中国物理B

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Stability analysis of multi-group deterministic and stochastic epidemic models with vaccination rate

王志刚, 高瑞梅, 樊晓明, 韩七星

2014 (9): 90201-090201. doi: 10.1088/1674-1056/23/9/090201

摘要 ( 745 )

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We discuss in this paper a deterministic multi-group MSIR epidemic model with a vaccination rate, the basic reproduction number R₀, a key parameter in epidemiology, is a threshold which determines the persistence or extinction of the disease. By using Lyapunov function techniques, we show if R₀ is greater than 1 and the deterministic model obeys some conditions, then the disease will prevail, the infective persists and the endemic state is asymptotically stable in a feasible region. If R₀ is less than or equal to 1, then the infective disappear so the disease dies out. In addition, stochastic noises around the endemic equilibrium will be added to the deterministic MSIR model in order that the deterministic model is extended to a system of stochastic ordinary differential equations. In the stochastic version, we carry out a detailed analysis on the asymptotic behavior of the stochastic model. In addition, regarding the value of R₀, when the stochastic system obeys some conditions and R₀ is greater than 1, we deduce the stochastic system is stochastically asymptotically stable. Finally, the deterministic and stochastic model dynamics are illustrated through computer simulations.

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A meshless algorithm with moving least square approximations for elliptic Signorini problems

王延冲, 李小林

2014 (9): 90202-090202. doi: 10.1088/1674-1056/23/9/090202

摘要 ( 826 )

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Based on the moving least square (MLS) approximations and the boundary integral equations (BIEs), a meshless algorithm is presented in this paper for elliptic Signorini problems. In the algorithm, a projection operator is used to tackle the nonlinear boundary inequality conditions. The Signorini problem is then reformulated as BIEs and the unknown boundary variables are approximated by the MLS approximations. Accordingly, only a nodal data structure on the boundary of a domain is required. The convergence of the algorithm is proven. Numerical examples are given to show the high convergence rate and high computational efficiency of the presented algorithm.

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Group solution for an unsteady non-Newtonian Hiemenz flow with variable fluid properties and suction/injection

H. M. El-Hawary, Mostafa A. A. Mahmoud, Reda G. Abdel-Rahman, Abeer S. Elfeshawey

2014 (9): 90203-090203. doi: 10.1088/1674-1056/23/9/090203

摘要 ( 635 )

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The theoretic transformation group approach is applied to address the problem of unsteady boundary layer flow of a non-Newtonian fluid near a stagnation point with variable viscosity and thermal conductivity. The application of a two-parameter group method reduces the number of independent variables by two, and consequently the governing partial differential equations with the boundary conditions transformed into a system of ordinary differential equations with the appropriate corresponding conditions. Two systems of ordinary differential equations have been solved numerically using a fourth-order Runge-Kutta algorithm with a shooting technique. The effects of various parameters governing the problem are investigated.

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Homotopic mapping solitary traveling wave solutions for the disturbed BKK mechanism physical model

周先春, 石兰芳, 韩祥临, 莫嘉琪

2014 (9): 90204-090204. doi: 10.1088/1674-1056/23/9/090204

摘要 ( 744 )

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Using the trial equation method, a Broer-Kau-Kupershmidt (BKK) mechanism physical model is obtained, and the exact and approximate solitary traveling wave solutions are found. As an example, it is pointed out that the solitary traveling wave approximate solutions have better accurate degree by using the homotopic mapping theory.

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Unsuitable use of spin and pseudospin symmetries with a pseudoscalar Cornell potential

L. B. Castro, A. S. de Castro

2014 (9): 90301-090301. doi: 10.1088/1674-1056/23/9/090301

摘要 ( 564 )

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The concepts of spin and pseudospin symmetries has been used as mere rhetorics to decorate the pseudoscalar potential [Chin. Phys. B 22 090301 (2013)]. It is also pointed out that a more complete analysis of the bound states of fermions in a pseudoscalar Cornell potential has already been published elsewhere.

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New 3-mode bosonic operator realization of SU(2) Lie algebra：From the point of view of squeezing

笪诚, 陈千帆, 范洪义

2014 (9): 90302-090302. doi: 10.1088/1674-1056/23/9/090302

摘要 ( 696 )

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We consider the quantum mechanical SU(2) transformation e^{2λ J_z}J_±e^{-2λ J_z}=e^±2λJ_± as if the meaning of squeezing with e^±2λ being squeezing parameter. By studying SU(2) operators (J_±,J_z) from the point of view of squeezing we find that (J_±,J_z) can also be realized in terms of 3-mode bosonic operators. Employing this realization, we find the natural representation (the eigenvectors of J₊ or J_-) of the 3-mode squeezing operator e^{2λ J_z}. The idea of considering quantum SU(2) transformation as if squeezing is liable for us to obtain the new bosonic operator realization of SU(2) and new squeezing operators.

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New approach to solving master equations of density operator for the Jaynes Cummings model with cavity damping

Seyed Mahmoud Ashrafi, Mohammad Reza Bazrafkan

2014 (9): 90303-090303. doi: 10.1088/1674-1056/23/9/090303

摘要 ( 752 )

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By introducing thermo-entangled state representation |η>, which can map master equations of density operator in quantum statistics as state-vector evolution equations, and using “dissipative interaction picture” we solve the master equation of Jaynes-Cummings model with cavity damping. In addition we derive the Wigner function for density operator when the atom is initially in the up state |↑> and the cavity mode is in coherent state.

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Exact solution of Dirac equation for Scarf potential with new tensor coupling potential for spin and pseudospin symmetries using Romanovski polynomials

A. Suparmi, C. Cari, U. A. Deta

2014 (9): 90304-090304. doi: 10.1088/1674-1056/23/9/090304

摘要 ( 586 )

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The bound state solutions of Dirac equations for a trigonometric Scarf potential with a new tensor potential under spin and pseudospin symmetry limits are investigated using Romanovski polynomials. The proposed new tensor potential is inspired by superpotential form in supersymmetric (SUSY) quantum mechanics. The Dirac equations with trigonometric Scarf potential coupled by a new tensor potential for the pseudospin and spin symmetries reduce to Schrödinger-type equations with a shape invariant potential since the proposed new tensor potential is similar to the superpotential of trigonometric Scarf potential. The relativistic wave functions are exactly obtained in terms of Romanovski polynomials and the relativistic energy equations are also exactly obtained in the approximation scheme of centrifugal term. The new tensor potential removes the degeneracies both for pseudospin and spin symmetries.

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Derivation of quantum Chernoff metric with perturbation expansion method

钟伟, 马健, 刘京, 王晓光

2014 (9): 90305-090305. doi: 10.1088/1674-1056/23/9/090305

摘要 ( 763 )

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We investigate a measure of distinguishability defined by the quantum Chernoff bound, which naturally induces the quantum Chernoff metric over a manifold of quantum states. Based on a quantum statistical model, we alternatively derive this metric by means of perturbation expansion. Moreover, we show that the quantum Chernoff metric coincides with the infinitesimal form of the quantum Hellinger distance, and reduces to the variant version of the quantum Fisher information for the single-parameter case. We also give the exact form of the quantum Chernoff metric for a qubit system containing a single parameter.

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Comments on “Distillability sudden death in qutrit–qutrit systems under thermal reservoirs”

Mazhar Ali

2014 (9): 90306-090306. doi: 10.1088/1674-1056/23/9/090306

摘要 ( 513 )

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In a recent paper (2012 Chin. Phys. B 21 084205), the authors studied the problem of distillability sudden death. We find that their equation of motion is incorrect and consequently the rest of the paper is wrong. Even apart from starting with a wrong equation of motion, their description of the phenomenon of distillability sudden death is totally misleading and needs to be rectified. To this aim, we show that certain initially prepared free-entangled states become bound-entangled in a finite time under thermal reservoirs. Moreover, in contrast with zero-temperature reservoirs, simple local unitary transformations cannot completely avoid distillability sudden death.

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Joint remote preparation of an arbitrary five-qubit Brown state via non-maximally entangled channels

常利伟, 郑世慧, 谷利泽, 肖达, 杨义先

2014 (9): 90307-090307. doi: 10.1088/1674-1056/23/9/090307

摘要 ( 610 )

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We firstly present a novel scheme for deterministic joint remote state preparation of an arbitrary five-qubit Brown state using four Greenberg-Horme-Zeilinger (GHZ) entangled states as the quantum channel. The success probability of this scheme is up to 1, which is superior to the existing ones. Moreover, the scheme is extended to the generalized case where three-qubit and four-qubit non-maximally entangled states are taken as the quantum channel. We simultaneously employ two common methods to reconstruct the desired state. By comparing these two methods, we draw a conclusion that the first is superior to the second-optimal positive operator-valued measure only taking into account the number of auxiliary particles and the success probability.

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Efficient remote preparation of arbitrary two-and three-qubit states via the χ state

马松雅, 罗明星

2014 (9): 90308-090308. doi: 10.1088/1674-1056/23/9/090308

摘要 ( 603 )

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The application of χ state are investigated in remote state preparation (RSP). By constructing useful measurement bases with the aid of Hurwitz matrix equation, we propose several RSP schemes of arbitrary two-and three-qubit states via the χ state as the entangled resource. It is shown that the original state can be successfully prepared with the probability 100% and 50% for real coefficients and complex coefficients, respectively. For the latter case, the special ensembles with unit success probability are discussed by the permutation group. It is worth mentioning that the novel measurement bases have no restrictions on the coefficients of the prepared state, which means that the proposed schemes are more applicable.

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Quantum secure direct communication network with hyperentanglement

Chang Ho Hong, Jino Heo, Jong In Lim, Hyung Jin Yang

2014 (9): 90309-090309. doi: 10.1088/1674-1056/23/9/090309

摘要 ( 663 )

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We propose a quantum secure direct communication protocol with entanglement swapping and hyperentanglement. Any two users, Alice and Bob, can communicate with each other in a quantum network, even though there is no direct quantum channel between them. The trust center, Trent, who provides a quantum channel to link them by performing entanglement swapping, cannot eavesdrop on their communication. This protocol provides a high channel capacity because it uses hyperentanglement, which can be generated using a beta barium borate crystal.

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Fast implementation of length-adaptive privacy amplification in quantum key distribution

张春梅, 李默, 黄靖正, Patcharapong Treeviriyanupab, 李宏伟, 李芳毅, 王川, 银振强, 陈巍, Keattisak Sripimanwat, 韩正甫

2014 (9): 90310-090310. doi: 10.1088/1674-1056/23/9/090310

摘要 ( 802 )

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Post-processing is indispensable in quantum key distribution (QKD), which is aimed at sharing secret keys between two distant parties. It mainly consists of key reconciliation and privacy amplification, which is used for sharing the same keys and for distilling unconditional secret keys. In this paper, we focus on speeding up the privacy amplification process by choosing a simple multiplicative universal class of hash functions. By constructing an optimal multiplication algorithm based on four basic multiplication algorithms, we give a fast software implementation of length-adaptive privacy amplification. “Length-adaptive” indicates that the implementation of privacy amplification automatically adapts to different lengths of input blocks. When the lengths of the input blocks are 1 Mbit and 10 Mbit, the speed of privacy amplification can be as fast as 14.86 Mbps and 10.88 Mbps, respectively. Thus, it is practical for GHz or even higher repetition frequency QKD systems.

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Landau damping and frequency-shift of a quadrupole mode in a disc-shaped rubidium Bose-Einstein condensate

阿孜古丽·热合木提, 彭胜强, 马晓栋

2014 (9): 90311-090311. doi: 10.1088/1674-1056/23/9/090311

摘要 ( 598 )

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The damping and frequency-shift in Landau mechanism of a quadrupole mode in a disc-shaped rubidium Bose-Einstein condensate are investigated by using the Hartree-Fock-Bogoliubov approximation. The practical relaxations of the elementary excitations and the orthometric relation among them are taken into account to obtain advisable calculation formula for damping as well as frequency-shift. The first approximation of Gaussian distribution function is employed for the ground-state wavefunction to suitably eliminate the divergence of the analytic three-mode coupling matrix elements. According to these methods, both Landau damping rate and frequency-shift of the quadrupole mode are analytically calculated. In addition, all the theoretical results agree with the experimental ones.

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Erratum：Classical interpretations of relativistic precessions

Sankar Hajra

2014 (9): 90401-090401. doi: 10.1088/1674-1056/23/9/090401

摘要 ( 785 )

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We point out an error in Eq. (19) in our original paper [Chin. Phys. B 23 040402 (2014)] and present the correct equation.

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Effects of Lévy noise and immune delay on the extinction behavior in a tumor growth model

郝孟丽, 徐伟, 谷旭东, 戚鲁媛

2014 (9): 90501-090501. doi: 10.1088/1674-1056/23/9/090501

摘要 ( 765 )

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The combined effects of Lévy noise and immune delay on the extinction behavior in a tumor growth model are explored. The extinction probability of tumor with certain density is measured by exit probability. The expression of the exit probability is obtained using the Taylor expansion and the infinitesimal generator theory. Based on numerical calculations, it is found that the immune delay facilitates tumor extinction when the stability index α<1, but inhibits tumor extinction when the stability index α>1. Moreover, larger stability index and smaller noise intensity are in favor of the extinction for tumor with low density. While for tumor with high density, the stability index and the noise intensity should be reduced to promote tumor extinction.

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Generation of countless embedded trumpet-shaped chaotic attractors in two opposite directions from a new three-dimensional system with no equilibrium point

孙常春

2014 (9): 90502-090502. doi: 10.1088/1674-1056/23/9/090502

摘要 ( 609 )

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A new three-dimensional (3D) continuous autonomous system with one parameter and three quadratic terms is presented firstly in this paper. Countless embedded trumpet-shaped chaotic attractors in two opposite directions are generated from the system as time goes on. The basic dynamical behaviors of the strange chaotic system are investigated. Another more complex 3D system with the same capability of generating countless embedded trumpet-shaped chaotic attractors is also put forward.

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Synchronous implementation of optoelectronic NOR and XNOR logic gates using parallel synchronization of three chaotic lasers

颜森林

2014 (9): 90503-090503. doi: 10.1088/1674-1056/23/9/090503

摘要 ( 746 )

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The parallel synchronization of three chaotic lasers is used to emulate optoelectronic logic NOR and XNOR gates via modulating the light and the current. We deduce a logical computational equation that governs the chaotic synchronization, logical input, and logical output. We construct fundamental gates based on the three chaotic lasers and define the computational principle depending on the parallel synchronization. The logic gate can be implemented by appropriately synchronizing two chaotic lasers. The system shows practicability and flexibility because it can emulate synchronously an XNOR gate, two NOR gates, and so on. The synchronization can still be deteceted when mismatches exist with a certain range.

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Fabrication and measurement of traceable pitch standard with a big area at trans-scale

邓晓, 李同保, 雷李华, 马艳, 马蕊, 翁浚婧, 李源

2014 (9): 90601-090601. doi: 10.1088/1674-1056/23/9/090601

摘要 ( 750 )

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Atom lithography with chromium can be utilized to fabricate a pitch standard,which is directly traceable to the wavelength of the laser standing waves. The result of a calibrated commercial AFM measurement demonstrates that the pitch standard is (212.8± 0.1) nm with a peak-to-valley-height (PTVH) better than 20 nm. The measurement results show the high period accuracy of traceability with the standing laser wavelength (λ/2=212.78 nm). The Cr nano-grating covers a 1000 μm×500 μm area, with a PTVH better than 10 nm. The feature width broadening of the Cr nanostructure has been experimentally observed along the direction of the standing waves. The PTVH along the Gaussian laser direction is similar to a Gaussian distribution. Highly uniform periodic nanostructures with a big area at the millimeter scale, and the surface growth uniformity of the Cr nano-grating, show its great potential in the application of a traceable pitch standard at trans-scales.

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Third-order optical intensity correlation measurements of pseudo-thermal light

陈希浩, 吴炜, 孟少英, 李明飞

2014 (9): 90701-090701. doi: 10.1088/1674-1056/23/9/090701

摘要 ( 809 )

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Third-order Hanbrury Brown-Twiss and double-slit interference experiments with a pseudo-thermal light are performed by recording intensities in single, double and triple optical paths, respectively. The experimental results verifies the theoretical prediction that the indispensable condition for achieving a interference pattern or ghost image in Nth-order intensity correlation measurements is the synchronous detection of the same light field by each reference detector, no matter the intensities recorded in one, or two, or N optical paths. It is shown that, when the reference detectors are scanned in the opposite directions, the visibility and resolution of the third-order spatial correlation function of thermal light is much better than that scanned in the same direction, but it is no use for obtaining the Nth-order interference pattern or ghost image in the thermal Nth-order interference or ghost imaging.

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Utilizing a shallow trench isolation parasitic transistor to characterize the total ionizing dose effect of partially-depleted silicon-on-insulator input/output n-MOSFETs

彭超, 胡志远, 宁冰旭, 黄辉祥, 樊双, 张正选, 毕大炜, 恩云飞

2014 (9): 90702-090702. doi: 10.1088/1674-1056/23/9/090702

摘要 ( 621 )

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We investigate the effects of ⁶⁰Co γ-ray irradiation on the 130 nm partially-depleted silicon-on-isolator (PDSOI) input/output (I/O) n-MOSFETs. A shallow trench isolation (STI) parasitic transistor is responsible for the observed hump in the back-gate transfer characteristic curve. The STI parasitic transistor, in which the trench oxide acts as the gate oxide, is sensitive to the radiation, and it introduces a new way to characterize the total ionizing dose (TID) responses in the STI oxide. A radiation enhanced drain induced barrier lower (DIBL) effect is observed in the STI parasitic transistor. It is manifested as the drain bias dependence of the radiation-induced off-state leakage and the increase of the DIBL parameter in the STI parasitic transistor after irradiation. Increasing the doping concentration in the whole body region or just near the STI sidewall can increase the threshold voltage of the STI parasitic transistor, and further reduce the radiation-induced off-state leakage. Moreover, we find that the radiation-induced trapped charge in the buried oxide leads to an obvious front-gate threshold voltage shift through the coupling effect. The high doping concentration in the body can effectively suppress the radiation-induced coupling effect.

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Molecular structure and analytical potential energy function of SeCO

张恒, 田端亮, 阎世英

2014 (9): 93101-093101. doi: 10.1088/1674-1056/23/9/093101

摘要 ( 786 )

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The density functional method (B3P86/6-311G) is used for calculating the possible structures of SeC, SeO, and SeCO molecules. The result shows that the ground state of the SeC molecule is ¹Σ, the equilibrium nuclear distance is R_SeC=0.1699 nm, and the dissociation energy is D_e=8.7246 eV. The ground state of the SeO molecule is ³Σ, with equilibrium nuclear distance R_SeO=0.1707 nm and dissociation energy D_e=7.0917 eV. There are two structures for the ground state of the SeCO molecule: Se=C=O and Se=O=C. The linear Se=C=O is ¹Σ. Its equilibrium nuclear distances and dissociation energy are R_SeC=0.1715 nm, R_CO=0.1176 nm and 18.8492 eV, respectively. The other structure Se=O=C is ¹Σ. Its equilibrium nuclear distances and dissociation energy are R_CO=0.1168 nm, R_SeO=0.1963 nm and 15.5275 eV, respectively. The possible dissociative limit of the SeCO molecule is analyzed. The potential energy function for the SeCO molecule has been obtained from the many-body expansion theory. The contour of the potential energy curve describes the structure characters of the SeCO molecule. Furthermore, contours of the molecular stretching vibration based on this potential energy function are discussed.

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Microwave photonic filter with a continuously tunable central frequency using an SOI high-Q microdisk resonator

刘力, 杨婷, 董建绩

2014 (9): 93201-093201. doi: 10.1088/1674-1056/23/9/093201

摘要 ( 699 )

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Utilizing a high-Q microdisk resonator (MDR) on a single silicon-on-insulator (SOI) chip, a compact microwave photonic filter (MPF) with a continuously tunable central frequency is proposed and experimentally demonstrated. Assisted by the optical single side-band (OSSB) modulation, the optical frequency response of the MDR is mapped to the microwave frequency response to form an MPF with a continuously tunable central frequency and a narrow 3-dB bandwidth. In the experiment, using an MDR with a compact size of 20×20 μ² and a high Q factor of 1.07×10⁵, we obtain a compact MPF with a high rejection ratio of about 40 dB, a 3-dB bandwidth of about 2 GHz, and a frequency tuning range larger than 12 GHz. Our approach may allow the implementation of very compact, low-cost, low-consumption, and integrated notch MPF in a silicon chip.

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Electric dipole moments of lithium atoms in Rydberg states

董慧杰, 黄可树, 李昌勇, 赵建明, 张临杰, 贾锁堂

2014 (9): 93202-093202. doi: 10.1088/1674-1056/23/9/093202

摘要 ( 606 )

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Recently, the diverse properties of Rydberg atoms, which probably arise from its large electric dipole moment (EDM), have been explored. In this paper, we report electric dipole moments along with Stark energies and charge densities of lithium Rydberg states in the presence of electric fields, calculated by matrix diagonalization. Huge electric dipole moments are discovered. In order to check the validity of the EDMs, we also use these electric dipole moments to calculate the Stark energies by numerical integration. The results agree with those calculated by matrix diagonalization.

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Atomic structure calculations for F-like tungsten

Sunny Aggarwal

2014 (9): 93203-093203. doi: 10.1088/1674-1056/23/9/093203

摘要 ( 543 )

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Energy levels, wavefunction compositions and lifetimes have been computed for all levels of 1s²2s²2p⁵, 1s²2s2p⁶, 1s²2s²2p⁴3s, 1s²2s²2p⁴3p, and 1s²2s²2p⁴3d configurations in highly charged F-like tungsten ion. The multiconfigurational Dirac-Fock method (MCDF) is adopted to generate the wavefunctions. We have also presented the transition wavelengths, oscillator strengths, transition probabilities, and line strengths for the electric dipole (E1) and magnetic quadrupole (M2) transition from the 1s²2s²2p⁵ ground configuration. We have performed parallel calculations with the flexible atomic code (FAC) for comparing the atomic data. The reliability of present data is assessed by comparison with other theoretical and experimental data available in the literature. Good agreement is found between our results and those obtained using different approaches confirm the quality of our results. Additionally, we have predicted some new atomic data for F-like W that were not available so far and may be important for plasma diagnostic analysis in fusion plasma.

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Controllable optical mirror of cesium atoms with four-wave mixing

周海涛, 王丹, 郭苗军, 郜江瑞, 张俊香

2014 (9): 93204-093204. doi: 10.1088/1674-1056/23/9/093204

摘要 ( 1004 )

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The controllable optical mirror is experimentally accomplished in a Λ-type three-level atomic system coupled with standing wave. It is shown that the reflection of probe light results from electromagnetically-induced-transparency-based four-wave mixing, therefore the reflection efficiency is highly dependent on the angle for phase matching condition between the probe and coupling fields. The measured reflection spectra show good agreement with dispersion compensation theory.

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Isolated attosecond pulse generation from atom radiated by a three-color laser pulse

秦岳飞, 郭福明, 李苏宇, 杨玉军, 陈高

2014 (9): 93205-093205. doi: 10.1088/1674-1056/23/9/093205

摘要 ( 690 )

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We theoretically investigate high-order harmonic and attosecond pulse generation from helium atom in a three-color laser field, which is synthesized by 10 fs/800 nm Ti-sapphire laser and a two-color field consisting of 30 fs/532 nm and 30 fs/1330 nm pulses. Compared with harmonic spectrum generated by a monochromatic field, the harmonics generated from the synthesized three-color field show a supercontinuum spectrum with a bandwidth of 235 eV, ranging from the 154th to the 306th order harmonic. This phenomenon can be attributed to the fact that the ionization of atoms as well as motion of ionized electron can be effectively controlled in the three-color field. Therefore, an isolated 46-as pulse can be generated by superposing supercontinuum from the 160th to the 210th order harmonics.

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An effective method of accelerating Bose gases using magnetic coils

卢海昌, 翟跃阳, 潘睿智, 杨仕锋

2014 (9): 93701-093701. doi: 10.1088/1674-1056/23/9/093701

摘要 ( 655 )

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Based on the experimental device which is a non-uniform magnetic field to trap an atom, we show how to obtain a certain velocity of a Bose gas by controlling the magnetic coils. By comparing the relationship of the different current supply and delay time versus the ultimate velocity of the atom, we theoretically predict the method of accelerating the gases to an expected velocity. This method is of great convenience and significance for the applications in cold atom physics and precision measurements.

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Comparison experiments of neon and helium buffer gases cooling in trapped ¹⁹⁹Hg⁺ ions linear trap

杨玉娜, 柳浩, 何跃宏, 杨智慧, 汪漫, 陈义和, 佘磊, 李交美

2014 (9): 93702-093702. doi: 10.1088/1674-1056/23/9/093702

摘要 ( 692 )

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The influences of different buffer gas, neon and helium, on ¹⁹⁹Hg⁺ clock transition are compared in trapped ¹⁹⁹Hg⁺linear trap. By the technique of time domain's Ramsey separated oscillatory fields, the buffer gas pressure frequency shifts of ¹⁹⁹Hg⁺ clock transition are measured to be (df/d P_Ne)(1/f)=1.8×10^-8 Torr^-1 for neon and (df/d P_He)(1/f)=9.1×10^-8 Torr^-1 for helium. Meanwhile, the line-width of ¹⁹⁹Hg⁺ clock transition spectrum with the buffer gas neon is narrower than that with helium at the same pressure. These experimental results show that neon is a more suitable buffer gas than helium in ¹⁹⁹Hg⁺ ions microwave frequency standards because of the ¹⁹⁹Hg⁺ clock transition is less sensitive to neon variations and the better cooling effect of neon. The optimum operating pressure for neon is found to be about 1.0×10^-5 Torr in our linear ion trap system.

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Solving the atmospheric scattering optical transfer function using the multi-coupled single scattering method

孙斌, 洪津, 孙晓兵

2014 (9): 94201-094201. doi: 10.1088/1674-1056/23/9/094201

摘要 ( 793 )

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The atmospheric scattering optical transfer function (OTF) is solved by applying the multi-coupled single scattering (MCSS) method to the three-dimensional radiative transfer equation (RTE) under the periodic ground condition. This approach is a direct hit to the atmospheric scattering OTF using the same original context of modulation transfer function (MTF) measurement, i.e., images of sinusoidal grating at different spatial frequencies. Both the amplitude and phase shift of the OTF at various zenith and azimuth angles can be obtained at an arbitrary spatial frequency.

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Scattering of a general partially coherent beam from a diffuse target in atmospheric turbulence

王利国, 吴振森, 王明军, 曹运华, 张耿

2014 (9): 94202-094202. doi: 10.1088/1674-1056/23/9/094202

摘要 ( 582 )

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The second-order and fourth-order statistical moments of the speckle field from a diffuse target in atmospheric turbulence are studied which have great influence on the performance of lidar systems. By expanding a general rotationally symmetric beam as a sum of Gaussian-Schell model (GSM) beams, the mean intensity of the general beam propagating over a distance in an atmospheric turbulence is formulated. Expressions for the degree of coherence (DOC) and the normalized intensity variance of the scattered field of a general beam from a rough surface in turbulence are derived based on the extended Huygens-Fresnel principle. The general expressions reduce to the well-known forms for a GSM beam. Another example for the general beam used in this paper is the collimated flat-topped beam. The results of both kinds of beams show that the intensity profile on the target plane is a key factor affecting the statistical characteristics of the speckle field. A larger beam spot on the target plane induces a smaller coherence length and a smaller normalized intensity variance of the received field. As turbulence gets stronger, the coherence length becomes smaller, and the normalized intensity variance firstly increases and declines to unity finally.

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Characterization of graphene-based photonic crystal in THz spectrum with finite-difference time domain method

林海, 徐笛, M. F. Pantoja, S. G. Garcia, 杨河林

2014 (9): 94203-094203. doi: 10.1088/1674-1056/23/9/094203

摘要 ( 885 )

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Graphene has been considered as a promising material which may find applications in the THz science. In this work, we numerically investigate tunable photonic crystals in the THz range based on stacked graphene/dielelctric layers, a complex pole-residue pair model is used to find the effective permittivity of graphene, which could be easily incorporated into the finite-difference time domain (FDTD) algorithm. Two different schemes of photonic crystal used for extending the bandgap have been simulated through this FDTD technique.

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Evolution of entanglement between qubits ultra-strongly coupling to a quantum oscillator

马悦, 董锟, 田贵花

2014 (9): 94204-094204. doi: 10.1088/1674-1056/23/9/094204

摘要 ( 590 )

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We investigate the dynamics of two qubits coupled with a quantum oscillator by using the adiabatic approximation method. We take account of the interaction between the qubits and show how the entanglement is affected by the interaction parameter. The most interesting result is that we can prolong the entanglement time or improve the entanglement degree by using an appropriate interaction parameter. As the generation and preservation of entanglement of qubits are crucial for quantum information processing, our research will be useful.

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Influence of a phonon bath in a quantum dot cavity QED system：Dependence of the shape

王伟胜, 张明亮, 陈芝得

2014 (9): 94205-094205. doi: 10.1088/1674-1056/23/9/094205

摘要 ( 678 )

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We present a systematic analysis on the role of the quantum dot (QD) shape in the influence of the phonon bath on the dynamics of a QD cavity QED system. The spectral functions of the phonon bath in three representative QD shapes: spherical, ellipsoidal, and disk, are calculated from the carrier wave functions subjected to the confinement potential provided by the corresponding shape. The obtained spectral functions are used to calculate three main effects brought by the phonon bath, i.e., the coupling renormalization, the off-resonance assisted feeding rate and the pure dephasing rate. It is found that the spectral function of a disk QD has the widest distribution, hence the phonon bath in a disk QD can lead to the smallest renormalization factor, the largest dephasing rate in the short time domains(≤ 2 ps), and the off-resonance assisted feeding can support the widest detuning. Except for the pure dephasing rate in the long time domains, all the influences brought by the phonon bath show serious shape dependence.

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Compression of the self-Q-switching in semiconductor disk lasers with single-layer graphene saturable absorbers

于振华, 田金荣, 宋晏蓉

2014 (9): 94206-094206. doi: 10.1088/1674-1056/23/9/094206

摘要 ( 4949 )

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We demonstrate the first use of single layer graphene for compressing self-Q-switching pulses in semiconductor disk lasers. The gain region of the semiconductor disk laser used InGaAs quantum wells with a central wavelength of 1030 nm. Due to self saturable absorption of the quantum wells, the disk laser emitted at the self-Q-switching state with a pulse width of 13 μs. By introducing the single layer graphene as a saturable absorber into the V-shaped laser cavity, the pulse width of the self-pulse was compressed to 2 μs with a lower pump power of 300 mW. As the pump power was increased, multiple pulses with the pulse width of 1.8 μs appeared. The compression factor was about 7.2.

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Specific mode output from multimode fiber oscillators by designing rare earth doping profiles

王文亮, 黄良金, 冷进勇, 郭少锋, 姜宗福

2014 (9): 94207-094207. doi: 10.1088/1674-1056/23/9/094207

摘要 ( 575 )

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Based on rate equations, a theoretical model of a fiber oscillator with a multimode gain fiber was built. We studied the effect of the rare earth doping profile in the core on the output characteristics of the multimode fiber oscillator. The results indicated that a pure fundamental mode can be obtained by partly doping the core of the large mode area (LMA) ytterbium doped fiber (YDF) in the fiber laser. Furthermore, a sole specific high-order mode can also be implemented by tailoring the rare earth doping profile according to the simulations. The mode coupling effect was also taken into account in the model. In spite of the mode coupling effect, the specific mode was able to dominate in the output of the fiber laser by utilizing the designed LMA YDF.

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33 W quasi-continuous-wave narrow-band sodium D_2a laser by sum-frequency generation in LBO

王鹏远, 谢仕永, 薄勇, 王保山, 左军卫, 王志超, 申玉, 张丰丰, 魏凯, 晋凯, 徐一汀, 许家林, 彭钦军, 张景园, 雷文强, 崔大复, 张雨东, 许祖彦

2014 (9): 94208-094208. doi: 10.1088/1674-1056/23/9/094208

摘要 ( 681 )

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We demonstrate an all-solid quasi-continuous-wave (QCW) narrow-band source tunable to sodium D_2a line at 589.159 nm. The source is based on sum-frequency mixing between lasers at 1064 nm and 1319 nm in a LBO crystal. The 1064 nm and 1319 nm lasers are produced from two diode side-pumped Nd:YAG master oscillator power amplifier (MOPA) laser systems, respectively. A 33 W output of 589 nm laser is obtained with beam quality factor M²=1.25, frequency stability better than ± 0.2 GHz and linewidth less than 0.44 GHz. A prototype 589 nm laser system is assembled, and a sodium laser guided star has been successfully observed in the field test.

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Fabrication of large-scale ripples on fluorine-doped tin oxide films by femtosecond laser irradiation

韩艳华, 李岩, 赵秀丽, 曲士良

2014 (9): 94209-094209. doi: 10.1088/1674-1056/23/9/094209

摘要 ( 620 )

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The large-scale uniform self-organized ripples are fabricated on fluorine-doped tin oxide (FTO) coated glass by femtosecond laser. They can be smoothly linked in a horizontal line with the moving of XYZ stage by setting its velocity and the repetition rate of the laser. The ripple-to-ripple linking can also be realized through line-by-line scanning on a vertical level. The mechanism analysis shows that the seeding effect plays a key role in the linking of ripples.

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Observation of tropospheric NO₂ by airborne multi-axis differential optical absorption spectroscopy in the Pearl River Delta region, south China

徐晋, 谢品华, 司福祺, 李昂, 吴丰成, 王杨, 刘建国, 刘文清, Andreas Hartl, Chan Ka Lok

2014 (9): 94210-094210. doi: 10.1088/1674-1056/23/9/094210

摘要 ( 779 )

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An airborne multi-axis differential optical absorption spectroscopic (AMAX-DOAS) instrument was developed and applied to measure tropospheric NO₂ in the Pearl River Delta region in the south of China. By combining the measurements in nadir and zenith directions and analyzing the UV and visible spectral region using the DOAS method, information about tropospheric NO₂ vertical columns was obtained. Strong tropospheric NO₂ signals were detected when flying over heavilly polluted regions and point sources like plants. The AMAX-DOAS results were compared with ground-based MAX-DOAS observations in the southwest of Zhuhai city using the same parameters for radiative transport calculations. The difference in vertical column data between the two instruments is about 8%. Our data were also compared with those from OMI and fair agreement was obtained with a correlation coefficient R of 0.61. The difference between the two instruments can be attributed to the different spatial resolution and the temporal mismatch during the measurements.

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Retinal axial focusing and multi-layer imaging with a liquid crystal adaptive optics camera

刘瑞雪, 郑贤良, 李大禹, 夏明亮, 胡立发, 曹召良, 穆全全, 宣丽

2014 (9): 94211-094211. doi: 10.1088/1674-1056/23/9/094211

摘要 ( 779 )

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With the help of adaptive optics (AO) technology, cellular level imaging of living human retina can be achieved. Aiming to reduce distressing feelings and to avoid potential drug induced diseases, we attempted to image retina with dilated pupil and froze accommodation without drugs. An optimized liquid crystal adaptive optics camera was adopted for retinal imaging. A novel eye stared system was used for stimulating accommodation and fixating imaging area. Illumination sources and imaging camera kept linkage for focusing and imaging different layers. Four subjects with diverse degree of myopia were imaged. Based on the optical properties of the human eye, the eye stared system reduced the defocus to less than the typical ocular depth of focus. In this way, the illumination light can be projected on certain retina layer precisely. Since that the defocus had been compensated by the eye stared system, the adopted 512×512 liquid crystal spatial light modulator (LC-SLM) corrector provided the crucial spatial fidelity to fully compensate high-order aberrations. The Strehl ratio of a subject with -8 diopter myopia was improved to 0.78, which was nearly close to diffraction-limited imaging. By finely adjusting the axial displacement of illumination sources and imaging camera, cone photoreceptors, blood vessels and nerve fiber layer were clearly imaged successfully.

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Designing analysis of the polarization beam splitter in two communication bands based on a gold-filled dual-corephotonic crystal fiber

范振凯, 李曙光, 范玉秋, 张婉, 安国文, 鲍亚杰

2014 (9): 94212-094212. doi: 10.1088/1674-1056/23/9/094212

摘要 ( 772 )

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We design a novel kind of polarization beam splitter based on a gold-filled dual-core photonic crystal fiber (DC-PCF). Owing to filling with two gold wires in this DC-PCF, its coupling characteristics can be changed greatly by the second-order surface plasmon polariton (SPP) and the resonant coupling between the surface plasmon modes and the fiber-core guided modes can enhance the directional power transfer in the two fiber-cores. Numerical results by using the finite element method show the extinction ratio at the wavethlengths of 1.327 μm and 1.55 μm can reach-58 dB and-60 dB and the bandwidths as the extinction ratio better than-12 dB are about 54 nm and 47 nm, respectively. Compared with the gold-unfilled DC-PCF, a 1.746-mm-long gold-filled DC-PCF is better applied to the polarization beam splitter in the two communication bands of λ=1.327 μm and 1.55 μm.

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Radiation-induced attenuation self-compensating effect in super-fluorescent fiber source

杨远洪, 索鑫鑫, 杨巍

2014 (9): 94213-094213. doi: 10.1088/1674-1056/23/9/094213

摘要 ( 504 )

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The compact super-fluorescent fiber source (SFS) output spectra variations at different pump currents and under different dose of gamma-ray radiation were measured and compared respectively. The radiation-induced attenuation (RIA) self-compensating effect in SFS based on photo-bleaching was found and the general mathematic model of SFS output spectra variations was made. The radiation-induced background attenuation (RIBA) at the pump wavelength was identified to be the main cause of the total output power and spectra variations and the variations can then be compensated by active control of the pump power to enhance the self-compensating effect. With closed-loop feedback control of pump current, double-pass backward (DPB) configuration and spectrum re-shaping technology, an SFS prototype was made and tested. The mean-wavelength stability of about 87.4 ppm and output power instability of less than 5% were achieved under up to 200 krad (Si) gamma-ray irradiation.

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Bifurcation and chaos analysis of a nonlinear electromechanical coupling relative rotation system

刘爽, 赵双双, 孙宝平, 张文明

2014 (9): 94501-094501. doi: 10.1088/1674-1056/23/9/094501

摘要 ( 627 )

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Hopf bifurcation and chaos of a nonlinear electromechanical coupling relative rotation system are studied in this paper. Considering the energy in air-gap field of AC motor, the dynamical equation of nonlinear electromechanical coupling relative rotation system is deduced by using the dissipation Lagrange equation. Choosing the electromagnetic stiffness as a bifurcation parameter, the necessary and sufficient conditions of Hopf bifurcation are given, and the bifurcation characteristics are studied. The mechanism and conditions of system parameters for chaotic motions are investigated rigorously based on the Silnikov method, and the homoclinic orbit is found by using the undetermined coefficient method. Therefore, Smale horseshoe chaos occurs when electromagnetic stiffness changes. Numerical simulations are also given, which confirm the analytical results.

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Nonlinear saturation amplitude of cylindrical Rayleigh–Taylor instability

刘万海, 于长平, 叶文华, 王立峰

2014 (9): 94502-094502. doi: 10.1088/1674-1056/23/9/094502

摘要 ( 564 )

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The nonlinear saturation amplitude (NSA) of the fundamental mode in the classical Rayleigh-Taylor instability with a cylindrical geometry for an arbitrary Atwood number is analytically investigated by considering the nonlinear corrections up to the third order. The analytic results indicate that the effects of the initial radius of the interface (r₀) and the Atwood number (A) play an important role in the NSA of the fundamental mode. The NSA of the fundamental mode first increases gently and then decreases quickly with increasing A. For a given A, the smaller the r₀/λ (λ is the perturbation wavelength), the larger the NSA of the fundamental mode. When r₀/λ is large enough (r₀ λ), the NSA of the fundamental mode is reduced to the prediction in the previous literatures within the framework of the third-order perturbation theory.

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Three-dimensional PIC/MCC simulation of electron deposition in JAEA 10 A ion sources

杨超, 印茂伟, 尚丽平, 韦爱勇

2014 (9): 95201-095201. doi: 10.1088/1674-1056/23/9/095201

摘要 ( 646 )

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A systematic research on the electron deposition process in the JAEA 10 A ion source is carried out by using a particle-in-cell/Monte Carlo collision simulation, which is based on a full three-dimensional self-developed code. Two parts are studied. One is the space and energy distribution of fast and slow electrons, the other is the vibration excitation collisions between electrons and hydrogen moleculars. The results show that the inhomogeneity of electrons comes from the Y direction drift of the fast electrons (T_e ≥qq25 eV) due to the action of the magnetic fields. This drift also increases the number of vibration excitation collisions in the -Y direction, and results in the increase of H_a in the -Y direction, eventually leading to the -Y drift of H^-. It explains the spatial non-uniformity in the JAEA 10 A ion source.

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Characteristics of a large gap uniform discharge excited by DC voltage at atmospheric pressure

李雪辰, 鲍文婷, 贾鹏英, 赵欢欢, 狄聪, 陈俊英

2014 (9): 95202-095202. doi: 10.1088/1674-1056/23/9/095202

摘要 ( 620 )

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A large-gap uniform discharge is ignited by a coaxial dielectric barrier discharge and burns between a needle anode and a plate cathode under a low sustaining voltage by feeding with flowing argon. The basic aspects of the large-gap uniform discharge are investigated by optical and spectroscopic methods. From the discharge images, it can be found that this discharge has similar regions with glow discharge at low pressure except a plasma plume region. Light emission signals from the discharge indicate that the plasma column is invariant with time, while there are some stochastic pulses in the plasma plume region. The optical emission spectra scanning from 300 nm to 800 nm are used to calculate the excited electron temperature and vibrational temperature of the large-gap uniform discharge. It has been found that the excited electron temperature almost keeps constant and the vibrational temperature increases with increasing discharge current. Both of them decreases with increasing gas flow rate.

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Photoelectric characteristics of silicon P-N junction with nanopillar texture：Analysis of X-ray photoelectron spectroscopy

刘静, 王嘉鸥, 伊福廷, 吴蕊, 张念, 奎热西

2014 (9): 96101-096101. doi: 10.1088/1674-1056/23/9/096101

摘要 ( 706 )

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Silicon nanopillars are fabricated by inductively coupled plasma (ICP) dry etching with the cesium chloride (CsCl) islands as masks originally from self-assembly. Wafers with nanopillar texture or planar surface are subjected to phosphorus (P) diffusion by liquid dopant source (POCl₃) at 870℃ to form P-N junctions with a depth of 300 nm. The X-ray photoelectron spectroscopy (XPS) is used to measure the Si 2p core levels of P-N junction wafer with nanopillar texture and planar surface. With a visible light excitation, the P-N junction produces a new electric potential for photoelectric characteristic, which causes the Si 2p core level to have a energy shift compared with the spectrum without the visible light. The energy shift of the Si 2p core level is -0.27 eV for the planar P-N junction and-0.18 eV for the nanopillar one. The difference in Si 2p energy shift is due to more space lattice defects and chemical bond breaks for nanopillar compared with the planar one.

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Transient competition between photocatalysis and carrier recombination in TiO₂ nanotube film loaded with Au nanoparticles

邵珠峰, 杨延强, 刘树田, 王强

2014 (9): 96102-096102. doi: 10.1088/1674-1056/23/9/096102

摘要 ( 629 )

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Highly ordered TiO₂ nanotube array (TNA) films are fabricated by using an anodic oxidation method. Au nanoparticles (NPs) films are decorated onto the top of TNA films with the aid of ion-sputtering and thermal annealing. An enhanced photocatalytic activity under ultraviolet C (UVC, 266 nm) light irradiation is obtained compared with that of the pristine TNA, which is shown by the steady-state photoluminescence (PL) spectra. Furthermore, a distinct blue shift in the nanosecond time-resolved transient photoluminescence (NTRT-PL) spectra is observed. Such a phenomenon could be well explained by considering the competition between the surface photocatalytic process and the recombination of the photo-generated carriers. The enhanced UV photocatalytic activities of the Au-TNA composite are evaluated through photo-degradation of methyl orange (MO) in an aqueous solution with ultraviolet-visible absorption spectrometry. Our current work may provide a simple strategy to synthesize defect-related composite photocatalytic devices.

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Uniaxial strain-dependent magnetic and electronic properties of(Ga,Mn)As nanowires

张晨辉, 向钢, 兰木, 张析

2014 (9): 96103-096103. doi: 10.1088/1674-1056/23/9/096103

摘要 ( 526 )

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Variations in magnetic and electronic properties as a function of uniaxial strain in wurtzite (Ga,Mn)As nanowires (NWs) grown along the [0001] direction were investigated based on density functional theory (DFT). We found that (Ga,Mn)As NWs are half-metal, and the ferromagnetic state is their stable ground state. The magnetism of the NWs is significantly affected by the strain and by the substituent position of Mn impurities. By examining charge densities near the Fermi level, we found that strain can regulate the conductive region of the NWs. More interestingly, the size of spin-down band gap of the NWs is tunable by adjusting uniaxial stress, and the NWs can be converted from indirect to direct band gap under tension.

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Structural stability and electronic properties of carbon star lattice monolayer

范雪兰, 牛春要, 王新全, 王建涛, 李捍东

2014 (9): 96104-096104. doi: 10.1088/1674-1056/23/9/096104

摘要 ( 524 )

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By means of the first-principles calculations, we have investigated the structural stability and electronic properties of carbon star lattice monolayer and nanoribbons. The phase stability of the carbon star lattice is verified through phonon-mode analysis and room temperature molecular dynamics simulations. The carbon star lattice is found to be metallic due to the large states across the Fermi-level contributed by p_z orbital. Furthermore, the nanoribbons are also found to be metallic and no spin polarization occurs, except for the narrowest nanoribbon with one C₁₂ ring, which has a ferromagnetic ground state. Our results show that carbon star lattice monolayer and nanoribbons have rich electronic properties with great potential in future electronic nanodevices.

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Anisotropy of elasticity and minimum thermal conductivity of monocrystal M₄AlC₃ (M=Ti, Zr, Hf)

丁艾玲, 李春梅, 王瑨, 敖靖, 李凤, 陈志谦

2014 (9): 96201-096201. doi: 10.1088/1674-1056/23/9/096201

摘要 ( 567 )

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The elastic constants, elastic anisotropy index, and anisotropic fractional ratios of Ti₄AlC₃, Zr₄AlC₃, and Hf₄AlC₃ are studied by using a plane wave method based on density functional theory. All compounds are characterized by the elastic anisotropy index. The bond length, population, and hardness of the three compounds are calculated. The degrees of hardness are then compared. The minimum thermal conductivity at high temperature limitation in the propagation direction of [0001] (0001) is calculated by the acoustic wave velocity, which indicates that the thermal conductivity is also anisotropic. Finally, the electronic structures of the compounds are analyzed numerically. We show that the bonding of the M₄AlC₃ lattice exhibits mixed properties of covalent bonding, ionic bonding, and metallic bonding. Moreover, no energy gap is observed at the Fermi level, indicating that various compounds exhibit metallic conductivity at the ground state.

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Converging spherical and cylindrical elastic-plastic waves of small amplitude

胡秋实, 赵锋

2014 (9): 96202-096202. doi: 10.1088/1674-1056/23/9/096202

摘要 ( 616 )

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Converging spherical and cylindrical elastic-plastic waves in an isotropic work-hardening medium is investigated on the basis of a finite difference method. The small amplitude pressure is applied instantaneously and maintained on the outer surface of a spherical or a cylindrical medium. It is found that for undercritical loading, the induced wave structure is an elastic front followed in turn by an expanding plastic region and an expanding elastic region. For supercritical loading, the elastic front is followed in turn by an expanding plastic region, a narrowing elastic region and an expanding plastic region. After yielding is initiated, the strength of the elastic front is constant and equal to the critical loading pressure. The motion of the continuous elastic-plastic interface is discussed in detail. Spatial distributions of pressure near the axis show the strength of the converging wave is nearly doubled in the reflecting stage.

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Enhancement in solar hydrogen generation efficiency using InGaN photoelectrode after surface roughening treatment with nano-sized Ni mask

陶涛, 智婷, 李民雪, 谢自力, 张荣, 刘斌, 李毅, 庄喆, 张国刚, 蒋府龙, 陈鹏, 郑有炓

2014 (9): 96203-096203. doi: 10.1088/1674-1056/23/9/096203

摘要 ( 589 )

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A significant enhancement in solar hydrogen generation efficiency has been achieved by inductive coupled etching (ICP) surface roughening treatment using nano-sized nickel mask. As much as 7 times improvement of photocurrent is demonstrated in comparison with a planar one fabricated from the same parent wafer. Under identical illumination conditions in HBr solution, the incident photon conversion efficiency (IPCE) shows an enhancement with a factor of 3, which even exceed 54% at 400 nm wavelength. We believe the enhancement is attributed to several facts including improvement in absorption, reacting area, carrier localization and carrier lifetime.

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Shear viscosity of aluminum studied by shock compression considering elasto-plastic effects

马小娟, 郝斌斌, 马海霞, 刘福生

2014 (9): 96204-096204. doi: 10.1088/1674-1056/23/9/096204

摘要 ( 762 )

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The strength always exists before the material melts. In this paper, the viscoelastic-plastic model is applied to improve the finite difference method, and the numerical solutions for the disturbance amplitude damping behavior of the sinusoidal shock front in a flyer-impact experiment are obtained. When the aluminum is shocked to 101 GPa, the effect of elastoplasticity on the zero-amplitude point of the oscillatory damping curve is the same as that of viscosity when η=700 Pa·s, and the real shear viscosity coefficient of the shocked aluminum is determined to be about 2800±100 Pa·s. Comparing the experiment data with the numerical results of the viscoelastic-plastic model, we find that the aluminum is close to melting at 101 GPa.

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Biometric feature extraction using local fractal auto-correlation

陈熙, 张家树

2014 (9): 96401-096401. doi: 10.1088/1674-1056/23/9/096401

摘要 ( 621 )

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Image texture feature extraction is a classical means for biometric recognition. To extract effective texture feature for matching, we utilize local fractal auto-correlation to construct an effective image texture descriptor. Three main steps are involved in the proposed scheme: (i) using two-dimensional Gabor filter to extract the texture features of biometric images; (ⅱ) calculating the local fractal dimension of Gabor feature under different orientations and scales using fractal auto-correlation algorithm; and (ⅲ) linking the local fractal dimension of Gabor feature under different orientations and scales into a big vector for matching. Experiments and analyses show our proposed scheme is an efficient biometric feature extraction approach.

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Phase behaviors of binary mixtures composed of banana-shaped and calamitic mesogens

M. Cvetinov, D. Ž. Obadović, M. Stojanović, A. Vajda, K. Fodor-Csorba, N. Eber, I. Ristić

2014 (9): 96402-096402. doi: 10.1088/1674-1056/23/9/096402

摘要 ( 827 )

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In this work, five mixtures with different concentrations of banana-shaped and calamitic compounds have been prepared and subsequently studied by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction on non-oriented samples. The phase sequences and molecular parameters of the binary systems are presented.

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Thermal conductivity of multi-walled carbon nanotubes：Molecular dynamics simulations

胡帼杰, 曹炳阳

2014 (9): 96501-096501. doi: 10.1088/1674-1056/23/9/096501

摘要 ( 665 )

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Heat conduction in single-walled carbon nanotubes (SWCNTs) has been investigated by using various methods, while less work has been focused on multi-walled carbon nanotubes (MWCNTs). The thermal conductivities of the double-walled carbon nanotubes (DWCNTs) with two different temperature control methods are studied by using molecular dynamics (MD) simulations. One case is that the heat baths (HBs) are imposed only on the outer wall, while the other is that the HBs are imposed on both the two walls. The results show that the ratio of the thermal conductivity of DWCNTs in the first case to that in the second case is inversely proportional to the ratio of the cross-sectional area of the DWCNT to that of its outer wall. In order to interpret the results and explore the heat conduction mechanisms, the inter-wall thermal transport of DWCNTs is simulated. Analyses of the temperature profiles of a DWCNT and its two walls in the two cases and the inter-wall thermal resistance show that in the first case heat is almost transported only along the outer wall, while in the second case a DWCNT behaves like parallel heat transport channels in which heat is transported along each wall independently. This gives a good explanation of our results and presents the heat conduction mechanisms of MWCNTs.

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Characterization of tetragonal distortion in a thick Al_0.2Ga_0.8N epilayer with an AlN interlayer by Rutherford backscattering/channeling

王欢, 姚淑德

2014 (9): 96801-096801. doi: 10.1088/1674-1056/23/9/096801

摘要 ( 665 )

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An Al_0.2Ga_0.8N/AlN/Al_0.2Ga_0.8N heterostructure was grown by metalorganic chemical vapor deposition on a sapphire (0001) substrate with a thick (>1 μm) GaN intermediate layer. The Al composition was determined by Rutherford backscattering (RBS). Using the channeling scan around an off-normal [1213] axis in the (1010) plane of the Al_0.2Ga_0.8N layer, the tetragonal distortion e_T, which is caused by the elastic strain in the epilayer, is investigated. The results show that e_T in the high-quality Al_0.2Ga_0.8N layer is dramatically released by the AlN interlayer from 0.66% to 0.27%.

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Direct growth of graphene on gallium nitride by using chemical vapor deposition without extra catalyst

赵云, 王钢, 杨怀超, 安铁雷, 陈闽江, 余芳, 陶立, 羊建坤, 魏同波, 段瑞飞, 孙连峰

2014 (9): 96802-096802. doi: 10.1088/1674-1056/23/9/096802

摘要 ( 670 )

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Graphene on gallium nitride (GaN) will be quite useful when the graphene is used as transparent electrodes to improve the performance of gallium nitride devices. In this work, we report the direct synthesis of graphene on GaN without an extra catalyst by chemical vapor deposition. Raman spectra indicate that the graphene films are uniform and about 5-6 layers in thickness. Meanwhile, the effects of growth temperatures on the growth of graphene films are systematically studied, of which 950℃ is found to be the optimum growth temperature. The sheet resistance of the grown graphene is 41.1 Ω/square, which is close to the lowest sheet resistance of transferred graphene reported. The mechanism of graphene growth on GaN is proposed and discussed in detail. XRD spectra and photoluminescence spectra indicate that the quality of GaN epi-layers will not be affected after the growth of graphene.

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Influence of reaction parameters on synthesis of high-quality single-layer graphene on Cu using chemical vapor deposition

杨贺, 申承民, 田园, 王高强, 林少雄, 张一, 顾长志, 李俊杰, 高鸿钧

2014 (9): 96803-096803. doi: 10.1088/1674-1056/23/9/096803

摘要 ( 648 )

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Large-area monolayer graphene samples grown on polycrystalline copper foil by thermal chemical vapor deposition with differing CH₄ flux and growth time are investigated by Raman spectra, scanning electron microscopy, atomic force microscopy, and scanning tunneling microscopy. The defects, number of layers, and quality of graphene are shown to be controllable through tuning the reaction conditions: ideally to 2-3 sccm CH₄ for 30 minutes.

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Characterization of deep acceptor level in as-grown ZnO thin film by molecular beam epitaxy

M. Asghar, K. Mahmood, M. A. Hasan, I. T. Ferguson, R. Tsu, M. Willder

2014 (9): 97101-097101. doi: 10.1088/1674-1056/23/9/097101

摘要 ( 611 )

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We report deep level transient spectroscopy results from ZnO layers grown on silicon by molecular beam epitaxy (MBE). The hot probe measurements reveal mixed conductivity in the as-grown ZnO layers, and the current-voltage (I-V) measurements demonstrate a good quality p-type Schottky device. A new deep acceptor level is observed in the ZnO layer having activation energy of 0.49± 0.03 eV and capture cross-section of 8.57×10^-18 cm². Based on the results from Raman spectroscopy, photoluminescence, and secondary ion mass spectroscopy (SIMS) of the ZnO layer, the observed acceptor trap level is tentatively attributed to a nitrogen-zinc vacancy complex in ZnO.

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An analytic model for gate-all-around silicon nanowire tunneling field effect transistors

刘颖, 何进, 陈文新, 杜彩霞, 叶韵, 赵巍, 吴文, 邓婉玲, 王文平

2014 (9): 97102-097102. doi: 10.1088/1674-1056/23/9/097102

摘要 ( 788 )

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An analytical model of gate-all-around (GAA) silicon nanowire tunneling field effect transistors (NW-TFETs) is developted based on the surface potential solutions in the channel direction and considering the band to band tunneling (BTBT) efficiency. The three-dimensional Poisson equation is solved to obtain the surface potential distributions in the partition regions along the channel direction for the NW-TFET, and a tunneling current model using Kane's expression is developed. The validity of the developed model is shown by the good agreement between the model predictions and the TCAD simulation results.

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Emergent reversible giant electroresistance in spacially confined La_0.325Pr_0.3Ca_0.375MnO₃ wires

崔丽敏, 李洁, 王佳, 张玉, 郑东宁

2014 (9): 97103-097103. doi: 10.1088/1674-1056/23/9/097103

摘要 ( 779 )

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Micro-patterning is considered to be a promising way to analyze phase-separated manganites. We investigate resistance in micro-patterned La_0.325Pr_0.3Ca_0.375MnO₃ wires with width of 10 μm, which is comparable to the phase separation scale in this material. A reentrant of insulating state at the metal-insulator temperature T_p is observed and a giant resistance change of over 90% driven by electric field is achieved by suppression of this insulating state. This resistance change is mostly reversible. The I-V characteristics are measured in order to analyze the origin of the giant electroresistance and two possible explanations are proposed.

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Effect of traps’adjacency on the electric field dependence of mobility in organic systems

何鋆, 陈小青, 侯晓远

2014 (9): 97201-097201. doi: 10.1088/1674-1056/23/9/097201

摘要 ( 603 )

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In some organic materials, varying the finite distance between adjacent carrier traps modifies the Coulomb potential around each trap, resulting in a more complex field-dependence of mobility, differing from (but not incompatible with) the usually considered relationship of ln μ ∝ √E, a relationship which has been successfully explained by the Poole-Frenkel effect. To investigate the influence of the adjacency of traps, a model system is proposed, which consists of two traps separated by distance α. Our numerical calculation shows that with increasing α, the dependence of mobility on the electric field changes from linear to exponential. Moreover, beyond a certain large α, i.e., as the distance to the nearest trap approaches infinity, the proposed model is essentially the same as the Poole-Frenkel effect. The proposed model accounts for the effect of the energy barrier shape, especially the effect of the location of the potential-energy maximum, a phenomenon which is not accommodated in the Poole-Frenkel model. Because the model assumes the Coulomb interaction between the adjacent traps, it applies to those charged traps which may exist in organic materials for various reasons.

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Band-stop optical nanofilters with split-ring resonators based on metal-insulator-metal structure

张会云, 申端龙, 张玉萍, 杨伟杰, 袁偲, 刘蒙, 尹贻恒, 吴志心

2014 (9): 97301-097301. doi: 10.1088/1674-1056/23/9/097301

摘要 ( 575 )

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Novel band-stop filters with circular split-ring resonators based on the metal-insulator-metal (MIM) structure are presented, with their transmission properties of SPPs propagating through the filter simulated by the finite-difference time-domain (FDTD) method. The variation of the gap of the split ring can affect the transmission characteristics, i.e., the transmission spectrum of SPPs exhibiting a shift, which is useful for modulating the filter. Linear and nonlinear media are used in the resonator respectively. By varying the refractive index of the linear medium, the transmission properties can be changed obviously, and the effect caused by changing the incident intensity with a nonlinear medium is similar. Several resonant modes that are applicable can be enhanced by changing the position of the gap of the split ring. Thus, the transmission properties can be modulated by adjusting the size of the gap, varying the refractive index, and changing the incident intensity of the input light. These methods may play significant roles in applications of optical integrated circuits and nanostructural devices.

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Remote excitation and remote detection of a single quantum dot using propagating surface plasmons on silver nanowire

李强, 魏红, 徐红星

2014 (9): 97302-097302. doi: 10.1088/1674-1056/23/9/097302

摘要 ( 563 )

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Using propagating surface plasmons (SPs) on a silver nanowire (NW), we demonstrate that a focused laser light at the end of the silver NW can excite a single quantum dot (QD) microns away from the excitation spot. The QD-NW interaction allows the excited QD convert part of its energy into propagating SPs, which then can be detected at remote sites. Simultaneous multi-QD remote excitation and remote detection can also be realized. Furthermore, the tight confinement of the propagating SPs around the NW surface enables the selective excitation of QDs very close in space, which cannot be realized under the conventional excitation condition. This remote excitation and remote detection approach may find applications in optical imaging and the sensing of chemical and biological systems.

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Deep-ultraviolet surface plasmon resonance of Al and Al_core/Al₂O_3shell nanosphere dimers for surface-enhanced spectroscopy

慈雪婷, 吴伯涛, 宋敏, 陈耿旭, 刘岩, 武愕, 曾和平

2014 (9): 97303-097303. doi: 10.1088/1674-1056/23/9/097303

摘要 ( 669 )

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The localized surface plasmon resonance properties of Al and Al_core/Al₂O_3shell nanosphere dimers with Al and Al core nanosphere radii of 20 nm and Al₂O₃ shell of 2 nm in the deep-ultraviolet region have been studied using the finite difference time domain method. The extinction spectra and the electric field distribution profiles of the two dimers for various gap distances between two individual nanospheres are compared with those of the corresponding monomers to reveal the extent of plasmon coupling. It is found that with the interparticle distance decreasing, a strong plasmon coupling between two Al or Al_core/Al₂O_3shell nanospheres is observed accompanied by a significant red shift in the extinction spectra at the parallel polarization direction of the incident light related to the dimer axis, while for the case of the perpendicular polarization direction, a weak plasmon coupling arises characterized by a slight blue shift in the extinction spectra. The electric field distribution profiles show that benefiting from the dielectric Al₂O₃ shell, the gap distance of Al_core/Al₂O_3shell nanosphere dimers can be tailored to < 1 nm scale and results in a very high electric field enhancement. The estimated surface-enhanced Raman scattering enhancement factors suggests that the Al_core/Al₂O_3shell nanosphere dimers with the gap of < 1 nm gave rise to an enhancement as high as 8.1×10⁷ for interparticle gap=0.5 nm. Our studies reveal that the Al_core/Al₂O_3shell nanosphere dimers may be promising substrates for surface-enhanced spectroscopy in the deep-ultraviolet region.

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Intersubband transitions in In_xAl_(1-x)N/In_yGa_(1-y)Nquantum well operating at 1.55 μm

Hassen Dakhlaoui

2014 (9): 97304-097304. doi: 10.1088/1674-1056/23/9/097304

摘要 ( 517 )

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In this paper, we theoretically study the effects of doping concentration N_D and an external electric field on the intersubband transitions in In_xAl_(1-x)N/In_yGa_(1-y)N single quantum well by solving the Schrödinger and Poisson equations self-consistently. Obtained results including transition energies, the band structure, and the optical absorption have been discussed. The lowest three intersubband transitions (E₂-E₁), (E₃-E₁), and (E₃-E₂) are calculated as functions of doping concentration N_D. By increasing the doping concentration N_D, the depletion effect can be reduced, and the ionized electrons will compensate the internal electric field which results from the spontaneous polarization. Our results show that an optimum concentration N_D exists for which the transition 0.8 eV (1.55 μm) is carried out. Finally, the dependence of the optical absorption α ₁₃ (ω) on the external electric field and doping concentration is studied. The maximum of the optical absorption can be red-shifted or blue-shifted through varying the doping concentration and the external electric field. The obtained results can be used for designing optical fiber telecommunications operating at 1.55 μm.

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Reverse blocking enhancement of drain field plate in Schottky-drain AlGaN/GaN high-electron mobility transistors

赵胜雷, 王媛, 杨晓蕾, 林志宇, 王冲, 张进成, 马晓华, 郝跃

2014 (9): 97305-097305. doi: 10.1088/1674-1056/23/9/097305

摘要 ( 680 )

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In this paper, we present the combination of drain field plate (FP) and Schottky drain to improve the reverse blocking capability, and investigate the reverse blocking enhancement of drain FP in Schottky-drain AlGaN/GaN high-electron mobility transistors (HEMTs). Drain FP and gate FP were employed in a two-dimensional simulation to improve the reverse blocking voltage (V_RB) and the forward blocking voltage (V_FB). The drain-FP length, the gate-FP length and the passivation layer thickness were optimized. V_RB and V_FB were improved from-67 V and 134 V to-653 V and 868 V respectively after optimization. Simulation results suggest that the combination of drain FP and Schottky drain can enhance the reverse blocking capability significantly.

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Organic magnetoresistance based on hopping theory

杨福江, 解士杰

2014 (9): 97306-097306. doi: 10.1088/1674-1056/23/9/097306

摘要 ( 715 )

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For the organic magnetoresistance (OMAR) effect, we suggest a spin-related hopping of carriers (polarons) based on Marcus theory. The mobility of polarons is calculated with the master equation (ME) and then the magnetoresistance (MR) is obtained. The theoretical results are consistent with the experimental observation. Especially, the sign inversion of the MR under different driving bias voltages found in the experiment is predicted. Besides, the effects of molecule disorder, hyperfine interaction (HFI), polaron localization, and temperature on the MR are investigated.

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Schottky forward current transport mechanisms in AlGaN/GaN HEMTs over a wide temperature range

武玫, 郑大勇, 王媛, 陈伟伟, 张凯, 马晓华, 张进成, 郝跃

2014 (9): 97307-097307. doi: 10.1088/1674-1056/23/9/097307

摘要 ( 800 )

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The behavior of Schottky contacts in AlGaN/GaN high electron mobility transistors (HEMTs) is investigated by temperature-dependent current-voltage (T-I-V) measurements from 300 K to 473 K. The ideality factor and barrier height determined based on the thermionic emission (TE) theory are found to be strong functions of temperature, while present a great deviation from the theoretical value, which can be expounded by the barrier height inhomogeneities. In order to determine the forward current transport mechanisms, the experimental data are analyzed using numerical fitting method, considering the temperature-dependent series resistance. It is observed that the current flow at room temperature can be attributed to the tunneling mechanism, while thermionic emission current gains a growing proportion with an increase in temperature. Finally, the effective barrier height is derived based on the extracted thermionic emission component, and an evaluation of the density of dislocations is made from the I-V characteristics, giving a value of 1.49×10⁷ cm^-2.

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Breakdown characteristics of AlGaN/GaN Schottky barrier diodes fabricated on a silicon substrate

蒋超, 陆海, 陈敦军, 任芳芳, 张荣, 郑有炓

2014 (9): 97308-097308. doi: 10.1088/1674-1056/23/9/097308

摘要 ( 845 )

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In this work, the breakdown characteristics of AlGaN/GaN planar Schottky barrier diodes (SBDs) fabricated on the silicon substrate are investigated. The breakdown voltage (BV) of the SBDs first increases as a function of the anode-to-cathode distance and then tends to saturate at larger inter-electrode spacing. The saturation behavior of the BV is likely caused by the vertical breakdown through the intrinsic GaN buffer layer on silicon, which is supported by the post-breakdown primary leakage path analysis with the emission microscopy. Surface passivation and field plate termination are found effective to suppress the leakage current and enhance the BV of the SBDs. A high BV of 601 V is obtained with a low on-resistance of 3.15 mΩ·cm².

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Fabrication and properties of high performance YBa₂Cu₃O_7-δ radio frequency SQUIDs with step-edge Josephson junctions

刘政豪, 魏玉科, 王达, 张琛, 马平, 王越

2014 (9): 97401-097401. doi: 10.1088/1674-1056/23/9/097401

摘要 ( 772 )

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We describe the fabrication of high performance YBa₂Cu₃O_7-δ (YBCO) radio frequency (RF) superconducting quantum interference devices (SQUIDs), which were prepared on 5 mm×5 mm LaAlO₃ (LAO) substrates by employing step-edge junctions (SEJs) and in flip-chip configuration with 12 mm×12 mm resonators. The step in the substrate was produced by Ar ion etching with step angles ranging from 47° to 61°, which is steep enough to ensure the formation of grain boundaries (GBs) at the step edges. The YBCO film was deposited using the pulsed laser deposition (PLD) technique with a film thickness half of the height of the substrate step. The inductance of the SQUID washer was designed to be about 157 pH. Under these circumstances, high performance YBCO RF SQUIDs were successfully fabricated with a typical flux-voltage transfer ratio of 83 mV/Φ ₀, a white flux noise of 29 μΦ ₀/√Hz, and the magnetic field sensitivity as high as 80 fT/√Hz. These devices have been applied in magnetocardiography and geological surveys.

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Effects of rotating noncircular scatterers on spin-wave band gaps of two-dimensional magnonic crystals

杨慧, 云国宏, 曹永军

2014 (9): 97501-097501. doi: 10.1088/1674-1056/23/9/097501

摘要 ( 605 )

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Using the plane-wave expansion method, the spin-wave band structures of two-dimensional magnonic crystals consisting of square arrays of different shape scatterers are calculated numerically, and the effects of rotating rectangle and hexagon scaterers on the gaps are studied, respectively. The results show that the gaps can be substantially opened and tuned by rotating the scatterers. This approach should be helpful in designing magnonic crystals with desired gaps.

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Magnetic phase transition and magnetocaloric effect in Mn_1-xZn_xCoGe alloys

沈程娟, 刘强, 龚元元, 王敦辉, 都有为

2014 (9): 97502-097502. doi: 10.1088/1674-1056/23/9/097502

摘要 ( 735 )

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The magnetic phase transition and magnetocaloric effect are studied in a series of Mn_1-xZn_xCoGe (x=0.01, 0.02, 0.04, and 0.08) alloys. By introducing a small quantity of Zn element, the structural transformation temperature of the MnCoGe alloy is greatly reduced and a first-order magnetostructural transition is observed. Further increasing the Zn concentration results in a second-order ferromagnetic transition. Large room-temperature magnetocaloric effects with small magnetic hysteresis are obtained in alloys with x=0.01 and 0.02, which suggests their potential application in magnetic refrigeration.

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Magnetic behaviors of cerium oxide-based thin films deposited using electrochemical method

彭英姿, 李源, 白茹, 霍德璇, 钱正洪

2014 (9): 97503-097503. doi: 10.1088/1674-1056/23/9/097503

摘要 ( 551 )

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Zn and Co multi-doped CeO₂ thin films have been prepared using an anodic electrochemical method. The structures and magnetic behaviors are characterized by several techniques, in which the oxygen states in the lattice and the absorptive oxygen bonds at the surface are carefully examined. The absorptive oxygen bond is about 50% of the total oxygen bond by using a semi-quantitative method. The value of actual stoichiometry δ' is close to 2. The experimental results indicate that the thin films are of a cerium oxide-based solid solution with few oxygen vacancies in the lattice and many absorptive oxygen bonds at the surface. Week ferromagnetic behaviors were evidenced by observed M-H hysteresis loops at room temperature. Furthermore, an evidence of relative ferromagnetic contributions was revealed by the temperature dependence of magnetization. It is believed that the ferromagnetic contributions exhibited in the M-H loops originate from the absorptive oxygen on the surface rather than the oxygen vacancies in the lattice.

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Micromagnetic simulation of Sm-Co/α-Fe/Sm-Co trilayers with various angles between easy axes and the film plane

张溪超, 赵国平, 夏静, 岳明, 袁新红, 谢林华

2014 (9): 97504-097504. doi: 10.1088/1674-1056/23/9/097504

摘要 ( 744 )

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Hysteresis loops and energy products have been calculated systematically by a three-dimensional (3D) software OOMMF for Sm-Co/α-Fe/Sm-Co trilayers with various thicknesses and β, where β is the angle between the easy axis and the field applied perpendicular to the film plane. It is found that trilayers with a perpendicular anisotropy possess considerably larger coercivities and smaller remanences and energy products compared with those with an in-plane anisotropy. Increase of β leads to a fast decrease of the maximum energy product as well as the drop of both remanence and coercivity. Such a drop is much faster than that in the single-phased hard material, which can explain the significant discrepancy between the experiment and the theoretical energy products. Some modeling techniques have been utilized with spin check procedures performed, which yield results in good agreement with the one-dimensional (1D) analytical and experimental data, justifying our calculations. Further, the calculated nucleation fields according to the 3D calculations are larger than those based on the 1D model, whereas the corresponding coercivity is smaller, leading to more square hysteresis loops and better agreement between experimental data and the theory.

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Multiferroic properties and exchange bias in Bi_1-xSr_xFeO₃ (x=0-0.6) ceramics

马争争, 李建青, 陈子鹏, 田召明, 胡晓军, 黄海军

2014 (9): 97505-097505. doi: 10.1088/1674-1056/23/9/097505

摘要 ( 652 )

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Multiferroic properties and exchange bias (EB) in Bi_1-xSr_xFeO₃ (x=0-0.6) ceramics synthesized by a modified Pechini method are investigated. Sr concentration dependence of structure distorting, ferroelectric properties, and dielectric properties were studied at room temperature. Appropriate Sr doping (x=0.05-0.2) has been found to decrease the conductivity, enhance ferroelectric properties and give rise to high dielectric constant. Compared with antiferromagnetic BiFeO₃ compound, BSFO-x (0 ≤ x ≤ 0.4) ceramics show weak ferromagnetism at room temperature, and their exchange bias field and vertical magnetization shift are observed and exhibit a strong dependence on the content of Sr. This observed EB effect which keeps stable in BSFO ceramics at 10 K tend to vanish at room temperature with Sr concentration over 0.4.

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Dielectric and ferroelectric properties of Sr₄CaSmTi₃Nb₇O₃₀ with tetragonal tungsten bronze structure

龚高尚, 方玉娇, 黄帅, 尹重阳, 袁松柳, 王丽光

2014 (9): 97701-097701. doi: 10.1088/1674-1056/23/9/097701

摘要 ( 853 )

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Sr₄CaSmTi₃Nb₇O₃₀ ceramics are synthesized and indexed as tetragonal tungsten bronze structure. The dielectric behavior and ferroelectric nature are investigated. Three dielectric anomalies are observed. The phase transition is a displacive phase transition with some diffusive characteristics, which indicates possible compositional variations within the materials on the microscopic scale. The weak distortion disappears in cooling process for differential scanning calorimetry measurement, and the large depression of Curie-Weiss temperature T₀ indicates the difficulty in forming macroferroelectric domain. The ferroelectric nature in these filled tungsten bronze niobates originates from the off-center displacement of B-site cations, but they are primarily dominated by A-site cation occupation. Both the radius and the valence of A1-site cations play an important role on ferroelectric properties of the filled tungsten bronze compounds. Existence of spontaneous polarization with a remanent polarization of 0.16 μC/cm² a coercive field of E_c=11.74 kV/cm confirms the room-temperature ferroelectric nature of Sr₄CaSmTi₃Nb₇O₃₀ ceramics.

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Transport properties and anomalous fatigue effect of Ag/Bi_0.9La_0.1FeO₃/La_0.7Sr_0.3MnO₃ heterostructures

高荣礼, 符春林, 蔡苇, 陈刚, 邓小玲, 杨怀文, 孙继荣, 沈保根

2014 (9): 97702-097702. doi: 10.1088/1674-1056/23/9/097702

摘要 ( 618 )

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The transport properties and fatigue effect of Ag/Bi_0.9La_0.1FeO₃/La_0.7Sr_0.3MnO₃ heterostructures are described. By examining the I-V curves, an anomalous fatigue effect was found and its influences on resistive states were studied. I-V curves combined with C-f spectra were used to directly analyze the transport properties and fatigue effect. Compared to the first I-V cycle state, this structure shows more than one order increase of resistance after 100 cycles of “I-V curve training”. The redistribution of oxygen vacancies in the depletion layer of Ag/Bi_0.9La_0.1FeO₃ is believed to be responsible for the different resistance mechanisms and tenfold magnitude drop in resistance. The resistive switching is understood to be caused by electric field-induced carrier trapping and detrapping, which changes the depletion layer thickness at the Ag/Bi_0.9La_0.1FeO₃ interface.

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Li-N dual-doped ZnO thin films prepared by an ion beam enhanced deposition method

谢建生, 陈强

2014 (9): 97703-097703. doi: 10.1088/1674-1056/23/9/097703

摘要 ( 641 )

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Li-N dual-doped ZnO films [ZnO:(Li,N)] with Li doping concentrations of 3 at.%-5 at.% were grown on a glass substrate using an ion beam enhanced deposition (IBED) method. An optimal p-type ZnO:(Li,N) film with the resistivity of 11.4 Ω·cm was obtained by doping 4 at.% of Li and 5 sccm flow ratio of N₂. The ZnO:(Li,N) films exhibited a wurtzite structure and good transmittance in the visible region. The p-type conductive mechanism of ZnO:(Li,N) films are attributed to the Li substitute Zn site (Li_Zn) acceptor. N doping in ZnO can forms the Li_i-N_O complex, which depresses the compensation of Li occupy interstitial site (Li_i) donors for Li_Zn acceptor and helps to achieve p-type ZnO:(Li,N) films. Room temperature photoluminescence measurements indicate that the UV peak (381 nm) is due to the shallow acceptors Li_Zn in the p-type ZnO:(Li,N) films. The band gap of the ZnO:(Li,N) films has a red-shift after p-type doping.

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Stability and elastic properties of Nb_xC_y compounds

高旭鹏, 蒋业华, 刘洋赈, 周荣, 冯晶

2014 (9): 97704-097704. doi: 10.1088/1674-1056/23/9/097704

摘要 ( 621 )

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Density functional theory (DFT) is applied to investigate the stability and mechanical properties of Nb_xC_y compounds. The structures of Nb_xC_y compounds are optimized, and the results are in good agreement with previous work. The calculated results of the cohesive energy and the formation enthalpy of Nb_xC_y show that they are thermodynamically stable structures, except for Pmc21-Nb₂C. The mechanical properties such as the bulk modulus, Young's modulus, the shear modulus, and Poisson's ratio are obtained by Voigt-Reuss-Hill approximation. The results show that the Young's modulus and shear modulus of NbC are larger than other Nb_xC_y compounds. The mechanical anisotropy is characterized by calculating several different anisotropic indexes and factors, such as universal anisotropic index (A^U), shear anisotropic factors (A₁, A₂, A₃), and percent anisotropy (A_B and A_G). The surface constructions of bulk and Young's moduli are illustrated to indicate the mechanical anisotropy. The hardness of Nb_xC_y compounds is also discussed in this paper. The estimated hardness for all Nb_xC_y compounds is less than 20 GPa.

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Spectroscopic properties of Yb³⁺-doped TeO₂-BaO-BaF₂-Nb₂O₅-based oxyfluoride tellurite glasses

林社宝, 王鹏飞, 佘江波, 郭海涛, 许慎诺, 于成龙, 刘春晓, 彭波

2014 (9): 97801-097801. doi: 10.1088/1674-1056/23/9/097801

摘要 ( 546 )

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A series of oxyfluoride glasses with the compositions of 75 mol% TeO₂, 10 mol% Nb₂O₅, (15 mol%-x) BaO, x BaF₂ (x=0 mol%, 5 mol%, 10 mol%, 15 mol%) doped with Yb₂O₃ were prepared by the melt-quenching method. Their emission cross-sections, fluorescence lifetimes, and gain properties were investigated by using the absorption spectra and the fluorescence decay curves. The results show that by substituting BaF₂ for BaO, the emission cross-section decreases from 1.37 pm² to 1.21 pm², and the fluorescence lifetime increases from 0.71 ms to 0.96 ms. These properties indicate that this oxyfluoride tellurite glass may have potential uses as the Yb₂O₃-doped gain medium in a solid laser.

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Effect of disorder on hyperbolic metamaterials

吕诚, 李伟, 蒋寻涯, 曹俊诚

2014 (9): 97802-097802. doi: 10.1088/1674-1056/23/9/097802

摘要 ( 737 )

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Based on a modified retrieving method, we demonstrate that hyperbolic metamaterials (HMs) have considerable robustness against disorders, even when the disorder strength is quite large. Our retrieval method is more precise when retrieving the parameters for anisotropic metamaterials. We also show that the light's negative refraction of an HM is nearly unaffected when relatively large disorders exist. These results help us to understand the HMs and they have a direct significance for experiments.

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Silica-covered Au nanoresonators for fluorescence modulating of a graphene quantum dot

王素凤, 何大伟, 王永生, 胡音, 段嘉华, 富鸣, 王闻硕

2014 (9): 97803-097803. doi: 10.1088/1674-1056/23/9/097803

摘要 ( 565 )

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We synthesize Au@SiO₂ composite particles with a core-shell structure, and utilize the Au@SiO₂ nanoparticles to modulate the fluorescence emission of the graphene quantum dot (GQD) through varying the silica shell thickness. The silica shell thickness can be easily controlled by varying the coating time. After silica coating, we investigate the influence of the silica thickness on the fluorescence emission of the GQD and find that the fluorescence property of the GQD can be changed as expected by varying the thickness of the silica shell. We propose an optimized coating time for the silica shell under the interaction of fluorescence quenching and enhancement.

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High quality sub-monolayer, monolayer, and bilayer graphene on Ru(0001)

徐文焱, 黄立, 阙炎德, 李恩, 张海刚, 林晓, 王业亮, 杜世萱, 高鸿钧

2014 (9): 98101-098101. doi: 10.1088/1674-1056/23/9/098101

摘要 ( 689 )

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High quality sub-monolayer, monolayer, and bilayer graphene were grown on Ru(0001). For the sub-monolayer graphene, the size of graphene islands with zigzag edges can be controlled by the dose of ethylene exposure. By increasing the dose of ethylene to 100 Langmuir at a high substrate temperature (800℃), high quality single-crystalline monolayer graphene was synthesized on Ru(0001). High quality bilayer graphene was formed by further increasing the dose of ethylene while reducing the cooling rate to 5℃/min. Raman spectroscopy revealed the vibrational states of graphene, G and 2D peaks appeared only in the bilayer graphene, which demonstrates that it behaves as the intrinsic graphene. Our present work affords methods to produce high quality sub-monolayer, monolayer, and bilayer graphene, both for basic research and applications.

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Effect of stress state on deformation and fracture of nanocrystalline copper：Molecular dynamics simulation

张亮, 吕程, Kiet Tieu, 裴林清, 赵星

2014 (9): 98102-098102. doi: 10.1088/1674-1056/23/9/098102

摘要 ( 666 )

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Deformation in a microcomponent is often constrained by surrounding joined material making the component under mixed loading and multiple stress states. In this study, molecular dynamics (MD) simulation are conducted to probe the effect of stress states on the deformation and fracture of nanocrystalline Cu. Tensile strain is applied on a Cu single crystal, bicrystal and polycrystal respectively, under two different tension boundary conditions. Simulations are first conducted on the bicrystal and polycrystal models without lattice imperfection. The results reveal that, compared with the performance of simulation models under free boundary condition, the transverse stress caused by the constrained boundary condition leads to a much higher tensile stress and can severely limit the plastic deformation, which in return promotes cleavage fracture in the model. Simulations are then performed on Cu single crystal and polycrystal with an initial crack. Under constrained boundary condition, the crack tip propagates rapidly in the single crystal in a cleavage manner while the crack becomes blunting and extends along the grain boundaries in the polycrystal. Under free boundary condition, massive dislocation activities dominate the deformation mechanisms and the crack plays a little role in both single crystals and polycrystals.

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Characterization of zirconium thin films deposited by pulsed laser deposition

刘伟, 万竟平, 蔡吴鹏, 梁建华, 周晓松, 龙兴贵

2014 (9): 98103-098103. doi: 10.1088/1674-1056/23/9/098103

摘要 ( 609 )

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Zirconium (Zr) thin films deposited on Si (100) by pulsed laser deposition (PLD) at different pulse repetition rates are investigated. The deposited Zr films exhibit a polycrystalline structure, and the X-ray diffraction (XRD) patterns of the films show the α Zr phase. Due to the morphology variation of the target and the laser-plasma interaction, the deposition rate significantly decreases from 0.0431 Å/pulse at 2 Hz to 0.0189 Å/pulse at 20 Hz. The presence of droplets on the surface of the deposited film, which is one of the main disadvantages of the PLD, is observed at various pulse repetition rates. Statistical results show that the dimension and the density of the droplets increase with an increasing pulse repetition rate. We find that the source of droplets is the liquid layer formed under the target surface. The dense nanoparticles covered on the film surface are observed through atomic force microscopy (AFM). The root mean square (RMS) roughness caused by valleys and islands on the film surface initially increases and then decreases with the increasing pulse repetition rate. The results of our investigation will be useful to optimize the synthesis conditions of the Zr films.

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Fabrication and characterization of direct-written 3D TiO₂ woodpile electromagnetic bandgap structures

李吉皎, 李勃, 彭琴梅, 周济, 李龙土

2014 (9): 98104-098104. doi: 10.1088/1674-1056/23/9/098104

摘要 ( 664 )

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Three groups of three-dimensional (3D) TiO₂ woodpile electromagnetic gap materials with tailed rheological properties were developed for direct-written fabrication. Appropriate amount of polyethyleneimine (PEI) dispersants allow the preparation of TiO₂ inks with a high solid content of 42 vol.%, which enables them to flow through the nozzles easily. The inks exhibit pseudoplastic behavior. The measured microwave characteristics of the results agree well with simulations based on plane wave expansion (PWE).

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Structures and optical properties of tungsten oxide thin films deposited by magnetron sputtering of WO₃ bulk：Effects of annealing temperatures

张锋, 王海千, 王松, 汪竟阳, 钟志成, 金叶

2014 (9): 98105-098105. doi: 10.1088/1674-1056/23/9/098105

摘要 ( 807 )

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Tungsten oxide thin films were deposited on glass substrates by the magnetron sputtering of WO₃ bulk at room temperature. The deposited films were annealed at different temperatures in air. The structural measurements indicate that the films annealed below 300℃ were amorphous, while the films annealed at 400℃ were mixed crystalline with hexagonal and triclinic phases of WO₃. It was observed that the crystallization of the annealed films becomes more and more distinct with an increase in the annealing temperature. At 400℃, nanorod-like structures were observed on the film surface when the annealing time was increased from 60 min to 180 min. The presence of W=O stretching, W-O-W stretching, W-O-W bending and various lattice vibration modes were observed in Raman measurements. The optical absorption behaviors of the films in the range of 450-800 nm are very different with changing annealing temperatures from the room temperature to 400℃. After annealing at 400℃, the film becomes almost transparent. Increasing annealing time at 400℃ can lead to a small blue shift of the optical gap of the film.

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Scatter correction method for cone-beam CT based on interlacing-slit scan

黄魁东, 张华, 史仪凯, 张亮, 徐哲

2014 (9): 98106-098106. doi: 10.1088/1674-1056/23/9/098106

摘要 ( 872 )

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Cone-beam computed tomography (CBCT) has the notable features of high efficiency and high precision, and is widely used in areas such as medical imaging and industrial non-destructive testing. However, the presence of the ray scatter reduces the quality of CT images. By referencing the slit collimation approach, a scatter correction method for CBCT based on the interlacing-slit scan is proposed. Firstly, according to the characteristics of CBCT imaging, a scatter suppression plate with interlacing slits is designed and fabricated. Then the imaging of the scatter suppression plate is analyzed, and a scatter correction calculation method for CBCT based on the image fusion is proposed, which can splice out a complete set of scatter suppression projection images according to the interlacing-slit projection images of the left and the right imaging regions in the scatter suppression plate, and simultaneously complete the scatter correction within the flat panel detector (FPD). Finally, the overall process of scatter suppression and correction is provided. The experimental results show that this method can significantly improve the clarity of the slice images and achieve a good scatter correction.

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Theoretical insights into the formation of thiolate-protected nanoparticles from gold (III) chloride

张学娜, 汪蓉, 薛奇

2014 (9): 98201-098201. doi: 10.1088/1674-1056/23/9/098201

摘要 ( 588 )

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Reaction pathways for the formation of thiolate-gold nanoparticles are investigated by density functional theory (DFT) and a new mechanism upon solvent polarity and tetraalkylammonium is obtained. In solvents with high polarities, [Au(I)SR]_n polymers can be formed as the precursor of metal ions prior to the addition of a reducing agent; while a product of [Cl…AuCl(HSR)] is identified as the precursor in solvents with low polarities, such as toluene and chloroform. In addition, tetraalkylammonium also has an obvious effect on the reactions when it is used as a phase transfer agent in the two-phase synthesis. These findings offer a systematic analysis on the pathways to thiolate-stabilized nanoparticles and give a favorable explanation by comparison with those in an experimental system.

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Tuning the phase separation in La_0.325Pr_0.3Ca_0.375MnO₃ using theelectric double-layer field effect

崔丽敏, 李洁, 张玉, 赵璐, 邓辉, 黄克强, 李贺康, 郑东宁

2014 (9): 98501-098501. doi: 10.1088/1674-1056/23/9/098501

摘要 ( 731 )

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Electric double-layer field effect experiments were performed on ultrathin films of La_0.325Pr_0.3Ca_0.375MnO₃, which is noted for its micrometer-scale phase separation. A clear change of resistance up to 220% was observed and the characteristic metal-insulator transition temperature T_P was also shifted. The changes of both the resistance and T_P suggest that the electric field induced not only tuning of the carrier density but also rebalancing of the phase separation states. The change of the charge-ordered insulating phase fraction was estimated to be temperature dependent, and a maximum of 16% was achieved in the phase separation regime. This tuning effect was partially irreversible, which might be due to an oxygen vacancy migration that is driven by the huge applied electric field.

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Introduction of F₄-TCNQ/MoO₃ layers for thermoelectric devices based on pentacene

吴双红, Ryosuke Nakamichi, Masatsugu Taned, 张其胜, Chihaya Adachi

2014 (9): 98502-098502. doi: 10.1088/1674-1056/23/9/098502

摘要 ( 988 )

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We introduced a dual electron accepting layer composed of tetrafluoro-tetracyanoquinodimethane (F₄-TCNQ) and MoO₃ for thermoelectric devices based on a pentacene layer. We found that the power factor is enhanced by placing an F₄-TCNQ layer directly in contact with the pentacene layer and it is also enhanced by placing a MoO₃ layer between the F₄-TCNQ layer and the Au electrode. By examining the contact resistance using a field effect transistor and a hole-only diode, we confirmed that the hole injection is improved due to the reduction of contact resistance at the interface between the MoO₃ layer and the Au electrode.

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Current-induced pseudospin polarization in silicene

王磊, 朱国宝

2014 (9): 98503-098503. doi: 10.1088/1674-1056/23/9/098503

摘要 ( 545 )

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The pseudospin polarization induced by an external electric field in silicene in the presence of weakly spin-independent impurities is considered theoretically in the linear response regime based on Green's function method. We study the effects of the interplay between the sublattice potential and the intrinsic spin orbit coupling on the pseudospin polarization. We show that the pseudospin polarization perpendicular to the electric field is independent of the impurity parameter, while the pseudospin polarization in the direction of the electric field is sensitive to the impurity parameter. The dependences of the pseudospin polarizations on the chemical potential are studied.

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Discrete energy transport in collagen molecules

Alain Mvogo, Germain H. Ben-Bolie, Timoléon C. Kofané

2014 (9): 98701-098701. doi: 10.1088/1674-1056/23/9/098701

摘要 ( 752 )

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The modulational instability in the three coupled α-polypeptide chains of a collagen molecule is investigated. Choosing symmetric and asymmetric solutions, and applying the so-called rotating-wave approximation, we describe the dynamics of the system by the discrete nonlinear Schrödinger (DNLS) equation. The linear stability analysis of the continuous wave solution is performed. The numerical simulations show the generation of trains of solitonic structures in the lattice with increasing amplitude as time progresses. The effect of damping and noise forces of the physiological temperature (T=300 K) introduces an erratic behavior to the formed patterns, reinforcing the idea that the energy used in metabolic processes is confined to specific regions for efficiency.

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Measurment of the energy spectrum of an electron beam extracted from an accelerator

胡涛, 王乃彦

2014 (9): 98702-098702. doi: 10.1088/1674-1056/23/9/098702

摘要 ( 691 )

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The electron energy spectrum is one of the most important characteristics of an electron beam that is extracted from a linear accelerator. The most direct way to determine an electron spectrum would be to use a magnetic spectrometer and this method could also give results with high precision and effectiveness. In this article we describe our design of a new multi-layer absorption method, which is based on the depth-dose curves method that can be used in most irradiation accelerators, and adds the Monte Carlo simulation and iterative algorithm in order to reconstruct the electron energy spectrum. In this article the energy spectrum was measured using these two methods, and good results were acquired. These results could be crosschecked, which made the results more reliable.

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Propagation of kink-antikink pair along microtubules as a control mechanism for polymerization and depolymerization processes

L. Kavitha, A. Muniyappan, S. Zdravković, M. V. Satarić, A. Marlewski, S. Dhamayanthi, D. Gopi

2014 (9): 98703-098703. doi: 10.1088/1674-1056/23/9/098703

摘要 ( 702 )

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Among many types of proteinaceous filaments, microtubules (MTs) constitute the most rigid components of the cellular cytoskeleton. Microtubule dynamics is essential for many vital cellular processes such as intracellular transport, metabolism, and cell division. We investigate the nonlinear dynamics of inhomogeneous microtubulin systems and the MT dynamics is found to be governed by a perturbed sine-Gordon equation. In the presence of various competing nonlinear inhomogeneities, it is shown that this nonlinear model can lead to the existence of kink and antikink solitons moving along MTs. We demonstrate kink-antikink pair collision in the framework of Hirota's bilinearization method. We conjecture that the collisions of the quanta of energy propagating in the form of kinks and antikinks may offer a new view of the mechanism of the retrograde and anterograde transport direction regulation of motor proteins in microtubulin systems.

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A modified interval subdividing based geometric calibration method for interior tomography

张峰, 闫镔, 李磊, 席晓琦, 江桦

2014 (9): 98704-098704. doi: 10.1088/1674-1056/23/9/098704

摘要 ( 634 )

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The interior tomography is commonly met in practice, whereas the self-calibration method for geometric parameters remains far from explored. To determine the geometry of interior tomography, a modified interval subdividing based method, which was originally developed by Tan et al.,^[11] was presented in this paper. For the self-calibration method, it is necessary to obtain the reconstructed image with only geometric artifacts. Therefore, truncation artifacts reduction is a key problem for the self-calibration method of an interior tomography. In the method, an interior reconstruction algorithm instead of the Feldkamp-Davis-Kress (FDK) algorithm was employed for truncation artifact reduction. Moreover, the concept of a minimum interval was defined as the stop criterion of subdividing to ensure the geometric parameters are determined nicely. The results of numerical simulation demonstrated that our method could provide a solution to the self-calibration for interior tomography while the original interval subdividing based method could not. Furthermore, real data experiment results showed that our method could significantly suppress geometric artifacts and obtain high quality images for interior tomography with less imaging cost and faster speed compared with the traditional geometric calibration method with a dedicated calibration phantom.

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Structural properties of a-SiO_x：H films studied by an improved infrared-transmission analysis method

王烁, 张晓丹, 熊绍珍, 赵颖

2014 (9): 98801-098801. doi: 10.1088/1674-1056/23/9/098801

摘要 ( 588 )

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An improved method of fitting point-by-point is proposed to determine the absorption coefficient from infrared (IR) transmittance. With no necessity of empirical correction factors, the absorption coefficient can be accurately determined for the films with thin thicknesses. Based on this method, the structural properties of the hydrogenated amorphous silicon oxide materials (a-SiO_x:H) are investigated. The oxygen-concentration-dependent variation of the Si-O-Si and the Si-H related modes in a-SiO_x:H materials is discussed in detail.

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Improved performance of P3HT：PCBM solar cells by both anode modification and short-wavelength energy utilization using Tb(aca)₃phen

卓祖亮, 王永生, 何大伟, 富鸣

2014 (9): 98802-098802. doi: 10.1088/1674-1056/23/9/098802

摘要 ( 535 )

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The performance of P3HT:PCBM solar cells was improved by anode modification using spin-coated Tb(aca)₃phen ultrathin films. The modification of the Tb(aca)₃phen ultrathin film between the indium tin oxide (ITO) anode and the PEDOT:PSS layer resulted in a maximum power conversion efficiency (PCE) of 2.99% compared to 2.66% for the reference device, which was due to the increase in the short-circuit current density (J_sc). The PCE improvement could be attributed to the short-wavelength energy utilization and the optimized morphology of the active layers. Tb(aca)₃phen with its strong down-conversion luminescence properties is suitable for the P3HT:PCBM blend active layer, and the absorption region of the ternary blend films is extended into the near ultraviolet region. Furthermore, the crystallization and the surface morphology of P3HT:PCBM films were improved with the Tb(aca)₃phen ultrathin film. The ultraviolent-visible absorption spectra, atomic force microscope (AFM), and X-ray diffraction (XRD) of the films were investigated. Both anode modification and short-wavelength energy utilization using Tb(aca)₃phen in P3HT:PCBM solar cells led to about a 12% PCE increase.

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A novel model and behavior analysis for a swarm of multi-agent systems with finite velocity

王良顺, 吴治海

2014 (9): 98901-098901. doi: 10.1088/1674-1056/23/9/098901

摘要 ( 684 )

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Inspired by the fact that in most existing swarm models of multi-agent systems the velocity of an agent can be infinite, which is not in accordance with the real applications, we propose a novel swarm model of multi-agent systems where the velocity of an agent is finite. The Lyapunov function method and LaSalle's invariance principle are employed to show that by using the proposed model all of the agents eventually enter into a bounded region around the swarm center and finally tend to a stationary state. Numerical simulations are provided to demonstrate the effectiveness of the theoretical results.

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Detecting community structure using label propagation with consensus weight in complex network

梁宗文, 李建平, 杨帆, Athina Petropulu

2014 (9): 98902-098902. doi: 10.1088/1674-1056/23/9/098902

摘要 ( 787 )

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Community detection is a fundamental work to analyse the structural and functional properties of complex networks. The label propagation algorithm (LPA) is a near linear time algorithm to find a good community structure. Despite various subsequent advances, an important issue of this algorithm has not yet been properly addressed. Random update orders within the algorithm severely hamper the stability of the identified community structure. In this paper, we executed the basic label propagation algorithm on networks multiple times, to obtain a set of consensus partitions. Based on these consensus partitions, we created a consensus weighted graph. In this consensus weighted graph, the weight value of the edge was the proportion value that the number of node pairs allocated in the same cluster was divided by the total number of partitions. Then, we introduced consensus weight to indicate the direction of label propagation. In label update steps, by computing the mixing value of consensus weight and label frequency, a node adopted the label which has the maximum mixing value instead of the most frequent one. For extending to different networks, we introduced a proportion parameter to adjust the proportion of consensus weight and label frequency in computing mixing value. Finally, we proposed an approach named the label propagation algorithm with consensus weight (LPAcw), and the experimental results showed that the LPAcw could enhance considerably both the stability and the accuracy of community partitions.

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New reconstruction and forecasting algorithm for TEC data

王俊, 盛峥, 江宇, 石汉青

2014 (9): 99401-099401. doi: 10.1088/1674-1056/23/9/099401

摘要 ( 583 )

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To reconstruct the missing data of the total electron content (TEC) observations, a new method is proposed, which is based on the empirical orthogonal functions (EOF) decomposition and the value of eigenvalue itself. It is a self-adaptive EOF decomposition without any prior information needed, and the error of reconstructed data can be estimated. The interval quartering algorithm and cross-validation algorithm are used to compute the optimal number of EOFs for reconstruction. The interval quartering algorithm can reduce the computation time. The application of the data interpolating empirical orthogonal functions (DINEOF) method to the real data have demonstrated that the method can reconstruct the TEC map with high accuracy, which can be employed on the real-time system in the future work.

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Polarized radiative transfer considering thermal emission in semitransparent media

贲勋, 易红亮, 谈和平

2014 (9): 99501-099501. doi: 10.1088/1674-1056/23/9/099501

摘要 ( 712 )

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The characteristics of the polarization must be considered for a complete and correct description of radiation transfer in a scattering medium. Observing and identifying the polarizition characteristics of the thermal emission of a hot semitransparent medium have a major significance to analyze the optical responses of the medium for different temperatures. In this paper, a Monte Carlo method is developed for polarzied radiative transfer in a semitransparent medium. There are mainly two kinds of mechanisms leading to polarization of light: specular reflection on the Fresnel boundary and scattering by particles. The determination of scattering direction is the key to solve polarized radiative transfer problem using the Monte Carlo method. An optimized rejection method is used to calculate the scattering angles. In the model, the treatment of specular reflection is also considered, and in the process of tracing photons, the normalization must be applied to the Stokes vector when scattering, reflection, or transmission occurs. The vector radiative transfer matrix (VRTM) is defined and solved using Monte Carlo strategy, by which all four Stokes elements can be determined. Our results for Rayleigh scattering and Mie scattering are compared well with published data. The accuracy of the developed Monte Carlo method is shown to be good enough for the solution to vector radiative transfer. Polarization characteristics of thermal emission in a hot semitransparent medium is investigated, and results show that the U and V parameters of Stokes vector are equal to zero, an obvious peak always appear in the Q curve instead of the I curve, and refractive index has a completely different effect on I from Q.

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Scintillation characterization for multiple incoherent uplink Gaussian beams

吴武明, 宁禹, 马阎星, 习锋杰, 许晓军

2014 (9): 99502-099502. doi: 10.1088/1674-1056/23/9/099502

摘要 ( 605 )

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By means of numerical simulations, we analyze the scintillation characterization for multiple incoherent uplink Gaussian beams under weak fluctuations cases. Because truly independent beams are difficult to create, we present a more general but approximate model for the multiple of beams traveling through partially correlated paths. This model compares with wave-optics simulations and highlights the reduced correlation coefficient as the beam separation is increased. The scintillation index of three and six incoherent uplink Gaussian beams is also induced. The result shows that the scintillation index decreases with the increase of beams amount and beam separation. When the beams amount and strength of atmospheric turbulence are fixed, the reduction of scintillation index is affected by the ratio of beams separation and the Fried length. The corresponding physical mechanisms for the results are discussed.

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