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    2014年, 第23卷, 第6期 刊出日期:2014-06-15 上一期    下一期
    GENERAL
    Impact of user influence on information multi-step communication in micro-blog
    吴越, 胡勇, 何小海, 邓垦
    2014 (6):  60101-060101.  doi: 10.1088/1674-1056/23/6/060101
    摘要 ( 127 )   PDF(2781KB) ( 676 )  
    User influence is generally considered as one of the most critical factors that affect the information cascading spreading. Based on the common assumption, this paper proposes a theoretical model to examine the force from user influence on the information multi-step communication in micro-blog. Multi-step of information communication is divided into first-step and non-first-step, and user influence is classified into five dimensions. Actual data from Sina micro-blog is collected to construct the model by means of an approach based on structural equations with Partial Least Squares (PLS) technique. Experimental results indicate that the dimensions of number of fans and authority significantly impact the information first-step communication. Leader rank has a positive impact on both first-step and non-first-step communication. Moreover, global centrality and weight of friends are positively related to the information non-first-step communication, but authority is found to have much less relation to it.
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    A novel hierarchy of differential–integral equations and their generalized bi-Hamiltonian structures
    翟云云, 耿献国, 何国亮
    2014 (6):  60201-060201.  doi: 10.1088/1674-1056/23/6/060201
    摘要 ( 176 )   PDF(187KB) ( 461 )  
    With the aid of the zero-curvature equation, a novel integrable hierarchy of nonlinear evolution equations associated with a 3×3 matrix spectral problem is proposed. By using the trace identity, the bi-Hamiltonian structures of the hierarchy are established with two skew-symmetric operators. Based on two linear spectral problems, we obtain the infinite many conservation laws of the first member in the hierarchy.
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    New generating function formulae of even- and odd-Hermite polynomials obtained and applied in the context of quantum optics
    范洪义, 展德会
    2014 (6):  60301-060301.  doi: 10.1088/1674-1056/23/6/060301
    摘要 ( 177 )   PDF(176KB) ( 933 )  
    By combining the operator Hermite polynomial method and the technique of integration within an ordered product of operators, for the first time we derive the generating function of even- and odd-Hermite polynomials which will be useful in constructing new optical field states. We then show that the squeezed state and photon-added squeezed state can be expressed by even- and odd-Hermite polynomials.
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    Quantum Fisher information and spin squeezing in one-axis twisting model
    钟伟, 刘京, 马健, 王晓光
    2014 (6):  60302-060302.  doi: 10.1088/1674-1056/23/6/060302
    摘要 ( 209 )   PDF(354KB) ( 492 )  
    We investigate the dependence of the average parameter estimation precision (APEP), which is defined by the quantum Fisher information, on the polar angle of the initial coherent spin state |θ00> in a one-axis twisting model. Jin et al. [New J. Phys. 11 (2009) 073049] found that the spin squeezing sensitively depends on the polar angle θ0 of the initial coherent spin state. We show explicitly that the APEP is robust to the initial polar angle θ0 in the vicinity of π/2 and a near-Heisenberg limit ∝2/N in quantum single-parameter estimation may still be achieved for states created with the nonlinear evolution of the nonideal coherent spin states θ0π/2. Based on this model, we also consider the effects of the collective dephasing on spin squeezing and the APEP.
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    Entanglement and non-Markovianity of a spin-S system in a dephasing environment
    范子龙, 田晶, 曾浩生
    2014 (6):  60303-060303.  doi: 10.1088/1674-1056/23/6/060303
    摘要 ( 248 )   PDF(469KB) ( 445 )  
    We study the entanglement (measured by negativity) evolution and the non-Markovianity for the dynamical process of a spin-S system embedded in dephasing environments. The exact analytical solution is presented, which shows that the decoherence function governs the evolutions of coherence, entanglement, and the non-Markovianity of the corresponding dynamical processes. For Ohmic and sub-Ohmic reservoirs, the negativity decreases monotonically in time and the corresponding dynamics is Markovian. While for super-Ohmic reservoirs with non-monotonic decoherence function, the negativity appears as the phenomenon of revival and the corresponding dynamics is non-Markovian. The relation between non-Markovianity and the system dimension is studied.
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    Characteristics of spectral-hole burning in Tm3+:YAG based on the perturbation theory
    张世宇, 马秀荣, 张双根, 陈雷, 王夏洋, 穆宽林, 王松
    2014 (6):  60304-060304.  doi: 10.1088/1674-1056/23/6/060304
    摘要 ( 165 )   PDF(329KB) ( 318 )  
    In this paper, the physical mechanism of the interaction between electromagnetic wave and spectral-hole burning crystal material is investigated in detail. In the small signal regime, a perturbation theory model is used to analyze the mechanism of spectral-hole burning. By solving the Liouville equation, three-order perturbation results are obtained. From the theoretic analysis, spectral-hole burning can be interpreted as a photon echo of the zero-order diffraction echo when the first optical pulse and the second optical pulse are overlapped in time. According to the model, the spectral-hole width is dependent on the chirp rate of the reading laser. When the chirp rate is slow with respect to the spectral features of interest, the spectral hole is closely mapped into time domain. For a fast chirp rate, distortions are observed. The results follow Maxwell-Bloch model and they are also in good agreement with the experimental results.
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    Efficient scheme for realizing quantum dense coding with GHZ state in separated low-Q cavities
    孙倩, 何娟, 叶柳
    2014 (6):  60305-060305.  doi: 10.1088/1674-1056/23/6/060305
    摘要 ( 131 )   PDF(382KB) ( 369 )  
    We propose an efficient scheme for realizing quantum dense coding with three-particle GHZ state in separated low-Q cavities. In this paper, the GHZ state is first prepared with three atoms trapped, respectively, in three spatial separated cavities. Meanwhile, with the assistance of a coherent optical pulse and X-quadrature homodyne measurement, we can implement quantum dense coding with three-particle GHZ state with a higher probability. Our scheme can also be generalized to realize N-particle quantum dense coding.
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    Generation of hyperentangled four-photon cluster state via cross-Kerr nonlinearity
    闫香, 於亚飞, 张智明
    2014 (6):  60306-060306.  doi: 10.1088/1674-1056/23/6/060306
    摘要 ( 148 )   PDF(369KB) ( 480 )  
    We propose a scheme for generating a hyperentangled four-photon cluster state that is simultaneously entangled in polarization modes and spatial modes. This scheme is based on linear optical elements, weak cross-Kerr nonlinearity, and homodyne detection. Therefore, it is feasible with current experimental technology.
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    Geometric discord for non-X states
    刘辰, 董裕力, 朱士群
    2014 (6):  60307-060307.  doi: 10.1088/1674-1056/23/6/060307
    摘要 ( 187 )   PDF(652KB) ( 479 )  
    The level surfaces of geometric discord for a class of two-qubit non-X states are investigated when the Bloch vectors are in arbitrary directions. The level surfaces of constant geometric discord are formed by three intersecting open tubes along three orthogonal directions. When Bloch vectors increase, the tubes along one or two directions shrink towards the center and may either totally disappear or the open tubes may become closed tubes when the Bloch vectors reach a critical value. In the generalized amplitude damping channel, the evolution of geometric discord shows double sudden changes when the parameter γ increases. In the phase damping channel, the freezing phenomenon of geometric discord also exists.
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    Performance of superconducting nanowire single-photon detector with the fan coupling antenna array
    王玉珏, 丁天, 马海强, 焦荣珍
    2014 (6):  60308-060308.  doi: 10.1088/1674-1056/23/6/060308
    摘要 ( 274 )   PDF(321KB) ( 391 )  
    The performance of superconducting nanowire single-photon detector (SNSPD) involving niobium nitride with the fan coupling antenna array is analyzed. The SNSPD has a high detection efficiency and counting rate. Hydrogen silsesquioxane and niobium nitride are filled in the gold grating deposited on the substrate in which the fan coupling antenna arrays are embedded. By changing the position of the fan coupling antenna array, the maximum area of optical intensity is obtained and the photon collection efficiency is increased by 26.5 times. The detection efficiency of SNSPD is improved without changing the detection speed. These parameters are important for designing a practical single-photon detector.
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    Enhanced arbitrated quantum signature scheme using Bell states
    王朝, 刘建伟, 尚涛
    2014 (6):  60309-060309.  doi: 10.1088/1674-1056/23/6/060309
    摘要 ( 154 )   PDF(255KB) ( 487 )  
    We investigate the existing arbitrated quantum signature schemes as well as their cryptanalysis, including intercept-resend attack and denial-of-service attack. By exploring the loopholes of these schemes, a malicious signatory may successfully disavow signed messages, or the receiver may actively negate the signature from the signatory without being detected. By modifying the existing schemes, we develop counter-measures to these attacks using Bell states. The newly proposed scheme puts forward the security of arbitrated quantum signature. Furthermore, several valuable topics are also presented for further research of the quantum signature scheme.
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    Nonautonomous dark soliton solutions in two-component Bose-Einstein condensates with a linear time-dependent potential
    李秋艳, 王双进, 李再东
    2014 (6):  60310-060310.  doi: 10.1088/1674-1056/23/6/060310
    摘要 ( 175 )   PDF(366KB) ( 392 )  
    We report the analytical nonautonomous soliton solutions (NSSs) for two-component Bose-Einstein condensates with the presence of a time-dependent potential. These solutions show that the time-dependent potential can affect the velocity of NSS. The velocity shows the characteristic of both increasing and oscillation with time. A detailed analysis for the asymptotic behavior of NSSs demonstrates that the collision of two NSSs of each component is elastic.
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    Circular geodesics and accretion disk in the spacetime of a black hole including global monopole
    孙旭东, 陈菊华, 王永久
    2014 (6):  60401-060401.  doi: 10.1088/1674-1056/23/6/060401
    摘要 ( 147 )   PDF(195KB) ( 380 )  
    We study circular time-like geodesics in the spacetime of a black hole including global monopole. We show that when the range of parameter changed the properties of the circular geodesics and the radiation of accretion disks are different. It follows that the properties of the accretion disk around black hole including global monopole can be different from that of a disk around Schwarzschild black hole.
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    Synchronization of the fractional-order generalized augmented Lü system and its circuit implementation
    薛薇, 徐进康, 仓诗建, 贾红艳
    2014 (6):  60501-060501.  doi: 10.1088/1674-1056/23/6/060501
    摘要 ( 226 )   PDF(2529KB) ( 778 )  
    In this paper, the synchronization of the fractional-order generalized augmented Lü system is investigated. Based on the predictor-corrector method, we obtain phase portraits, bifurcation diagrams, Lyapunov exponent spectra, and Poincaré maps of the fractional-order system and find that a four-wing chaotic attractor exists in the system when the system parameters change within certain ranges. Further, by varying the system parameters, rich dynamical behaviors occur in the 2.7-order system. According to the stability theory of a fractional-order linear system, and adopting the linearization by feedback method, we have designed a nonlinear feedback controller in our theoretical analysis to implement the synchronization of the drive system with the response system. In addition, the synchronization is also shown by an electronic circuit implementation for the 2.7-order system. The obtained experiment results accord with the theoretical analyses, which further demonstrate the feasibility and effectiveness of the proposed synchronization scheme.
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    Tracking problem under a time-varying topology
    董立静, 柴森春, 张百海, 阮盛强
    2014 (6):  60502-060502.  doi: 10.1088/1674-1056/23/6/060502
    摘要 ( 179 )   PDF(506KB) ( 421 )  
    This paper studies the multi-agent tracking problem of a third-order maneuvering target under uncertain communication environments. Each tracking agent is assumed to be a third-order system and can only use its own and neighbors' position, velocity, and acceleration information to design its control input. In this work, the uncertain communication environments are modelled by a finite number of constant Laplacian matrices together with their corresponding scheduling functions. Sufficient conditions for the existence of a tracking strategy have been expressed in terms of the solvability of linear matrix inequalities. Finally, a numerical example is employed to demonstrate the effectiveness of the proposed tracking strategy.
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    Abundant solutions of Wick-type stochastic fractional 2D KdV equations
    Hossam A. Ghany, Abd-Allah Hyder
    2014 (6):  60503-060503.  doi: 10.1088/1674-1056/23/6/060503
    摘要 ( 165 )   PDF(191KB) ( 436 )  
    A modified fractional sub-equation method is applied to Wick-type stochastic fractional two-dimensional (2D) KdV equations. With the help of a Hermit transform, we obtain a new set of exact stochastic solutions to Wick-type stochastic fractional 2D KdV equations in the white noise space. These solutions include exponential decay wave solutions, soliton wave solutions, and periodic wave solutions. Two examples are explicitly given to illustrate our approach.
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    Exponential synchronization of chaotic Lur'e systems with time-varying delay via sampled-data control
    R. Rakkiyappan, R. Sivasamy, S. Lakshmanan
    2014 (6):  60504-060504.  doi: 10.1088/1674-1056/23/6/060504
    摘要 ( 267 )   PDF(709KB) ( 549 )  
    In this paper, we study the exponential synchronization of chaotic Lur'e systems with time-varying delays via sampled-data control by using sector nonlinearties. In order to make full use of information about sampling intervals and interval time-varying delays, new Lyapunov-Krasovskii functionals with triple integral terms are introduced. Based on the convex combination technique, two kinds of synchronization criteria are derived in terms of linear matrix inequalities, which can be efficiently solved via standard numerical software. Finally, three numerical examples are provided to demonstrate the less conservatism and effectiveness of the proposed results.
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    Fusion, fission, and annihilation of complex waves for the (2+1)-dimensional generalized Calogero-Bogoyavlenskii-Schiff system
    朱维婷, 马松华, 方建平, 马正义, 朱海平
    2014 (6):  60505-060505.  doi: 10.1088/1674-1056/23/6/060505
    摘要 ( 137 )   PDF(880KB) ( 528 )  
    With the help of the symbolic computation system, Maple and Riccati equation (ξ'=a0+a1 ξ+a2 ξ2), expansion method, and a linear variable separation approach, a new family of exact solutions with q=lx+my+nt+Γ(x,y,t) for the (2+1)-dimensional generalized Calogero-Bogoyavlenskii-Schiff system (GCBS) are derived. Based on the derived solitary wave solution, some novel localized excitations such as fusion, fission, and annihilation of complex waves are investigated.
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    Spatial geometric constraints histogram descriptors based on curvature mesh graph for 3D pollen particles recognition
    谢永华, 徐赵飞, Hans Burkhardt
    2014 (6):  60701-060701.  doi: 10.1088/1674-1056/23/6/060701
    摘要 ( 212 )   PDF(783KB) ( 377 )  
    This paper presents one novel spatial geometric constraints histogram descriptors (SGCHD) based on curvature mesh graph for automatic three-dimensional (3D) pollen particles recognition. In order to reduce high dimensionality and noise disturbance arising from the abnormal record approach under microscopy, the separated surface curvature voxels are extracted as primitive features to represent the original 3D pollen particles, which can also greatly reduce the computation time for later feature extraction process. Due to the good invariance to pollen rotation and scaling transformation, the spatial geometric constraints vectors are calculated to describe the spatial position correlations of the curvature voxels on the 3D curvature mesh graph. For exact similarity evaluation purpose, the bidirectional histogram algorithm is applied to the spatial geometric constraints vectors to obtain the statistical histogram descriptors with fixed dimensionality, which is invariant to the number and the starting position of the curvature voxels. Our experimental results compared with the traditional methods validate the argument that the presented descriptors are invariant to different pollen particles geometric transformations (such as posing change and spatial rotation), and high recognition precision and speed can be obtained simultaneously.
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    Stability analysis of Markovian jumping stochastic Cohen–Grossberg neural networks with discrete and distributed time varying delays
    M. Syed Ali
    2014 (6):  60702-060702.  doi: 10.1088/1674-1056/23/6/060702
    摘要 ( 191 )   PDF(218KB) ( 457 )  
    In this paper, the global asymptotic stability problem of Markovian jumping stochastic Cohen-Grossberg neural networks with discrete and distributed time-varying delays (MJSCGNNs) is considered. A novel LMI-based stability criterion is obtained by constructing a new Lyapunov functional to guarantee the asymptotic stability of MJSCGNNs. Our results can be easily verified and they are also less restrictive than previously known criteria and can be applied to Cohen-Grossberg neural networks, recurrent neural networks, and cellular neural networks. Finally, the proposed stability conditions are demonstrated with numerical examples.
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    ATOMIC AND MOLECULAR PHYSICS
    Calculations on polarization properties of alkali metal atoms using Dirac-Fock plus core polarization method
    唐永波, 李承斌, 乔豪学
    2014 (6):  63101-063101.  doi: 10.1088/1674-1056/23/6/063101
    摘要 ( 256 )   PDF(273KB) ( 459 )  
    A semi-empirical atomic structure model method is developed in the framework of a relativistic case. This method starts from Dirac-Fock calculations using B-spline basis set. The core-valence electron correction is then treated in a semi-empirical core polarization potential. As an application, the polarization properties of alkali metal atoms, including the static polarizabilities and long-range two-body dispersion coefficients, have been calculated. Our results are in good agreement with the results obtained from ab initio relativistic many-body perturbation method and the available experimental measurements.
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    Intermediate sp-hybridization for chemical bonds in nonplanar covalent molecules of carbon
    曹则贤
    2014 (6):  63102-063102.  doi: 10.1088/1674-1056/23/6/063102
    摘要 ( 213 )   PDF(227KB) ( 391 )  
    General representations for symmetrical and asymmetrical intermediate sp-hybridization are provided, with which the development of electronic structure in C3v-symmetrical C2H6 and the bonding configuration in C60 have been analyzed as an example. The spherical structure of C60 does not necessarily require the fourth hybrid, h4, to lie along the radial direction. Rather, h4 runs at an angle of 3.83° from the radius, in the plane bisecting a pentagon, to achieve maximum overlap with adjacent h4-hybrids. By virtue of these representations, a number of properties of covalent molecules and solids can be conveniently calculated. This work might be particularly helpful for the study of C-C bonding in curved structures of carbon, such as fullerenes, carbon nanotubes, and buckled graphene.
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    Theoretical studies on a series of nitroaliphatic energetic compounds
    曾晖, 赵俊
    2014 (6):  63103-063103.  doi: 10.1088/1674-1056/23/6/063103
    摘要 ( 203 )   PDF(241KB) ( 330 )  
    Density functional theory calculations at the B3LYP/6-311G** level are performed to study the geometric and electronic structures of a series of nitroaliphatic compounds. The heats of formation (HOF) are predicted through the designed isodesmic reactions. Thermal stabilities are evaluated via the homolytic bond dissociation energies (BDEs). Further, the correlation is developed between impact sensitivity h50% and the ratio (BDE/E) of the weakest BDE to the total energy E containing zero point energy correction. In addition, the relative stability of the title compounds is evaluated based on the analysis of calculated Mulliken population and the energy gaps between the frontier orbitals. The calculated BDEs, HOFs, and energy gaps consistently indicate that compound 1,1,1,6,6,6-hexanitro-3-hexyne is the most unstable and the compound 3,3,4,4,-tetranitro-hexane is the most stable. These results provide basic information for the molecular design of novel high energetic density materials.
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    Fast high-resolution nuclear magnetic resonance spectroscopy through indirect zero-quantum coherence detection in inhomogeneous fields
    柯汉平, 陈浩, 林雁勤, 韦芝良, 蔡淑惠, 张志勇, 陈忠
    2014 (6):  63201-063201.  doi: 10.1088/1674-1056/23/6/063201
    摘要 ( 234 )   PDF(556KB) ( 327 )  
    In many cases, high-resolution nuclear magnetic resonance (NMR) spectra are virtually impossible to obtain by conventional nuclear magnetic resonance methods because of inhomogeneity of magnetic field and inherent heterogeneity of sample. Although conventional intramolecular zero-quantum coherence (ZQC) can be used to obtain high-resolution spectrum in inhomogeneous field, the acquisition takes rather long time. In this paper, a spatially encoded intramolecular ZQC technique is proposed to fast acquire high-resolution NMR spectrum in inhomogeneous field. For the first time, the gradient-driven decoding technique is employed to selectively acquire intramolecular ZQC signals. Theoretical analyses and experimental observations demonstrate that high-resolution NMR spectral information can be retrieved within several scans even when the field inhomogeneity is severe enough to erase most spectral information. This work provides a new way to enhance the acquisition efficiency of high-resolution intramolecular ZQC spectroscopy in inhomogeneous fields.
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    Scattering of particles in wave beam based on series expansion
    李应乐, 李瑾, 董群锋, 王明军
    2014 (6):  63301-063301.  doi: 10.1088/1674-1056/23/6/063301
    摘要 ( 183 )   PDF(265KB) ( 330 )  
    Based on the orthogonalities of the vector wave functions, the expressions of scattering fields are developed as the particle in the zero order field and in the first order fields of x, y, and z, respectively. A general relation between the expansion coefficients of scattering field and incident field is presented. Taking the elliptical beam for example, the scattering property of a particle in beam is investigated. After analyzing the effects of the beam waist, irradiating distance, etc. on scattering property, the validity of the proposed algorithm is demonstrated. Results show that the beam waist may improve the particle identification property and the particle has a strong scattering both in the forward direction and in the backward direction. The method proposed is simple and is a new way of researching the scattering from particles in electromagnetic beams.
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    Measurement of 129Xe frequency shift due to Cs-129Xe collisions
    房建成, 万双爱, 陈瑶
    2014 (6):  63401-063401.  doi: 10.1088/1674-1056/23/6/063401
    摘要 ( 210 )   PDF(475KB) ( 399 )  
    Enhancement factor κ0, which characterizes NMR and EPR frequency shifts for Cs-129Xe, is measured for the first time. The enhancement factor κ0 was measured to be (702±41) at 80 ℃ and (653±20) at 90 ℃, using the NMR frequency shift, detected by atomic magnetometer at a low magnetic field of 100 nT. This result is useful for predicting the EPR frequency shifts for Cs and the NMR frequency shifts for 129Xe in spin-exchange cells.
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    Second-order Born calculation of coplanar symmetric (e, 2e) process on Mg
    张永志, 王旸, 周雅君
    2014 (6):  63402-063402.  doi: 10.1088/1674-1056/23/6/063402
    摘要 ( 182 )   PDF(294KB) ( 306 )  
    The second-order distorted wave Born approximation (DWBA) method is employed to investigate the triple differential cross sections (TDCS) of coplanar doubly symmetric (e, 2e) collisions for magnesium at excess energies of 6 eV-20 eV. Comparing with the standard first-order DWBA calculations, the inclusion of the second-order Born term in the scattering amplitude improves the degree of agreement with experiments, especially for backward scattering region of TDCS. This indicates that the present second-order Born term is capable to give a reasonable correction to DWBA model in studying coplanar symmetric (e, 2e) problems of two-valence-electron target in low energy range.
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    Assessment of delocalized and localized molecular orbitals through electron momentum spectroscopy
    刘源, 张凌峰, 宁传刚
    2014 (6):  63403-063403.  doi: 10.1088/1674-1056/23/6/063403
    摘要 ( 266 )   PDF(543KB) ( 512 )  
    Recently, there was a hot controversy about the concept of localized orbitals, which was triggered by Grushow's work titled "Is it time to retire the hybrid atomic orbital?" [J. Chem. Educ. 88, 860 (2011)]. To clarify the issue, we assess the delocalized and localized molecular orbitals from an experimental view using electron momentum spectroscopy. The delocalized and localized molecular orbitals based on various theoretical models for CH4, NH3, and H2O are compared with the experimental momentum distributions. Our results show that the delocalized molecular orbitals rather than the localized ones can give a direct interpretation of the experimental (e, 2e) results.
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    Theoretical analysis on fully differential cross sections for C6+ impact ionization of helium
    方小英, 张瑞芳, 段慧晓, 孙世艳, 贾祥富
    2014 (6):  63404-063404.  doi: 10.1088/1674-1056/23/6/063404
    摘要 ( 195 )   PDF(333KB) ( 362 )  
    Fully differential cross sections (FDCS) are calculated within a four-body model for single ionization of helium by C6+ impact at the incident energy of 100 MeV/a.u. (atomic unit). The results are compared with experimental data and other theoretical predictions. It is shown that our results are in very good agreement with experiment for three small momentum transfers in the scattering plane; however, some significant discrepancies are still present at the largest momentum transfer in both the scattering plane and the perpendicular plane. In actuality, the problem has not been explained by the theory during the last decade. Accordingly, the contributions of different scattering amplitudes to FDCS are analyzed. It is found that for the largest momentum transfer the cross section arising from a destructive interference of the three amplitudes is much smaller than the experimental data. However, the cross section due to the constructive interference of two scattering amplitudes between projectile-ionized electron interaction and projectile-passive electron interaction almost approaches the experimental data.
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    Influence of Ni on Cu precipitation in Fe–Cu–Ni ternary alloy by an atomic study
    朱露珊, 赵世金
    2014 (6):  63601-063601.  doi: 10.1088/1674-1056/23/6/063601
    摘要 ( 252 )   PDF(1455KB) ( 539 )  
    The early aging Cu precipitations in Fe-3%Cu and Fe-3%Cu-4%Ni ternary alloys are investigated by molecular dynamics (MD) simulations. The results show that the average size of Cu clusters in Fe-3%Cu-4%Ni alloy is larger than that in Fe-3%Cu alloy. The diffusion of Cu is accelerated by Ni according to the mean square displacement (MSD). Furthermore, the whole formation process of Cu-rich clusters is analyzed in detail, and it is found that the presence of Ni promotes small Cu-rich clusters to be combined into big ones. Ni atoms prefer to stay at the combination positions of small clusters energetically due to a large number of the first nearest neighbor Cu-Ni interactions, which is verified by first-principles calculations based on density functional theory (DFT).
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    ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
    Split-ring-based metamaterial for far-field subwavelength focusing based on time reversal
    黄海燕, 丁帅, 王秉中, 臧锐
    2014 (6):  64101-064101.  doi: 10.1088/1674-1056/23/6/064101
    摘要 ( 148 )   PDF(623KB) ( 318 )  
    In this paper, split-ring-based metamaterial sheets are designed for the purpose of achieving far-field subwavelength focusing, with the aid of a time-reversal technique. The metamaterial sheets are inserted into a subwavelength array consisting of four element antennas, with the element spacing being as small as 1/15 of a wavelength. Experiments are performed to investigate the effect of the metamaterial sheets on the focusing resolution. The results demonstrate that in the presence of the metamaterial sheets, the subwavelength array exhibits the ability to achieve super-resolution focusing, while there is no super-resolution focusing without the metamaterial sheets. Further investigation shows that the metamaterial sheets are contributive to achieving super-resolution by weakening the cross-correlations of the channel impulse responses between the array elements.
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    An encryption scheme based on phase-shifting digital holography and amplitude-phase disturbance
    花丽丽, 徐宁, 杨庚
    2014 (6):  64201-064201.  doi: 10.1088/1674-1056/23/6/064201
    摘要 ( 152 )   PDF(1894KB) ( 548 )  
    In this paper, we propose an encryption scheme based on phase-shifting digital interferometry. According to the original system framework, we add a random amplitude mask and replace the Fourier transform by the Fresnel transform. We develop a mathematical model and give a discrete formula based on the scheme, which makes it easy to implement the scheme in computer programming. The experimental results show that the improved system has a better performance in security than the original encryption method. Moreover, it demonstrates a good capability of anti-noise and anti-shear robustness.
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    Detection of the spatiotemporal field of a single-shot terahertz pulse based on spectral holography
    王晓雷, 费扬, 李璐杰, 王强, 朱竹青
    2014 (6):  64202-064202.  doi: 10.1088/1674-1056/23/6/064202
    摘要 ( 225 )   PDF(1388KB) ( 365 )  
    According to electro-optical sampling theory, we propose a new method to detect the spatiotemporal field of a single-shot terahertz pulse by spectral holography for the first time. The single-shot terahertz pulse is coupled into a broadened chirped femtosecond pulse according to electro-optical sampling theory in the detecting system. Then the reference wave and the signal wave are split by Dammann grating and spread into the interference band-pass filter. The filtered sub-waves are at different central-frequencies because of the different incident angles. These sub-waves at different central-frequencies interfere to form sub-holograms, which are recorded in a single frame of a charge coupled device (CCD). The sub-holograms are numerically processed, and the spatiotemporal field distribution of the original terahertz pulse is reconstructed. The computer simulations verify the feasibility of the proposed method.
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    Generation of high-energy dual-wavelength domain wall pulse with low repetition rate in an HNLF-based fiber ring laser
    罗智超, 林振彬, 李金玉, 朱鹏飞, 宁秋奕, 邢晓波, 罗爱平, 徐文成
    2014 (6):  64203-064203.  doi: 10.1088/1674-1056/23/6/064203
    摘要 ( 196 )   PDF(1122KB) ( 530 )  
    The generation of high-energy dual-wavelength domain wall pulse with a low repetition rate is demonstrated in a highly nonlinear fiber (HNLF)-based fiber ring laser. By introducing the intracavity birefringence-induced spectral filtering effect, the dual-wavelength lasing operation can be achieved. In order to enhance the cross coupling effect between the two lasing beams for domain wall pulse formation, a 215-m HNLF is incorporated into the laser cavity. Experimentally, it is found that the dual-wavelength domain wall pulse with a repetition rate of 77.67 kHz could be efficiently obtained through simply rotating the polarization controller (PC). At a maximum pump power of 322 mW, the 655-nJ single pulse energy in cavity is obtained. The proposed configuration provides a simpler and more efficient way to generate high energy pulse with a low repetition rate.
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    Systematical analysis of mode-locked fiber lasers using single-walled carbon nanotube saturable absorbers
    张晓, 宋晏蓉
    2014 (6):  64204-064204.  doi: 10.1088/1674-1056/23/6/064204
    摘要 ( 167 )   PDF(2255KB) ( 500 )  
    The output characteristics of the Er-doped mode-locked fiber laser using a single-walled carbon nanotube saturable absorber are investigated theoretically with a nonlinear Schrödinger equation and a saturable absorption equation using realistic parameters. Stable self-starting mode-locking pulses are achieved under net normal, net zero, and net anomalous cavity group velocity dispersion (GVD) respectively. A spectrum with a flat top is obtained from the net normal cavity GVD laser while a spectrum with Kelly side-bands is obtained from the net anomalous cavity GVD laser. The characteristics of the pulse duration changing with cavity GVD and modulation depth of the single-walled carbon nanotubes are discussed. The characteristics of the mode-locking pulses from net normal, net zero, and net anomalous cavity GVD mode-locked fiber lasers are compared. These systematical results are useful for designing mode-locked fiber lasers with saturable absorbers made by different kinds of carbon nano-materials.
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    Multi-wavelength measurements of aerosol optical absorption coefficients using a photoacoustic spectrometer
    刘强, 黄宏华, 王尧, 王贵师, 曹振松, 刘锟, 陈卫东, 高晓明
    2014 (6):  64205-064205.  doi: 10.1088/1674-1056/23/6/064205
    摘要 ( 264 )   PDF(1232KB) ( 357 )  
    The atmospheric aerosol absorption capacity is a critical parameter determining its direct and indirect effects on climate. Accurate measurement is highly desired for the study of the radiative budget of the Earth. A multi-wavelength (405 nm, 532 nm, 780 nm) aerosol absorption meter based on photoacoustic spectroscopy (PAS) invovling a single cylindrical acoustic resonator is developed for measuring the aerosol optical absorption coefficients (OACs). A sensitivity of 1.3 Mm-1 (at 532 nm) is demonstrated. The aerosol absorption meter is successfully tested through measuring the OACs of atmospheric nigrosin and ambient aerosols in the suburbs of Hefei city. The absorption cross section and absorption Ångström exponent (AAE) for ambient aerosol are determined for characterizing the component of the ambient aerosol.
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    Generation of the wavelength-tunable XUV pulse using the two-color and three-color infrared pulses
    冯立强, 刘航, 刘兴江
    2014 (6):  64206-064206.  doi: 10.1088/1674-1056/23/6/064206
    摘要 ( 127 )   PDF(1632KB) ( 325 )  
    We present an efficient method to generate an ultrashort wavelength-tunable XUV pulse by using the harmonic selective enhancement scheme. The results show that by properly controlling the delay times of a two-color field or a three-color field, selective enhancement of the harmonics with photon energies between 80 eV and 315 eV can be obtained. Further, a wavelength-tunable and bandwidth-controllable XUV radiation can be obtained by Fourier transformation of these enhanced harmonics.
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    Ultrashort pulse breaking in optical fiber with third-order dispersion and quintic nonlinearity
    钟先琼, 张晓霞, 程科, 向安平
    2014 (6):  64207-064207.  doi: 10.1088/1674-1056/23/6/064207
    摘要 ( 157 )   PDF(1334KB) ( 337 )  
    The optical wave breaking (OWB) characteristics in terms of the pulse shape, spectrum, and frequency chirp, in the normal dispersion regime of an optical fiber with both the third-order dispersion (TOD) and quintic nonlinearity (QN) are numerically calculated. The results show that the TOD causes the asymmetry of the temporal- and spectral-domain, and the chirp characteristics. The OWB generally appears near the pulse center and at the trailing edge of the pulse, instead of at the two edges of the pulse symmetrically in the case of no TOD. With the increase of distance, the relation of OWB to the TOD near the pulse center increases quickly, leading to the generation of ultra-short pulse trains, while the OWB resulting from the case of no TOD at the trailing edge of the pulse disappears gradually. In addition, the positive (negative) QN enhances (weakens) the chirp amount and the fine structures, thereby inducing the OWB phenomena to appear earlier (later). Thus, the TOD and the positive (negative) QN are beneficial (detrimental) to the OWB and the generation of ultra-short pulse trains.
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    Gap solitons in parity–time complex superlattice with dual periods
    王红成, 凌东雄, 张绍强, 朱兴, 何影记
    2014 (6):  64208-064208.  doi: 10.1088/1674-1056/23/6/064208
    摘要 ( 242 )   PDF(1686KB) ( 462 )  
    A theory is presented to investigate the existence and propagation stability of gap solitons in a parity-time (PT) complex superlattice with dual periods. In this superlattice, the real and imaginary parts are both in the form of superlattices with dual periods. In the self-focusing nonlinearity, PT solitons can exist in the semi-infinite gap. However, only those gap solitons with low powers can propagate stably, whereas the high-power solitons present periodic oscillation and simultaneously suffer energy decay. In the self-defocusing nonlinearity, PT solitons only exist in the first gap and all these solitons are stable.
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    A further study on the spreading and directionality of Gaussian array beams in non-Kolmogorov turbulence
    陆璐, 季小玲, 邓金平, 李晓庆
    2014 (6):  64209-064209.  doi: 10.1088/1674-1056/23/6/064209
    摘要 ( 140 )   PDF(497KB) ( 344 )  
    It is found that in free space, the curves of the mean-squared beam width may each have a cross point at a certain propagation distance zc. For Gaussian array beams, the analytical expressions of zc are derived. For the coherent combination, zc is larger than that for the incoherent combination. However, in non-Kolmogorov turbulence, the cross point disappears, and the Gaussian array beams will have the same directionality in terms of the angular spread. Furthermore, a short propagation distance is needed to reach the same directionality when the generalized exponent is equal to 3.108. In particular, it is shown that the condition obtained in previous studies is not necessary for laser beams to have the same directionality in turbulence, which is explained physically. On the other hand, the relative average intensity distributions at the position where the Gaussian array beams have the same mean-squared beam width are also examined.
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    Precipitation efficiency and its relationship to physical factors
    周玉淑, 李小凡, 高守亭
    2014 (6):  64210-064210.  doi: 10.1088/1674-1056/23/6/064210
    摘要 ( 261 )   PDF(945KB) ( 359 )  
    The precipitation efficiency and its relationship to physical factors are examined by analyzing a two-dimensional cloud-resolving model simulation during TOGA COARE in this study. The basic physical factors include convective available potential energy, water-vapor convergence, vertical wind shear, cloud ratio, sea surface temperature, air temperature, and precipitable water. Precipitation efficiencies do not show a close relationship to air temperature nor to sea surface temperature nor to precipitable water. The precipitation efficiency increases as the water-vapor convergence rate increases and vertical wind shear weakens, whereas it decreases as the convective available potential energy dissipates and anvil clouds develop.
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    Green long-after-glow luminescence of Tb3+ in Sr2SiO4
    王齐, 邱建备, 宋志国, 周大成, 徐旭辉
    2014 (6):  64211-064211.  doi: 10.1088/1674-1056/23/6/064211
    摘要 ( 268 )   PDF(1303KB) ( 826 )  
    The green long-after-glow luminescence from Tb3+-doped Sr2SiO4 phosphors, which are synthesized by the high temperature solid state reaction in a reductive atmosphere, is observed in this paper. The results show that under ultraviolet excitation, the obtained phosphors produce an intense green-lighting-emission from the Tb3+, and the green-lighting long-after-glow luminescence related to Tb3+ can last half an hour after the irradiation source has been removed. Moreover, the effects of co-doping Li+, Dy3+, Er3+, Gd3+, and Yb3+ with Tb3+ on the decay properties and thermoluminescence properties are investigated to confirm the long-after-glow mechanism.
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    Hydrothermal synthesis and up-conversion luminescence of Ho3+/Yb3+ co-doped CaF2
    杨征, 郭崇峰, 陈叶青, 李琳, 李婷, 郑仲铉
    2014 (6):  64212-064212.  doi: 10.1088/1674-1056/23/6/064212
    摘要 ( 190 )   PDF(2642KB) ( 484 )  
    CaF2:Ho3+/Yb3+ nano-particles with intense green up-conversion (UC) luminescence are successfully synthesized via a facile hydrothermal approach by using NH4F as the fluoride source and Na2EDTA as a chelating reagent. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and UC emission spectra are used to characterize the structures, shapes, and luminescent properties of the samples. The effects from fluoride sources and chelating reagents on the formations of CaF2 nano-particles are investigated, and the formation process is also deduced. Under the excitation of a 980-nm laser diode, the samples each show a green up-conversion emission centered at 540 nm corresponding to the 5S2/5F45I8 transitions of Ho3+. Moreover, the UC mechanisms of Ho3+/Yb3+ co-doped CaF2 nano-particles are also discussed.
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    Rectification effect in asymmetric Kerr nonlinear medium
    刘晚果, 潘风明, 蔡力伟
    2014 (6):  64213-064213.  doi: 10.1088/1674-1056/23/6/064213
    摘要 ( 159 )   PDF(1864KB) ( 383 )  
    Based on the transfer matrix method, the recursion of an electromagnetic wave propagating in an asymmetric Kerr nonlinear medium is analytically formulated, from which the rectification effect is clearly presented. The effects on the rectification region of the linear part and nonlinear coefficient of permittivity are both studied, and the energy densities before and after rectification are discussed. We use a rectifying factor to describe the intensity of the rectification effect. The result shows that every transmission peak is divided into two parts when the symmetry is broken, and nonlinear asymmetry has a more significant effect on the rectification effect than the linear asymmetry. The rectification intensity and area will be enlarged when the asymmetry factor is increased in a certain range.
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    Phase-locked all-optical differential polarization demodulation
    史骥, 李政勇, 张革, 王海洋, 王一旭, 吴重庆
    2014 (6):  64214-064214.  doi: 10.1088/1674-1056/23/6/064214
    摘要 ( 216 )   PDF(387KB) ( 341 )  
    A novel scheme of differential polarization demodulation is presented and demonstrated based on a polarized asymmetrical Mach-Zehnder interferometer configuration with polarization control. To enhance the stability of the demodulator, a phase-lock device is designed, and it is composed of a symmetric 3×3 coupler and a feedback circuit. For further establishing a differential polarization-shift keying (DPolSK) transmission system, we successfully carry out the demodulation experiments on 10-Gb/s DPolSK optical signals for the first time. Due to the all-optical structure with phase-lock, our scheme is available to realize the DPolSK optical communication in practical optical fiber systems.
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    Orbit-orbit interaction and photonic orbital Hall effect in reflection of a light beam
    张进, 周新星, 凌晓辉, 陈世贞, 罗海陆, 文双春
    2014 (6):  64215-064215.  doi: 10.1088/1674-1056/23/6/064215
    摘要 ( 179 )   PDF(2232KB) ( 675 )  
    We examine the orbit-orbit interaction when a paraxial beam with intrinsic orbital angular momentum (IOAM) reflects at an air-glass interface. The orbital-dependent splitting of the beam intensity distribution arises due to the interaction between IOAM and extrinsic orbital angular momentum (EOAM). In addition, we find that the beam centroid shows an orbital-dependent rotation when seen along the propagation axis. However, the motion of the beam centroid related to the orbit-orbit interaction undergoes a straight line trajectory with a small angle inclining from the propagation axis. Similar to a previously developed spin-dependent splitting in the photonic spin Hall effect, the orbital-dependent splitting could lead to the photonic orbital Hall effect.
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    Partially coherent Gaussian-Schell model pulse beam propagation in slant atmospheric turbulence
    李亚清, 吴振森, 王明军
    2014 (6):  64216-064216.  doi: 10.1088/1674-1056/23/6/064216
    摘要 ( 143 )   PDF(468KB) ( 390 )  
    Based on the extended Huygens-Fresnel principle, a two-frequency, two-point cross-spectral density function of partially coherent Gaussian-Schell model pulse (GSMP) beam propagation in slant atmospheric turbulence is derived. Using the Markov approximation method and on the assumption that (ω1 - ω2)/(ω1 + ω2) ≤ 1, the theory obtained is valid for turbulence of any strength and can be applied to narrow-band signals. The expressions for average beam intensity, the beam size, and the two-frequency complex degree of coherence of a GSMP beam are obtained. The numerical results are presented, and the effects of the frequency, initial pulse width, initial beam radius, zenith angle, and outer scales on the complex degree of coherence are discussed. This study provides a better understanding of the second-order statistics of a GSMP beam propagating through atmospheric turbulence in the space-frequency domain.
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    Tunable microwave signal generation based on an Opto-DMD processor and a photonic crystal fiber
    王涛, 桑新柱, 颜玢玢, 艾琪, 李妍, 陈笑, 张颖, 陈根祥, 宋菲君, 张霞, 王葵如, 苑金辉, 余重秀, 肖峰, Alameh Kamal
    2014 (6):  64217-064217.  doi: 10.1088/1674-1056/23/6/064217
    摘要 ( 183 )   PDF(666KB) ( 363 )  
    Frequency-tunable microwave signal generation is proposed and experimentally demonstrated with a dual-wavelength single-longitudinal-mode (SLM) erbium-doped fiber ring laser based on a digital Opto-DMD processor and four-wave mixing (FWM) in a high-nonlinear photonic crystal fiber (PCF). The high-nonlinear PCF is employed for the generation of the FWM to obtain stable and uniform dual-wavelength oscillation. Two different short passive sub-ring cavities in the main ring cavity serve as mode filters to make SLM lasing. The two lasing wavelengths are electronically selected by loading different gratings on the Opto-DMD processor controlled with a computer. The wavelength spacing can be smartly adjusted from 0.165 nm to 1.08 nm within a tuning accuracy of 0.055 nm. Two microwave signals at 17.23 GHz and 27.47 GHz are achieved. The stability of the microwave signal is discussed. The system has the ability to generate a 137.36-GHz photonic millimeter signal at room temperature.
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    High conversion efficiency, high power density Q-switched fiber laser
    陈霄, 肖起榕, 金光勇, 闫平, 巩马理
    2014 (6):  64218-064218.  doi: 10.1088/1674-1056/23/6/064218
    摘要 ( 180 )   PDF(499KB) ( 433 )  
    An acoustic-optic Q-switched all-fiber laser with a high-repetition-rate, a short pulse width, a wide spectrum, and a high conversion efficiency is experimentally demonstrated. In the laser configuration, a (1+1)×1 side-pumping coupler is introduced to perform backward pumping, and a 10/130-um Yb fiber is adopted. The acoustic-optic component operates in the first direction, achieving a Q-switched pulse with a repetition rate adjustable in the range of 20 kHz-80 kHz. Under a repetition rate of 20 kHz and a pump power of 6.76 W, the fiber laser obtains a highly efficient and stable pulse output, with an average power of 4.3 W, a pulse width of 56 ns, a peak power of 3.83 kW, and a power density of 1.39×1010 W/cm2. Particularly, the optic-optic conversion efficiency of the laser reaches as high as 64%. Another feature of the pulsed laser is that the high reflection mirror reflects the pump light as well, which brings the secondary absorption of the pump power into the gain fiber.
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    Reverse electric field Monte Carlo simulation for vector radiative transfer in the atmosphere
    李绪友, 孙波, 于莹莹
    2014 (6):  64219-064219.  doi: 10.1088/1674-1056/23/6/064219
    摘要 ( 170 )   PDF(333KB) ( 452 )  
    In this paper, a reverse electric field Monte Carlo (REMC) method is proposed to study the vector radiation transfer in the atmosphere. The REMC is based on tracing the multiply scattered electric field to simulate the vector transmitted radiance. The reflected intensities with different total optical depth values are obtained, which accord well with the results in the previous research. Stokes vector and the degree of polarization are numerically investigated. The simulation result shows that when the solar zenith angle is determined, the zenith angle of detector has two points, of which the degree of polarization does not change with the ground albedo and the optical depth. The two points change regularly with the solar zenith angle. Moreover, our REMC method can be applied to the vector radiative transfer in the atmosphere-ocean system.
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    Cumulative solutions of nonlinear longitudinal vibration in isotropic solid bars
    钱祖文
    2014 (6):  64301-064301.  doi: 10.1088/1674-1056/23/6/064301
    摘要 ( 120 )   PDF(197KB) ( 255 )  
    Based on the strain invariant relationship and taking the high-order elastic energy into account, a nonlinear wave equation is derived, in which the excitation, linear damping, and the other nonlinear terms are regarded as the first-order correction to the linear wave equation. To solve the equation, the biggest challenge is that the secular terms exist not only in the fundamental wave equation but also in the harmonic wave equation (unlike the Duffing oscillator, where they exist only in the fundamental wave equation). In order to overcome this difficulty and to obtain a steady periodic solution by the perturbation technique, the following procedures are taken: (i) for the fundamental wave equation, the secular term is eliminated and therefore a frequency response equation is obtained; (ii) for the harmonics, the cumulative solutions are sought by the Lagrange variation parameter method. It is shown by the results obtained that the second- and higher-order harmonic waves exist in a vibrating bar, of which the amplitude increases linearly with the distance from the source when its length is much more than the wavelength; the shift of the resonant peak and the amplitudes of the harmonic waves depend closely on nonlinear coefficients; there are similarities to a certain extent among the amplitudes of the odd- (or even-) order harmonics, based on which the nonlinear coefficients can be determined by varying the strain and measuring the amplitudes of the harmonic waves in different locations.
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    Research on the discrete variational method for a Birkhoffian system
    刘世兴, 花巍, 郭永新
    2014 (6):  64501-064501.  doi: 10.1088/1674-1056/23/6/064501
    摘要 ( 202 )   PDF(242KB) ( 345 )  
    In this paper, we present a new integration algorithm based on the discrete Pfaff-Birkhoff principle for Birkhoffian systems. It is proved that the new algorithm can preserve the general symplectic geometric structures of Birkhoffian systems. A numerical experiment for a damping oscillator system is conducted. The result shows that the new algorithm can better simulate the energy dissipation than the R-K method, which illustrates that we can numerically solve the dynamical equations by the discrete variational method in a Birkhoffian framework for the systems with a general symplectic structure. Furthermore, it is demonstrated that the results of the numerical experiments are determined not by the constructing methods of Birkhoffian functions but by whether the numerical method can preserve the inherent nature of the dynamical system.
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    Analysis of composite material interface crack face contact and friction effects using a new node-pairs contact algorithm
    钟志鹏, 何郁波, 万水
    2014 (6):  64601-064601.  doi: 10.1088/1674-1056/23/6/064601
    摘要 ( 217 )   PDF(883KB) ( 351 )  
    A new node-pairs contact algorithm is proposed to deal with a composite material or bi-material interface crack face contact and friction problem (e.g., resistant coating and thermal barrier coatings) subjected to complicated load conditions. To decrease the calculation scale and calculation errors, the local Lagrange multipliers are solved only on a pair of contact nodes using the Jacobi iteration method, and the constraint modification of the tangential multipliers are required. After the calculation of the present node-pairs Lagrange multiplier, it is turned to next contact node-pairs until all node-pairs have finished. Compared with an ordinary contact algorithm, the new local node-pairs contact algorithm is allowed a more precise element on the contact face without the stiffness matrix singularity. The stress intensity factors (SIFs) and the contact region of an infinite plate central crack are calculated and show good agreement with those in the literature. The contact zone near the crack tip as well as its influence on singularity of stress fields are studied. Furthermore, the frictional contacts are also considered and found to have a significant influence on the SIFs. The normalized mode-Ⅱ stress intensity factors ??? for the friction coefficient decrease by 16% when f changes from 1 to 0.
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    Slip effects on streamline topologies and their bifurcations for peristaltic flows of a viscous fluid
    Z. Asghar, N. Ali
    2014 (6):  64701-064701.  doi: 10.1088/1674-1056/23/6/064701
    摘要 ( 160 )   PDF(1128KB) ( 364 )  
    We discuss the effects of the surface slip on streamline patterns and their bifurcations for the peristaltic transport of a Newtonian fluid. The flow is in a two-dimensional symmetric channel or an axisymmetric tube. An exact expression for the stream function is obtained in the wave frame under the assumptions of long wavelength and low Reynolds number for both cases. For the discussion of the particle path in the wave frame, a system of nonlinear autonomous differential equations is established and the methods of dynamical systems are used to discuss the local bifurcations and their topological changes. Moreover, all types of bifurcations and their topological changes are discussed graphically. Finally, the global bifurcation diagram is used to summarize the bifurcations.
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    Critical condition for the transformation from Taylor cone to cone-jet
    魏承, 冮铁强, 陈立杰, 赵阳
    2014 (6):  64702-064702.  doi: 10.1088/1674-1056/23/6/064702
    摘要 ( 206 )   PDF(947KB) ( 389 )  
    An energy method is proposed to investigate the critical transformation condition from a Taylor cone to a cone-jet. Based on the kinetic theorem, the system power allocation and the electrohydrodynamics stability are discussed. The numerical results indicate that the energy of the liquid cone tip experiences a maximum value during the transformation. With the proposed jetting energy, we give the critical transformation condition under which the derivative of jetting energy with respect to the surface area is greater than or equal to the energy required to form a unit of new liquid surface.
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    The interaction between zonal flow and Rossby waves with scalar nonlinearity
    张喜平, 赵强
    2014 (6):  64703-064703.  doi: 10.1088/1674-1056/23/6/064703
    摘要 ( 179 )   PDF(275KB) ( 311 )  
    The nonlinear interactions between zonal flow and Rossby waves are studied by numerical simulations with focus on the effects of scalar nonlinearity. The numerical results show that the scalar nonlinearity has an appreciable influence on the Rossby dipole evolution and can reduce the threshold of the disturbance energy increase.
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    PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
    Characteristics of dual-frequency capacitively coupled SF6/O2 plasma and plasma texturing of multi-crystalline silicon
    徐东升, 邹帅, 辛煜, 苏晓东, 王栩生
    2014 (6):  65201-065201.  doi: 10.1088/1674-1056/23/6/065201
    摘要 ( 119 )   PDF(1047KB) ( 648 )  
    Due to it being environmentally friendly, much attention has been paid to the dry plasma texturing technique serving as an alternative candidate for multicrystalline silicon (mc-Si) surface texturing. In this paper, capacitively coupled plasma (CCP) driven by a dual frequency (DF) of 40.68 MHz and 13.56 MHz is first used for plasma texturing of mc-Si with SF6/O2 gas mixture. Using a hairpin resonant probe and optical emission techniques, DF-CCP characteristics and their influence on mc-silicon surface plasma texturing are investigated at different flow rate ratios, pressures, and radio-frequency (RF) input powers. Experimental results show that suitable plasma texturing of mc-silicon occurs only in a narrow range of plasma parameters, where electron density ne must be larger than 6.3×109 cm-3 and the spectral intensity ratio of the F atom to that of the O atom ([F]/[O]) in the plasma must be between 0.8 and 0.3. Out of this range, no cone-like structure is formed on the mc-silicon surface. In our experiments, the lowest reflectance of about 7.3% for mc-silicon surface texturing is obtained at an [F]/[O] of 0.5 and ne of 6.9×109 cm-3.
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    A tunable dual-narrowband band-pass filter using plasma quantum well structure
    戴燚, 刘少斌, 王身云, 孔祥鲲, 陈忱
    2014 (6):  65202-065202.  doi: 10.1088/1674-1056/23/6/065202
    摘要 ( 206 )   PDF(873KB) ( 332 )  
    A tunable dual-narrowband pass-band filter is designed. A one-dimensional photonic crystal (1D PC) is comprised of alternate dielectric layer and vacuum layer. Two quantum wells (QWs) as defects can be constructed by sandwiching two plasma slabs symmetrically in the 1D PC, and a dual-narrowband pass-band filter is formed. The conventional finite-difference time-domain (FDTD) method and piecewise linear current density recursive convolution (PLCDRC)-FDTD method are applied to the dielectric and plasma, respectively. The simulation results illustrate that the dual-narrowband frequencies can be tuned by changing the plasma frequency. The pass band interval and the half-power bandwidths (-3-dB band widths) are related to the space interval between two QWs.
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    Energy spectrum of multi-radiation of X-rays in a low energy Mather-type plasma focus device
    Farzin M. Aghamir, Reza A. Behbahani
    2014 (6):  65203-065203.  doi: 10.1088/1674-1056/23/6/065203
    摘要 ( 195 )   PDF(1353KB) ( 421 )  
    The multi-radiation of X-rays was investigated with special attention to their energy spectrum in a Mather-type plasma focus device (operated with argon gas). The analysis is based on the effect of anomalous resistances. To study the energy spectrum, a four-channel diode X-ray spectrometer was used along with a special set of filters. The filters were suitable for detection of medium range X-rays as well as hard X-rays with energy exceeding 30 keV. The results indicate that the anomalous resistivity effect during the post pinch phase may cause multi-radiation of X-rays with a total duration of 300± 50 ns. The significant contribution of Cu-Kα was due to the medium range X-rays, nonetheless, hard X-rays with energies greater than 15 keV also participate in the process. The total emitted X-ray energy in the forms of Cu-Kα and Cu-Kβ was around 0.14± 0.02 (J/Sr) and 0.04± 0.01 (J/Sr), respectively. The total energy of the emitted hard X-ray (> 15 keV) was around 0.12± 0.02 (J/Sr).
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    Synthesis of ZrSiN composite films using a plasma focus device
    R. Ahmad, T. Hussain, I. A. Khan, R. S. Rawat
    2014 (6):  65204-065204.  doi: 10.1088/1674-1056/23/6/065204
    摘要 ( 154 )   PDF(1312KB) ( 396 )  
    ZrSiN thin films are synthesized by using plasma focus through various numbers of focus shots (10, 20, and 30), with samples placed at 9 cm away from the tip of the anode. Crystal structures, surface morphologies, and elemental compositions of ZrSiN films are characterized by an X-ray diffractometer (XRD) and scanning electron microscope (SEM) attached with energy dispersive X-ray spectroscopy (EDS). XRD patterns confirm the formations of polycrystalline ZrSiN films. Crystallinity of nitride increases with the increase of focus shot number. The average crystallite size of zirconium nitride increases from 27 ± 3 nm to 73 ± 8 nm and microstrain decreases from 2.28 to 1.0 with the increase of the focus shot number. SEM results exhibit the formations of granular and oval-shaped microstructures, depending on the number of focus shots. EDS results confirm the presences of silicon, zirconium, nitrogen, and oxygen in the composite films. The content values of Zr and N in the composite films increase with the increase of the focus shot number.
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    Observation and analysis of halo current in EAST
    陈大龙, 沈飙, 钱金平, 孙有文, 刘广君, 石同辉, 庄会东, 肖炳甲
    2014 (6):  65205-065205.  doi: 10.1088/1674-1056/23/6/065205
    摘要 ( 160 )   PDF(1205KB) ( 403 )  
    Plasma in a typically elongated cross-section tokamak (for example, EAST) is inherently unstable against vertical displacement. When plasma loses the vertical position control, it moves downward or upward, leading to disruption, and a large halo current is generated helically in EAST typically in the scrape-off layer. When flowing into the vacuum vessel through in-vessel components, the halo current will give rise to a large J×B force acting on the vessel and the in-vessel components. In EAST VDE experiment, part of the eddy current is measured in halo sensors, due to the large loop voltage. Primary experimental data demonstrate that the halo current first lands on the outer plate and then flows clockwise, and the analysis of the information indicates that the maximum halo current estimated in EAST is about 0.4 times the plasma current and the maximum value of TPF×Ih/IP0 is 0.65, furthermore Ih/ Ip0 and TPF×Ih/Ip0 tend to increase with the increase of Ip0. The test of the strong gas injection system shows good success in increasing the radiated power, which may be effective in reducing the halo current.
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    Ray tracing method for the grazing incidence flat-field imaging soft X-ray spectrometer
    董全力, 刘运全, 腾浩, 李英骏, 张杰
    2014 (6):  65206-065206.  doi: 10.1088/1674-1056/23/6/065206
    摘要 ( 187 )   PDF(703KB) ( 355 )  
    A ray tracing method is introduced for helping adjustment and spectra analysis of the grazing incidence flat-field imaging soft X-ray spectrometer. For a single point source, the spectra images obtained by separate components, the toroidal mirror, and the grazing incidence flat-field concave grating with varied line spaces are given respectively. The calculated spectral images of the single point source by the spectrometer are also given for comparison with measurements with different experimental alignments.
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    CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
    Structural and magnetic properties of BiFe1-xCrxO3 synthesized samples
    S. S. Arafat
    2014 (6):  66101-066101.  doi: 10.1088/1674-1056/23/6/066101
    摘要 ( 224 )   PDF(596KB) ( 499 )  
    Chromium doping effects on the structure and the magnetic properties of bismuth ferrite BiFe1-xCrxO3 (x=0-0.3) (BFCxO) polycrystalline samples are examined. The Perovskite-type oxide samples are synthesized by the conventional solid state reaction at a high pressure of 7 GPa and a temperature of 1273 K. The X-ray powder diffraction patterns at room temperature show that all the samples with x=0.0-0.3 are described by the rhombohedral structure. In the meantime, it is revealed that the doping of Cr can induce noticeable lattice distortions in the doping samples, and the largest distortion is observed in the case x=0.1. The magnetic hysteresis loops measured at room temperature exhibit week ferromagnetic behaviors of the samples and the magnetization is found to increase with the increase in Cr concentration. The temperature-dependent magnetization curves indicate antiferromagnetic features in samples. Moreover, Cr-doping tends to reduce the ordering temperature.
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    Electrohydrodynamic direct-writing of conductor-insulator-conductor multi-layer interconnection
    郑高峰, 裴艳博, 王翔, 郑建毅, 孙道恒
    2014 (6):  66102-066102.  doi: 10.1088/1674-1056/23/6/066102
    摘要 ( 170 )   PDF(608KB) ( 373 )  
    A multi-layer interconnection structure is a basic component of electronic devices, and printing of the multi-layer interconnection structure is the key process in printed electronics. In this work, electrohydrodynamic direct-writing (EDW) is utilized to print the conductor-insulator-conductor multi-layer interconnection structure. Silver ink is chosen to print the conductor pattern, and a polyvinylpyrrolidone (PVP) solution is utilized to fabricate the insulator layer between the bottom and top conductor patterns. The influences of EDW process parameters on the line width of the printed conductor and insulator patterns are studied systematically. The obtained results show that the line width of the printed structure increases with the increase of the flow rate, but decreases with the increase of applied voltage and PVP content in the solution. The average resistivity values of the bottom and top silver conductor tracks are determined to be 1.34×10-7 Ω·m and 1.39×10-7 Ω·m, respectively. The printed PVP layer between the two conductor tracks is well insulated, which can meet the insulation requirement of the electronic devices. This study offers an alternative, fast, and cost-effective method of fabricating conductor-insulator-conductor multi-layer interconnections in the electronic industry.
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    Retarded thermal oxidation of strained Si substrate
    孙家宝, 唐晓雨, 杨周伟, 施毅, 赵毅
    2014 (6):  66103-066103.  doi: 10.1088/1674-1056/23/6/066103
    摘要 ( 170 )   PDF(867KB) ( 368 )  
    Strained Si is recognized as a necessary technology booster for modern integrated circuit technology. However, the thermal oxidation behaviors of strained Si substrates are not well understood yet despite their importance. In this study, we for the first time experimentally find that all types of strained Si substrates (uniaxial tensile, uniaxial compressive, biaxial tensile, and biaxial compressive) show smaller thermal oxidation rates than an unstrained Si substrate. The possible mechanisms for these retarded thermal oxidation rates in strained Si substrates are also discussed.
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    The generalized planar fault energy, ductility, and twinnability of Al and Al-RE (RE=Sc, Y, Dy, Tb, Nd) at different temperatures:A first-principles study
    吴小志, 刘利利, 王锐, 刘庆
    2014 (6):  66104-066104.  doi: 10.1088/1674-1056/23/6/066104
    摘要 ( 182 )   PDF(516KB) ( 452 )  
    The genearlized planar fault energies of Al and Al-RE (RE = Sc, Y, Dy, Tb, Nd) alloys have been investigated using first-principles methods combined with a quasiharmonic approach. The stacking fault energies, unstable stacking fault energies, and unstable twinning energies decrease slightly with increasing temperature. The ductility parameter D, the relative barrier difference δusut, and the twinnability τa of Al and Al-RE alloys at different temperatures have been determined. It is found that the ductilities of Al and Al alloys are nearly the same and the ductilities increase slightly with increasing temperature. The RE alloying elements make twinning more likely and the twinnabilities of Al and Al alloys decrease with increasing temperature.
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    Irradiation effect of yttria-stabilized zirconia by high dose dual ion beam irradiation
    张艳文, 王绪, 刘士毅, 唐美雄, 赵子强, 张鹏, 王宝义, 曹兴忠
    2014 (6):  66105-066105.  doi: 10.1088/1674-1056/23/6/066105
    摘要 ( 152 )   PDF(864KB) ( 498 )  
    Yttria-stabilized zirconia (YSZ) is irradiated with 2.0-MeV Au2+ ions and 30-keV He+ ions. Three types of He, Au, Au+He (successively) ion irradiation are performed. The maximum damage level of a sequential dual ion beam implanted sample is smaller than single Au ion implanted sample. A comparable volume swelling is found in a sequential dual ion beam irradiated sample and it is also found in a single Au ion implanted sample. Both effects can be explained by the partial reorganization of the dislocation network into weakly damaged regions in the dual ion beam implanted YSZ. A vacancy-assisted helium trapping/diffusion mechanism in the dual ion beam irradiated condition is discussed. No phase transformation or amorphization behavior happens in all types of ion irradiated YSZ.
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    Polythiophene encapsulated inside (13, 0) CNT:A nano-hybrid system
    Tayebeh Movlarooy
    2014 (6):  66201-066201.  doi: 10.1088/1674-1056/23/6/066201
    摘要 ( 174 )   PDF(3044KB) ( 505 )  
    We present a first-principles calculation on the electronic and optical properties of a hybrid nanotube system consisting of a (13, 0) single-walled carbon nanotube encapsulated by polythiophene. This hybrid-system represents a complete new type of matter and is known as the peapod system. We analyze how the polythiophene changes the electronic and optical properties of the nanotube. In particular, we examine new features in the dielectric function due to the transitions between the states of the polymer and the nanotube. The electronic structure of the combined system appears to be a simple superposition of the individual constituents. The density functional theory calculations demonstrate van der Waals interaction as the bonding mechanism between the tube and the encapsulated molecule.
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    Electronic structures and energy band properties of Be- and S-doped wurtzite ZnO
    郑树文, 范广涵, 何苗, 张涛
    2014 (6):  66301-066301.  doi: 10.1088/1674-1056/23/6/066301
    摘要 ( 161 )   PDF(488KB) ( 483 )  
    The energy band properties, density of states, and band alignment of the BexZn1-xO1-ySy alloy (Be- and S-doped wurtzite ZnO) are investigated by the first-principles method. BexZn1-xO1-ySy alloy is a direct band gap semiconductor, the valence band maximum (VBM) and the conduction band minimum (CBM) of BexZn1-xO1-ySy are dominated by S 3p and Zn 4s states, respectively. The band gap and lattice constant of BexZn1-xO1-ySy alloy can be modulated by changing the doped content values x and y. With the increase in Be content value x in the BexZn1-xO1-ySy alloy, the band gap increases and the lattice constant reduces, but the situation is just the opposite when increasing the S content value y in the BexZn1-xO1-ySy alloy. Because the lattice constant of Be0.375Zn0.625O0.75S0.25 alloy is well matched with that of ZnO and its energy gap is large compared with that of ZnO, so the Be0.375Zn0.625O0.75S0.25 alloy is suitable for serving as the blocking material for a high-quality ZnO-based device.
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    Phase transition and thermal expansion property of Cr2-xZr0.5xMg0.5xMo3O12 solid solution
    宋文博, 王俊俏, 李志远, 刘献省, 袁保合, 梁二军
    2014 (6):  66501-066501.  doi: 10.1088/1674-1056/23/6/066501
    摘要 ( 152 )   PDF(2131KB) ( 379 )  
    Compounds with the formula Cr2-xZr0.5xMg0.5xMo3O12 (x = 0.0, 0.3, 0.5, 0.9, 1.3, 1.5, 1.7, 1.9) are synthesized, and the effects of Zr4 + and Mg2+ co-incorporation on the phase transition, thermal expansion, and Raman mode are investigated. It is found that Cr2-xZr0.5xMg0.5xMo3O12 crystallize into monoclinic structures for x ≤ 1.3 and orthorhombic structures for x ≥ 1.5 at room temperature. The phase transition temperature from a monoclinic to an orthorhombic structure of Cr2Mo3O12 can be reduced by the partial substitution of (ZrMg)6+ for Cr3+. The overall linear thermal expansion coefficient decreases with the increase of the (ZrMg)6+ content in an orthorhombic structure sample. The co-incorporation of Zr4 + and Mg2+ in the lattice results in the occurrence of new Raman modes and the hardening of the symmetric vibrational modes, which are attributed to the MoO4 tetrahedra sharing corners with ZrO6/MgO6 octahedra and to the strengthening of Mo-O bonds due to less electronegativities of Zr4+ and Mg2+ than Cr3+, respectively.
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    Binding energies of impurity states in strained wurtzite GaN/AlxGa1-xN heterojunctions with finitely thick potential barriers
    冯振宇, 班士良, 朱俊
    2014 (6):  66801-066801.  doi: 10.1088/1674-1056/23/6/066801
    摘要 ( 192 )   PDF(292KB) ( 386 )  
    Ground state binding energies of donor impurities in a strained wurtzite GaN/AlxGa1-xN heterojunction with a potential barrier of finite thickness are investigated using a variational approach combined with a numerical computation. The built-in electric field due to the spontaneous and piezoelectric polarization, the strain modification due to the lattice mismatch near the interfaces, and the effects of ternary mixed crystals are all taken into account. It is found that the binding energies by using numerical wave functions are obviously greater than those by using variational wave functions when impurities are located in the channel near the interface of a heterojunction. Nevertheless, the binding energies using the former functions are obviously less than using the later functions when impurities are located in the channel far from an interface. The difference between our numerical method and the previous variational method is huge, showing that the former should be adopted in further work for the relevant problems. The binding energies each as a function of hydrostatic pressure are also calculated. But the change is unobvious in comparison with that obtained by the variational method.
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    Atomic diffusion across Ni50Ti50–Cu explosive welding interface:Diffusion layer thickness and atomic concentration distribution
    陈仕洋, 武振伟, 刘凯欣
    2014 (6):  66802-066802.  doi: 10.1088/1674-1056/23/6/066802
    摘要 ( 196 )   PDF(904KB) ( 465 )  
    Molecular dynamics simulations are carried out to study atomic diffusion in the explosive welding process of Ni50Ti50-Cu (at.%). By using a hybrid method which combines molecular dynamics simulation and classical diffusion theory, the thickness of the diffusion layer and the atomic concentration distribution across the welding interface are obtained. The results indicate that the concentration distribution curves at different times have a geometric similarity. According to the geometric similarity, the atomic concentration distribution at any time in explosive welding can be calculated. Ni50Ti50-Cu explosive welding and scanning electron microscope experiments are done to verify the results. The simulation results and the experimental results are in good agreement.
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    Effects of annealing temperature on the electrical property and microstructure of aluminum contact on n-type 3C-SiC
    代冲冲, 刘学超, 周天宇, 卓世异, 石彪, 施尔畏
    2014 (6):  66803-066803.  doi: 10.1088/1674-1056/23/6/066803
    摘要 ( 167 )   PDF(717KB) ( 309 )  
    The 3C-SiC thin films used herein are grown on Si substrates by chemical vapor deposition. Al contacts with different thickness values are deposited on the 3C-SiC/Si (100) structure by the magnetron sputtering method and are annealed at different temperatures. We focus on the effects of the annealing temperature on the ohmic contact properties and microstructure of Al/3C-SiC structure. The electrical properties of Al contacts to n-type 3C-SiC are characterized by the transmission line method. The crystal structures and chemical phases of Al contacts are examined by X-ray diffraction, Raman spectra, and transmission electron microscopy, respectively. It is found that the Al contacts exhibit ohmic contact behaviors when the annealing temperature is below 550 ℃, and they become Schottky contacts when the annealing temperature is above 650 ℃. A minimum specific contact resistance of 1.8 ×10-4 Ω·cm2 is obtained when the Al contact is annealed at 250 ℃.
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    Sputtering pressure influence on growth morphology, surface roughness, and electrical resistivity for strong anisotropy beryllium film
    罗炳池, 李恺, 康晓丽, 张吉强, 何玉丹, 罗江山, 吴卫东, 唐永建
    2014 (6):  66804-066804.  doi: 10.1088/1674-1056/23/6/066804
    摘要 ( 140 )   PDF(2148KB) ( 837 )  
    The strong anisotropy beryllium (Be) films are fabricated at different sputtering pressures by direct current magnetron sputtering. With the increase of pressure, the deposition rate of Be film first increases, and when the pressure exceeds 0.8 Pa, it gradually descends. The X-ray diffraction analysis indicates that Be film is of α-Be phase, its surface always reveals the (101) crystal plane possessing the low surface energy. As for the growth morphology of Be film, the surface is mainly characterized by the fibrous grains, while the cross section shows a transition from a columnar grain to a mixed grain consisting of a cone-shaped grain and a columnar grain as the sputtering pressure increases. The large grain fraction decays exponentially from 75.0% to 59.3% with the increase of sputtering pressure p, which can improve the grain size uniformity. The surface roughness increases due to the insufficient atom diffusion, which is comparable to its decrease due to the etching effect at p < 0.8 Pa, while it increases drastically at p > 0.8 Pa, and this increase is dominated by the atom diffusion. The electrical resistivity values of Be films range from 1.7 uΩ·m to 2.7 uΩ·m in the range 0.4 Pa-1.2 Pa, which is 50 times larger than the bulk resistivity.
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    Preparation and characterization of thick cubic boron nitride films
    王明娥, 马国佳, 董闯, 巩水利
    2014 (6):  66805-066805.  doi: 10.1088/1674-1056/23/6/066805
    摘要 ( 147 )   PDF(344KB) ( 346 )  
    Cubic boron nitride (c-BN) films are prepared by the radio frequency magnetron sputtering technique. The stresses and crystallinities of the films are estimated by the Fourier transform infrared spectroscopy of c-BN samples, including the peak shifts and varieties of full widths at half maximum. The effects of the B-C-N interlayer and the two-stage deposition method on the c-BN films are investigated. Then the thick and stable c-BN films are prepared by a combination of the two methods. The properties of the interlayer and film are also characterized.
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    CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
    Partial-SOI high voltage laterally double-diffused MOS with a partially buried n+-layer
    胡盛东, 武星河, 朱志, 金晶晶, 陈银晖
    2014 (6):  67101-067101.  doi: 10.1088/1674-1056/23/6/067101
    摘要 ( 182 )   PDF(1752KB) ( 591 )  
    A novel partial silicon-on-insulator laterally double-diffused metal-oxide-semiconductor transistor (PSOI LDMOS) with a thin buried oxide layer is proposed in this paper. The key structure feature of the device is an n+-layer, which is partially buried on the bottom interface of the top silicon layer (PBNL PSOI LDMOS). The undepleted interface n+-layer leads to plenty of positive charges accumulated on the interface, which will modulate the distributions of the lateral and vertical electric fields for the device, resulting in a high breakdown voltage (BV). With the same thickness values of the top silicon layer (10 μm) and buried oxide layer (0.375 μm), the BV of the PBNL PSOI LDMOS increases to 432 V from 285 V of the conventional PSOI LDMOS, which is improved by 51.6%.
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    Electronic and magnetic properties of BiFeO3 with intrinsic defects:First-principles prediction
    杨瑞鹏, 林思贤, 方潇功, 秦明辉, 高兴森, 曾敏, 刘俊明
    2014 (6):  67102-067102.  doi: 10.1088/1674-1056/23/6/067102
    摘要 ( 169 )   PDF(2676KB) ( 945 )  
    The electronic structure, magnetism, and dielectric functions of BiFeO3 with intrinsic vacancies, including Bi-, Fe-, and O-vacancies (denoted as VFe, VBi, and VO, respectively) are investigated using the first-principles density functional theory plus U calculations. It is revealed that the structural distortions associated with those vacancies impose significant influences on the total density of state and magnetic behaviors. The existence of VBi favors the excitation of the O2p state into the band gap at 0.4 eV, while the O2p and Fe3d orbitals are co-excited into the band gap around 0.45 eV in VFe. Consequently, a giant net magnetic moment of 1.96 uB is generated in VFe, and a relatively small moment of 0.13 uB is induced in VBi, whereas VO seems magnetically inactive. The giant magnetic moment generated in VFe originates from the suppression of the spatially modulated antiferromagnetic spin structure. Furthermore, VFe and VBi have strong influences on dielectric function, and induce some strong peaks to occur in the lower energy level. In contrast, VO has a small effect.
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    Improved crystal quality of GaN film with the in-plane lattice-matched In0.17Al0.83N interlayer grown on sapphire substrate using pulsed metal–organic chemical vapor deposition
    李亮, 杨林安, 薛军帅, 曹荣涛, 许晟瑞, 张进成, 郝跃
    2014 (6):  67103-067103.  doi: 10.1088/1674-1056/23/6/067103
    摘要 ( 213 )   PDF(1120KB) ( 526 )  
    We report on an improvement in the crystal quality of GaN film with an In0.17Al0.83N interlayer grown by pulsed metal-organic chemical vapor deposition, which is in-plane lattice-matched to GaN films. The indium composition of about 17% and the reductions of both screw and edge threading dislocations (TDs) in GaN film with the InAlN interlayer are estimated by high resolution X-ray diffraction. Transmission electron microscopy (TEM) measurements are employed to understand the mechanism of reduction in TD density. Raman and photoluminescence measurements indicate that the InAlN interlayer can improve the crystal quality of GaN film, and verify that there is no additional residual stress induced into the GaN film with InAlN interlayer. Atomic force microscopy measurement shows that the InAlN interlayer brings in a smooth surface morphology of GaN film. All the results show that the insertion of the InAlN interlayer is a convenient method to achieve excellent crystal quality in GaN epitaxy.
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    Ferromagnetic-insulators-modulated transport properties on the surface of a topological insulator
    郭俊吉, 廖文虎
    2014 (6):  67104-067104.  doi: 10.1088/1674-1056/23/6/067104
    摘要 ( 167 )   PDF(340KB) ( 515 )  
    Transport properties on the surface of a topological insulator (TI) under the modulation of a two-dimensional (2D) ferromagnet/ferromagnet junction are investigated by the method of wave function matching. The single ferromagnetic barrier modulated transmission probability is expected to be a periodic function of the polarization angle and the planar rotation angle, that decreases with the strength of the magnetic proximity exchange increasing. However, the transmission probability for the double ferromagnetic insulators modulated n-n junction and n-p junction is not a periodic function of polarization angle nor planar rotation angle, owing to the combined effects of the double ferromagnetic insulators and the barrier potential. Since the energy gap between the conduction band and the valence band is narrowed and widened respectively in ranges of 0≤θ<π/2 and π/2<θπ, the transmission probability of the n-n junction first increases rapidly and then decreases slowly with the increase of the magnetic proximity exchange strength. While the transmission probability for the n-p junction demonstrates an opposite trend on the strength of the magnetic proximity exchange because the band gaps contrarily vary. The obtained results may lead to the possible realization of a magnetic/electric switch based on TIs and be useful in further understanding the surface states of TIs.
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    RAPID COMMUNICATION
    Electrically tunable resonant terahertz transmission in subwavelength hole arrays
    张莹, 刘应开, 韩家广
    2014 (6):  67301-067301.  doi: 10.1088/1674-1056/23/6/067301
    摘要 ( 298 )   PDF(278KB) ( 638 )  
    An actively enhanced resonant transmission in a plasmonic array of subwavelength holes is demonstrated by use of terahertz time-domain spectroscopy. By connecting this two-dimensional element into an electrical circuit, tunable resonance enhancement is observed in arrays made from good and relatively poor metals. The tunable feature is attributed to the nonlinear electric response of the periodic hole array film, which is confirmed by its voltage-current behavior. This finding could lead to a unique route to active plasmonic devices, such as tunable filters, spatial modulators, and integrated terahertz optoelectronic components.
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    CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
    Switching and Fano resonance via exciton-plasmon interaction
    李建波, 贺梦冬, 王新军, 彭小芳, 陈丽群
    2014 (6):  67302-067302.  doi: 10.1088/1674-1056/23/6/067302
    摘要 ( 293 )   PDF(1319KB) ( 512 )  
    We further study theoretically the properties of switching and Fano resonance in a hybrid nanosystem consisting of two quantum dots (QDs) and a metal nanowire via exciton-plasmon interaction. The transmission of the single plasmon can be switched on or off in a wide-frequency region by adjusting the transition frequencies of the QDs and the phase of the propagating plasmon. Specifically, the dynamical mechanism of Fano-type transmission is further revealed and analyzed in detail.
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    Theoretical study of molecular hydrogen and spiltover hydrogen storage on two-dimensional covalent-organic frameworks
    刘秀英, 何杰, 于景新, 栗正新, 樊志琴
    2014 (6):  67303-067303.  doi: 10.1088/1674-1056/23/6/067303
    摘要 ( 167 )   PDF(1330KB) ( 452 )  
    Molecular hydrogen and spiltover hydrogen storages on five two-dimensional (2D) covalent-organic frameworks (COFs) (PPy-COF, TP-COF, BTP-COF, COF-18 Å, and HHTP-DPB COF) are investigated using the grand canonical Monte Carlo (GCMC) simulations and the density functional theory (DFT), respectively. The GCMC simulated results show that HHTP-DPB COF has the best performance for hydrogen storage, followed by BTP-COF, TP-COF, COF-18 Å, and PPy-COF. However, their adsorption amounts at room temperature are all too low to meet the uptake target set by US Department of Energy (US-DOE) and enable practical applications. The effects of pore size, surface area, and isosteric heat of hydrogen on adsorption amount are considered, which indicate that these three factors are all the important factors for determining the H2 adsorption amount. The chemisorptions of spiltover hydrogen atoms on these five COFs represented by the cluster models are investigated using the DFT method. The saturation cluster models are constructed by considering all possible adsorption sites for these cluster models. The average binding energy of a hydrogen atom and the saturation hydrogen storage density are calculated. The large average binding energy indicates that the spillover process may proceed smoothly and reversibly. The saturation hydrogen storage density is much larger than the physisorption uptake of H2 molecules at 298 K and 100 bar (1 bar = 105 Pa), and is close to or exceeds the 2010 US-DOE target of 6 wt% for hydrogen storage. This suggests that the hydrogen storage capacities of these COFs by spillover may be significantly enhanced. Thus 2D COFs studied in this paper are suitable hydrogen storage media by spillover.
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    Vacancy effect on the doping of silicon nanowires:A first-principles study
    刘阳, 梁培, 舒海波, 曹丹, 董前民, 王乐
    2014 (6):  67304-067304.  doi: 10.1088/1674-1056/23/6/067304
    摘要 ( 217 )   PDF(1246KB) ( 461 )  
    The influence of vacancy defect on the doping of silicon nanowires is systematically studied by the first-principles calculations. The atomic structures and electronic properties of vacancies and vacancy-boron (vacancy-phosphor) complexes in H-passivated silicon nanowire with a diameter of 2.3 nm are explored. The results of geometry optimization indicate that a central vacancy can exist stably, while the vacancy at the edge of the nanowire undergoes a local surface reconstruction, which results in the extradition of the vacancy out of the nanowire. Total-energy calculations indicate that the central vacancy tends to form a vacancy-dopant defect pair. Further analysis shows that n-type doping efficiency is strongly inhibited by the unintentional vacancy defect. In contrast, the vacancy defect has little effect on p-type doping. Our results suggest that the vacancy defect should be avoided during the growth and the fabrication of devices.
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    Modulating magnetism of nitrogen-doped zigzag graphene nanoribbons
    赵尚骞, 吕燕, 吕文刚, 梁文杰, 王恩哥
    2014 (6):  67305-067305.  doi: 10.1088/1674-1056/23/6/067305
    摘要 ( 253 )   PDF(1581KB) ( 525 )  
    We present a study of electronic properties of zigzag graphene nanoribbons (ZGNRs) substitutionally doped with nitrogen atoms at a single edge by first principle calculations. We find that the two edge states near the Fermi level separate due to the asymmetric nitrogen-doping. The ground states of these systems become ferromagnetic because the local magnetic moments along the undoped edges remain and those along the doped edges are suppressed. By controlling the charge-doping level, the magnetic moments of the whole ribbons are modulated. Proper charge doping leads to interesting half-metallic and single-edge conducting ribbons which would be helpful for designing graphene-nanoribbon-based spintronic devices in the future.
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    Martensitic transformation and giant magnetic entropy change in Ni42.8Mn40.3Co5.7Sn11.2 alloy
    陈峰华, 宫长伟, 郭艳萍, 张敏刚, 柴跃生
    2014 (6):  67501-067501.  doi: 10.1088/1674-1056/23/6/067501
    摘要 ( 228 )   PDF(1581KB) ( 388 )  
    The crystal structure, phase transition, and magnetocaloric effect in Ni42.8Mn40.3Co5.7Sn11.2 alloy are investigated by structure analysis and magnetic measurements. A large magnetic entropy change of 45.6 J/kg·K is obtained at 215 K under a magnetic field of 30 kOe (1 Oe = 79.5775 A·m-1). The effective refrigerant capacity of Ni42.8Mn40.3Co5.7Sn11.2 alloy reaches 72.1 J/kg under an applied field changing from 0 to 30 kOe. The external magnetic field shifts the martensitic transition temperature about 3-4 K/10 kOe towards low temperature, indicating that magnetic field can retard the phase transition to a certain extent. The origin of large magnetic entropy change is discussed in the paper.
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    Defect types and room temperature ferromagnetism in N-doped rutile TiO2 single crystals
    秦秀波, 李东翔, 李瑞琴, 张鹏, 李玉晓, 王宝义
    2014 (6):  67502-067502.  doi: 10.1088/1674-1056/23/6/067502
    摘要 ( 170 )   PDF(290KB) ( 430 )  
    The magnetic properties and defect types of virgin and N-doped TiO2 single crystals are probed by superconducting quantum interference device (SQUID), X-ray photoelectron spectroscopy (XPS), and positron annihilation analysis (PAS). Upon N doping, a twofold enhancement of the saturation magnetization is observed. Apparently, this enhancement is not related to an increase in oxygen vacancy, rather to unpaired 3d electrons in Ti3+, arising from titanium vacancies and the replacement of O with N atoms in the rutile structure. The production of titanium vacancies can enhance the room temperature ferromagnetism (RTFM), and substitution of O with N is the onset of ferromagnetism by inducing relatively strong ferromagnetic ordering.
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    Types of the jump phenomenon in the angular dependence of the noncollinear exchange bias
    杨红萍, 白宇浩
    2014 (6):  67503-067503.  doi: 10.1088/1674-1056/23/6/067503
    摘要 ( 291 )   PDF(353KB) ( 376 )  
    Based on the principle of minimal energy and the coherent rotation model, two types of the jump phenomena, complete and incomplete jump phenomenon, are proved to exist in the angular dependence of the exchange bias with noncollinear unidirectional and uniaxial anisotropies. It is found that the transition between complete and incomplete jump phenomena occurs on condition that the exchange-coupling constant exceeds a critical value. Additionally, two different modes of the magnetization rotation, the whole-plane rotation, and the half-plane rotation are present in the magnetization reversal process, and they are dependent on the direction of the external field. Furthermore, the equations of the critical angle, at which orientation the exchange bias field reaches a maximum value and the coercivity disappears, are also derived in this paper. The numerical calculations in this paper are consistent with the relevant experimental observations, indicating that our method to study the angular dependence of the exchange bias as well as the magnetization reversal behaviors is valid. Our discussion about the jump phenomenon, the critical angle, and the modes of the magnetization reversal can explain the observed differences in results between different experiments.
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    A new manganese-based single-molecule magnet with a record-high antiferromagnetic phase transition temperature
    崔岩, 李艳荣, 李瑞元, 王云平
    2014 (6):  67504-067504.  doi: 10.1088/1674-1056/23/6/067504
    摘要 ( 191 )   PDF(491KB) ( 404 )  
    We perform both dc and ac magnetic measurements on the single crystal of Mn3O(Et-sao)3(ClO4)(MeOH)3 single-molecule magnet (SMM) when the sample is preserved in air for different durations. We find that, during the oxidation process, the sample develops into another SMM with a smaller anisotropy energy barrier and a stronger antiferromagnetic intermolecular exchange interaction. The antiferromagnetic transition temperature observed at 6.65 K in the new SMM is record-high for the antiferromagnetic phase transition in all the known SMMs. Compared to the original SMM, the only apparent change for the new SMM is that each molecule has lost three methyl groups as revealed by four-circle x-ray diffraction (XRD), which is thought to be the origin of the stronger antiferromagnetic intermolecular exchange interaction.
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    Fabricating GeO2 passivation layer by N2O plasma oxidation for Ge NMOSFETs application
    林猛, 安霞, 黎明, 云全新, 李敏, 李志强, 刘朋强, 张兴, 黄如
    2014 (6):  67701-067701.  doi: 10.1088/1674-1056/23/6/067701
    摘要 ( 175 )   PDF(410KB) ( 701 )  
    In this paper, oxidation of Ge surface by N2O plasma is presented and experimentally demonstrated. Results show that 1.0-nm GeO2 is achieved after 120-s N2O plasma oxidation at 300 ℃. The GeO2/Ge interface is atomically smooth. The interface state density of Ge surface after N2O plasma passivation is about ~ 3×1011 cm-2·eV-1. With GeO2 passivation, the hysteresis of metal-oxide-semiconductor (MOS) capacitor with Al2O3 serving as gate dielectric is reduced to ~ 50 mV, compared with ~ 130 mV of the untreated one. The Fermi-level at GeO2/Ge interface is unpinned, and the surface potential is effectively modulated by the gate voltage.
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    Design of a varactor-tunable metamaterial absorber
    林宝勤, 达新宇, 赵尚弘, 蒙文, 李凡, 方英武, 王甲富
    2014 (6):  67801-067801.  doi: 10.1088/1674-1056/23/6/067801
    摘要 ( 346 )   PDF(801KB) ( 583 )  
    In this paper, we design a varactor-tunable metamaterial absorber (MA). The tunable MA is based on a mushroom-type high impedance surface (HIS), in which varactors are loaded between adjacent metal patches to adjust the capacitance and tune the resonance frequency, the primary ground plane is etched as the bias network to bias all of the varactors in parallel, and another ultra-thin grounded film is attached to the bottom. Its absorption characteristics are realized for electrically dielectric loss. The simulated values of a sample indicate that a tunable frequency range from 2.85 GHz to 2.22 GHz is achieved by adjusting the varactor capacitance from 0.1 pF to 2.0 pF, and better than 0.97 absorbance is realized; in addition, the tunable frequency range is expanded from 4.12 GHz to 1.70 GHz after optimization.
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    An effective surface-enhanced Raman scattering template based on gold nanoparticle/silicon nanowire arrays
    王明利, 张常兴, 吴正龙, 井西利, 许海军
    2014 (6):  67802-067802.  doi: 10.1088/1674-1056/23/6/067802
    摘要 ( 392 )   PDF(1380KB) ( 1203 )  
    A large-scale Si nanowire array (SiNWA) is fabricated with gold (Au) nanoparticles by simple metal-assisted chemical etching and metal reduction processes. The three-dimensional nanostructured Au/SiNWA is evaluated as an active substrate for surface-enhanced Raman scattering (SERS). The results show that the detection limit for rhodamine 6G is as low as 10-7 M, and the Raman enhancement factor is as large as 105 with a relative standard deviation of less than 25%. After the calibration of the Raman peak intensities of rhodamine 6G and thiram, organic molecules could be quantitatively detected. These results indicate that Au/SiNWA is a promising SERS-active substrate for the detection of biomolecules present in low concentrations. Our findings are an important advance in SERS substrates to allow fast and quantitative detection of trace organic contaminants.
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    N vacancy, substitutional O, and Al defects in the bandgap of composition-tunable nonstoichiometric AlN powder
    张电, 刘发民, 蔡鲁刚
    2014 (6):  67803-067803.  doi: 10.1088/1674-1056/23/6/067803
    摘要 ( 116 )   PDF(1589KB) ( 531 )  
    AlN powders are prepared by direct nitridation via Al liquid and vapor phases in mixed atmospheres of N2 and NH3 with different NH3/N2 ratios. The reaction analysis reveals that NH3 acts as catalyst for N2 dissociation and the transportations of N, O, and Al in the liquid phase are different from those in the vapor phase. Accordingly, the products are Al-rich and composition-tunable nonstoichiometric AlN in which N, O, and Al content values change with nitridation atmosphere and temperature, leading to the variation of the relevant defect concentration. Therefore, the AlN powders exhibit prominent absorption bands around 5.30, 3.40, and 1.50 eV, which are tentatively assigned to VN, ON donors, and AlN acceptor respectively. Furthermore, a new donor named [VN-ON] complex is predicted at 4.40 eV within the 5.90 eV bandgap. It is demonstrated that the optical spectra of nonstoichiometric AlN are preferable to the nominal stoichimometric one for the identification of the defects energy level.
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    INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
    Near field enhancement and absorption properties of the double cylindrical microcavities based on triple-band metamaterial absorber
    衡航, 杨理
    2014 (6):  68101-068101.  doi: 10.1088/1674-1056/23/6/068101
    摘要 ( 163 )   PDF(685KB) ( 376 )  
    We numerically study the near field enhancement and absorption properties inside the double cylindrical microcavities based on triple-band metamaterial absorber. The compact single unit cell consists of concentric gold rings each with a gold disk in the center, and a metallic ground plane separated by a dielectric layer. At the normal incidence of electromagnetic radiation, the obtained reflection spectra show that the resonance frequencies of the double microcavities are 16.65 THz, 20.65 THz, and 25.65THz, respectively. We also calculate the values of contrast C (C=1-Rmin), which can reach 95%, 97%, and 95% at the corresponding frequencies by optimizing the geometry parameters of structure. Moreover, we demonstrate that the multilayer structure with subwavelength electromagnetic confinement allows 104~105-fold enhancement of the electromagnetic energy density inside the double cavities, which contains the most energy of the incoming electromagnetic radiation. Moreover, the proposed structure will be insensitive to the polarization of the incident wave due to the symmetry of the double cylindrical microcavities. The proposed optical metamaterial is a promising candidate as an absorbing element in scientific and technical applications because of its extreme confinement, multiband absorptions, and polarization insensitivity.
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    Depth-dependent mosaic tilt and twist in GaN epilayer:An approximate evaluation
    张金风, 聂玉虎, 周勇波, 田坤, 哈微, 肖明, 张进成, 郝跃
    2014 (6):  68102-068102.  doi: 10.1088/1674-1056/23/6/068102
    摘要 ( 163 )   PDF(399KB) ( 711 )  
    An approach based on depth-sensitive skew-angle x-ray diffraction (SAXRD) is presented for approximately evaluating the depth-dependent mosaic tilt and twist in wurtzite c-plane GaN epilayers. It is found that (103) plane and (101) plane, among the lattice planes not perpendicular to the sample surface, are the best choices to measure the depth profiles of tilt and twist for a GaN epilayer with a thickness of less than 2 μm according to the diffraction geometry of SAXRD. As an illustration, the depth-sensitive (103)/(101) ω -scans of a 1.4-μm GaN film grown by metal-organic chemical vapor deposition on sapphire substrate are measured and analyzed to show the feasibility of this approach.
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    Evolution of magnetic domain structure of martensite in Ni-Mn-Ga films under the interplay of the temperature and magnetic field
    谢忍, 韦俊, 刘仲武, 唐妍梅, 唐涛, 唐少龙, 都有为
    2014 (6):  68103-068103.  doi: 10.1088/1674-1056/23/6/068103
    摘要 ( 154 )   PDF(1097KB) ( 486 )  
    Ferromagnetic shape memory Ni-Mn-Ga films with 7M modulated structure were prepared on MgO (001) substrates by magnetron sputtering. Magnetization process with a typical two-hysteresis loop indicates the occurrence of the reversible magnetic field-induced reorientation. Magnetic domain structure and twin structure of the film were controlled by the interplay of the magnetic and temperature field. With cooling under an out-of-plane magnetic field, the evolution of magnetic domain structure reveals that martensitic transformation could be divided into two periods: nucleation and growth. With an in-plane magnetic field applied to a thermomagnetic-treated film, the evolution of magnetic domain structure gives evidence of a reorientation of twin variants of martensite. A microstructural model is described to define the twin structure and to produce the magnetic domain structure at the beginning of martensitic transformation; based on this model, the relationship between the twin structure and the magnetic domain structure for the treated film under an in-plane field is also described.
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    Effects of the vibrational and rotational excitation of reagent on the stereodynamics of the reaction S(3P) + H2→SH + H
    单广玲, 王美山, 杨传路, 李艳青
    2014 (6):  68201-068201.  doi: 10.1088/1674-1056/23/6/068201
    摘要 ( 184 )   PDF(663KB) ( 421 )  
    Quasiclassical trajectory (QCT) calculations are first carried out to study the stereodynamics of the S(3P) + H2→SH + H reaction based on the ab initio 13A" potential energy surface (PES) (Lü et al. 2012 J. Chem. Phys. 136 094308). The QCT-calculated reaction probabilities and cross sections for the S + H2 (v = 0, j = 0) reaction are in good agreement with the previous quantum mechanics (QM) results. The vector properties including the alignment, orientation, and polarizationdependent differential cross sections (PDDCSs) of the product SH are presented at a collision energy of 1.8 eV. The effects of the vibrational and rotational excitations of reagent on the stereodynamics are also investigated and discussed in the present work. The calculated QCT results indicate that the vibrational and rotational excitations of reagent play an important role in determining the stereodynamic properties of the title reaction.
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    Characteristics of titanium oxide memristor with coexistence of dopant drift and a tunnel barrier
    田晓波, 徐晖
    2014 (6):  68401-068401.  doi: 10.1088/1674-1056/23/6/068401
    摘要 ( 151 )   PDF(2390KB) ( 1065 )  
    The recent published experimental data of titanium oxide memristor devices which are tested under the same experimental conditions exhibit the strange instability and complexity of these devices. Such undesired characteristics preclude the understanding of the device conductive processes and the memristor-based practical applications. The possibility of the coexistence of dopant drift and tunnel barrier conduction in a memristor provides preliminary explanations for the undesired characteristics. However, current research lacks detailed discussion about the coexistence case. In this paper, dopant drift and tunnel barrier-based theories are first analyzed for studying the relations between parameters and physical variables which affect characteristics of memristors, and then the influences of each parameter change on the conductive behaviors in the single and coexistence cases of the two mechanisms are simulated and discussed respectively. The simulation results provide further explanations of the complex device conduction. Theoretical methods of eliminating or reducing the coexistence of the two mechanisms are proposed, in order to increase the stability of the device conduction. This work also provides the support for optimizing the fabrications of memristor devices with excellent performance.
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    Three-dimensional particle-in-cell method of simulating high power terahertz gyrotrons with planar structure
    陈再高, 王建国, 王玥, 乔海亮, 郭伟杰, 张殿辉
    2014 (6):  68402-068402.  doi: 10.1088/1674-1056/23/6/068402
    摘要 ( 227 )   PDF(884KB) ( 422 )  
    Based on analyzing the large-signal theory of the planar gyrotron, it is suggested that a simplified structure of the device is used for simulating this kind of device, with the working characteristics of the device kept unchanged, i.e., the same as those of the device with the original structure. Thus, the computational burden can be significantly reduced. Using the proposed method, we simulate a planar gyrotron with its simplified parameters by using the UNIPIC-3D code. Numerical results show that the working frequency, output power, and electron efficiency are respectively about 0.813 THz, 14 kW, and 21%.
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    Positive gate-bias temperature instability of ZnO thin-film transistor
    刘玉荣, 苏晶, 黎沛涛, 姚若河
    2014 (6):  68501-068501.  doi: 10.1088/1674-1056/23/6/068501
    摘要 ( 353 )   PDF(445KB) ( 906 )  
    The positive gate-bias temperature instability of a radio frequency (RF) sputtered ZnO thin-film transistor (ZnO TFT) is investigated. Under positive gate-bias stress, the saturation drain current and OFF-state current decrease, and the threshold voltage shifts toward the positive direction. The stress amplitude and stress temperature are considered as important factors in threshold-voltage instability, and the time dependences of threshold voltage shift under various bias temperature stress conditions could be described by a stretched-exponential equation. Based on the analysis of hysteresis behaviors in current-voltage and capacitance-voltage characteristics before and after the gate-bias stress, it can be clarified that the threshold-voltage shift is predominantly attributed to the trapping of negative charge carriers in the defect states located at the gate-dielectric/channel interface.
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    Enhanced performances of InGaN/GaN-based blue light-emitting diode with InGaN/AlInGaN superlattice electron blocking layer
    卓祥景, 章俊, 李丹伟, 易翰翔, 任志伟, 童金辉, 王幸福, 陈鑫, 赵璧君, 王伟丽, 李述体
    2014 (6):  68502-068502.  doi: 10.1088/1674-1056/23/6/068502
    摘要 ( 401 )   PDF(1549KB) ( 534 )  
    InGaN/AlInGaN superlattice (SL) is designed as the electron blocking layer (EBL) of an InGaN/GaN-based light-emitting diode (LED). The energy band structure, polarization field at the last-GaN-barrier/EBL interface, carrier concentration, radiative recombination rate, electron leakage, internal quantum efficiency (IQE), current-voltage (I-V) performance curve, light output-current (L-I) characteristic, and spontaneous emission spectrum are systematically numerically investigated using APSYS simulation software. It is found that the fabricated LED with InGaN/AlInGaN SL EBL exhibits higher light output power, low forward voltage, and low current leakage compared with those of its counterparts. Meanwhile, the efficiency droop can be effectively mitigated. These improvements are mainly attributed to the higher hole injection efficiency and better electron confinement when InGaN/AlInGaN SL EBL is used.
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    Ising model on evolution networks and its application on opinion formation
    朱小龙, 张海天, 桑建平, 黄胜友, 邹宪武
    2014 (6):  68701-068701.  doi: 10.1088/1674-1056/23/6/068701
    摘要 ( 211 )   PDF(1045KB) ( 374 )  
    Many phenomena show that in a favorable circumstance an agent still has an updating possibility, and in an unfavorable circumstance an agent also has a possibility of holding its own state and reselecting its neighbors. To describe this kind of phenomena an Ising model on evolution networks was presented and used for consensus formation and separation of opinion groups in human population. In this model the state-holding probability p and selection-rewiring probability q were introduced. The influence of this mixed dynamics of spin flips and network rewiring on the ordering behavior of the model was investigated. p hinders ordering of opinion networks and q accelerates the dynamical process of networks. Influence of q on the ordering and separating stems from its effect on average path length of networks.
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    Mechano-chemical selections of two competitive unfolding pathways of a single DNA i-motif
    徐悦, 陈虎, 璩玉杰, 黎明, 欧阳钟灿, 刘冬生, 严洁
    2014 (6):  68702-068702.  doi: 10.1088/1674-1056/23/6/068702
    摘要 ( 232 )   PDF(1439KB) ( 426 )  
    The DNA i-motif is a quadruplex structure formed in tandem cytosine-rich sequences in slightly acidic conditions. Besides being considered as a building block of DNA nano-devices, it may also play potential roles in regulating chromosome stability and gene transcriptions. The stability of i-motif is crucial for these functions. In this work, we investigated the mechanical stability of a single i-motif formed in the human telomeric sequence 5'-(CCCTAA)3CCC, which revealed a novel pH and loading rate-dependent bimodal unfolding force distribution. Although the cause of the bimodal unfolding force species is not clear, we proposed a phenomenological model involving a direct unfolding favored at lower loading rate or higher pH value, which is subject to competition with another unfolding pathway through a mechanically stable intermediate state whose nature is yet to be determined. Overall, the unique mechano-chemical responses of i-motif-provide a new perspective to its stability, which may be useful to guide designing new i-motif-based DNA mechanical nano-devices.
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    Effects of polarization and p-type GaN resistivity on the spectral response of InGaN/GaN multiple quantum well solar cells
    杨静, 赵德刚, 江德生, 刘宗顺, 陈平, 李亮, 吴亮亮, 乐伶聪, 李晓静, 何晓光, 王辉, 朱建军, 张书明, 张宝顺, 杨辉
    2014 (6):  68801-068801.  doi: 10.1088/1674-1056/23/6/068801
    摘要 ( 219 )   PDF(429KB) ( 456 )  
    Effects of polarization and p-type GaN resistivity on the spectral response of InGaN/GaN multiple quantum well (MQW) solar cells are investigated. It is found that due to the reduction of piezoelectric polarization and the enhancement of tunneling transport of photo-generated carriers in MQWs, the external quantum efficiency (EQE) of the solar cells increases in a low energy spectral range (λ >370 nm) when the barrier thickness value decreases from 15 nm to 7.5 nm. But the EQE decreases abruptly when the barrier thickness value decreases down to 3.75 nm. The reasons for these experimental results are analyzed. We are aware that the reduction of depletion width in MQW region, caused by the high resistivity of the p-type GaN layer may be the main reason for the abnormally low EQE value at long wavelengths (λ >370 nm).
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    GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
    In-situ high pressure X-ray diffraction studies of orthoferrite SmFeO3
    李娜娜, 李岩, 李会, 唐瑞莲, 赵永胜, 韩丹丹, 马艳梅, 崔启良, 朱品文, 王欣
    2014 (6):  69101-069101.  doi: 10.1088/1674-1056/23/6/069101
    摘要 ( 171 )   PDF(623KB) ( 812 )  
    The high-pressure behaviors of SmFeO3 are investigated by angle-dispersive synchrotron X-ray powder diffraction under a pressure of up to 40.3 GPa at room temperature. The crystal structure of SmFeO3 remains stable at up to the highest pressure. The different pressure coefficients of the normalized axial compressibility are obtained to be β a = 0.60×10-3 GPa-1, β b = 0.79×10-3 GPa-1, β c = 1.28×10-3 GPa-1, and the bulk modulus (B0) is determined to be 293(3) GPa by fitting the pressure-volume data using the Birch-Murnaghan equation of state. Furthermore, the larger compressibility of the FeO6 octahedra suggests the evolution of the orthorhombic structure towards higher symmetry configuration at high pressures.
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    Phase-field study of the second phase particle effect on texture evolution of polycrystalline material
    卢艳丽, 张刘超, 周影影, 陈铮
    2014 (6):  69102-069102.  doi: 10.1088/1674-1056/23/6/069102
    摘要 ( 200 )   PDF(1133KB) ( 869 )  
    The second phase particle effect on texture evolution of polycrystalline material is studied through phase-field method. A unique field variable is introduced into the phase-field model to represent the second phase particles. Elastic interaction between particles and grains is also considered. Results indicate that in the presence of second phase particles the average particle diameter turns smaller than in the absence of these particles and retards texture formation by pinning effect. The second phase particles change the strain energy profile, which tremendously influences the pinning effect.
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    Three-dimensional spiral structure of tropical cyclone under four-force balance
    刘式适, 付遵涛, 刘式达
    2014 (6):  69201-069201.  doi: 10.1088/1674-1056/23/6/069201
    摘要 ( 121 )   PDF(212KB) ( 271 )  
    The steady axis-symmetrical atmosphere dynamical equations are used for describing spiral structure of tropical cyclones under four-force (pressure gradient force, Coriolis force, centrifugal force, and friction force) balance, and the dynamical systems of three-dimensional (3D) velocity field are introduced. The qualitative analysis of the dynamical system shows that there are down 3D spiral structures in eye of tropical cyclone and tropical cyclone is 3D counterclockwise up spiral structure. These results are consistent with the observed tropical cyclone on the weather map.
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    Impact of GNSS radio occultation bending angle data assimilation in YH4DVAR system
    朱孟斌, 张卫民, 曹小群, 余意
    2014 (6):  69202-069202.  doi: 10.1088/1674-1056/23/6/069202
    摘要 ( 176 )   PDF(954KB) ( 454 )  
    Global Navigation Satellite System (GNSS) radio occultation measurements have been assimilated into the four-dimensional variational data assimilation system (YH4DVAR) using a one-dimensional bending angle operator (GBAO) as a new type of observation. For the sake of verifying the impact of GNSS radio occultation (RO) measurements to the data assimilation system, three experiments have been conducted. The statistical results of the analysis error experiment and forecast skill experiment show that the GNSS RO measurements have an impact on the analysis system. The typhoon forecast experiment shows the impact on the important weather process. They all have a positive impact on the weather forecast. Lastly, we look forward to future work on the observation system simulation experiment (OSSE) to investigate the impact of GNSS RO measurements as a function of observation number, which is an effective method to estimate the saturation of the observation number.
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    The two annual northward jumps of the West Pacific Subtropical High and their relationship with summer rainfall in Eastern China under global warming
    叶天舒, 支蓉, 赵俊虎, 龚志强
    2014 (6):  69203-069203.  doi: 10.1088/1674-1056/23/6/069203
    摘要 ( 195 )   PDF(1855KB) ( 388 )  
    The two northward jumps of summer West Pacific Subtropical High (WPSH) are defined based on the pentad-scale ridge data of the WPSH ridge in 1951 to 2012. The times of the northward jumps are found to have obvious inter-annual and decadal characteristics, i.e., the occurrence of the first northward jump of WPSH shows a "consistently early-consistently late" decadal pattern, with the transition around 1980; the occurrence of the second northward jump of WPSH shows a "consistently late-consistently early-consistently late" decadal pattern, with the transitions about 1955 and 1978, respectively, which is consistent with global warming. In the meantime, the times of the two northward jumps not only have a good correspondence to the beginning and ending dates of the rainy season, but also greatly influence the position of the main rain belt in Eastern China. When the first northward jump occurs early, the main rain belt is located from just north of 30° N to the south of North China, while the opposite situation appears when the first jump occurs late. When the second jump occurs early, more rain falls over North China and South China, but less falls in the Yangtze River region, while the opposite situation appears when the second jump occurs late. In the four cases when abnormalities occur in the same year as early or late northward jumps, the position of the main rain belt can be considered as a superposition of isolated abnormal effects of the two northward jumps. Moreover, the prophase and synchronous forces of the sea surface temperature in the Pacific has great influence on the times of the northward jumps, and the driving forces of the two jumps differ.
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