absorption enhancement. The absorption mechanism is explained by the scattering/absorption cross section of the isolated scatterer. Three types of resonant modes which can induce efficient absorption are revealed. Due to the fact that the frequencies of the resonant modes are related to the size of the scatterers, anechoic layers with scatterers of mixed size can broaden the absorption band. A genetic optimization algorithm is adopted to design the anechoic layer with scatterers of mixed size at a desired frequency band from 2 kHz to 10 kHz for normal incidence, and the influence of the incident angle is also discussed.
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    Higher-order differential variational principle and differential equations of motion for mechanical systems in event space
    张相武, 李院院, 赵小侠, 罗文峰
    2014 (10):  104501-104501.  doi: 10.1088/1674-1056/23/10/104501
    摘要 ( 127 )   PDF(245KB) ( 349 )  
    In this paper we study the higher-order differential variational principle and differential equations of motion for mechanical systems in event space. Based on the higher-order d'Alembert principle of the system, the higher-order velocity energy and the higher-order acceleration energy of the system in event space are defined, the higher-order d'Alembert-Lagrange principle of the system in event space is established, and the parametric forms of Euler-Lagrange, Nielsen and Appell for this principle are given. Finally, the higher-order differential equations of motion for holonomic systems in event space are obtained.
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    Hopf bifurcation control for a coupled nonlinear relativerotation system with time-delay feedbacks
    刘爽, 李雪, 谈书贤, 李海滨
    2014 (10):  104502-104502.  doi: 10.1088/1674-1056/23/10/104502
    摘要 ( 172 )   PDF(422KB) ( 740 )  
    This paper investigates the Hopf bifurcations resulting from time delay in a coupled relative-rotation system with time-delay feedbacks. Firstly, considering external excitation, the dynamical equation of relative rotation nonlinear dynamical system with primary resonance and 1:1 internal resonance under time-delay feedbacks is deduced. Secondly, the averaging equation is obtained by the multiple scales method. The periodic solution in a closed form is presented by a perturbation approach. At last, numerical simulations confirm that time-delay theoretical analyses have influence on the Hopf bifurcation point and the stability of periodic solution.
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    MHD boundary layer flow of Casson fluid passing through an exponentially stretching permeable surface with thermal radiation
    Swati Mukhopadhyay, Iswar Ch, ra Moindal, Tasawar Hayat
    2014 (10):  104701-104701.  doi: 10.1088/1674-1056/23/10/104701
    摘要 ( 162 )   PDF(500KB) ( 770 )  
    This article numerically examines the boundary layer flow due to an exponentially stretching surface in the presence of an applied magnetic field. Casson fluid model is used to characterize the non-Newtonian fluid behavior. The flow is subjected to suction/blowing at the surface. Analysis is carried out in presence of thermal radiation and prescribed surface heat flux. In this study, an exponential order stretching velocity and prescribed exponential order surface heat flux are accorded with each other. The governing partial differential equations are first converted into nonlinear ordinary differential equations by using appropriate transformations and then solved numerically. The effect of increasing values of the Casson parameter is to suppress the velocity field. However the temperature is enhanced when Casson parameter increases. It is found that the skin-friction coefficient increases with increasing values of suction parameter. Temperature also increases for large values of power index n in both suction and blowing cases at the boundary. It is observed that the thermal radiation enhances the effective thermal diffusivity and hence the temperature rises.
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    Experimental study on supersonic film cooling on the surface of a blunt body in hypersonic flow
    付佳, 易仕和, 王小虎, 何霖, 葛勇
    2014 (10):  104702-104702.  doi: 10.1088/1674-1056/23/10/104702
    摘要 ( 207 )   PDF(1941KB) ( 506 )  
    The experimental study focuses on the heat flux on a double cone blunt body in the presence of tangential-slot supersonic injection into hypersonic flow. The tests are conducted in a contoured axisymmetric nozzle with Mach numbers of 7.3 and 8.1, and the total temperature is about 900 K. The injection Mach number is 3.2, and total temperature is 300 K. A constant voltage circuit is developed to supply the temperature detectors instead of the normally used constant current circuit. The schlieren photographs are presented additionally to visualize the flow and help analyze the pressure relationship between the cooling flow and the main flow. The dependence of the film-cooling effectiveness on flow parameters, i.e. the blow ratio, the convective Mach number, and the attack angle, is determined. A semi-empirical formula is tested by the present data, and is improved for a better correlation.
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    Convection and correlation of coherent structure in turbulent boundary layer using tomographic particle image velocimetry
    王维, 管新蕾, 姜楠
    2014 (10):  104703-104703.  doi: 10.1088/1674-1056/23/10/104703
    摘要 ( 194 )   PDF(5316KB) ( 407 )  
    The present experimental work focuses on a new model for space-time correlation and the scale-dependencies of convection velocity and sweep velocity in turbulent boundary layer over a flat wall. A turbulent boundary layer flow at Reθ=2460 is measured by tomographic particle image velocimetry (tomographic PIV). It is demonstrated that arch, cane, and hairpin vortices are dominant in the logarithmic layer. Hairpins and hairpin packets are responsible for the elongated low-momentum zones observed in the instantaneous flow field. The conditionally-averaged coherent structures systemically illustrate the key roles of hairpin vortice in the turbulence dynamic events, such as ejection and sweep events and energy transport. The space-time correlations of instantaneous streamwise fluctuation velocity are calculated and confirm the new elliptic model for the space-time correlation instead of Taylor hypothesis. The convection velocities derived from the space-time correlation and conditionally-averaged method both suggest the scaling with the local mean velocity in the logarithmic layer. Convection velocity result based on Fourier decomposition (FD) shows stronger scale-dependency in the spanwise direction than in streamwise direction. Compared with FD, the proper orthogonal decomposition (POD) has a distinct distribution of convection velocity for the large-and small-scales which are separated in light of their contributions of turbulent kinetic energy.
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    Numerical study of fast ion behavior in the presence of magnetic islands and toroidal field ripple in the EAST tokamak
    张伟, 胡立群, 孙有文, 丁斯晔, 张子君, 刘松林
    2014 (10):  105201-105201.  doi: 10.1088/1674-1056/23/10/105201
    摘要 ( 151 )   PDF(10101KB) ( 355 )  
    A peculiar first orbit loss type was found apart from the normal ones when we use ORBIT code to simulate fast ion orbits in the EAST tokamak. Fast ion orbits were studied in the presence of toroidal field (TF) ripple and magnetohydrodynamic (MHD) perturbations. We analyzed the properties of the drifted orbits in detail and compared their differences, finding that the combined effects of ripple and magnetic islands are much greater than the effects of either one of them alone. Then we investigated the orbit deviations as a function of pitch angle in different radial positions. The modeling results demonstrate that the loss of trapped particles is mainly caused by the ripple, while MHD perturbation mainly plays an important role in the passing particles. Furthermore we modeled the loss rate using different equilibriums. Results prove that a higher beta can indeed improve the confinement of fast ions, while a little change in the q profile can make the topologies of magnetic islands become quite different and results in quite different total particle losses.
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    A radial non-uniform helicon equilibrium discharge model
    成玉国, 程谋森, 王墨戈, 李小康
    2014 (10):  105202-105202.  doi: 10.1088/1674-1056/23/10/105202
    摘要 ( 244 )   PDF(858KB) ( 642 )  
    Helicon discharges have attracted great attention in the electric propulsion community in recent years. To acquire the equilibrium properties, a self-consistent model is developed, which combines the helicon/Trivelpiece-Gould (TG) waves-plasma interaction mechanism and the plasma flow theory under the confinement of the magnetic field. The calculations reproduce the central peak density phenomenon observed in the experiments. The results show that when operating in the wave coupling mode, high magnetic field strength B0 results in the deviation of the central density versus B0 from the linear relationship, while the density rise becomes flatter as the radiofrequency (rf) input power Prf grows, and the electron temperature Te radial profile is mainly determined by the characteristic of the rf energy deposition. The model could provide suggestions in choosing the B0 and Prf for medium power helicon thrusters.
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    Nitriding molybdenum: Effects of duration and fill gas pressure when using 100-Hz pulse DC discharge technique
    U. Ikhlaq, R. Ahmad, M. Shafiq, S. Saleem, M. S. Shah, T. Hussain, I. A. Khan, K. Abbas, M. S. Abbas
    2014 (10):  105203-105203.  doi: 10.1088/1674-1056/23/10/105203
    摘要 ( 190 )   PDF(3113KB) ( 658 )  
    Molybdenum is nitrided by a 100-Hz pulsed DC glow discharge technique for various time durations and fill gas pressures to study the effects on the surface properties of molybdenum. X-ray diffractometry (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) are used for the structural and morphological analysis of the nitrided layers. Vickers' microhardness tester is utilized to investigate surface microhardness. Phase analysis shows the formation of more molybdenum nitride molecules for longer nitriding durations at fill gas pressures of 2 mbar and 3 mbar (1 bar=105 Pa). A considerable increase in surface microhardness (approximately by a factor of 2) is observed for longer duration (10 h) and 2-mbar pressure. Longer duration (10 h) and 2-mbar fill gas pressure favors the formation of homogeneous, smooth, hard layers by the incorporation of more nitrogen.
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    Oxygen vacancy-induced room-temperature ferromagnetism in D-D neutron irradiated single-crystal TiO2 (001) rutile
    许楠楠, 李公平, 潘小东, 王云波, 陈景升, 包良满
    2014 (10):  106101-106101.  doi: 10.1088/1674-1056/23/10/106101
    摘要 ( 258 )   PDF(558KB) ( 451 )  
    Remarkable room temperature ferromagnetism in pure single-crystal rutile TiO2 (001) samples irradiated by D-D neutron has been investigated. By combining X-ray diffraction and positron annihilation lifetime, the contracted lattice has been clearly identified in irradiated TiO2, where Ti4+ ions can be easily reduced to the state of Ti3+. As there were no magnetic impurities that could contaminate the samples during the whole procedure, some Ti3+ ions reside on interstitial or substituted sites accompanied by oxygen vacancies should be responsible for the ferromagnetism.
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    Pattern imprinting in deep sub-micron static random access memories induced by total dose irradiation
    郑齐文, 余学峰, 崔江维, 郭旗, 任迪远, 丛忠超, 周航
    2014 (10):  106102-106102.  doi: 10.1088/1674-1056/23/10/106102
    摘要 ( 159 )   PDF(473KB) ( 396 )  
    Pattern imprinting in deep sub-micron static random access memories (SRAMs) during total dose irradiation is investigated in detail. As the dose accumulates, the data pattern of memory cells loading during irradiation is gradually imprinted on their background data pattern. We build a relationship between the memory cell's static noise margin (SNM) and the background data, and study the influence of irradiation on the probability density function of ΔSNM, which is the difference between two data sides' SNMs, to discuss the reason for pattern imprinting. Finally, we demonstrate that, for micron and deep sub-micron devices, the mechanism of pattern imprinting is the bias-dependent threshold shift of the transistor, but for a deep sub-micron device the shift results from charge trapping in the shallow trench isolation (STI) oxide rather than from the gate oxide of the micron-device.
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    A model of crack based on dislocations in smectic A liquid crystals
    范天佑, 唐志毅
    2014 (10):  106103-106103.  doi: 10.1088/1674-1056/23/10/106103
    摘要 ( 141 )   PDF(219KB) ( 500 )  
    A plastic crack model for smectic A liquid crystals under longitudinal shear is suggested. The solution of the screw dislocation in smectic A is the key to the correct result that we obtained by overcoming a longstanding puzzle. We further use the dislocation pile-up principle and the singular integral equation method to construct the solution of the crack in the phase. From the solution, we can determine the size of the plastic zone at the crack tip and the crack tip opening (tearing) displacement, which are the parameters relevant to the local stability/instability of materials. Our results may be useful for developing soft-matter mechanics.
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    Elastic fields around a nanosized elliptichole in decagonal quasicrystals
    李联和, 云国宏
    2014 (10):  106104-106104.  doi: 10.1088/1674-1056/23/10/106104
    摘要 ( 155 )   PDF(225KB) ( 461 )  
    Based on the variational principle, a continuum theory of surface elasticity and new boundary conditions for quasicrystals is proposed. The effect of the residual surface stress on a decagonal quasicrystal that is weakened by a nanoscale elliptical hole is considered. The explicit expressions for the hoop stress along the edge of the hole are obtained using the Stroh formalism. The results show that the residual surface stress and the shape of the hole have a significant effect on the elastic state around the hole.
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    Molecular dynamics simulation of an argon cluster filled inside carbon nanotubes
    崔树稳, 朱如曾, 王小松, 杨洪秀
    2014 (10):  106105-106105.  doi: 10.1088/1674-1056/23/10/106105
    摘要 ( 194 )   PDF(1747KB) ( 493 )  
    The effects of the diameters of single-walled carbon nanotubes (SWCNTs) (7.83 Å to 27.40 Å) and temperature (20 K-45 K) on the equilibrium structure of an argon cluster are systematically studied by molecular dynamics simulation with consideration of the SWCNTs to be fixed. Since the diameters of SWCNTs with different chiralities increase when temperature is fixed at 20 K, the equilibrium structures of the argon cluster transform from monoatomic chains to helical and then to multishell coaxial cylinders. Chirality has almost no noticeable influence on these cylindrosymmetric structures. The effects of temperature and a non-equilibrium sudden heating process on the structures of argon clusters in SWCNTs are also studied by molecular dynamics simulation.
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    Epitaxial evolution on buried cracks in a strain-controlled AlN/GaN superlattice interlayer between AlGaN/GaN multiple quantum wells and a GaN template
    黄呈橙, 张霞, 许福军, 许正昱, 陈广, 杨志坚, 唐宁, 王新强, 沈波
    2014 (10):  106106-106106.  doi: 10.1088/1674-1056/23/10/106106
    摘要 ( 211 )   PDF(1130KB) ( 473 )  
    Epitaxial evolution of buried cracks in a strain-controlled AlN/GaN superlattice interlayer (IL) grown on GaN template, resulting in crack-free AlGaN/GaN multiple quantum wells (MQW), was investigated. The processes of filling the buried cracks include crack formation in the IL, coalescence from both side walls of the crack, build-up of an MQW-layer hump above the cracks, lateral expansion and merging with the surrounding MQW, and two-dimensional step flow growth. It was confirmed that the filling content in the buried cracks is pure GaN, originating from the deposition of the GaN thin layer directly after the IL. Migration of Ga adatoms into the cracks plays a key role in the filling the buried cracks.
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    Segregation of alloying atoms at a tilt symmetric grain boundary in tungsten and their strengthening and embrittling effects
    李志武, 孔祥山, 刘伟, 刘长松, 方前峰
    2014 (10):  106107-106107.  doi: 10.1088/1674-1056/23/10/106107
    摘要 ( 288 )   PDF(549KB) ( 452 )  
    We investigate the segregation behavior of alloying atoms (Sr, Th, In, Cd, Ag, Sc, Au, Zn, Cu, Mn, Cr, and Ti) near Σ3 (111) [110] tilt symmetric grain boundary (GB) in tungsten and their effects on the intergranular embrittlement by performing first-principles calculations. The calculated segregation energies suggest that Ag, Au, Cd, In, Sc, Sr, Th, and Ti prefer to occupy the site in the mirror plane of the GB, while Cu, Cr, Mn, and Zn intend to locate at the first layer nearby the GB core. The calculated strengthening energies predict Sr, Th, In, Cd, Ag, Sc, Au, Ti, and Zn act as embrittlers while Cu, Cr, and Mn act as cohesion enhancers. The correlation of the alloying atom's metal radius with strengthening energy is strong enough to predict the strengthening and embrittling behavior of alloying atoms; that is, the alloying atom with larger metal radius than W acts as an embrittler and the one with smaller metal radius acts as a cohesion enhancer.
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    First-principles calculations of structural, electronic, and thermodynamic properties of ZnO1-xSx alloys
    Muhammad Zafar, Shabbir Ahmed, M. Shakil, M. A. Choudhary
    2014 (10):  106108-106108.  doi: 10.1088/1674-1056/23/10/106108
    摘要 ( 196 )   PDF(385KB) ( 566 )  
    In this study the pseudo-potential method is used to investigate the structural, electronic, and thermodynamic properties of ZnO1-xSx semiconductor materials. The results show that the electronic properties are found to be improved when calculated by using LDA+U functional as compared with local density approximation (LDA). At various concentrations the ground-state properties are determined for bulk materials ZnO, ZnS, and their tertiary alloys in cubic zinc-blende phase. From the results, a minor difference is observed between the lattice parameters from Vegard's law and other calculated results, which may be due to the large mismatch between lattice parameters of binary compounds ZnO and ZnS. A small deviation in the bulk modulus from linear concentration dependence is also observed for each of these alloys. The thermodynamic properties, including the phonon contribution to Helmholtz free energy ΔF, phonon contribution to internal energy ΔE, and specific heat at constant-volume CV, are calculated within quasi-harmonic approximation based on the calculated phonon dispersion relations.
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    Enhancement of ferromagnetic resonance in Al2O3-doped Co2FeAl Heusler alloy film prepared by oblique sputtering
    李山东, 蔡志义, 徐洁, 曹晓琴, 杜洪磊, 薛倩, 高小洋, 谢施名
    2014 (10):  106201-106201.  doi: 10.1088/1674-1056/23/10/106201
    摘要 ( 150 )   PDF(579KB) ( 393 )  
    Large and variable in-plane uniaxial magnetic anisotropy in a nanocrystalline (Co2FeAl)97.8(Al2O3)2.2 soft magnetic thin film is obtained by an oblique sputtering method without being induced by magnetic field or post annealing. The in-plane uniaxial magnetic anisotropy varies from 50 Oe to 180 Oe (1 Oe=79.5775 A·m-1) by adjusting the sample's position. As a result, the ferromagnetic resonance frequency of the film increases from 1.9 GHz to 3.75 GHz.
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    Thermal transport properties of defective graphene: A molecular dynamics investigation
    杨宇霖, 卢宇
    2014 (10):  106501-106501.  doi: 10.1088/1674-1056/23/10/106501
    摘要 ( 319 )   PDF(708KB) ( 630 )  
    In this work the thermal transport properties of graphene nanoribbons with randomly distributed vacancy defects are investigated by the reverse non-equilibrium molecular dynamics method. We find that the thermal conductivity of the graphene nanoribbons decreases as the defect coverage increases and is saturated in a high defect ratio range. Further analysis reveals a strong mismatch in the phonon spectrum between the unsaturated carbon atoms in 2-fold coordination around the defects and the saturated carbon atoms in 3-fold coordination, which induces high interfacial thermal resistance in defective graphene and suppresses the thermal conductivity. The defects induce a complicated bonding transform from sp2 to hybrid sp-sp2 network and trigger vibration mode density redistribution, by which the phonon spectrum conversion and strong phonon scattering at defect sites are explained. These results shed new light on the understanding of the thermal transport behavior of graphene-based nanomaterials with new structural configurations and pave the way for future designs of thermal management phononic devices.
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    Stacking stability of MoS2 bilayer: An ab initio study
    陶鹏, 郭怀红, 杨腾, 张志东
    2014 (10):  106801-106801.  doi: 10.1088/1674-1056/23/10/106801
    摘要 ( 590 )   PDF(1304KB) ( 1024 )  
    The study of the stacking stability of bilayer MoS2 is essential since a bilayer has exhibited advantages over single layer MoS2 in many aspects for nanoelectronic applications. We explored the relative stability, optimal sliding path between different stacking orders of bilayer MoS2, and (especially) the effect of inter-layer stress, by combining first-principles density functional total energy calculations and the climbing-image nudge-elastic-band (CI-NEB) method. Among five typical stacking orders, which can be categorized into two kinds (Ⅰ: AA, AB and Ⅱ: AA', AB', A'B), we found that stacking orders with Mo and S superposing from both layers, such as AA' and AB, is more stable than the others. With smaller computational efforts than potential energy profile searching, we can study the effect of inter-layer stress on the stacking stability. Under isobaric condition, the sliding barrier increases by a few eV/(uc·GPa) from AA' to AB', compared to 0.1 eV/(uc·GPa) from AB to [AB]. Moreover, we found that interlayer compressive stress can help enhance the transport properties of AA'. This study can help understand why inter-layer stress by dielectric gating materials can be an effective means to improving MoS2 on nanoelectronic applications.
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    First-principles calculations on Si (220) located 6H-SiC (1010) surface with different stacking sites
    贺小敏, 陈治明, 蒲红斌, 李连碧, 黄磊
    2014 (10):  106802-106802.  doi: 10.1088/1674-1056/23/10/106802
    摘要 ( 119 )   PDF(900KB) ( 592 )  
    6H-SiC (1010) surface and Si (220)/6H-SiC (1010) interface with different stacking sites are investigated using first-principles calculations. Surface energies of 6H-SiC (1010) (case Ⅰ, case Ⅱ, and case Ⅲ) are firstly studied and the surface calculation results show that case Ⅱ and case Ⅲ are more stable than case Ⅰ. Then, the adhesion energies, fracture toughness values, interfacial energies, densities of states, and electronic structures of Si (220)/6H-SiC (1010) interfaces for three stacking models (AM, BM, and CM) are calculated. The CM model has the highest adhesion energy and the lowest interfacial energy, suggesting that the CM is stronger and more thermodynamically stable than AM and BM. Densities of states and the total charge densities give evidence that interfacial bonding is formed at the interface and that Si-Si and Si-C are induced due to the hybridization of C-2p and Si-3p. Moreover, the Si-C is much stronger than Si-Si at the interface, implying that the contribution of the interfacial bonding mainly comes from Si-C rather than Si-Si.
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    Influence of roughness on the detection of mechanical characteristics of low-k film by the surface acoustic waves
    肖夏, 陶冶, 孙远
    2014 (10):  106803-106803.  doi: 10.1088/1674-1056/23/10/106803
    摘要 ( 126 )   PDF(262KB) ( 365 )  
    The surface acoustic wave (SAW) technique is a precise and nondestructive method to detect the mechanical characteristics of the thin low dielectric constant (low-k) film by matching the theoretical dispersion curve with the experimental dispersion curve. In this paper, the influence of sample roughness on the precision of SAW mechanical detection is investigated in detail. Random roughness values at the surface of low-k film and at the interface between this low-k film and the substrate are obtained by the Monte Carlo method. The dispersive characteristic of SAW on the layered structure with rough surface and rough interface is modeled by numerical simulation of finite element method. The Young's moduli of the Black DiamondTM samples with different roughness values are determined by SAWs in the experiment. The results show that the influence of sample roughness is very small when the root-mean-square (RMS) of roughness is smaller than 50 nm and correlation length is smaller than 20 μm. This study indicates that the SAW technique is reliable and precise in the nondestructive mechanical detection for low-k films.
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    Analysis of phase shift of surface plasmon polaritons at metallic subwavelength hole arrays
    李江艳, 邱康生, 马海强
    2014 (10):  106804-106804.  doi: 10.1088/1674-1056/23/10/106804
    摘要 ( 229 )   PDF(594KB) ( 448 )  
    We present the transmission spectra of light transmitting a metallic thin film perforated with differently shaped subwavelength hole arrays, which are calculated by a plane-wave-based transfer matrix method. We analyze the transmission peak positions and the phase-shift angles of different surface plasmon polariton (SPP) modes by using the microscopic theoretical model proposed by Haitao Liu and Philippe Lalanne [Liu Haitao and Lalanne Philippe 2008 Nature 452 728], in which the phase shift properties of the SPPs scattered by the subwavelength hole arrays are considered. The results show that the transmission peak position and the minus phase shift angle of the SPP increase as the hole size increases. On the other hand, the effective dielectric constant of the metallic film can be deduced by the microscopic theoretical model.
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    Low-resistance Ohmic contact on polarization-dopedAlGaN/GaN heterojunction
    李世彬, 余宏萍, 张婷, 陈志, 吴志明
    2014 (10):  107101-107101.  doi: 10.1088/1674-1056/23/10/107101
    摘要 ( 170 )   PDF(392KB) ( 761 )  
    High electronic density is achieved by polarization doping without an impurity dopant in graded AlGaN films. Low specific contact resistance is studied on the polarization-doped AlGaN/GaN heterojunctions by using the transmission line method (TLM). The sheet density of polarization-doped AlGaN/GaN heterojunction is 6×1014 cm -2 at room temperature. The linearly graded material structure is demonstrated by X-ray diffraction. The carrier concentration and mobility are characterized by a temperature-dependent Hall measurement. Multiple-layer metal (Ti/Al/Ti/Au) is deposited and annealed at 650℃ to realize the Ohmic contacts on the graded AlGaN/GaN heterojunctions.
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    Electronic structure and optical properties of MgxZn1-xS bulk crystal using first-principles calculations
    余志强, 徐智谋, 武兴会
    2014 (10):  107102-107102.  doi: 10.1088/1674-1056/23/10/107102
    摘要 ( 159 )   PDF(666KB) ( 644 )  
    We perform the first-principles calculations within the framework of density functional theory to determine the electronic structure and optical properties of MgxZn1-xS bulk crystal. The results indicate that the electronic structure and optical properties of MgxZn1-xS bulk crystal are sensitive to the Mg impurity composition. In particular, the MgxZn1-xS bulk crystal displays a direct band structure and the band gap increases from 2.05 eV to 2.91 eV with Mg dopant composition value x increasing from 0 to 0.024. The S 3p electrons dominate the top of valence band, while the Zn 4s electrons and Zn 3p electrons occupy the bottom of conduction band in MgxZn1-xS bulk crystal. Moreover, the dielectric constant decreases and the optical absorption peak obviously has a blue shift. The calculated results provide important theoretical guidance for the applications of MgxZn1-xS bulk crystal in optical detectors.
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    Influence of electron-phonon interaction on the properties of transport through double quantum dot with ferromagnetic leads
    罗侃, 王发强, 梁瑞生, 任珍珍
    2014 (10):  107103-107103.  doi: 10.1088/1674-1056/23/10/107103
    摘要 ( 138 )   PDF(460KB) ( 349 )  
    Electronic transport through a vibrating double quantum dot (DQD) in contact with noncollinear ferromagnetic (FM) leads is investigated. The state transition between the two dots of the DQD is excited by an AC microwave driving field. The corresponding currents and differential conductance are calculated in the Coulomb blockade regime by means of the Born-Markov master equation. It is shown that the interplay between electrons and phonons gives rise to phonon-assisted tunneling resonances and Franck-Condon blockade under certain conditions. In noncollinear magnetic configurations, spin-blockade effects are also observed, and the angle of polarization has some influence on the transport characteristics.
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    Transverse Zeeman background correction method for air mercury measurement
    李传新, 司福祺, 刘文清, 周海金, 江宇, 胡仁志
    2014 (10):  107104-107104.  doi: 10.1088/1674-1056/23/10/107104
    摘要 ( 202 )   PDF(488KB) ( 360 )  
    By utilizing a natural mercury lamp, the transverse Zeeman background correction method, which is used for trace mercury measurement in air, is studied. In this paper, a natural mercury lamp is used as a light source, and is placed in a 1.78-T magnetic field. The lamp emits two linearly polarized light beams σ± and π of 253.65-nm resonance line, which are used as bias light and absorbing light, respectively. A polarization modulation system is used to allow σ ± and π light beams to pass through alternately with a certain frequency. A multipath optical cell with 12-m optical path is used to increase optical distance. Based on the system described above, the influence caused by UV absorbing gases, such as NO2, SO2, acetone, benzene, and O3, is analyzed. The results show that it may reduce the detection limit when the concentrations of these gases exceed 83.4 ppm, 20.3 ppm, 142.3 ppm, 0.85 ppm, and 0.55 ppm, respectively. The detection limit of the system is calculated and can achieve up to 1.44 ng/m3 in 10 minutes. Measurements on mercury sample gas and air are carried out, and the measured data are compared with the data of RA-915 mercury analyzer (Russia). The result shows that the correlation coefficient reaches up to 0.967. The experimental results indicate that the transverse Zeeman background correction method can be used to quantify trace mercury in air with high-precision.
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    Ferromagnetic barrier-induced negative differential conductance on the surface of a topological insulator
    2014 (10):  107301-107301.  doi: 10.1088/1674-1056/23/10/107301
    摘要 ( 229 )   PDF(283KB) ( 365 )  
    The effect of the negative differential conductance of a ferromagnetic barrier on the surface of a topological insulator is theoretically investigated. Due to the changes of the shape and position of the Fermi surfaces in the ferromagnetic barrier, the transport processes can be divided into three kinds: the total, partial, and blockade transmission mechanisms. The bias voltage can give rise to the transition of the transport processes from partial to blockade transmission mechanisms, which results in a considerable effect of negative differential conductance. With appropriate structural parameters, the current-voltage characteristics show that the minimum value of the current can reach to zero in a wide range of the bias voltage, and then a large peak-to-valley current ratio can be obtained.
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    Analysis of optoelectronic properties of TiO2 nanowiers/Si heterojunction arrays
    Saeideh Ramezani Sani
    2014 (10):  107302-107302.  doi: 10.1088/1674-1056/23/10/107302
    摘要 ( 169 )   PDF(242KB) ( 427 )  
    The optoelectronic properties of n-TiO2NW/p-Si heterojunction fabricated by depositing TiO2 nanowires on a p-Si substrate are studied. Under excitation at a wavelength of 370 nm, the TiO2 nanowires produce a light emission at 435 nm due to the emission of free excitons. The I-V characteristics are measured to investigate the heterojunction effects under the dark environment and ultraviolet (UV) illumination. n-TiO2NW/p-Si has a p-n junction formed in the n-TiO2/p-Si heterojunction. TiO2NW/Si photodiode produces a photocurrent larger than dark current under UV illumination. It is observed that UV photons are absorbed in TiO2 and the heterojunction shows a 0.034-A/W responsivity at 4-V reverse bias.
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    Mechanism of improving forward and reverse blocking voltages in AlGaN/GaN HEMTs by using Schottky drain
    赵胜雷, 宓珉瀚, 侯斌, 罗俊, 王毅, 戴杨, 张进成, 马晓华, 郝跃
    2014 (10):  107303-107303.  doi: 10.1088/1674-1056/23/10/107303
    摘要 ( 181 )   PDF(1455KB) ( 838 )  
    In this paper, we demonstrate that a Schottky drain can improve the forward and reverse blocking voltages (BVs) simultaneously in AlGaN/GaN high-electron mobility transistors (HEMTs). The mechanism of improving the two BVs is investigated by analysing the leakage current components and by software simulation. The forward BV increases from 72 V to 149 V due to the good Schottky contact morphology. During the reverse bias, the buffer leakage in the Ohmic-drain HEMT increases significantly with the increase of the negative drain bias. For the Schottky-drain HEMT, the buffer leakage is suppressed effectively by the formation of the depletion region at the drain terminal. As a result, the reverse BV is enhanced from -5 V to -49 V by using a Schottky drain. Experiments and the simulation indicate that a Schottky drain is desirable for power electronic applications.
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    Electron states scattering off line edges on the surface of topological insulator
    邵怀华, 刘一曼, 周小英, 周光辉
    2014 (10):  107304-107304.  doi: 10.1088/1674-1056/23/10/107304
    摘要 ( 165 )   PDF(630KB) ( 447 )  
    We study the local density of states (LDOS) for electrons scattering off the line edge of an atomic step defect on the surface of a three-dimensional (3D) topological insulator (TI) and the line edge of a finite 3D TI, where the front surface and side surface meet with different Fermi velocities, respectively. By using a δ-function potential to model the edges, we find that the bound states existed along the step line edge significantly contribute to the LDOS near the edge, but do not modify the exponential behavior away from it. In addition, the power-law decaying behavior for LDOS oscillation away from the step is understood from the spin rotation for surface states scattering off the step defect with magnitude depending on the strength of the potential. Furthermore, the electron refraction and total reflection analogous to optics occurred at the line edge where two surfaces meet with different Fermi velocities, which leads to the LDOS decaying behavior in the greater Fermi velocity side similar to that for a step line edge. However, in the smaller velocity side the LDOS shows a different decaying behavior as x-1/2, and the wavevector of LDOS oscillation is no longer equal to the diameter of the constant energy contour of surface band, but is sensitively dependent on the ratio of the two Fermi velocities. These effects may be verified by STM measurement with high precision.
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    Effects of shape of terminus on excitation of surfaceplasmon modes on metal nanowires
    乔雅楠, 杨树
    2014 (10):  107305-107305.  doi: 10.1088/1674-1056/23/10/107305
    摘要 ( 110 )   PDF(1915KB) ( 413 )  
    The effects of the shape of a nanowire terminus on the excited surface plasmon polariton (SPP) modes are investigated. The conical terminus and terminus cut at a certain angle are studied. For the first time, the quantitative mode decompositions are carried out to derive the full information about excited SPP modes. It is demonstrated that tuning the shape of the terminus provides an effective method to control the composition of excited SPP modes on metal nanowires. It is especially found that some important patterns, such as the pure TM0 mode and the superposition of TM0 and HE+1 or HE-1 modes, can be generated by some specific shapes of the terminus, whereas there is no way to produce these patterns using flat-end nanowires.
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    Effects of different dopants on switching behavior of HfO2-based resistive random access memory
    邓宁, 庞华, 吴畏
    2014 (10):  107306-107306.  doi: 10.1088/1674-1056/23/10/107306
    摘要 ( 148 )   PDF(953KB) ( 2086 )  
    In this study the effects of doping atoms (Al, Cu, and N) with different electro-negativities and ionic radii on resistive switching of HfO2-based resistive random access memory (RRAM) are systematically investigated. The results show that forming voltages and set voltages of Al/Cu-doped devices are reduced. Among all devices, Cu-doped device shows the narrowest device-to-device distributions of set voltage and low resistance. The effects of different dopants on switching behavior are explained with deferent types of CFs formed in HfO2 depending on dopants: oxygen vacancy (Vo) filaments for Al-doped HfO2 devices, hybrid filaments composed of oxygen vacancies and Cu atoms for Cu-doped HfO2 devices, and nitrogen/oxygen vacancy filaments for N-doped HfO2 devices. The results suggest that a metal dopant with a larger electro-negativity than host metal atom offers the best comprehensive performance.
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    Interfacial thermal resistance between high-density polyethylene (HDPE) and sapphire
    郑鲲, 祝捷, 马永梅, 唐大伟, 王佛松
    2014 (10):  107307-107307.  doi: 10.1088/1674-1056/23/10/107307
    摘要 ( 184 )   PDF(401KB) ( 506 )  
    To improve the thermal conductivity of polymeric composites, the numerous interfacial thermal resistance (ITR) inside is usually considered as a bottle neck, but the direct measurement of the ITR is hardly reported. In this paper, a sandwich structure which consists of transducer/high density polyethylene (HDPE)/sapphire is prepared to study the interface characteristics. Then, the ITRs between HDPE and sapphire of two samples with different HDPE thickness values are measured by time-domain thermoreflectance (TDTR) method and the results are ~ 2×10-7 m2· K· W-1. Furthermore, a model is used to evaluate the importance of ITR for the thermal conductivity of composites. The model's analysis indicates that reducing the ITR is an effective way of improving the thermal conductivity of composites. These results will provide valuable guidance for the design and manufacture of polymer-based thermally conductive materials.
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    Optical conductivity as a probe of a hidden Fermi-liquidbehavior in BaFe1.904Ni0.096As2
    杨彦兴, 熊锐, 方之颢, 许兵, 肖宏, 邱祥冈, 石兢, 王凯
    2014 (10):  107401-107401.  doi: 10.1088/1674-1056/23/10/107401
    摘要 ( 185 )   PDF(400KB) ( 546 )  
    We measured the infrared reflectivity of BaFe1.904Ni0.096As2 single crystal from room temperature down to 20 K. Two Drude terms and a Lorentz term well describe the real part of the optical conductivity σ1(ω). We fit the reciprocal of static optical conductivity 1/σ1(0) by the power law ρ(T)=ρ0+ATn with n=1.6. The “broad” Drude component exhibits an incoherent background with a T-independent scattering rate 1/τb, while the other “narrow” one reveals a T-quadratic scattering rate 1/τn, indicating a hidden Fermi-liquid behavior in BaFe1.904Ni0.096As2 compound.
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    Precursor evolution and growth mechanism of BTO/YBCO films by TFA-MOD process
    王洪艳, 丁发柱, 古宏伟, 张腾, 彭星煜
    2014 (10):  107402-107402.  doi: 10.1088/1674-1056/23/10/107402
    摘要 ( 219 )   PDF(1251KB) ( 469 )  

    In this study, BaTiO3 (BTO)-doped YBCO films are prepared on LaAlO3 (100) single-crystal substrates by metal-organic decomposition (MOD) using trifluoroacetate (TFA) precursor solutions. The critical current density (Jc) of BTO/YBCO film is as high as 10 MA/cm2 (77 K, 0 T). The BTO peak is found in the X-ray diffraction (XRD) pattern of a final YBCO superconductivity film. Moreover, a comprehensive study of the precursor evolution is conducted mainly by X-ray analysis and μ-Raman spectroscopy. It is found that the TFA begins to decompose at the beginning of the thermal process, and then further decomposes as temperature increases, and at 700℃ BTO nanoparticles begin to appear. It suggests that the YBCO film embedded with BTO nanoparticles, whose critical current density (Jc) is enhanced, is successfully prepared by an easily scalable chemical solution deposition technique.

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    Phase constitution and microstructure of Ce-Fe-B strip-casting alloy
    严长江, 郭帅, 陈仁杰, 李东, 闫阿儒
    2014 (10):  107501-107501.  doi: 10.1088/1674-1056/23/10/107501
    摘要 ( 302 )   PDF(702KB) ( 878 )  
    The strip-casting technique plays an important role in fabricating high coercivity sintered magnet. In this paper, we investigate the phase constitution and the microstructure of rapidly solidified Ce-Fe-B alloy fabricated by strip-casting. We find that the Ce2Fe14B phase coexists with Fe, Fe2B, and CeFe2 phases in the Ce-Fe-B strips. The eutectic structure consisting of Fe and Fe2B is encased in Ce2Fe14B grains, which is blocked by the CeFe2 grains at triple junctions, indicating that the microstructure of Ce-Fe-B strip is characteristic of a peritectic solidification. Thermal analysis indicates that the large supercooling of Ce2Fe14B results in the residual Fe and Fe2B. The microstructural optimization in Ce-Fe-B strips without Fe and Fe2B could be achieved by a heat treatment of 1000℃.
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    Asymmetric exchange bias training effect in spin glass (FeAu)/FeNi bilayers
    芮文彬, 何茂诚, 游彪, 时钟, 周仕明, 肖明文, 高远, 张维, 孙力, 杜军
    2014 (10):  107502-107502.  doi: 10.1088/1674-1056/23/10/107502
    摘要 ( 261 )   PDF(405KB) ( 404 )  
    A significant exchange bias (EB) training effect has been observed in sputter deposited FeAu/FeNi bilayers, wherein the exchange field (HE) exhibits a special sign-changeable temperature dependence. Very interestingly, despite the absence of multiple easy axes in the FeAu spin glass (SG) layer, HE drops abruptly between the first and second magnetic cycles, which is followed by a more gradual continuous change in the subsequent cycles. This training behavior cannot be described by the empirical n-1/2 law because of the asymmetric magnetization reversal processes. We propose modifying Binek's model to include the asymmetric changes of the pinning SG spins at the descending and ascending branches. This new model successfully describes the EB training effect in FeAu/FeNi bilayers.
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    Cation distributions estimated using the magnetic moments of the spinel ferrites Co1-xCrxFe2O4 at 10 K
    尚志丰, 齐伟华, 纪登辉, 徐静, 唐贵德, 张晓云, 李壮志, 郎莉莉
    2014 (10):  107503-107503.  doi: 10.1088/1674-1056/23/10/107503
    摘要 ( 136 )   PDF(1594KB) ( 743 )  
    (A)[B]2O4 ferrite samples with the composition Co1-xCrxFe2O4 (0.0 ≤ x ≤ 1.0) are prepared using a hydrothermal method, and subjected to calcining in a tube furnace with an argon-flow at 1673 K for 2 h. X-ray diffraction patterns indicate that each of all the samples has a single phase cubic spinel structure with a space group of Fd3 m. Magnetic measurements show that the saturation magnetization decreases with as the Cr content x increases. The cation distribution of the samples is estimated by fitting the dependence of the magnetic moments on x at 10 K, using the quantum mechanical model previously proposed by our group. The calculated sum of the content values of the Cr3+ and Cr2+ cations occupying the (A) sites increases as the value of x increases. In the fitting process, the magnetic moment directions of the Cr3+ and Cr2+ cations are assumed to be antiparallel to those of the Fe and Co cations, respectively, which is in accordance with Hund's rules.
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    Temperature dependence of the photothermal laser cooling efficiency for a micro-cantilever
    丁丽萍, 毛添华, 付号, 曹更玉
    2014 (10):  107801-107801.  doi: 10.1088/1674-1056/23/10/107801
    摘要 ( 173 )   PDF(420KB) ( 436 )  
    The relationship between the photothermal cooling efficiency of a micro-cantilever's mechanical mode and the environmental temperature is studied. The micro-cantilever and a polished fiber end form a low finesse Fabry-Perot (FP) cavity. Experimental results in a temperature range from 77 K to 298 K show that temperature has an obvious influence on photothermal cooling efficiency. The photothermal cooling efficiency, η ph, at 100 K is 10 times that at 298 K. This accords well with the theoretical analysis that the high photothermal cooling efficiency can be achieved when photothermal response time, τph, and mechanical resonant frequency, ω0, are close to the optimal photothermal cooling condition ω0 τph=1. Our study provides an important approach for high effective photothermal cooling and high-sensitivity measurement for force microscopy.
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    Photo-induced intramolecular electron transfer and intramolecular vibrational relaxation of rhodamine 6G in DMSO revealed by multiplex transient grating spectroscopy
    蒋礼林, 刘伟龙, 宋云飞, 孙山林
    2014 (10):  107802-107802.  doi: 10.1088/1674-1056/23/10/107802
    摘要 ( 218 )   PDF(1124KB) ( 877 )  
    Photo-induced intramolecular electron transfer (PIET) and intramolecular vibrational relaxation (IVR) dynamics of the excited state of rhodamine 6G (Rh6G +) in DMSO are investigated by multiplex transient grating. Two major components are resolved in the dynamics of Rh6G+. The first component, with a lifetime τPIET=140 fs-260 fs, is attributed to PIET from the phenyl ring to the xanthene plane. The IVR process occurring in the range τIVR=3.3 ps-5.2 ps is much slower than the first component. The PIET and IVR processes occurring in the excited state of Rh6G + are quantitatively determined, and a better understanding of the relationship between these processes is obtained.
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    Mid-gap photoluminescence and magnetic properties of GaMnN films grown by metal-organic chemical vapor deposition
    邢海英, 徐章程, 崔明启, 谢玉芯, 张国义
    2014 (10):  107803-107803.  doi: 10.1088/1674-1056/23/10/107803
    摘要 ( 136 )   PDF(289KB) ( 448 )  
    Metal-organic chemical vapor deposition (MOCVD) grown ferromagnetic GaMnN films are investigated by photoluminescence (PL) measurement with a mid-gap excitation wavelength of 405 nm. A sharp PL peak at 1.8 eV is found and the PL intensity successively decreases with the addition of Mn, in which the Mn concentration of sample A is below 1% ([Mn] A=0.75%) but its PL intensity is stronger than other samples'. The 1.8-eV PL peak is attributed to the recombination of electrons in the t2 state of the neutral Mn3+ acceptor with holes in the valence band. With Mn concentration increasing, the intensity of the PL peak decreases and the magnetic increment reduces in our samples. The correlation between the PL peak intensity and ferromagnetism of the samples is discussed in combination with the experimental results.
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    Pressure-dependent terahertz optical characterization of heptafluoropropane
    冷文秀, 戈立娜, 徐山森, 詹洪磊, 赵昆
    2014 (10):  107804-107804.  doi: 10.1088/1674-1056/23/10/107804
    摘要 ( 204 )   PDF(719KB) ( 509 )  
    Heptafluoropropane (HFP), as the best alternative to halon fire-suppression agents, is now a widely used fire extinguishing agent. The current studies of HFP, concentrating on the extinguishing mechanisms of flames and decomposition products, in general deal with the destructive and high temperature cases. In this paper, terahertz time-domain spectra are used to characterize HFP at different pressures. Optical parameters of HFP, such as absorption coefficient, refractive index, and relative permittivity, and their relationship with concentration of samples, are discussed. The absorption peak of HFP at 0.3 THz depends strongly on the applied pressure, and the corresponding parameters increase almost linearly with increasing HFP concentration. The present study lays a foundation for future extensive applications.
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    Energy transfer relation of a novel Ce3+/Pr3+/Eu3+ co-doped Sr2.975-xLaxAlO4+xF1-x solid solution phosphor
    王延泽, 马健, 孙亮, 李蕊, 王达健
    2014 (10):  107805-107805.  doi: 10.1088/1674-1056/23/10/107805
    摘要 ( 135 )   PDF(615KB) ( 541 )  
    The photoluminescence properties and energy transfer of a new Ce3+/Pr3+/Eu3+ co-doped solid-solution composition of Sr2.975-xLaxAlO4+xF1-x (LSAF) phosphor are investigated. Upon doping Pr3+ into lattices of LSAF:Ce host, a shoulder emission peak is observed at about 620 nm, owing to the transition of 1D23H4. Addition of Eu3+ to LSAF:Ce3+, Pr3+ phosphor results in a sharp emission peaked at 675 nm for the 5D07F3 transition and an increase of the intensity of red emission for Pr3+ with increasing Eu3+ concentration. The pathways of energy transfer among Ce3+, Pr3+, and Eu3+ are proposed to be responsible for color addition of a red component to the primary yellow emission, enabling a potential adjustable color for blue excitable warm white.
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    Optimum fluorescence emission around 1.8 μm for LiYF4 single crystals of various Tm3+-doping concentrations
    李珊珊, 夏海平, 符立, 董艳明, 谷雪梅, 章践立, 王冬杰, 张约品, 江浩川, 陈宝玖
    2014 (10):  107806-107806.  doi: 10.1088/1674-1056/23/10/107806
    摘要 ( 162 )   PDF(399KB) ( 413 )  
    In this paper, optical spectra of LiYF4 single crystals doped with Tm3+ ions of various concentrations are reported. The emission intensity at 1.8 μm first increases with increasing Tm3+ concentration, and reaches a maximum value when the concentration of Tm3+ is about 1.28 mol%, then it decreases rapidly as the concentration of Tm3+ further increases to 3.49 mol%. The emission lifetime at 1.8 μm also shows a similar tendency to the emission intensity. The maximum lifetime of 1.8 μm is measured to be 17.68 ms for the sample doped with Tm3+ of 1.28 mol%. The emission cross section of 3F4 level is calculated. The maximum reaches 3.76×10-21 cm2 at 1909 nm. The cross relaxation (3H6, 3H43F4,3F4
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    Terahertz plasmon and surface-plasmon modes in cylindrical metallic nanowires
    吴平, 徐文, 李龙龙, 卢铁城, 吴卫东
    2014 (10):  107807-107807.  doi: 10.1088/1674-1056/23/10/107807
    摘要 ( 222 )   PDF(336KB) ( 469 )  
    We present a theoretical study on collective excitation modes associated with plasmon and surface-plasmon oscillations in cylindrical metallic nanowires. Based on a two-subband model, the dynamical dielectric function matrix is derived under the random-phase approximation. An optic-like branch and an acoustic-like branch, which are free of Landau damping, are observed for both plasmon and surface-plasmon modes. Interestingly, for surface-plasmon modes, we find that two branches of the dispersion relation curves converge at a wavevector qz=qmax beyond which no surface-plasmon mode exists. Moreover, we examine the dependence of these excitation modes on sample parameters such as the radius of the nanowires. It is found that in metallic nanowires realized by state-of-the-art nanotechnology the intra-and inter-subband plasmon and surface-plasmon frequencies are in the terahertz bandwidth. The frequency of the optic-like modes decreases with increasing radius of the nanowires, whereas that of the acoustic-like modes is not sensitive to the variation of the radius. This study is pertinent to the application of metallic nanowires as frequency-tunable terahertz plasmonic devices.
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    Plasmon-induced absorption in stacked metamaterials based on phase retardation
    万明理, 袁书卿, 代克杰, 宋月丽, 周丰群, 何金娜
    2014 (10):  107808-107808.  doi: 10.1088/1674-1056/23/10/107808
    摘要 ( 131 )   PDF(284KB) ( 497 )  
    In this paper, based on the constructive interference of plasmonic dipolar and quadrupolar modes, a classical analogue of electromagnetically induced absorption (EIA) is demonstrated theoretically in a stacked metamaterial consisting of a short metal strip (which acts as a bright resonator) and a long metal strip (acting as a dark resonator), which has been reported to support the electromagnetically induced transparency (EIT) effect. The transition from EIA to EIT can be clearly observed in the absorbance spectra via varying the vertical spacing between two resonant oscillators. With the help of the coupled two-oscillator model, the phase shift between the bright and dark resonance modes is calculated by fitting the simulated absorbance spectra, which reveals the physical mechanisms behind constructive and destructive interference effects in EIT/EIA metamaterials.
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    Influences of anionic and cationic dopants on the morphology andoptical properties of PbS nanostructures
    Ramin Yousefi, Mohsen Cheragizade, Farid Jamali-Sheini, M. R. Mahmoudian, Abdolhossein Saaédi, Nay Ming Huang
    2014 (10):  108101-108101.  doi: 10.1088/1674-1056/23/10/108101
    摘要 ( 183 )   PDF(1551KB) ( 562 )  
    Selenium and zinc are used as anionic and cationic dopant elements to dope PbS nanostructures. The undoped and doped PbS nanostructures are grown using a thermal evaporation method. Scanning electron microscopy (SEM) results show similar morphologies for the undoped and doped PbS nanostructures. X-ray diffraction (XRD) patterns of three sets of the nanostructures indicate that these nanostructures each have a PbS structure with a cubic phase. Evidence of dopant incorporation is demonstrated by X-ray photoelectron spectroscopy (XPS). Raman spectra of the synthesized samples confirm the XRD results and indicate five Raman active modes, which relate to the PbS cubic phase for all the nanostructures. Room temperature photoluminescence (PL) and UV-Vis spectrometers are used to study optical properties of the undoped and doped PbS nanostructures. Optical characterization shows that emission and absorption peaks are in the infrared (IR) region of the electromagnetic spectrum for all PbS nanostructures. In addition, the optical studies of the doped PbS nanostructures reveal that the band gap of the Se-doped PbS is smaller, and the band gap of the Zn-doped PbS is bigger than the band gap of the undoped PbS nanostructures.
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    K2S-activated carbons developed from coal and their methane adsorption behaviors
    冯艳艳, 杨文, 储伟
    2014 (10):  108201-108201.  doi: 10.1088/1674-1056/23/10/108201
    摘要 ( 123 )   PDF(620KB) ( 546 )  
    The main purpose of this work is to prepare various activated carbons by K2S activation of coal with size fractions of 60-80 meshes, and investigate the microporosity development and corresponding methane storage capacities. Raw coal is mixed with K2S powder, and then heated at 750℃-900℃ for 30 min-150 min in N2 atmosphere to produce the adsorbents. The texture and surface morphology are characterized by a N2 adsorption/desorption isotherm at 77 K and scanning electron microscopy (SEM). The chemical properties of carbons are confirmed by ultimate analysis. The crystal structure and degree of graphitization are tested by X-ray diffraction and Raman spectra. The relationship between sulfur content and the specific surface area of the adsorbents is also determined. K2S activation is helps to bring about better development of pore texture. These adsorbents are microporous materials with textural parameters increasing in a range of specific surface area 72.27 m2/g-657.7 m2/g and micropore volume 0.035 cm3/g-0.334 cm3/g. The ability of activated carbons to adsorb methane is measured at 298 K and at pressures up to 5.0 MPa by a volumetric method. The Langmuir model fits the experimental data well. It is concluded that the high specific surface area and micropore volume of activated carbons do determine methane adsorption capacity. The adsorbents obtained at 800℃ for 90 min with K2S/raw coal mass ratios of 1.0 and 1.2 show the highest methane adsorption capacities amounting to 106.98 mg/g and 106.17 mg/g, respectively.
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    Theoretical and numerical studies on a planar gyrotronwith transverse energy extraction
    陈再高, 王建国, 王玥
    2014 (10):  108401-108401.  doi: 10.1088/1674-1056/23/10/108401
    摘要 ( 142 )   PDF(457KB) ( 421 )  
    In this paper, we study the planar gyrotron theoretically and numerically. Applying the large-signal theory to the planar gyrotron, the wave equation of electric field and the equation of motion of an electron are simultaneously solved to obtain some characteristic parameters, such as the phase-space plot of electrons, working frequency, startup time, electronic efficiency, and output power of the device. To verify the formulations used in this paper, three-dimensional particle simulations are performed on the same device, and the numerical results accord well with those obtained by using the large-signal theory. Theoretical and numerical results show that the electronic efficiency can reach 21% for the prototype of the planar gyrotron working at the frequency of 0.81 THz.
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    Modified GIT model for predicting wind-speed behavior of low-grazing-angle radar sea clutter
    张玉石, 张金鹏, 黎鑫, 吴振森
    2014 (10):  108402-108402.  doi: 10.1088/1674-1056/23/10/108402
    摘要 ( 311 )   PDF(435KB) ( 419 )  
    A modified GIT model for describing the variational trend of mean clutter reflectivity as a function of wind speed is proposed. It uses two slope adjustment factors and two critical wind-speed factors to define and adjust the increasing slope of reflectivity with respect to wind speed. In addition, it uses a constant factor to compensate the overall amplitude of clutter reflectivity. The performance of the modified GIT model has been verified on the basis of the L-band low-grazing-angle radar sea clutter data. The results are in good agreement with the experimental data, indicating that the model is more effective in predicting the wind-speed behavior of clutter reflectivity than the conventional GIT model, especially for lower and higher wind speeds. We believe that the proposed model can provide deeper insights into the relationship between radar sea clutter reflectivity and sea state conditions.
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    Investigation of strain effect on the hole mobility in GOI tri-gate pFETs including quantum confinement
    秦洁宇, 杜刚, 刘晓彦
    2014 (10):  108501-108501.  doi: 10.1088/1674-1056/23/10/108501
    摘要 ( 201 )   PDF(570KB) ( 318 )  
    The strain impact on hole mobility in the GOI tri-gate pFETs is investigated by simulating the strained Ge with quantum confinement from band structure to electro-static distribution as well as the effective mobility. Lattice mismatch strain induced by HfO2 warps and reshapes the valence subbands, and reduces the hole effective masses. The maximum value of hole density is observed near the top corners of the channel. The hole density is decreased by the lattice mismatch strain. The phonon scattering rate is degraded by strain, which results in higher hole mobility.
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    Initial conformation of kinesin’s neck linker
    耿轶钊, 纪青, 刘书霞, 晏世伟
    2014 (10):  108701-108701.  doi: 10.1088/1674-1056/23/10/108701
    摘要 ( 211 )   PDF(1342KB) ( 523 )  
    How ATP binding initiates the docking process of kinesin's neck linker is a key question in understanding kinesin mechanisms. By exploiting a molecular dynamics method, we investigate the initial conformation of kinesin's neck linker in its docking process. We find that, in the initial conformation, the neck linker has interactions with β0 and forms a 'cover-neck bundle' structure with β0. From this initial structure, the formation of extra turns and the docking of the cover-neck bundle structure can be achieved. The motor head provides a forward force on the initial cover-neck bundle structure through ATP-induced rotation. This force, together with the hydrophobic interaction of ILE327 with the hydrophobic pocket on the motor head, drives the formation of the extra turn and initiates the neck linker docking process. Based on these findings, a pathway from ATP binding-induced motor head rotation to neck linker docking is proposed.
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    Reconstruction of a 6-MeV bremsstrahlung spectrum by multi-layer absorption based on LiF:Mg, Cu, P
    黄建微, 王乃彦
    2014 (10):  108702-108702.  doi: 10.1088/1674-1056/23/10/108702
    摘要 ( 146 )   PDF(698KB) ( 414 )  
    In this paper, TLD (LiF: Mg, Cu, P) is used as detector. A multi-layer absorption (MLA) model is designed. Combined with Monte-Carlo processes, a bremsstrahlung X-ray spectrum is reconstructed by an iterative method; the reconstructed results agree with the results of simulations by the MCNP process essentially, especially in middle energy region.
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    Plasticity-induced characteristic changes of pattern dynamics and the related phase transitions in small-world neuronal networks
    黄旭辉, 胡岗
    2014 (10):  108703-108703.  doi: 10.1088/1674-1056/23/10/108703
    摘要 ( 169 )   PDF(3965KB) ( 427 )  
    Phase transitions widely exist in nature and occur when some control parameters are changed. In neural systems, their macroscopic states are represented by the activity states of neuron populations, and phase transitions between different activity states are closely related to corresponding functions in the brain. In particular, phase transitions to some rhythmic synchronous firing states play significant roles on diverse brain functions and disfunctions, such as encoding rhythmical external stimuli, epileptic seizure, etc. However, in previous studies, phase transitions in neuronal networks are almost driven by network parameters (e.g., external stimuli), and there has been no investigation about the transitions between typical activity states of neuronal networks in a self-organized way by applying plastic connection weights. In this paper, we discuss phase transitions in electrically coupled and lattice-based small-world neuronal networks (LBSW networks) under spike-timing-dependent plasticity (STDP). By applying STDP on all electrical synapses, various known and novel phase transitions could emerge in LBSW networks, particularly, the phenomenon of self-organized phase transitions (SOPTs): repeated transitions between synchronous and asynchronous firing states. We further explore the mechanics generating SOPTs on the basis of synaptic weight dynamics.
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    Consensus of heterogeneous multi-agent systems based on sampled data with a small sampling delay
    王娜, 吴治海, 彭力
    2014 (10):  108901-108901.  doi: 10.1088/1674-1056/23/10/108901
    摘要 ( 240 )   PDF(348KB) ( 550 )  
    In this paper, consensus problems of heterogeneous multi-agent systems based on sampled data with a small sampling delay are considered. First, a consensus protocol based on sampled data with a small sampling delay for heterogeneous multi-agent systems is proposed. Then, the algebra graph theory, the matrix method, the stability theory of linear systems, and some other techniques are employed to derive the necessary and sufficient conditions guaranteeing heterogeneous multi-agent systems to asymptotically achieve the stationary consensus. Finally, simulations are performed to demonstrate the correctness of the theoretical results.
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    Network dynamics and its relationships to topology andcoupling structure in excitable complex networks
    张立升, 谷伟凤, 胡岗, 弭元元
    2014 (10):  108902-108902.  doi: 10.1088/1674-1056/23/10/108902
    摘要 ( 316 )   PDF(1184KB) ( 514 )  
    All dynamic complex networks have two important aspects, pattern dynamics and network topology. Discovering different types of pattern dynamics and exploring how these dynamics depend on network topologies are tasks of both great theoretical importance and broad practical significance. In this paper we study the oscillatory behaviors of excitable complex networks (ECNs) and find some interesting dynamic behaviors of ECNs in oscillatory probability, the multiplicity of oscillatory attractors, period distribution, and different types of oscillatory patterns (e.g., periodic, quasiperiodic, and chaotic). In these aspects, we further explore strikingly sharp differences among network dynamics induced by different topologies (random or scale-free topologies) and different interaction structures (symmetric or asymmetric couplings). The mechanisms behind these differences are explained physically.
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    Physical analysis on improving the recovery accuracy of the Earth’s gravity field by a combination of satellite observations in along-track and cross-track directions
    郑伟, 许厚泽, 钟敏, 员美娟
    2014 (10):  109101-109101.  doi: 10.1088/1674-1056/23/10/109101
    摘要 ( 111 )   PDF(1826KB) ( 438 )  
    The physical investigations on the accuracy improvement to the measurement of the Earth's gravity field recovery are carried out based on the next-generation Pendulum-A/B out-of-plane twin-satellite formation in this paper. Firstly, the Earth's gravity field complete up to degree and order 100 is, respectively, recovered by the collinear and pendulum satellite formations using the orbital parameters of the satellite and the matching accuracies of key payloads from the twin GRACE satellites. The research results show that the accuracy of the Earth's gravity field model from the Pendulum-A/B satellite formation is about two times higher than from the collinear satellite formation, and the further improvement of the determination accuracy of the Earth's gravity field model is feasible by the next-generation Pendulum-A/B out-of-plane twin-satellite formation. Secondly, the Earth's gravity field from Pendulum-A/B complete up to degree and order 100 is accurately recovered based on the orbital parameters of the satellite (e.g., an orbital altitude of 400 km, an intersatellite range of 100 km, an orbital inclination of 89° and an orbital eccentricity of 0.001), the matching accuracies of space-borne instruments (e.g. 10 -6 m in the intersatellite range, 10 -3 m in the orbital position, 10 -6 m/s in orbital velocity, and 10 -11 m/s2 in non-conservative force), an observation time of 30 days and a sampling interval of 10 s. The measurement accuracy of the Earth's gravity field from the next-generation Pendulum-A/B out-of-plane twin-satellite formation is full of promise for being improved by about 10 times compared with that from the current GRACE satellite formation. Finally, the physical requirements for the next-generation Pendulum-A/B out-of-plane twin-satellite formation are analyzed, and it is proposed that the satellite orbital altitude be preferably designed to be close to 400± 50 km and the matching precision of key sensors from the Pendulum-A/B mission be about one order of magnitude higher than from the GRACE program.
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    Study of typical space wave-particle coupling eventspossibly related with seismic activity
    张振霞, 王辰宇, 申旭辉, 李新乔, 吴书贵
    2014 (10):  109401-109401.  doi: 10.1088/1674-1056/23/10/109401
    摘要 ( 162 )   PDF(3433KB) ( 474 )  
    Based on the DEMETER satellite, we found two space wave-particle coupling events during February 2010 that took place in the range of the McIlwain parameter L (1.27~1.37). There are strong spatial and temporal correlation between the particle bursts (PBs) and the electromagnetic disturbances of the coupling events. The two PBs show different energy spectrum characteristics, while the corresponding electromagnetic disturbances concentrated on different frequency ranges. In agreement with the prediction of the theory of wave-particle interaction, we conclude that the two wave-particle interactions can be probably explained as follows: one is electron-dominant precipitation with energy of 0.09 MeV~0.2 MeV induced by a VLF electromagnetic wave with the frequencies of 14 kHz~20 kHz, and another is proton-dominant precipitation with energies of 0.65 MeV~2.85 MeV induced by a VLF electromagnetic wave with the frequency of ≤ 100 Hz. For the first time, these particle bursts' origins, from electrons or protons detected by the Instrument for the Detection of Particles (IDP) on board, are inferred by theoretical calculation, although the instrument has no ability to identify the particle species.
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    Variational regularization method of solving the Cauchy problem for Laplace’s equation: Innovation of the Grad-Shafranov (GS) reconstruction
    颜冰, 黄思训
    2014 (10):  109402-109402.  doi: 10.1088/1674-1056/23/10/109402
    摘要 ( 224 )   PDF(274KB) ( 542 )  
    The simplified linear model of Grad-Shafranov (GS) reconstruction can be reformulated into an inverse boundary value problem of Laplace's equation. Therefore, in this paper we focus on the method of solving the inverse boundary value problem of Laplace's equation. In the first place, the variational regularization method is used to deal with the ill-posedness of the Cauchy problem for Laplace's equation. Then, the 'L-Curve' principle is suggested to be adopted in choosing the optimal regularization parameter. Finally, a numerical experiment is implemented with a section of Neumann and Dirichlet boundary conditions with observation errors. The results well converge to the exact solution of the problem, which proves the efficiency and robustness of the proposed method. When the order of observation error δ is 10 -1, the order of the approximate result error can reach 10 -3.
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