中国物理B

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Multi-agent coordination in directed moving neighbourhood random networks

尚轶伦

2010 (7): 70201-070201. doi: 10.1088/1674-1056/19/7/070201

摘要 ( 1752 )

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This paper considers the consensus problem of dynamical multiple agents that communicate via a directed moving neighbourhood random network. Each agent performs random walk on a weighted directed network. Agents interact with each other through random unidirectional information flow when they coincide in the underlying network at a given instant. For such a framework, we present sufficient conditions for almost sure asymptotic consensus. Numerical examples are taken to show the effectiveness of the obtained results.

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The super-classical-Boussinesq hierarchy and its super-Hamiltonian structure

陶司兴, 夏铁成

2010 (7): 70202-070202. doi: 10.1088/1674-1056/19/7/070202

摘要 ( 1545 )

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Based on the constructed Lie superalgebra, the super-classical-Boussinesq hierarchy is obtained. Then, its super-Hamiltonian structure is obtained by making use of super-trace identity. Furthermore, the super-classical-Boussinesq hierarchy is also integrable in the sense of Liouville.

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Variational iteration method for solving compressible Euler equations

赵国忠, 蔚喜军, 徐云, 朱江

2010 (7): 70203-070203. doi: 10.1088/1674-1056/19/7/070203

摘要 ( 1725 )

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This paper applies the variational iteration method to obtain approximate analytic solutions of compressible Euler equations in gas dynamics. This method is based on the use of Lagrange multiplier for identification of optimal values of parameters in a functional. Using this method, a rapid convergent sequence is produced which converges to the exact solutions of the problem. Numerical results and comparison with other two numerical solutions verify that this method is very convenient and efficient.

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A novel evolving scale-free model with tunable attractiveness

刘绚, 刘天琪, 王昊, 李兴源

2010 (7): 70204-070204. doi: 10.1088/1674-1056/19/7/070204

摘要 ( 1734 )

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In this paper, a new evolving model with tunable attractiveness is presented. Based on the Barabasi—Albert (BA) model, we introduce the attractiveness of node which can change with node degree. Using the mean-field theory, we obtain the analytical expression of power-law degree distribution with the exponent γ ∈ (3,∞). The new model is more homogeneous and has a lower clustering coefficient and bigger average path length than the BA model.

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Simulation of x-ray transmission through an ellipsoidal capillary

林晓燕, 李玉德, 孙天希, 潘秋丽

2010 (7): 70205-070205. doi: 10.1088/1674-1056/19/7/070205

摘要 ( 1581 )

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This paper develops a simulation program for x-ray transmission in an ellipsoidal capillary based on a ray-tracing method. The influence of the parameters of ellipsoidal capillary and x-ray energy on transmission efficiency, full width at half maximum and power density gain of x-ray beams through an ellipsoidal capillary was analysed by this program. It shows that the particular rules of the ellipsoidal capillary x-ray lens are different from the polycapillary lens. Furthermore, this analysis method can be applied to the optimized design of ellipsoidal capillary.

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New transformation of Wigner operator in phase space quantum mechanics for the two-mode entangled case

范洪义, 袁洪春

2010 (7): 70301-070301. doi: 10.1088/1674-1056/19/7/070301

摘要 ( 1381 )

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As a natural and important extension of Fan's paper (Fan Hong-Yi 2010 Chin. Phys. B 19 040305) by employing the formula of operators' Weyl ordering expansion and the bipartite entangled state representation this paper finds a new two-fold complex integration transformation about the Wigner operator Δ ( μ,v ) (in its entangled form) in phase space quantum mechanics, and its inverse transformation. In this way, some operator ordering problems regarding to ( a₁⁺-a₂) and (a₁+a₂⁺) can be solved and the contents of phase space quantum mechanics can be enriched, where a_i,a_i⁺ are bosonic creation and annihilation operators, respectively.

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Bright and dark soliton solutions in growing Bose—Einstein condensates

宋伟为, 李秋艳, 李再东, 傅广生

2010 (7): 70503-070503. doi: 10.1088/1674-1056/19/7/070503

摘要 ( 1822 )

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This paper develops the Hirota method carefully for applying into the growing model of quasi-one-dimensional Bose—Einstein condensations with attractive and repulsive interaction, respectively. After a tedious calculation it obtains the exact bright and dark soliton solutions analytically. It shows that the growing model has the important effect on the soliton amplitude and the time-dependent potential only contributes to the phase and phase velocity. A detailed analysis for the asymptotic behaviour of two-soliton solutions shows that the collision of two soliton is elastic.

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Stochastic resonance in a time-delayed bistable system subject to multiplicative and additive noise

郭锋, 周玉荣, 张宇

2010 (7): 70504-070504. doi: 10.1088/1674-1056/19/7/070504

摘要 ( 1601 )

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This paper investigates the stochastic resonance in a time-delayed bistable system subjected to multiplicative and additive white noise and asymmetric dichotomous noise. Under the adiabatic approximation condition, the expression of the signal-to-noise ratio (SNR) is obtained. It finds that the SNR is a non-monotonic function of the delayed times, of the amplitude of the driving square-wave signal, as well as of the asymmetry of the dichotomous noise. In addition, the SNR varies non-monotonously with the intensities of the multiplicative and additive noise as well as the system parameters. Moreover, the SNR depends non-monotonically on the correlate rate of the dichotomous noise.

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Characterisation of the plasma density with two artificial neural network models

王腾, 高向东, 李炜

2010 (7): 70505-070505. doi: 10.1088/1674-1056/19/7/070505

摘要 ( 1605 )

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This paper establishes two artificial neural network models by using a multi layer perceptron algorithm and radial based function algorithm in order to predict the plasma density in a plasma system. In this model, the input layer is composed of five neurons: the radial position, the axial position, the gas pressure, the microwave power and the magnet coil current. The output layer is the target output neuron: the plasma density. The accuracy of prediction is tested with the experimental data obtained by the Langmuir probe. The effectiveness of two artificial neural network models are demonstrated, the results show good agreements with corresponding experimental data. The ability of the artificial neural network model to predict the plasma density accurately in an electron cyclotron resonance-plasma enhanced chemical vapour deposition system can be concluded, and the radial based function is more suitable than the multi layer perceptron in this work.

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Dynamical analysis and circuit simulation of a new three-dimensional chaotic system

王爱元, 凌志浩

2010 (7): 70506-070506. doi: 10.1088/1674-1056/19/7/070506

摘要 ( 1563 )

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This paper reports a new three-dimensional autonomous chaotic system. It contains six control parameters and three nonlinear terms. Two cross-product terms are respectively in two equations. And one square term is in the third equation. Basic dynamic properties of the new system are investigated by means of theoretical analysis, numerical simulation, sensitivity to initial, power spectrum, Lyapunov exponent, and Poincaré diagrams. The dynamic properties affected by variable parameters are also analysed. Finally, the chaotic system is simulated by circuit. The results verify the existence and implementation of the system.

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A specific state variable for a class of 3D continuous fractional-order chaotic systems

周平, 程元明, 邝菲

2010 (7): 70507-070507. doi: 10.1088/1674-1056/19/7/070507

摘要 ( 1528 )

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A specific state variable in a class of 3D continuous fractional-order chaotic systems is presented. All state variables of fractional-order chaotic systems of this class can be obtained via a specific state variable and its (q-order and 2q-order) time derivatives. This idea is demonstrated by using several well-known fractional-order chaotic systems. Finally, a synchronization scheme is investigated for this fractional-order chaotic system via a specific state variable and its (q-order and 2q-order) time derivatives. Some examples are used to illustrate the effectiveness of the proposed synchronization method.

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Fault diagnosis of time-delay complex dynamical networks using output signals

刘昊, 宋玉蓉, 樊春霞, 蒋国平

2010 (7): 70508-070508. doi: 10.1088/1674-1056/19/7/070508

摘要 ( 1579 )

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This paper proposes a novel approach for fault diagnosis of a time-delay complex dynamical network. Unlike the other methods, assuming that the dynamics of the network can be described by a linear stochastic model, or using the state variables of nodes in the network to design an adaptive observer, it only uses the output variable of the nodes to design an observer and an adaptive law of topology matrix in the observer of a complex network, leading to simple design of the observer and easy realisation of topology monitoring for the complex networks in real engineering. The proposed scheme can monitor any changes of the topology structure of a time-delay complex network. The effectiveness of this method is successfully demonstrated by virtue of a complex networks with Lorenz model.

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Projective synchronisation with non-delayed and delayed coupling in complex networks consisting of identical nodes and different nodes

杜瑞瑾, 董高高, 田立新, 郑松, 孙梅

2010 (7): 70509-070509. doi: 10.1088/1674-1056/19/7/070509

摘要 ( 1634 )

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This paper first investigates the projective synchronisation problem with non-delayed and delayed coupling between drive-response dynamical networks consisting of identical nodes and different nodes. Based on Lyapunov stability theory, several nonlinear controllers are applied to achieve the projective synchronisation between the drive-response dynamical networks; simultaneously the topological structure of the drive dynamical complex networks can be exactly identified. Moreover, numerical examples are presented to verify the feasibility and effectiveness of the theorems.

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Implementation of a novel two-attractor grid multi-scroll chaotic system

罗小华, 涂正伟, 刘希瑞, 蔡昌, 梁亦龙, 龚璞

2010 (7): 70510-070510. doi: 10.1088/1674-1056/19/7/070510

摘要 ( 1730 )

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This paper proposed a method of generating two attractors in a novel grid multi-scroll chaotic system. Based on a newly generated three-dimensional system, a two-attractor grid multi-scroll attractor system can be generated by adding two triangular waves and a sign function. Some basic dynamical properties, such as equilibrium points, bifurcations, and phase diagrams, were studied. Furthermore, the system was experimentally confirmed by an electronic circuit. The circuit simulation results and numerical simulation results verified the feasibility of this method.

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Outer synchronization between two different fractional-order general complex dynamical networks

武相军, 卢宏涛

2010 (7): 70511-070511. doi: 10.1088/1674-1056/19/7/070511

摘要 ( 1452 )

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Outer synchronization between two different fractional-order general complex dynamical networks is investigated in this paper. Based on the stability theory of the fractional-order system, the sufficient criteria for outer synchronization are derived analytically by applying the nonlinear control and the bidirectional coupling methods. The proposed synchronization method is applicable to almost all kinds of coupled fractional-order general complex dynamical networks. Neither a symmetric nor irreducible coupling configuration matrix is required. In addition, no constraint is imposed on the inner-coupling matrix. Numerical examples are also provided to demonstrate the validity of the presented synchronization scheme. Numeric evidence shows that both the feedback strength k and the fractional order α can be chosen appropriately to adjust the synchronization effect effectively.

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Generating Li—Yorke chaos in a stable continuous-time T—S fuzzy model via time-delay feedback control

孙秋野, 张化光, 赵琰

2010 (7): 70512-070512. doi: 10.1088/1674-1056/19/7/070512

摘要 ( 1456 )

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This paper investigates the chaotification problem of a stable continuous-time T—S fuzzy system. A simple nonlinear state time-delay feedback controller is designed by parallel distributed compensation technique. Then, the asymptotically approximate relationship between the controlled continuous-time T—S fuzzy system with time-delay and a discrete-time T—S fuzzy system is established. Based on the discrete-time T—S fuzzy system, it proves that the chaos in the discrete-time T—S fuzzy system satisfies the Li—Yorke definition by choosing appropriate controller parameters via the revised Marotto theorem. Finally, the effectiveness of the proposed chaotic anticontrol method is verified by a practical example.

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Synchronization between two different chaotic systems with noise perturbation

孙永征, 阮炯

2010 (7): 70513-070513. doi: 10.1088/1674-1056/19/7/070513

摘要 ( 1535 )

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This paper investigates the chaotic synchronization between the noise-perturbed Lorenz system and one of the noise-perturbed Chen and Lü systems. Based on the active control method and the Lyapunov theory in stochastic differential equations, sufficient conditions for the stability of the error dynamics are derived. Numerical simulations are also shown to demonstrate the effectiveness of these theoretic results.

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The analysis of complex behaviours of a novel three dimensional autonomous system

董高高, 郑松, 田立新, 杜瑞瑾, 孙梅

2010 (7): 70514-070514. doi: 10.1088/1674-1056/19/7/070514

摘要 ( 1558 )

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This paper introduces a new three dimensional autonomous system with five equilibrium points. It demonstrates complex chaotic behaviours within a wide range of parameters, which are described by phase portraits, Lyapunov exponents, frequency spectrum, etc. Analysis of the bifurcation and Poincaré map is used to reveal mechanisms of generating these complicated phenomena. The corresponding electronic circuits are designed, exhibiting experimental chaotic attractors in accord with numerical simulations. Since frequency spectrum analysis shows a broad frequency bandwidth, this system has perspective of potential applications in such engineering fields as secure communication.

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Synchronization and bidirectional communication without delay line using strong mutually coupled semiconductor lasers

李光辉, 王安帮, 冯野, 汪洋

2010 (7): 70515-070515. doi: 10.1088/1674-1056/19/7/070515

摘要 ( 1515 )

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This paper numerically demonstrates synchronization and bidirectional communication without delay line by using two semiconductor lasers with strong mutual injection in a face-to-face configuration. These results show that both of the two lasers' outputs synchronize with their input chaotic carriers. In addition, simulations demonstrate that this kind of synchronization can be used to realize bidirectional communications without delay line. Further studies indicate that within a small deviation in message amplitudes of two sides (±6%), the message can be extracted with signal-noise-ratio more than 10 dB; and the signal-noise-ratio is extremely sensitive to the message rates mismatch of two sides, which may be used as a key of bidirectional communication.

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Numerical study of anomalous dynamic scaling behaviour of (1+1)-dimensional Das Sarma—Tamborenea model

寻之朋, 唐刚, 韩奎, 郝大鹏, 夏辉, 周伟, 杨细全, 温荣吉, 陈玉岭

2010 (7): 70516-070516. doi: 10.1088/1674-1056/19/7/070516

摘要 ( 1459 )

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In order to discuss the finite-size effect and the anomalous dynamic scaling behaviour of Das Sarma—Tamborenea growth model, the (1+1)-dimensional Das Sarma—Tamborenea model is simulated on a large length scale by using the kinetic Monte—Carlo method. In the simulation, noise reduction technique is used in order to eliminate the crossover effect. Our results show that due to the existence of the finite-size effect, the effective global roughness exponent of the (1+1)-dimensional Das Sarma—Tamborenea model systematically decreases with system size L increasing when L > 256. This finding proves the conjecture by Aarao Reis[Aarao Reis F D A 2004 Phys. Rev. E 70 031607]. In addition, our simulation results also show that the Das Sarma—Tamborenea model in 1+1 dimensions indeed exhibits intrinsic anomalous scaling behaviour.

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Effect of following strength on pedestrian counter flow

邝华, 李兴莉, 韦艳芳, 宋涛, 戴世强

2010 (7): 70517-070517. doi: 10.1088/1674-1056/19/7/070517

摘要 ( 1731 )

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This paper proposes a modified lattice gas model to simulate pedestrian counter flow by considering the effect of following strength which can lead to appropriate responses to some complicated situations. Periodic and open boundary conditions are adopted respectively. The simulation results show that the presented model can reproduce some essential features of pedestrian counter flows, e.g., the lane formation and segregation effect. The fundamental diagrams show that the complete jamming density is independent of the system size only when the width W and the length L are larger than some critical values respectively, and the larger asymmetrical conditions can better avoid the occurrence of deadlock phenomena. For the mixed pedestrian flow, it can be found that the jamming cluster is mainly caused by those walkers breaking the traffic rules, and the underlying mechanism is analysed. Furthermore, the comparison of simulation results and the experimental data is performed, it is shown that this modified model is reasonable and more realistic to simulate and analyse pedestrian counter flow.

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H_∞ consensus control of a class of second-order multi-agent systems without relative velocity measurement

张文广, 曾德良, 郭振凯

2010 (7): 70518-070518. doi: 10.1088/1674-1056/19/7/070518

摘要 ( 1629 )

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This paper studies consensus control problems for a class of second-order multi-agent systems without relative velocity measurement. Some dynamic neighbour-based rules are adopted for the agents in the presence of external disturbances. A sufficient condition is derived to make all agents achieve consensus while satisfying desired H_∞ performance. Finally, numerical simulations are provided to show the effectiveness of our theoretical results.

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A new method of detecting interferogram in differential phase-contrast imaging system based on special structured x-ray scintillator screen

刘鑫, 郭金川, 牛憨笨

2010 (7): 70701-070701. doi: 10.1088/1674-1056/19/7/070701

摘要 ( 1643 )

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An x-ray scintillator screen with a special structure, functioning as detector and analyser grating, was proposed for collecting the interferogram of differential phase contrast imaging without absorption grating and difficulty of fabrication by a state of the art technique. On the basis of phase grating diffraction, a detecting model of the scintillator screen was built for analysing the phase and absorption information of objects. According to the analysis, a new method of phase retrievals based on two-images and the optimal structure of screen were presented.

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Two-dimensional multiplicity fluctuation analysis of target residues in nuclear collisions

张东海, 牛耀婕, 王立春, 闫文君, 高丽娟, 李明星, 武丽萍, 李惠玲, 李俊生

2010 (7): 72501-072501. doi: 10.1088/1674-1056/19/7/072501

摘要 ( 1313 )

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Multiplicity fluctuation of the target residues emitted in the interactions in a wide range of projectile energies from 500 A MeV to 60 A GeV is investigated in the framework of two-dimensional scaled factorial moment methodology. The evidence of non-statistical multiplicity fluctuation is found in ¹⁶O—AgBr collisions at 60 A GeV, but not in ⁵⁶Fe—AgBr collisions at 500 A MeV, ⁸⁴Kr—AgBr collisions at 1.7 A GeV, ¹⁶O—AgBr collisions at 3.7 A GeV and ¹⁹⁷Au—AgBr collisions at 10.7 A GeV.

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The (e, 2e) triple differential cross sections of Cu⁺ (3p) in coplanar asymmetric geometry

周丽霞, 燕友果, 门福殿

2010 (7): 73401-073401. doi: 10.1088/1674-1056/19/7/073401

摘要 ( 1602 )

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The three-body distorted-wave Born approximation has been used to calculate the (e, 2e) triple differential cross sections (TDCSs) of Cu⁺ (3p) in different kinematical variables in coplanar asymmetric geometry. The angles 4o, 10o and 20o were selected as the scattering electron angles. Under high incident energy (≥ 500 eV) and high asymmetric detection energy, the binary peaks showed abnormal splits. Such abnormal splits have not been observed in atomic target and outer valence orbitals of ionic target, which indicates that an (e, 2e) process for inner valence orbitals of ionic target would be more complicated than outer valence orbitals. Furthermore, some pronounced peaks appeared at certain ejected angles. We considered that these pronounced peaks are probably related to one kind of double-binary collision.

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Coalescence between Cu₅₇ and Cu₅₈ clusters at a room temperature: molecular dynamics simulations

张林, 李蔚, 王绍青

2010 (7): 73601-073601. doi: 10.1088/1674-1056/19/7/073601

摘要 ( 1654 )

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Three coalescence processes of Cu₅₇—Cu₅₇, Cu₅₇—Cu₅₈, and Cu₅₈—Cu₅₈ clusters at 300 K are investigated by employing molecular dynamics simulations. According to the evolutions of mean square displacement and local atom packing, the coalescence process can be separated into three stages including an approaching stage, a coalescing stage, and a coalesced stage. The simulations show that the coalescence processes and the formed products are sensitive to the respective initial structures of, and the relative configuration between, the two coalescing icosahedron—based clusters.

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An angular cutoff composite model for investigation on electromagnetic scattering from two-dimensional rough sea surfaces

聂丁, 张民

2010 (7): 74101-074101. doi: 10.1088/1674-1056/19/7/074101

摘要 ( 1446 )

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Based on the local configuration angle division to select the corresponding method for electromagnetic scattering calculation from rough sea surface, this paper presents an angular cutoff composite model: when the local scattered angle is in the specular region that is given by an approximately 20 degrees cone around the specular direction, the Kirchhoff approximation is applied to evaluate the specular reflection, which dominates the total scattering in this region; the small perturbation method is employed to handle the diffuse reflection which is predominant as the local scattered angle is situated out of the specular region. Numerical results are compared with those of experimental and theoretical models in several configurations as a function of incident angle, wind speed, wind direction. The comparison of numerical results of other experimental and theoretical models in several configurations shows that the new composite model is robust to give accurate numerical evaluations for the sea surface scattering.

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Polarimetric scattering from a two-dimensional improved sea fractal surface

刘伟, 郭立新, 吴振森

2010 (7): 74102-074102. doi: 10.1088/1674-1056/19/7/074102

摘要 ( 1348 )

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This paper studies the influence of wind parameters and fractal dimension from an improved two-dimensional sea fractal surface on the polarimetric scattering by using facet integration. A two-dimensional improved sea surface simulated is discretized into three matrices of sea surface facets including a height matrix and two slope matrices on orthogonal directions. Based on the Kirchhoff approximation, the polarimetric scattered field is derived in the Cartesian coordinate system by integration of three matrices mentioned above. Finally, the fully polarised radar cross section is numerically simulated and the dependence of the polarimetric scattering on the sea fractal surface, such as the wind speed, the wind direction, as well as the fractal dimension, is discussed in detail.

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Investigation on the Doppler shifts induced by 1-D ocean surface wave displacements by the first order small slope approximation theory: comparison of hydrodynamic models

王运华, 张彦敏, 郭立新

2010 (7): 74103-074103. doi: 10.1088/1674-1056/19/7/074103

摘要 ( 1556 )

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Based on the first order small slope approximation theory (SSA-I) for oceanic surface electromagnetic scattering, this paper predicts the Doppler shifts induced by wave displacements. Theoretical results from three distinct hydrodynamic models are compared: a linear model, the nonlinear Barrick model, and the nonlinear Creamer model. Meanwhile, the predicted Doppler shifts are also compared with the results associated to the resonant Bragg waves and the so-called long waves in the framework of the two-scale model. The dependences of the predicted Doppler shifts on the incident angle, the radar frequency, and the wind speed are discussed. At large incident angles, the predicted Doppler shifts for the linear and nonlinear Barrick models are found to be insensitive to the wind speed and this phenomenon is not coincident with the experimental data. The conclusions obtained in this paper are promising for better understanding the properties of time dependent radar echoes from oceanic surfaces.

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Relations between chirp transform and Fresnel diffraction, Wigner distribution function and a fast algorithm for chirp transform

石鹏, 曹国威, 李永平

2010 (7): 74201-074201. doi: 10.1088/1674-1056/19/7/074201

摘要 ( 1549 )

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Two physical interpretations of chirp transform related to Fresnel diffraction and Wigner distribution function are given. The chirp transform can be regarded as a Fresnel diffraction observed on a spherical tangent to the diffraction plane, or a rotation and stretching transformation of the Wigner distribution function space. A general fast algorithm for the numerical calculation of chirp transform is developed by employing two fast Fourier transform algorithms. The algorithm, by which a good evaluation can be achieved, unifies the calculations of Fresnel diffraction, arbitrary fractional-order Fourier transforms and other scalar diffraction systems. The algorithm is used to calculate the Fourier transform of a Gaussian function and the Fourier transform, the Fresnel transform, the Fractional-order Fourier transforms of a rectangle function to evaluate the performance of this algorithm. The calculated results are in good agreement with the analytical results, both in the amplitude and phase.

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Focusing of elliptically polarized Gaussian beams through an annular high numerical aperture

陈宝算, 蒲继雄

2010 (7): 74202-074202. doi: 10.1088/1674-1056/19/7/074202

摘要 ( 1597 )

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Based on the vectorial Debye theory, the focusing properties of the Gaussian beam through an annular high numerical aperture are studied numerically, including the intensity, the phase and the orbital angular momentum properties. Then the influence of certain parameters on the focusing properties is also investigated. It is shown that sub-wavelength elliptical light spots can be obtained. And there exists a vortex in the longitudinal component of the focused field even though the incident beam is Gaussian beam, indicating that the spin angular momentum of the elliptically polarized Gaussian beam is converted into the orbital angular momentum by the focusing.

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Theory of Z-scan technique using Gaussian—Bessel beams with a phase object

金肖, 税敏, 王玉晓, 李常伟, 杨俊义, 张学如, 杨昆, 宋瑛林

2010 (7): 74203-074203. doi: 10.1088/1674-1056/19/7/074203

摘要 ( 1438 )

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This paper reports the theoretical study of combining Z-scan technique with Gauss—Bessel (GB) beams beside a phase object (PO) to measure the third-order nonlinear susceptibility components. By using this method, the sign of refractive index which depends on the shape of the close aperture Z-scan curve can be easily determined. Meanwhile, the magnitude of nonlinear coefficients can also be deduced by theoretical fit. The proposed method is advantageous for high sensitivity and imposes a lower stress in the cases of fragile materials, since small pulse energy is enough for the measurement of nonlinear coefficients. Predictions of the models are compared with Gaussian Z-scan measurement and GB Z-scan measurement. By using GB beams with a PO, the sensitivity of Z-scan measurements is found to be a factor of over 60 times greater than for Gaussian beams and 2 times greater than for Gaussian-Bessel beams.

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Experimental study of regional fractal speckle produced in large angle scattering

宋洪胜, 程传福, 刘云燕, 刘桂媛, 滕树云

2010 (7): 74204-074204. doi: 10.1088/1674-1056/19/7/074204

摘要 ( 1347 )

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Using the interference of speckle and the spherical reference wave, we extract the real and the imaginary parts of the complex amplitudes of the speckle in large angle scattering. By calculating the spatial correlation functions of intensity, we find that the speckle has a property of regional fractality, i.e. the fractal exponent equals 1 in a small spatial region and it becomes less than 1 in a bigger region. The empirical analytic expression of the intensity correlation function is gained. The probability density distributions of the intensities and the complex amplitudes show that the regional fractal speckle still obeys zero-mean circular complex Gaussian statistics.

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Inversion formula and Parseval theorem for complex continuous wavelet transforms studied by entangled state representation

胡利云, 范洪义

2010 (7): 74205-074205. doi: 10.1088/1674-1056/19/7/074205

摘要 ( 1611 )

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In a preceding letter (2007 Opt. Lett. 32 554) we propose complex continuous wavelet transforms and found Laguerre—Gaussian mother wavelets family. In this work we present the inversion formula and Parseval theorem for complex continuous wavelet transform by virtue of the entangled state representation, which makes the complex continuous wavelet transform theory complete. A new orthogonal property of mother wavelet in parameter space is revealed.

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The Wigner function and phase properties of superposition of two coherent states with the vacuum state

王月媛, 王继成, 刘树田

2010 (7): 74206-074206. doi: 10.1088/1674-1056/19/7/074206

摘要 ( 1630 )

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This paper discusses some statistical properties of the superposition of two coherent states with a vacuum state, such as sub-Poissonian photon statistics and negativity of the Wigner function. Phase probability distribution and phase variance are calculated. Special cases of the constructed superposition states are presented. The results show that depending on the vacuum state coefficient γ and the coherent state coefficient α, it can generate a variety of nonclassical states.

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Single-atom entropy squeezing and quantum entanglement in Tavis--Cummings model with atomic motion

邹艳

2010 (7): 74207-074207. doi: 10.1088/1674-1056/19/7/074207

摘要 ( 1416 )

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We examine the single-atom entropy squeezing and the atom—field entanglement in a system of two moving two-level atoms interacting with a single-mode coherent field in a lossless resonant cavity. Our numerical calculations indicate that the squeezing period, the squeezing time and the maximal squeezing can be controlled by appropriately choosing the atomic motion and the field-mode structure. The atomic motion leads to a periodical time evolution of entanglement between the two-atom and the field. Moreover, there exists corresponding relation between the time evolution properties of the atomic entropy squeezing and that of the entanglement between the two atoms and the field.

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Coherent control of negative refraction based on local-field enhancement and dynamically induced chirality

巴诺, 高金伟, 田杏霞, 吴熙, 吴金辉

2010 (7): 74208-074208. doi: 10.1088/1674-1056/19/7/074208

摘要 ( 1524 )

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This paper studies the electromagnetic response of a coherently driven dense atomic ensemble to a weak probe. It finds that negative refraction with little absorption may be achieved in the presence of local-field enhanced interaction and dynamically induced chirality. The complex refractive index governing the probe refraction and absorption depends critically on the atomic density, the steady population distribution, the coherence dephasings, and the frequency detunings, and is also sensitive to the phase of the driving field because the photonic transition paths form a close loop. Thus, it can periodically tune the refractive index at a fixed frequency from negative to positive values and vice versa just by modulating the driving phase. Moreover, the optimal negative refraction is found to be near the probe magnetic resonance, which then requires the electric fields of the probe and the drive being on two-photon resonance due to the dipole synchronisation.

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Analytical solution of microwave transition spectral lines for ⁸⁷Rb atoms in a Hanle configuration

胡正峰, 邓见辽, 马易升, 何慧娟, 王育竹

2010 (7): 74209-074209. doi: 10.1088/1674-1056/19/7/074209

摘要 ( 1481 )

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This paper theoretically investigates the microwave transition spectrum of ⁸⁷Rb atomic D1 line with specially prepared atomic state in a Hanle configuration. The approximate analytical results have shown that the 0—0 transition spectral line has the highest contrast and can be applied to microwave frequency standards.

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Einstein－Podolsky－Rosen entanglement in bad cavity case

袁绥洪, 胡响明

2010 (7): 74210-074210. doi: 10.1088/1674-1056/19/7/074210

摘要 ( 1441 )

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This paper explores continuous variable entanglement in four-wave mixing when the atomic relaxation time is comparable to and longer than the cavity relaxation time. In this case the atomic memory is included in the field correlations and the entanglement in the output fields can be significantly enhanced. Einstein—Podolsky—Rosen (EPR) entanglement is achievable even in the bad cavity limit. This shows the EPR entanglement generation without need of good cavity.

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A 980 nm Yb-doped single-mode fibre laser with 946 nm Nd:YAG laser as pump source

李平雪, 邹淑珍, 张雪霞, 李港

2010 (7): 74211-074211. doi: 10.1088/1674-1056/19/7/074211

摘要 ( 1367 )

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Based on rate equations, this paper gives expressions of the output power, the pump power threshold, the slope efficiency, the fibre optimal length and the laser gain of a quasi-three-level Yb-doped fibre laser. The gain relationship between quasi-three-level system and four-level system is also given, which provides a theoretical basis for suppressing the four-level transmissions. In the experiment, we adopt the backward pumping configuration and use a linear cavity. The Yb-doped fibre laser has an output power of 372 mW of single-mode laser emission at 980 nm with a slope efficiency of 21.2% when the fibre length is 29.5~cm close to an optimal fibre length in theory. The experimental results accord well with the theoretical analyses.

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All-normal-dispersion Yb-doped mode-locked fibre laser and its stability analysis

孔令杰, 肖晓晟, 杨昌喜

2010 (7): 74212-074212. doi: 10.1088/1674-1056/19/7/074212

摘要 ( 1631 )

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We experimentally demonstrate an all-normal-dispersion Yb-doped mode-locked fibre laser with no intentional spectral filter inserted. Pulses with 1.1 nJ pulse energy at a repetition rate of 20.4 MHz are achieved. A theoretical model of the fibre laser is derived, whose coefficients are explicitly dependent on the orientations of the wave plates and the polarizer. Based on the model, stability diagrams of both the mode-locking and the continuous wave regimes of the laser are presented. The influence of group-velocity dispersion (GVD) and cavity length on the stability of mode-locking is also discussed.

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Photonic band structures of quadrangular multiconnected networks

宋欢欢, 杨湘波

2010 (7): 74213-074213. doi: 10.1088/1674-1056/19/7/074213

摘要 ( 1415 )

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By means of the network equation and generalized dimensionless Floquet—Bloch theorem, this paper investigates the properties of the band number and width for quadrangular multiconnected networks (QMNs) with a different number of connected waveguide segments (NCWSs) and various matching ratio of waveguide length (MRWL). It is found that all photonic bands are wide bands when the MRWL is integer. If the integer attribute of MRWL is broken, narrow bands will be created from the wide band near the centre of band structure. For two-segment-connected networks and three-segment-connected networks, it obtains a series of formulae of the band number and width. On the other hand, it proposes a so-called concept of two-segment-connected quantum subsystem and uses it to discuss the complexity of the band structures of QMNs. Based on these formulae, one can dominate the number, width and position of photonic bands within designed frequencies by adjusting the NCWS and MRWL. There would be potential applications for designing optical switches, optical narrow-band filters, dense wavelength-division-multiplexing devices and other correlative waveguide network devices.

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Composite metamaterial enabled excellent performance of microstrip antenna array

唐明春, 肖绍球, 官剑, 柏艳英, 高山山, 王秉中

2010 (7): 74214-074214. doi: 10.1088/1674-1056/19/7/074214

摘要 ( 1731 )

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This paper reports that the split ring resonators and complementary split ring resonators are compounded to construct a novel compact composite metamaterial. The composite metamaterial exhibits a unique property of blocking electromagnetic wave propagating in two directions near the resonant frequency. An example of two-element microstrip antenna array demonstrates that the developed metamaterial enables array performance that is an improvement in comparison with the traditional one, including mutual coupling suppression of 9.07 dB, remarkable side lobe suppression and gain improvement of 2.14 dB. The mechanism of performance enhancement is analysed based on the electric field and Poynting vector distributions in array. The present work not only is a meaningful exploration of new type composite metamaterial design, but also opens up possibilities for extensive metamaterial applications to antenna engineer.

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Two-dimensional non-spatial filtering based on holographic Bragg gratings

何焰蓝, 郑浩斌, 谭吉春, 丁道一, 郑光威, 王晓东, 王逍

2010 (7): 74215-074215. doi: 10.1088/1674-1056/19/7/074215

摘要 ( 1485 )

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The filter made up of two gratings performs as a two-dimensional non-spatial filtering. This paper reports that the volume Bragg gratings are fabricated by interfering two collimated coherent laser beams in photopolymer. Diffraction efficiency of a single grating is up to 78% in Bragg's condition, then a two-dimensional non-spatial filter, which consists of two volume Bragg gratings and a half-wave plate, enables the laser beam filtered in two dimensions with the diffraction efficiency of 54%. The Bragg's condition and effect of polarisation on performances of the two-dimension filter are also discussed.

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Monolithic optical gates based on integration of evanescently-coupled uni-traveling-carrier photodiodes and electroabsorption modulators

张云霄, 廖栽宜, 赵玲娟, 潘教青, 朱洪亮, 王圩

2010 (7): 74216-074216. doi: 10.1088/1674-1056/19/7/074216

摘要 ( 1272 )

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We report on chip-scale optical gates based on the integration of evanescent waveguide unitraveling-carrier photodiodes (EC-UTC-PDs) and intra-step quantum well electroabsorption modulators (IQW-EAMs) on n-InP substrates. These devices exhibit simultaneously 2.1 GHz and -16.2 dB RF-gain at 21 GHz with a 450 Ω thin-film resistor and a bypass capacitor integrated on a chip.

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Theoretical and experimental analyses of recording mark microstructures in signal waveform modulation optical disc

刘海龙, 裴京, 倪屹, 潘龙法, 唐毅

2010 (7): 74217-074217. doi: 10.1088/1674-1056/19/7/074217

摘要 ( 1467 )

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In this paper, we propose a dynamic mastering process model for signal waveform modulation (SWM) optical disc. To form the ideal microstructures and solve the problems in the SWM master manufacturing process, we use this model to simulate the three-dimensional mark profiles in the SWM read-only disc. The simulated micro-patterns of recording pits and lands are employed to optimize the writing strategy and provide a quantitative basis for manufacturing the sub-pits and sub-lands. The simulation mark profiles are compared with the experimental ones, which are produced with the optimized writing strategy parameters. Comparison results demonstrate that the simulated profiles are highly consistent with the actual ones.

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Polarisation-sensitive four-wave mixing and soliton self-frequency shift effect in the highly birefringent photonic crystal fibre

苑金辉, 桑新柱, 余重秀, 忻向军, 李曙光, 周桂耀, 侯蓝田

2010 (7): 74218-074218. doi: 10.1088/1674-1056/19/7/074218

摘要 ( 1640 )

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By adjusting the polarisation state of the pump at 805 nm parallel to slow (x) and fast (y) axes of the highly birefringent photonic crystal fibre with zero dispersion wavelengths 790 nm and 750 nm, this paper demonstrates the efficient polarisation-sensitive four wave mixing involved in pump, anti-Stokes and Stokes signals and soliton self-frequency shift effects induced by the phase-matching between red-shifted solitons and blue-shifted dispersive waves. If the reduction of coupling efficiency to the circular pump laser mode or other circular fibres due to asymmetry of the core is neglected, more than 98% of the total input power is kept in a single linear polarisation. Controlled dispersion characteristic of the doublet of fundamental guided-modes results in achieving light field strongly confined in principal axes of photonic crystal fibre, and enhancing the corresponding nonlinear-optical process through the remarkable nonlinear birefringence.

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Determination of the parameters of a linear-viscoelastic thin layer using the normally-incident ultrasonic waves

姚桂锦, 吕卫国, 宋若龙, 崔志文, 张香林, 王克协

2010 (7): 74301-074301. doi: 10.1088/1674-1056/19/7/074301

摘要 ( 1549 )

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This paper proposes a method of simultaneous determination of the four layer parameters (mass density, longitudinal velocity, the thickness and attenuation) of an immersed linear-viscoelastic thin layer by using the normally-incident reflected and transmitted ultrasonic waves. The analytical formula of the layer thickness related to the measured transmitted transfer functions is derived. The two determination steps of the four layer parameters are developed, in which acoustic impedance, time-of-flight and attenuation are first determined by the reflected transfer functions. Using the derived formula, it successively calculates and determines the layer thickness, longitudinal velocity and mass density by the measured transmitted transfer functions. According to the two determination steps, a more feasible and simplified measurement setups is described. It is found that only three signals (the reference waves, the reflected and transmitted waves) need to be recorded in the whole measurement for the determination of the four layer parameters. A study of the stability of the determination method against the experimental noises and the error analysis of the four layer parameters are made. This study lays the theoretical foundation of the practical measurement of a linear-viscoelastic thin layer.

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Scattering of light waves by electron electrostatic waves in laser produced plasmas

刘占军, 项江, 郑春阳, 朱少平, 曹莉华, 贺贤土, 王宇钢

2010 (7): 75201-075201. doi: 10.1088/1674-1056/19/7/075201

摘要 ( 1634 )

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The propagation of light waves in an underdense plasma is studied using one-dimensional Vlasov—Maxwell numerical simulation. It is found that the light waves can be scattered by electron plasma waves as well as other heavily and weakly damping electron wave modes, corresponding to stimulated Raman and Brilluoin-like scatterings. The stimulated electron acoustic wave scattering is also observed as a high scattering level. High frequency plasma wave scattering is also observed. These electron electrostatic wave modes are due to a non-thermal electron distribution produced by the wave—particle interactions. The collision effects on stimulated electron acoustic wave and the laser intensity effects on the scattering spectra are also investigated.

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Laser-produced plasma helium-like titanium Kα x-ray source and its application to Rayleighben-Taylor instability study

王瑞荣, 陈伟民, 王伟, 董佳钦, 肖沙里

2010 (7): 75202-075202. doi: 10.1088/1674-1056/19/7/075202

摘要 ( 1362 )

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Several experiments are performed on the ShenGuang-II laser facility to investigate an x-ray source and test radiography concepts. X-ray lines emitted from laser-produced plasmas are the most practical means of generating these high intensity sources. By using a time-integrated space-resolved keV spectroscope and pinhole camera, potential helium-like titanium Kα x-ray backlighting (radiography) line source is studied as a function of laser wavelength, ratio of pre-pulse intensity to main pulse intensity, and laser intensity (from 7.25 to ～11.3× 10¹⁵ W/cm²⁾. One-dimensional radiography using a grid consisting of 5 μm Au wires on 16 μm period and the pinhole-assisted point projection is tested. The measurements show that the size of the helium-like titanium Kα source from a simple foil target is larger than 100 μm, and relative x-ray line emission conversion efficiency ξ_x from the incident laser light energy to helium-like titanium K-shell spectrum increases significantly with pre-pulse intensity increasing, increases rapidly with laser wavelength decreasing, and increases moderately with main laser intensity increasing. It is also found that a gold gird foils can reach an imaging resolution better than 5-μm featured with high contrast. It is further demonstrated that the pinhole-assisted point projection at such a level will be a novel two-dimensional imaging diagnostic technique for inertial confinement fusion experiments.

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Effects of substrate-ion density gradients on light-ion acceleration from ultraintense laser pulse irradiated thin-foils

刘明伟, 李儒新, 夏长权, 刘建胜, 徐至展

2010 (7): 75203-075203. doi: 10.1088/1674-1056/19/7/075203

摘要 ( 1354 )

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A general solution of the electrostatic potential that determines the maximum light-ion energy is derived for the test-particle acceleration model by taking into account the influence of the substrate-ion density gradient. It is shown that the substrate-ion density structure is also dependent on laser pulse duration. In the picosecond or sub-picosecond regime, the decreasing density gradient of the substrate-ions leads to an evident reduction in the acceleration efficiency of the light-ions. However, this kind of influence is negligible in the ultrashort regime.

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Spatially-resolved spectroscopic diagnosing of aluminum wire array Z-pinch plasmas on QiangGuang-I facility

叶凡, 李正宏, 秦义, 蒋树庆, 薛飞彪, 杨建伦, 徐荣昆, 金永杰

2010 (7): 75204-075204. doi: 10.1088/1674-1056/19/7/075204

摘要 ( 1509 )

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Spatially-resolved crystal spectrometers with a high spectral resolution are developed to diagnose K-shell x-ray radiation from Z-pinch plasmas. These diagnostic apparatuses are successfully applied to aluminum wire array Z-pinch experiments on QiangGuang-I facility, a driver with a pulsed current up to about 1.5 MA in 80 ns. Time-integrated experimental results show that the K-shell x-ray emission lines of aluminum Z-pinch plasmas are dominated by line emissions from helium-like ionisation state. Bright spots that might have higher electron temperature or density are produced randomly in location and size along the z-axis during implosions. According to the experimental data, the electron temperature and the ion density are estimated to be between 250 eV and 310 eV, and between 7.0×10¹⁹cm^-3 and 4.0×10¹⁹ cm^-3 respectively, while the ion temperature is inferred to be about 10.2 keV, which is much higher than the electron temperature.

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X-ray backlighting of two-wire Z-pinch plasma using X-pinch

赵彤, 邹晓兵, 张然, 王新新

2010 (7): 75205-075205. doi: 10.1088/1674-1056/19/7/075205

摘要 ( 1598 )

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Two 50-μm Mo wires in parallel used as a Z-pinch load are electrically exploded with a pulsed current rising to 275 kA in 125 ns and their explosion processes are backlighted using an X-pinch as an x-ray source. The backlighting images show clearly the processes similar to those occurring in the initial stages of a cylindrical wire-array Z-pinch, including the electric explosion of single wires characterised by the dense wire cores surrounded by a low-density coronal plasma, the expansion of the exploding wire, the sausage instability (m=0) in the coronal plasma around each wire, the motion of the coronal plasma as well as the wire core toward the current centroid, the formation of the precursor plasma column with a twist structure something like that of higher mode instability, especially the kink instability (m=1).

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Advanced high-pressure plasma diagnostics with hairpin resonator probe surrounded by film and sheath

徐金洲, 石建军, 张菁, 张琪, 中村圭二, 菅井秀郎

2010 (7): 75206-075206. doi: 10.1088/1674-1056/19/7/075206

摘要 ( 1605 )

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The hairpin probe using microwave resonance in plasma is applicable to high pressure 1.33×10³—1.01×10⁵ Pa)) as developed recently. In this work, an analytic model of the hairpin resonator probe surrounded by a thin dielectric layer and a sheath layer is proposed. The correction factor due to these surroundings is analytically found and confirmed by electromagnetic field finite difference time domain simulation, thus enabling the accurate measurement of electron density in a high-pressure non-equilibrium uniform discharge.

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Relation between space-charge-limiting current and electric field enhancement factor at curved surface cathode

刘国治, 杨占峰

2010 (7): 75207-075207. doi: 10.1088/1674-1056/19/7/075207

摘要 ( 1472 )

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A two-dimensional solution of space-charge-limiting current for a high current vacuum diode with a spherical cathode is presented. The relation between space-charge-limiting current and electric field enhancement factor at the cathode surface for the diode with a curved surface cathode is also discussed. It is shown that compared with the current given by the conventional Child—Langmuir law, which describes the one-dimensional space-charege-limiting current, the two-dimensional space-charge-limiting current in such a diode is enhanced due to the electric-field enhancement along the cathode surface. Among practical parameter ranges, enhancement factor η_b approximately satisfies η_b ≈ Aβⁿ, where β is the electric field enhancement factor at the cathode surface, and n is a constant between 1 and 2, which is confirmed to be universal for the diodes with curved surface cathodes.

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Structural and electrical properties of single crystalline and bi-crystalline ZnO thin films grown by molecular beam epitaxy

路忠林, 邹文琴, 徐明祥, 张凤鸣

2010 (7): 76101-076101. doi: 10.1088/1674-1056/19/7/076101

摘要 ( 1504 )

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C-oriented ZnO epitaxial thin films are grown separately on the a-plane and c-plane sapphire substrates by using a molecular-beam epitaxy technique. In contrast to single crystalline ZnO films grown on a-plane sapphire, the films grown on c-plane sapphire are found to be bi-crystalline; some domains have a 30o rotation to reduce the large mismatch between the film and the substrate. The presence of these rotation domains in the bi-crystalline ZnO thin film causes much more carrier scatterings at the boundaries, leading to much lower mobility and smaller mean free path of the mobile carriers than those of the single crystalline one. In addition, the complex impedance spectra are also studied to identify relaxation mechanisms due to the domains and/or domain boundaries in both the single crystalline and bi-crystalline ZnO thin films.

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Preparation and NO₂-gas sensing property of individual β-Ga₂O₃ nanobelt

马海林, 范多旺, 牛晓山

2010 (7): 76102-076102. doi: 10.1088/1674-1056/19/7/076102

摘要 ( 1800 )

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Monoclinic gallium oxide (β-Ga₂O₃) nanobelts are synthesized from gallium and oxygen by thermal evaporation in an argon atmosphere and their NO₂ sensing properties are studied at room temperature. Electron microscopy studies show that the nanobelts have breadths ranging from 30 to 50 nm and lengths up to tens of micrometers. Both the x-ray diffraction (XRD) and the selected are electron diffraction (SAED) examinations indicate that β-Ga₂O₃ nanobelts have grown into single crystals. Room temperature NO₂ sensing tests show that the current of individual β-Ga₂O₃ nanobelt decreases quickly, and then gently when the NO₂ concentration increases from low to high. It is caused by the NO₂ molecule chemisorption and desorption processes in the surface of β-Ga₂O₃ nanobelt.

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A novel radio frequency coil for veterinary magnetic resonance imaging system

孟斌, 黄开文, 王为民

2010 (7): 76103-076103. doi: 10.1088/1674-1056/19/7/076103

摘要 ( 1739 )

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In this article, a novel designed radio frequency (RF) coil is designed and built for the imaging of puppies in a V-shape permanent magnetic resonance imaging (MRI) system. Two sets of Helmholtz coil pairs with a V-shape structure are used to improve the holding of an animal in the coil. The homogeneity and the sensitivity of the RF field in the coil are analysed by theoretical calculation. The size and the shape of the new coil are optimized and validated by simulation through using the finite element method (FEM). Good magnetic resonance (MR) images are achieved on a shepherd dog.

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Correlation of magnetic anisotropy with dielectric anisotropy in fluorinated phenyl bicyclohexane liquid crystal

马恒, Onnagawa Hiroyoshi, Sugimori Sigeru, Toriyama Kazuhisa

2010 (7): 76104-076104. doi: 10.1088/1674-1056/19/7/076104

摘要 ( 1468 )

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Temperature dependence of magnetic anisotropy of homologous nematic fluorinated phenyl bicyclohexane liquid crystals is measured by a magneto-electric method. The result shows that the diamagnetic property is slightly influenced by the positions and the numbers of fluorine atoms substituted at the phenyl ring. By investigating the correlation of the dielectric anisotropy with the magnetic anisotropy, a novel explanation is proposed for the behaviour of the molecular dipole—dipole dimerization in the polar liquid crystal compounds.

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A simple theoretical model for evaluating the ability to form a single crystal

金云飞, 明辰, 叶祥熙, 王为民, 宁西京

2010 (7): 76105-076105. doi: 10.1088/1674-1056/19/7/076105

摘要 ( 1427 )

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A simple theoretical model proposed recently to evaluate the ability of bulk materials to form single crystals is further tested via vast molecular dynamics simulations of growth for fcc (Ni, Cu, Al, Ar) and hcp (Mg) crystals, especially applied to the growth of bcc (Fe) crystal, showing that the validity of the model is independent of crystal types and the interaction potentials of the constitute atoms.

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Investigation of dislocations in 8^circ off-axis 4H-SiC epilayer

苗瑞霞, 张玉明, 张义门, 汤晓燕, 盖庆丰

2010 (7): 76106-076106. doi: 10.1088/1674-1056/19/7/076106

摘要 ( 1444 )

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This paper reports that the etching morphology of dislocations in 8o off-axis 4H-SiC epilayer is observed by using a scanning electronic microscope. It is found that different types of dislocations correspond with different densities and basal plane dislcation (BPD) array and threading edge dislocation (TED) pileup group lie along some certain crystal directions in the epilayer. It is concluded that the elastic energy of threading screw dislocations (TSDs) is highest and TEDs is lowest among these dislocations, so the density of TSDs is lower than TEDs. The BPDs can convert to TEDs but TSDs can only propagate into the epilyer in spite of the higher elastic energy than TEDs. The reason of the form of BPDs array in epilayer is that the big step along the basal plane caused by face defects blocked the upstream atoms, and TEDs pileup group is that the dislocations slide is blocked by dislocation groups in epilayer.

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Characterisation of the high-pressure structural transition and elastic properties in boron arsenic

吕兵, 令狐荣锋, 易勇, 杨向东

2010 (7): 76201-076201. doi: 10.1088/1674-1056/19/7/076201

摘要 ( 1335 )

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This paper carries out the First principles calculation of the crystal structures (zinc blende (B3) and rocksalt (B1)) and phase transition of boron arsenic (BAs) based on the density-functional theory. Using the relation between enthalpy and pressure, it finds that the transition phase from the B3 structural to the B1 structural occurs at the pressure of 113.42GPa. Then the elastic constants C₁₁, C₁₂, C₄₄, bulk modulus, shear modulus, Young modulus, anisotropy factor, Kleinman parameter and Poisson ratio are discussed in detail for two polymorphs of BAs. The results of the structural parameters and elastic properties in B3 structure are in good agreement with the available theoretical and experimental values.

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Correcting the systematic error of the density functional theory calculation: the alternate combination approach of genetic algorithm and neural network

王婷婷,李文龙,陈章辉,缪灵

2010 (7): 76401-076401. doi: 10.1088/1674-1056/19/7/076401

摘要 ( 1506 )

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The alternate combinational approach of genetic algorithm and neural network (AGANN) has been presented to correct the systematic error of the density functional theory (DFT) calculation. It treats the DFT as a black box and models the error through external statistical information. As a demonstration, the AGANN method has been applied in the correction of the lattice energies from the DFT calculation for 72 metal halides and hydrides. Through the AGANN correction, the mean absolute value of the relative errors of the calculated lattice energies to the experimental values decreases from 4.93% to 1.20% in the testing set. For comparison, the neural network approach reduces the mean value to 2.56%. And for the common combinational approach of genetic algorithm and neural network, the value drops to 2.15%. The multiple linear regression method almost has no correction effect here.

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Thermal transport property of Ge₃₄ and d-Ge investigated by molecular dynamics and the Slack's equation

王汉夫, 禇卫国, 郭延军, 金灏

2010 (7): 76501-076501. doi: 10.1088/1674-1056/19/7/076501

摘要 ( 1529 )

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In this study, we evaluate the values of lattice thermal conductivity $\kappa_{\rm L}$ of type II Ge clathrate (Ge₃₄) and diamond phase Ge crystal (d-Ge) with the equilibrium molecular dynamics (EMD) method and the Slack's equation. The key parameters of the Slack's equation are derived from the thermodynamic properties obtained from the lattice dynamics (LD) calculations. The empirical Tersoff's potential is used in both EMD and LD simulations. The thermal conductivities of d-Ge calculated by both methods are in accordance with the experimental values. The predictions of the Slack's equation are consistent with the EMD results above 250 K for both Ge₃₄ and d-Ge. In a temperature range of 200—1000 K, the $\kappa_{\rm L}$ value of d-Ge is about several times larger than that of Ge₃₄.

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Thermodynamic theory of the Tolman's length

朱如曾, 王小松

2010 (7): 76801-076801. doi: 10.1088/1674-1056/19/7/076801

摘要 ( 1393 )

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There still exists controversy on the sign and magnitude of the Tolman's length and the Tolman's gap. Further experimental, computational and theoretical investigations on them are needed to solve this problem. In 2006, Blokhuis and Kuipers obtained a rigorous relationship between the Tolman's length and other thermodynamic quantities for the single-component liquid—vapour system. In the present paper, we derive two general relationships between the Tolman's length and other thermodynamic quantities for the single-component liquid—vapour system. The relationship derived by Blokhuis and Kuipers and an earlier result turn out to be two special cases of our results.

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A novel method for sacrificial layer release in MEMS devices fabrication

石莎莉, 陈大鹏, 景玉鹏, 欧毅, 叶甜春, 徐秋霞

2010 (7): 76802-076802. doi: 10.1088/1674-1056/19/7/076802

摘要 ( 1311 )

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During the forming process of the free-standing structure or the functional cavity when releasing the high aspect ratio sacrificial layer, such structures tend to stick to the substrate due to capillary force. This paper describes the application of pull-in length conception as design rules to a novel `dimpled' method in releasing sacrificial layer. Based on the conception of pull-in length in adhering phenomenon, the fabrication and releasing sacrificial layer methods using micro bumps based on the silicon substrate were presented. According to the thermal isolation performances of one kind of micro electromechanical system device thermal shear stress sensor, the sacrificial layers were validated to be successfully released.

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Effects of InGaN barriers with low indium content on internal quantum efficiency of blue InGaN multiple quantum wells

汪莱, 王嘉星, 赵维, 邹翔, 罗毅

2010 (7): 76803-076803. doi: 10.1088/1674-1056/19/7/076803

摘要 ( 1584 )

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Blue In_0.2Ga_0.8N multiple quantum wells (MQWs) with In_xGa₁ _{- x}N (x=0.01-0.04) barriers are grown by metal organic vapour phase epitaxy. The internal quantum efficiencies (IQEs) of these MQWs are studied in a way of temperature-dependent photoluminescence spectra. Furthermore, a 2-channel Arrhenius model is used to analyse the nonradiative recombination centres (NRCs). It is found that by adopting the InGaN barrier beneath the lowest well, it is possible to reduce the strain hence the NRCs in InGaN MQWs. By optimizing the thickness and the indium content of the InGaN barriers, the IQEs of InGaN/InGaN MQWs can be increased by about 2.5 times compared with conventional InGaN/GaN MQWs. On the other hand, the incorporation of indium atoms into the intermediate barriers between adjacent wells does not improve IQE obviously. In addition, the indium content of the intermediate barriers should match with that of the lowest barrier to avoid relaxation.

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Microstructure and strain analysis of GaN epitaxial films using in-plane grazing incidence x-ray diffraction

郭希, 王玉田, 赵德刚, 江德生, 朱建军, 刘宗顺, 王辉, 张书明, 邱永鑫, 徐科, 杨辉

2010 (7): 76804-076804. doi: 10.1088/1674-1056/19/7/076804

摘要 ( 1837 )

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This paper investigates the major structural parameters, such as crystal quality and strain state of (001)-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition, using an in-plane grazing incidence x-ray diffraction technique. The results are analysed and compared with a complementary out-of-plane x-ray diffraction technique. The twist of the GaN mosaic structure is determined through the direct grazing incidence measurement of (100) reflection which agrees well with the result obtained by extrapolation method. The method for directly determining the in-plane lattice parameters of the GaN layers is also presented. Combined with the biaxial strain model, it derives the lattice parameters corresponding to fully relaxed GaN films. The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established, reaching to a maximum level of —0.89 GPa.

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Band structure and absorption coefficient in GaN/AlGaN quantum wires

姚文杰, 俞重远, 刘玉敏

2010 (7): 77101-077101. doi: 10.1088/1674-1056/19/7/077101

摘要 ( 1827 )

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The band structures of rectangular GaN/AlGaN quantum wires are modeled by using a parabolic effective-mass theory. The absorption coefficients are calculated in a contact-density matrix approach based on the band structure. The results obtained indicate that the peak absorption coefficients augment with the increase of the injected carrier density, and the optical gain caused by interband transition is polarization anisotropic. For the photon energy near 1.55 eV, we can obtain relatively large peak gain. The calculations support the previous results published in the recent literature.

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Electronic structure and optical properties of rutile RuO₂ from first principles

杨则金, 郭云东, 李劲, 刘锦超, 戴伟, 程新路, 杨向东

2010 (7): 77102-077102. doi: 10.1088/1674-1056/19/7/077102

摘要 ( 1462 )

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The systematic trends of electrionic structure and optical properties of rutile (P4₂/mnm) RuO₂have been calculated by using the plane-wave norm-conserving pseudopotential density functional theory (DFT) method within the generalised gradient approximation (GGA) for the exchange—correlation potential. The obtained equilibrium structure parameters are in excellent agreement with the experimental data. The calculated bulk modulus and elastic constants are also in good agreement with the experimental data and available theoretical calculations. Analysis based on electronic structure and pseudogap reveals that the bonding nature in RuO₂ is a combination of covalent, ionic and metallic bonds. Based on a Kramers—Kronig analysis of the reflectivity, we have obtained the spectral dependence of the real and imaginary parts of the complex dielectric constant (ε₁ and ε₂ , respectively) and the refractive index (n); and comparisons have shown that the theoretical results agree well with the experimental data as well. Meanwhile, we have also calculated the absorption coefficient, reflectivity index, electron energy loss function of RuO₂ for radiation up to 30 eV. As a result, the predicted reflectivity index is in good agreement with the experimental data at low energies.

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Electronic band transformation from indirect gap to direct gap in Si—H compound

丁建宁, 王君雄, 袁宁一, 坎标, 陈效双

2010 (7): 77103-077103. doi: 10.1088/1674-1056/19/7/077103

摘要 ( 1476 )

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The electronic band structures of periodic models for Si—H compounds are investigated by the density functional theory. Our results show that the Si—H compound changes from indirect-gap semiconductor to direct-gap semiconductor with the increase of H content. The density of states, the partial density of states and the atomic charge population are examined in detail to explore the origin of this phenomenon. It is found that the Si—Si bonds are affected by H atoms, which results in the electronic band transformation from indirect gap to direct gap. This is confirmed by the nearest neighbour semi-empirical tight-binding (TB) theory.

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Coexistence of magnetic and ferroelectric properties in Y_0.1Co_1.9MnO₄

刘毅

2010 (7): 77201-077201. doi: 10.1088/1674-1056/19/7/077201

摘要 ( 1630 )

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The magnetic, conductivity, and dielectric properties have been investigated in single-phase polycrystalline Y_0.1Co_1.9MnO₄. The temperature-dependent magnetisation reveals the ferromagnetic transition in sample at a low temperature (～186 K). Magnetisation as a function of field H (M—H loop) indicated the weak ferromagnetism of the sample at room temperature. The constant ε and dielectric loss tgδ measurements represent a ferroelectric phase transition at a higher temperature (～650 K), while the conductivity shows an insulator—metallic transition. The ferroelectric hysterisis loops and capacitance—voltage measurements confirm the ferroelectric nature of the sample at room temperature. The observed ferromagnetism and ferroelectric nature in this material suggests a potential multiferroic application.

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Energy band alignment of PbTe/CdTe(111) interface determined by ultraviolet photoelectron spectra using synchrotron radiation

蔡春锋, 吴惠桢, 斯剑霄, 金树强, 张文华, 许杨, 朱骏发

2010 (7): 77301-077301. doi: 10.1088/1674-1056/19/7/077301

摘要 ( 1560 )

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The energy band structure with type-I alignment at the PbTe/CdTe(111) heterojunction interface is determined by the ultraviolet photoelectron spectrum using synchrotron radiation. The valence band and conduction band offsets are obtained to be 0.09±0.12 and 1.19±0.12 eV, respectively. These results are in agreement with theoretically predicted ones. The accurate determination of the valence band and conduction band offsets is useful for the fundamental understanding of the mid-infrared light emission from the PbTe/CdTe heterostructures and its application in devices.

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Spin-dependent transport through an interacting quantum dot system

黄睿, 吴绍全, 闫从华

2010 (7): 77302-077302. doi: 10.1088/1674-1056/19/7/077302

摘要 ( 1365 )

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Using an equation of motion technique, we report on a theoretical analysis of transport characteristics of a spin-valve system formed by a quantum dot coupled to ferromagnetic leads, whose magnetic moments are oriented at an angle θ with respect to each other, and a mesoscopic ring by the Anderson Hamiltonian. We analyse the density of states of this system, and our results reveal that the density of states show some noticeable characteristics depending on the relative angle θ of magnetic moment M, and the spin-polarised strength P in ferromagnetic leads, and also the magnetic flux Φ and the number of lattice sites N_R in the mesoscopic ring. These effects might have some potential applications in spintronics.

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AlGaN/GaN MIS-HEMT using NbAlO dielectric layer grown by atomic layer deposition

毕志伟, 冯倩, 郝跃, 王党会, 马晓华, 张进成, 全思, 许晟瑞

2010 (7): 77303-077303. doi: 10.1088/1674-1056/19/7/077303

摘要 ( 1808 )

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We present an AlGaN/GaN metal—insulator—semiconductor high electron mobility transistor (MIS-HEMT) with an NbAlO high-k dielectric deposited by atomic layer deposition (ALD). Surface morphology of samples are observed by atomic force microscopy (AFM), indicating that the ALD NbAlO has an excellent-property surface. Moreover, the sharp transition from depletion to accumulation in capacitance—voltage (C—V)curse of MIS-HEMT demonstrates the high quality bulk and interface properties of NbAlO on AlGaN. The fabricated MIS-HEMT with a gate length of 0.5 μ m exhibits a maximum drain current of 960 mA/mm, and the reverse gate leakage current is almost 3 orders of magnitude lower than that of reference HEMT. Based on the improved direct-current operation, the NbAlO can be considered to be a potential gate oxide comparable to other dielectric insulators.

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InP-based InGaAs/InAlGaAs digital alloy quantum well laser structure at 2 μm

顾溢, 王凯, 李耀耀, 李成, 张永刚

2010 (7): 77304-077304. doi: 10.1088/1674-1056/19/7/077304

摘要 ( 1620 )

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The structural and optical characteristics of InP-based compressively strained InGaAs quantum wells have been significantly improved by using gas source molecular beam epitaxy grown InAs/In_0.53Ga_0.47As digital alloy triangular well layers and tensile In_0.53Ga_0.47As/InAlGaAs digital alloy barrier layers. The x-ray diffraction and transmission electron microscope characterisations indicate that the digital alloy structures present favourable lattice quality. Photoluminescence (PL) and electroluminescence (EL) measurements show that the use of digital alloy barriers offers better optical characteristics than that of conventional random alloy barriers. A significantly improved PL signal of around 2.1 μ m at 300 K and an EL signal of around 1.95 μ m at 100 K have been obtained.

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Properties of C₆₀ thin film transistor based on polystyrene

周建林, 牛巧利

2010 (7): 77305-077305. doi: 10.1088/1674-1056/19/7/077305

摘要 ( 1406 )

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This paper reports that the n-type organic thin-film transistors have been fabricated by using C₆₀ as the active layer and polystyrene as the dielectric. The properties of insulator and the growth characteristic of C₆₀ film were carefully investigated. By choosing different source/drain electrodes, a device with good performance can be obtained. The highest electron field effect mobility about 1.15 cm²/(V·s) could reach when Barium was introduced as electrodes. Moreover, the C₆₀ transistor shows a negligible 'hysteresis effect' contributed to the hydroxyl-free of insulator. The result suggests that polymer dielectrics are promising in applications among n-type organic transistors.

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A novel partial silicon on insulator high voltage LDMOS with low-k dielectric buried layer

罗小蓉, 王元刚, 邓浩, Florin Udrea

2010 (7): 77306-077306. doi: 10.1088/1674-1056/19/7/077306

摘要 ( 1574 )

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A novel partial silicon-on-insulator (PSOI) high voltage device with a low-k (relative permittivity) dielectric buried layer (LK PSOI) and its breakdown mechanism are presented and investigated by MEDICI. At a low k value the electric field strength in the dielectric buried layer (E_I) is enhanced and a Si window makes the substrate share the vertical drop, resulting in a high vertical breakdown voltage; in the lateral direction, a high electric field peak is introduced at the Si window, which modulates the electric field distribution in the SOI layer; consequently, a high breakdown voltage (BV) is obtained. The values of E_I and BV of LK PSOI with k_I=2 on a 2 μm thick SOI layer over 1 μm thick buried layer are enhanced by 74% and 19%, respectively, compared with those of the conventional PSOI. Furthermore, the Si window also alleviates the self-heating effect.

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Kondo transport through a quantum dot coupled with side quantum-dot structures

江兆潭

2010 (7): 77307-077307. doi: 10.1088/1674-1056/19/7/077307

摘要 ( 1625 )

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This paper investigates Kondo transport properties in a quadruple quantum dot (QD) based on the slave-boson mean field theory and the non-equilibrium Green's function. In the quadruple QD structure one Kondo-type QD sandwiched between two leads is side coupled to two separate QD structures: a single-QD atom and a double-QD molecule. It shows that the conductance valleys and peaks always appear in pairs and by tuning the energy levels in three side QDs, the one-, two-, or three-valley conductance pattern can be obtained. Furthermore, it finds that whether the valley and the peak can appear is closely dependent on the specific values of the interdot couplings and the energy level difference between the two QDs in the molecule. More interestingly, an extra novel conductance peak can be produced by the coexistence of the two different kinds of side QD structures.

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Paramagnetism in Cu-doped ZnO

徐庆宇, 郑晓红, 龚佑品

2010 (7): 77501-077501. doi: 10.1088/1674-1056/19/7/077501

摘要 ( 1898 )

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Zn_0.98Cu_0.02O powders are prepared by the sol—gel method. A small number of CuO impurity phases are observed by the x-ray diffraction, indicating the solubility of Cu in ZnO is less than 2 at.%. The Zn_0.98Cu_0.02O powders exhibit diamagnetism at 300 K and paramagnetism at 5 K. After subtracting the diamagnetic contribution of ZnO bulk and the paramagnetic contribution of defects, Cu ions exhibit weak paramagnetism. By codoping Cu with Co or Mn in ZnO, only paramagnetism is observed at room temperature.

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Influence of the distance between two voltage contacts on giant magneto-impedance of Co-based amorphous wires

张树玲, 邢大伟, 孙剑飞

2010 (7): 77502-077502. doi: 10.1088/1674-1056/19/7/077502

摘要 ( 1295 )

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The Co₇₅ Fe_4.2Si₈B₁₂Nb_0.8 amorphous wires of 30 μ m in diameter are produced by melt extraction and annealing at 450 oC for 20 min in vacuum with a longitudinal or transverse field of 40 kA/m. Distances between the two voltage contacts of 6, 5, 4 and 2 mm are obtained by moving the two voltage contacts towards the centre of the sample at the same time. Results indicate that magneto-impedance response is dependent on the distance significantly. As distance decreases from 6 to 2 mm, △Z/Z reduces from 609% to 95% and giant magneto-impedance (GMI) profiles change from two-peak to single-peak. Besides, field sensitivity improves from 0.47%/(A/m) to 0.76%/(A/m) when the single-peak GMI just appears. It is therefore concluded that actual measurements can be made comparable only by taking into account the influence of distance between two voltage contacts for a magneto-impedance measurement.

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Frustration and intermediate dimerized phase in spin ladder system

石洞, 文瑞, 刘光华, 田光善

2010 (7): 77503-077503. doi: 10.1088/1674-1056/19/7/077503

摘要 ( 1884 )

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This paper studies a spin ladder model which possesses frustrating interactions. By using both the bosonization and the density matrix renormalization group techniques, it shows that the intermediate columnar dimerized phase, which exists in a narrow parameter region of the so-called J₁-J₂ model, vanishes if the interchain frustration is weak and anisotropic. Therefore, it concludes that the frustrating interaction indeed plays an important role in producing such a phase. As a complementary to our previous investigation, it reaches a more complete picture of the quantum phase transition in the frustrated spin ladder systems.

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The hysteresis loops of a ferroelectric bilayer film with surface transition layers

崔莲, 吕天全, 孙普男, 薛惠杰

2010 (7): 77701-077701. doi: 10.1088/1674-1056/19/7/077701

摘要 ( 1489 )

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Based on the transverse Ising model in the framework of the mean field approximation, this paper discusses a ferroelectric bilayer film with the surface transition layers within each constituent slab and an antiferroelectric interfacial coupling between two slabs. The hysteresis loop of a bilayer film is investigated. The results show that the surface transition layer in a ferroelectric bilayer film plays a significant role in realizing the multiple-state memory.

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Investigation on dependence of BiFeO₃ dielectric property on oxygen content

娄艳辉, 宋桂林, 常方高, 王照奎

2010 (7): 77702-077702. doi: 10.1088/1674-1056/19/7/077702

摘要 ( 1356 )

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The influence of oxygen content on the dielectric property of BiFeO₃ ceramics is studied by experiment and first-principles calculation. The experimental result demonstrates that the dielectric constant of BiFeO₃ is strongly dependent on introduced oxygen and oxygen vacancies. By comparison with BiFeO₃, the introduced oxygen and oxygen vacancies can lead to a reduction in dielectric constant of BiFeO_$\delta$ at a lower frequency. The first-principles calculation also shows a similar result when photon energy is in a range of 2.0—4.1 eV. A likely explanation is that this oxygen content dependence may be ascribed to the distortion of Fe—O octahedron structure due to oxygen vacancies or excess oxygen ions in the crystal structure of BiFeO₃.

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Ultraviolet laser-induced photovoltaic effects in miscut ferroelectric LiNbO₃ single crystals

李小明, 王芳, 赵昆, 赵嵩卿

2010 (7): 77801-077801. doi: 10.1088/1674-1056/19/7/077801

摘要 ( 1554 )

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This paper investigates the photovoltaic properties of miscut LiNbO₃ single crystal with different thicknesses under irradiation of a 248 nm ultraviolet laser pulse with 20 ns duration without an applied bias. Nanosecond photovoltaic response is observed and faster rise time is obtained in thinner samples. In accord with the 248 nm laser duration, the full width at half maximum of the photovoltaic signals keeps a constant of ～20 ns. With decrease of the crystal thickness, the photovoltaic sensitivity was improved rapidly at first and then decreased, and the maximum photovoltage occurred at 0.38 mm-thick single crystal. The present results demonstrate that decreasing the LiNbO₃ single crystal thickness can obtain faster response time and improve the photovoltaic sensitivity.

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A multilevel nano-scale interconnection RLC delay model

朱樟明, 修利平, 杨银堂

2010 (7): 77802-077802. doi: 10.1088/1674-1056/19/7/077802

摘要 ( 1481 )

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Based on the multilevel interconnections temperature distribution model and the RLC interconnection delay model of the integrate circuit, this paper proposes a multilevel nano-scale interconnection RLC delay model with the method of numerical analysis, the proposed analytical model has summed up the influence of the configuration of multilevel interconnections, the via heat transfer and self-heating effect on the interconnection delay, which is closer to the actual situation. Delay simulation results show that the proposed model has high precision within 5% errors for global interconnections based on the 65 nm CMOS interconnection and material parameter, which can be applied in nanometer CMOS system chip computer-aided design.

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Enhanced optical transmission through double-layer gold slit arrays

谢素霞, 李宏建, 周昕, 徐海清, 付少丽

2010 (7): 77803-077803. doi: 10.1088/1674-1056/19/7/077803

摘要 ( 1474 )

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We investigate the relationship between the transmission and the layer distance of double-layer gold slit arrays by using the finite-difference time-domain method. The results show that the transmission properties can be influenced strongly by layer distance. We attribute the two types of resonant modes to surface plasmon resonance and the localised waveguide resonance. We find that the localised waveguide transmission peak redshifts and becomes broader with increasing layer distance D. We also describe and explain the splitting, shift, and degeneration of the surface plasmon resonant transmission peak theoretically. In addition, to clarify the physical mechanism of the transmission behaviours, we analyse the distributions of electric field and total energy for the three transmission peaks with distance D=45 nm for the double-layer system. Light transporting behaviours are mostly concentrated in the region of the slits as well as the interspaces of the two layers, and for different resonant wavelengths the electric field and energy distributions are different. It is expected that the results obtained here will be helpful for designing subwavelength metallic grating devices.

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Quantum cutting downconversion by cooperative energy transfer from Bi³⁺ to Yb³⁺ in Y₂O₃ phosphor

韦先涛, 赵江波, 陈永虎, 尹民, 李勇

2010 (7): 77804-077804. doi: 10.1088/1674-1056/19/7/077804

摘要 ( 1723 )

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Bi³⁺ and Yb³⁺ codoped cubic Y₂O₃ phosphors are prepared by pechini sol—gel method. Strong near-infrared (NIR) emission around 980 nm from Yb^{3 +}(²F^{_{5 / 2}}→²F^{_{7 / 2}}) is observed under ultraviolet light excitation. A broad excitation band ranging from 320 to 360 nm, owing to the 6s² →6s6p transition of Bi^{3 +}ions, is recorded when the Yb^{3 +}emission is monitored, which suggests a very efficient energy transfer from Bi^{3 +}ions to Yb^{3 +}ions. The Yb^{3 +}concentration dependences of both the Bi^{3 +}and the Yb^{3 +}emissions are investigated. The decay curve of Bi^{3 +}emission under the excitation of 355 nm pulse laser is used to explore the Bi^{3 + →}Yb^{3 +}energy transfer process. Cooperative energy transfer (CET) is discussed as a possible mechanism for the near-infrared emission.

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The fluorescence and thermoluminescence characteristics of α-Al₂O₃:C ceramics

张斌, 陆神洲, 张浩佳, 杨秋红

2010 (7): 77805-077805. doi: 10.1088/1674-1056/19/7/077805

摘要 ( 1471 )

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This paper reports that polycrystalline α-Al₂O₃:C ceramics are fabricated by conventional ceramics process. The excitation, emission spectra, thermoluminescence (TL) and optical stimulated luminescence (OSL) of α-Al₂O₃:C polycrystalline ceramics are investigated. There exists 410nm maximum emission peak which is caused by recombination of an electron with F⁺ centre to produce an excited F centre. The samples show three clear TL glow peaks at 405, 493 and 610K. The attenuation constant of exponentially decaying fast component (τ₁) and slow component(τ₂) of OSL curve are 8.43s and 41.73s, respectively. Those fluorescence and thermoluminescence characteristics are similar with α-Al₂O₃:C crystal.

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Relationship between positron bulk lifetime and lattice constants—research on NaCl-type crystals

张杰, 陈祥磊, 叶邦角

2010 (7): 77806-077806. doi: 10.1088/1674-1056/19/7/077806

摘要 ( 1473 )

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The positron lifetimes of some compounds with NaCl-type crystal structure are calculated with the method of atomic superposition approximation (ATSUP) based on the theories of local-density-approximation (LDA) and general-gradient-approximation (GGA). The systematical results are fitted to a curve as a function of lattice constants. The positron bulk lifetimes of some other compounds with NaCl-type crystal structure, which are deduced from the systematical results, are in agreement with the experimental results given in other literature.

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Discussions on the non-equilibrium effects in the quantitative phase field model of binary alloys

王志军, 王锦程, 杨根仓

2010 (7): 78101-078101. doi: 10.1088/1674-1056/19/7/078101

摘要 ( 1370 )

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All the quantitative phase field models try to get rid of the artificial factors of solutal drag, interface diffusion and interface stretch in the diffuse interface. These artificial non-equilibrium effects due to the introducing of diffuse interface are analysed based on the thermodynamic status across the diffuse interface in the quantitative phase field model of binary alloys. Results indicate that the non-equilibrium effects are related to the negative driving force in the local region of solid side across the diffuse interface. The negative driving force results from the fact that the phase field model is derived from equilibrium condition but used to simulate the non-equilibrium solidification process. The interface thickness dependence of the non-equilibrium effects and its restriction on the large scale simulation are also discussed.

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Quasistatic magnetic fields generated by a nonrelativistic intense laser pulse in uniform underdense plasma

张蕾, 董全力, 王首钧, 盛政明, 张杰

2010 (7): 78701-078701. doi: 10.1088/1674-1056/19/7/078701

摘要 ( 1667 )

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Quasistatic magnetic fields generated by nonrelativistic intense linearly polarized (LP) and circularly polarized (CP) laser pulses in an initially uniform underdense plasma in the collision-dominated limit are investigated analytically. Using a selfconsistent analytical model, we perform a detailed derivation of quasistatic magnetic fields in the laser pulse envelope in the collision-dominated limit to obtain exact analytical expressions for magnetic fields and discuss the dependence of magnetic fields on laser and plasma parameters. Equations for quasistatic magnetic fields including both axial component B_z and the azimuthal one B_θ are derived simultaneously from such a selfconsistent model. The dependence of quasistatic magnetic field on incident laser intensity, transverse focused radius of laser pulse, electron density and electron temperature is discussed.

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Active ferromagnetic shimming of the permanent magnet for magnetic resonance imaging scanner

唐昕, 洪礼明, 俎栋林

2010 (7): 78702-078702. doi: 10.1088/1674-1056/19/7/078702

摘要 ( 1476 )

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This paper presents an approach of active ferromagnetic shimming for C-type permanent magnetic resonance imaging (MRI) magnet. It is designed to reduce inhomogeneity of magnetostatic field of C-type permanent magnet to meet the stringent requirement for MRI applications. An optimal configuration (locations and thicknesses) of active ferromagnetic pieces is generated through calculation according to the initial field map and the demanded final homogeneity specifications. This approach uses a minimisation technique which makes the sum of squared magnetic moment minimum to restrict the amount of the active ferromagnetic material used and the maximal thickness of pieces stacked at each hole location in the shimming boards. Simulation and experimental results verify that the method is valid and efficient.

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Diagnosis of dynamic process over rainband of landfall typhoon

冉令坤, 杨文霞, 楚艳丽

2010 (7): 79201-079201. doi: 10.1088/1674-1056/19/7/079201

摘要 ( 1511 )

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This paper introduces a new physical parameter — thermodynamic shear advection parameter combining the perturbation vertical component of convective vorticity vector with the coupling of horizontal divergence perturbation and vertical gradient of general potential temperature perturbation. For a heavy-rainfall event resulting from the landfall typhoon 'Wipha', the parameter is calculated by using National Centres for Enviromental Prediction/National Centre for Atmospheric Research global final analysis data. The results showed that the parameter corresponds to the observed 6 h accumulative rainband since it is capable of catching hold of the dynamic and thermodynamic disturbance in the lower troposphere over the observed rainband. Before the typhoon landed, the advection of the parameter by basic-state flow and the coupling of general potential temperature perturbation with curl of Coriolis force perturbation are the primary dynamic processes which are responsible for the local change of the parameter. After the typhoon landed, the disturbance is mainly driven by the combination of five primary dynamic processes. The advection of the parameter by basic-state flow was weakened after the typhoon landed.

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Growth of linear matter perturbations and current observational constraints

付响云, 吴普训, 余洪伟

2010 (7): 79801-079801. doi: 10.1088/1674-1056/19/7/079801

摘要 ( 1327 )

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We discuss, using a recently proposed parametrization for the growth index of linear matter perturbations, the observational constraints on the wCDM model and the Dvali—Gabadadze—Porrati (DGP) model with all current growth factor data. We find that the wCDM model is allowed by the observations at the 1$\sigma$ confidence level, while the DGP model is only consistent with observations at 2$\sigma$ confidence level.

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