Table of Content

20 July 2009, Volume 18 Issue 7 Previous Issue    Next Issue

GENERAL

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Evolutionary prisoner's dilemma game on highly clustered community networks Liu Yong-Kui, Li Zhi, Chen Xiao-Jie, Wang Long 2009, 18 (7):  2623-2628.  doi: 10.1088/1674-1056/18/7/001 Abstract ( 0 )   PDF (196KB) ([an error occurred while processing this directive])   This paper studies the evolutionary prisoner's dilemma game on a highly clustered community network in which the clustering coefficient and the community size can be tuned. It finds that the clustering coefficient in such a degree-homogeneous network inhibits the emergence of cooperation for the entire range of the payoff parameter. Moreover, it finds that the community size can also have a marked influence on the evolution of cooperation, with a larger community size leading to not only a lower cooperation level but also a smaller threshold of the payoff parameter above which cooperators become extinct.

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A new method to obtain approximate symmetry of nonlinear evolution equation from perturbations Zhang Zhi-Yong, Yong Xue-Lin, Chen Yu-Fu 2009, 18 (7):  2629-2633.  doi: 10.1088/1674-1056/18/7/002 Abstract ( 0 )   PDF (153KB) ([an error occurred while processing this directive])   A novel method for obtaining the approximate symmetry of a partial differential equation with a small parameter is introduced. By expanding the independent variable and the dependent variable in the small parameter series, we obtain more affluent approximate symmetries. The method is applied to two perturbed nonlinear partial differential equations and new approximate solutions are derived.

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Noether conserved quantities and Lie point symmetries of difference Lagrange--Maxwell equations and lattices Fu Jing-Li, Nie Ning-Ming, Huang Jian-Fei, Jimé nez Salvador, Tang Yi-Fa, Vá zquez Luis, Zhao Wei-Jia 2009, 18 (7):  2634-2641.  doi: 10.1088/1674-1056/18/7/003 Abstract ( 0 )   PDF (230KB) ([an error occurred while processing this directive])   This paper presents a method to find Noether-type conserved quantities and Lie point symmetries for discrete mechanico-electrical dynamical systems, which leave invariant the set of solutions of the corresponding difference scheme. This approach makes it possible to devise techniques for solving the Lagrange--Maxwell equations in differences which correspond to mechanico-electrical systems, by adapting existing differential equations. In particular, it obtains a new systematic method to determine both the one-parameter Lie groups and the discrete Noether conserved quantities of Lie point symmetries for mechanico-electrical systems. As an application, it obtains the Lie point symmetries and the conserved quantities for the difference equation of a model that represents a capacitor microphone.

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Application of quantum algorithms to direct measurement of concurrence of a two-qubit pure state Wang Hong-Fu, Zhang Shou 2009, 18 (7):  2642-2648.  doi: 10.1088/1674-1056/18/7/004 Abstract ( 0 )   PDF (184KB) ([an error occurred while processing this directive])   This paper proposes a method to measure directly the concurrence of an arbitrary two-qubit pure state based on a generalized Grover quantum iteration algorithm and a phase estimation algorithm. The concurrence can be calculated by applying quantum algorithms to two available copies of the bipartite system, and a final measurement on the auxiliary working qubits gives a better estimation of the concurrence. This method opens new prospects of entanglement measure by the application of quantum algorithms. The implementation of the protocol would be an important step toward quantum information processing and more complex entanglement measure of the finite-dimensional quantum system with an arbitrary number of qubits.

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Relativistic thermodynamic properties of a weakly interacting Fermi gas in a weak magnetic field Men Fu-Dian, Liu Hui, Fan Zhao-Lan, Zhu Hou-Yu 2009, 18 (7):  2649-2653.  doi: 10.1088/1674-1056/18/7/005 Abstract ( 0 )   PDF (162KB) ([an error occurred while processing this directive])   This paper derives the analytical expression of free energy for a weakly interacting Fermi gas in a weak magnetic field, by using the methods of quantum statistics as well as considering the relativistic effect. Based on the derived expression, the thermodynamic properties of the system at both high and low temperatures are given and the relativistic effect on the properties of the system is discussed. It shows that, in comparison with a nonrelativistic situation, the relativistic effect changes the influence of temperature on the thermodynamic properties of the system at high temperatures, and changes the influence of particle-number density on them at extremely low temperature. But the relativistic effect does not change the influence of the magnetic field and inter-particle interactions on the thermodynamic properties of the system at both high and extremely low temperatures.

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Thermodynamic stability of interacting fermions system with matrix eigenvalue method Qin Fang, Chen Ji-Sheng 2009, 18 (7):  2654-2658.  doi: 10.1088/1674-1056/18/7/006 Abstract ( 0 )   PDF (203KB) ([an error occurred while processing this directive])   A matrix eigenvalue method is applied to analyse the thermodynamic stability of two-component interacting fermions. The non-relativistic and ultra-relativistic d=1, 2,3 dimensions have been discussed in detail, respectively. The corresponding stability region has been given according to the two-body interaction strength and the particle number density ratio.

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Effects of localized impurity on a dark soliton in a Bose--Einstein condensate with an external magnetic trap Li Hong, Wang Dong-Ning 2009, 18 (7):  2659-2666.  doi: 10.1088/1674-1056/18/7/007 Abstract ( 0 )   PDF (404KB) ([an error occurred while processing this directive])   The dynamics of a dark soliton has been investigated in a Bose--Einstein condensate with an external magnetic trap, and the effects of localized impurity on the dynamics are discussed by the variational approach based on the renormalized integrals of motion. The reciprocal movement of the dark soliton is discussed by performing a standard linear analysis, and it is found that the effects of the localized impurity depend strictly on the positive or negative value of the impurity strength corresponding to the repulsive or attractive impurity. The numerical results confirm the theoretical analysis, and show that the effects also depend on the effective nonlinear coefficient and the harmonic frequency.

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Experiment and application of parameter-induced stochastic resonance in an over-damped random linear system Jiang Shi-Qi, Hou Min-Jie, Jia Chun-Hua, He Ji-Rong, Gu Tian-Xiang 2009, 18 (7):  2667-2673.  doi: 10.1088/1674-1056/18/7/008 Abstract ( 0 )   PDF (256KB) ([an error occurred while processing this directive])   This paper investigates the parameter-induced stochastic resonance using experimental methods in an over-damped random linear system with asymmetric dichotomous noise. Non-monotonic dependence of signal-to-noise ratio on the system parameter is observed. Several potential applications of parameter-induced stochastic resonance are given in circuits.

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A novel fractional-order hyperchaotic system and its synchronization Zhou Ping, Wei Li-Jia, Cheng Xue-Feng 2009, 18 (7):  2674-2679.  doi: 10.1088/1674-1056/18/7/009 Abstract ( 0 )   PDF (230KB) ([an error occurred while processing this directive])   In this paper, a novel hyperchaotic system with one nonlinear term and its fractional order system are proposed. Furthermore, synchronization between two fractional-order systems with different fractional-order values is achieved. The proposed synchronization scheme is simple and theoretically rigorous. Numerical simulations are in agreement with the theoretical analysis.

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A novel four-wing chaotic attractor generated from a three-dimensional quadratic autonomous system Dong En-Zeng, Chen Zai-Ping, Chen Zeng-Qiang, Yuan Zhu-Zhi 2009, 18 (7):  2680-2689.  doi: 10.1088/1674-1056/18/7/010 Abstract ( 0 )   PDF (1360KB) ([an error occurred while processing this directive])   This paper presents a new 3D quadratic autonomous chaotic system which contains five system parameters and three quadratic cross-product terms, and the system can generate a single four-wing chaotic attractor with wide parameter ranges. Through theoretical analysis, the Hopf bifurcation processes are proved to arise at certain equilibrium points. Numerical bifurcation analysis shows that the system has many interesting complex dynamical behaviours; the system trajectory can evolve to a chaotic attractor from a periodic orbit or a fixed point as the proper parameter varies. Finally, an analog electronic circuit is designed to physically realize the chaotic system; the existence of four-wing chaotic attractor is verified by the analog circuit realization.

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Fine-grained permutation entropy as a measure of natural complexity for time series Liu Xiao-Feng, Wang Yue 2009, 18 (7):  2690-2695.  doi: 10.1088/1674-1056/18/7/011 Abstract ( 0 )   PDF (298KB) ([an error occurred while processing this directive])   In a recent paper [2002 Phys. Rev. Lett. 88 174102], Bandt and Pompe propose permutation entropy (PE) as a natural complexity measure for arbitrary time series which may be stationary or nonstationary, deterministic or stochastic. Their method is based on a comparison of neighbouring values. This paper further develops PE, and proposes the concept of fine-grained PE (FGPE) defined by the order pattern and magnitude of the difference between neighbouring values. This measure excludes the case where vectors with a distinct appearance are mistakenly mapped onto the same permutation type, and consequently FGPE becomes more sensitive to the dynamical change of time series than does PE, according to our simulation and experimental results.

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Critical behaviour of the ferromagnetic Ising model on a triangular lattice Luo Zhi-Huan, Loan Mushtaq, Liu Yan, Lin Jian-Rong 2009, 18 (7):  2696-2702.  doi: 10.1088/1674-1056/18/7/012 Abstract ( 0 )   PDF (249KB) ([an error occurred while processing this directive])   We use a new updated algorithm scheme to investigate the critical behaviour of the two-dimensional ferromagnetic Ising model on a triangular lattice with the nearest neighbour interactions. The transition is examined by generating accurate data for lattices with L= 8, 10, 12, 15, 20, 25, 30, 40 and 50. The updated spin algorithm we employ has the advantages of both a Metropolis algorithm and a single-update method. Our study indicates that the transition is continuous at Tc= 3.6403({2}). A convincing finite-size scaling analysis of the model yields υ=0.9995(21), β / υ = 0.12400({17}), γ / υ = 1.75223(22), γ '/υ=1.7555(22), α/υ= 0.00077(420) (scaling) and α / υ = 0.0010(42) (hyperscaling). The present scheme yields more accurate estimates for all the critical exponents than the Monte Carlo method, and our estimates are shown to be in excellent agreement with their predicted values.

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Dynamic characteristics and simulation of traffic flow with slope He Hong-Di, Lu Wei-Zhen, Xue Yu, Dong Li-Yun 2009, 18 (7):  2703-2708.  doi: 10.1088/1674-1056/18/7/013 Abstract ( 0 )   PDF (1443KB) ([an error occurred while processing this directive])   This paper proposes a new traffic model to describe traffic flow with slope under consideration of the gravity effect. Based on the model, stability analysis is conducted and a numerical simulation is performed to explore the characteristics of the traffic flow with slope. The result shows that the perturbation of the system is an inherent one, which is induced by the slope. In addition, the hysteresis loop is represented through plotting the figure of velocity against headway and highly depends on the slope angle. The kinematic wave at high density is also obtained through reproducing the phenomenon of stop-and-go traffic, which is significant to explore the phase transition of traffic flow and the evolution of traffic congestion.

ATOMIC AND MOLECULAR PHYSICS

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Density functional study of Al-doped Au clusters Zhao Li-Xia, Feng Xiao-Juan, Cao Ting-Ting, Liang Xiao, Luo You-Hua 2009, 18 (7):  2709-2718.  doi: 10.1088/1674-1056/18/7/014 Abstract ( 0 )   PDF (1960KB) ([an error occurred while processing this directive])   The equilibrium geometries and electronic properties of AunAl, up to n=13, have been systematically investigated using the density functional theory. The results show that, for the AunAl clusters, two patterns are identified. Pattern one (n=2, 3, 8), the lowest-energy geometries prefer two-dimensional structures. Pattern two (n=4-7, 9--13), the lowest-energy geometries prefer three-dimensional structures. According to the analysis of the binding energy and the fragmentation energy, AunAl clusters with odd n are found to be more stable than those with even n. The same trend of alternation can be illuminated according to the computational results in the HOMO--LUMO gap, the ionization potential, and the electron affinities. The Al atom not only changes the structures of pure gold clusters, but also enhances their stabilities. NBO analysis indicates 6s orbital of Au atom hybridizes with 3p orbital of Al atom.

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Dynamical entanglement for Fermi coupled stretching and bending modes Hou Xi-Wen, Cheng Chuan-Ming 2009, 18 (7):  2719-2723.  doi: 10.1088/1674-1056/18/7/015 Abstract ( 0 )   PDF (562KB) ([an error occurred while processing this directive])   The dynamical entanglement for Fermi coupled C--H stretch and bend vibrations in molecule CHD3 is studied in terms of two negativities and the reduced von Neumann entropy, where initial states are taken to be direct products of photon-added coherent states on each mode. It is demonstrated that the negativity defined by the sum of negative eigenvalues of the partial transpose of density matrices is positively correlated with the von Neumann entropy. The entanglement difference between photon-added coherent states and usual coherent states is discussed as well.

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Isotopic effect of Cl2+ rovibronic spectra in the A-X system Wu Ling, Yang Xiao-Hua, Chen Yang-Qin 2009, 18 (7):  2724-2728.  doi: 10.1088/1674-1056/18/7/016 Abstract ( 0 )   PDF (165KB) ([an error occurred while processing this directive])   This paper studies the isotopic effect of Cl2+ rovibronic spectra in the A2Пu (Ω = 1/2) - X2Пg(Ω= 1/2) system. Based on the experimental results of the molecular constants of 35Cl2+, it calculates the vibrational isotope shifts of the (2, 7) and (3, 7) band between the isotopic species 35Cl2+, 35Cl37Cl+ and 37Cl2+, and estimates the rotational constants of both A2Пu and X 2Пg states for the minor isotopic species 35Cl37Cl+ and 37Cl2+. The experimental results of the spectrum of 35Cl37Cl+ (3, 7) band proves the above mentioned theoretical calculation. The molecular constants and thus resultant rovibronic spectrum for 37Cl2+ were predicted, which will be helpful for further experimental investigation.

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Observation of the near transform-limited high-resolution tunable far-ultraviolet light Zheng Huai-Bin, Zhang Yan-Peng, Nie Zhi-Qiang, Li Chang-Biao, Song Jian-Ping, Li Chuang-She, Lu Ke-Qing 2009, 18 (7):  2729-2733.  doi: 10.1088/1674-1056/18/7/017 Abstract ( 0 )   PDF (408KB) ([an error occurred while processing this directive])   This paper studies the near transform-limited high-resolution tunable far-ultraviolet light which is generated by narrow-band tunable light both theoretically and experimentally. It presents the theoretical work on conversion efficiency of sum-frequency, which is restricted by phase-matching angle, walk-off angle and phase distortion and so on, and conducts an experiment to check this work successfully. Also the origin of chirp of a dye laser is analysed.

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X-ray absorption near the edge structure and x-ray photoelectron spectroscopy studies on pyrite prepared by thermally sulfurizing iron films Zhang Hui, Liu Ying-Shu, Wang Bao-Yi, Wei Long, Kui Re-Xi, Qian Hai-Jie 2009, 18 (7):  2734-2738.  doi: 10.1088/1674-1056/18/7/018 Abstract ( 0 )   PDF (695KB) ([an error occurred while processing this directive])   This paper reports how pyrite films were prepared by thermal sulfurization of magnetron sputtered iron films and characterized by x-ray absorption near edge structure spectra and x-ray photoelectron spectroscopy on a 4B9B beam line at the Beijing Synchrotron Radiation Facility. The band gap of the pyrite agrees well with the optical band gap obtained by a spectrophotometer. The octahedral symmetry of pyrite leads to the splitting of the d orbit into t_{\rm 2g} and e_{\rm g} levels. The high spin and low spin states were analysed through the difference of electron exchange interaction and the orbital crystal field. Only when the crystal field splitting is higher than 1.5 eV, the two weak peaks above the white lines can appear, and this was approved by experiments in the present work.

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Guided transmission of oxygen ions through Al2O3 nanocapillaries Chen Yi-Feng, Chen Xi-Meng, Lou Feng-Jun, Xu Jin-Zhang, Shao Jian-Xiong, Sun Guang-Zhi, Wang Jun, Xi Fa-Yuan, Yin Yong-Zhi, Wang Xing-An, Xu Jun-Kui, Cui Ying, Ding Bao-Wei 2009, 18 (7):  2739-2743.  doi: 10.1088/1674-1056/18/7/019 Abstract ( 0 )   PDF (814KB) ([an error occurred while processing this directive])   The transmissions of oxygen ions through Al2O3 nanocapillaries each 50~nm in diameter and 10~μ m in length at a series of different tilt angles are measured, where the ions with energies ranging from 10 to 60~keV and charge states from 1 up to 6 are involved. The angular distribution and the transmission yields of transported ions are investigated. Our results indicate both the existence of a guiding effect when ions pass through the capillary and a significant dependence of the ion transmission on the energy and the charge state of the ions. The guiding effects are observed to be enhanced at lower projectile energies and higher charge states. Meanwhile, the results also exhibit that the transmission yields increase as the tilt angle decreases at a given energy and charge state.

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The effect of dynamical screening on helium (e, 2e) fully differential cross-sections Sun Shi-Yan, Jia Xiang-Fu, Miao Xiang-Yang, Zhang Jun-Feng, Xie Yi, Li Xiong-Wei, Shi Wen-Qiang 2009, 18 (7):  2744-2748.  doi: 10.1088/1674-1056/18/7/020 Abstract ( 0 )   PDF (1041KB) ([an error occurred while processing this directive])   This paper presents the fully differential cross sections (FDCS) for 102eV electron impact single ionization of helium for both the coplanar and perpendicular plane asymmetric geometries within the framework of dynamically screened three-Coulomb-wave theory. Comparisons are made with the experimental data and those of the three-Coulomb wave function model and second-order distorted-wave Born method. The angular distribution and relative heights of the present FDCS is found to be in very good agreement with the experimental data in the perpendicular plane geometry. It is shown that dynamical screening effects are significant in this geometry. Three-body coupling is expected to be weak in the coplanar geometry, although the precise absolute value of the cross section is still sensitive to the interaction details.

CLASSICAL AREAS OF PHENOMENOLOGY

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Small-signal analysis of a rectangular helix structure traveling-wave-tube Fu Cheng-Fang, Wei Yan-Yu, Duan Zhao-Yun, Wang Wen-Xiang, Gong Yu-Bin 2009, 18 (7):  2749-2756.  doi: 10.1088/1674-1056/18/7/021 Abstract ( 0 )   PDF (1350KB) ([an error occurred while processing this directive])   This paper investigates the properties of traveling wave-beam interaction in a rectangular helix traveling-wave-tube (TWT) for a solid sheet electron beam. The `hot' dispersion equation is obtained by means of the self-consistent field theory. The small signal analysis, which includes the effects of the beam parameters and slow-wave structure (SWS) parameters, is carried out by theoretical computation. The numerical results show that the bandwidth and the small-signal gain of the rectangular helix TWT increase as the beam current increases; and the beam voltage not obviously influences the small signal gain. Among different rectangular helix structures, the small-signal gain increases as the width of the rectangular helix SWS increases, however, the bandwidth decreases whether structure parameters a and L or ψ and L are fixed or not. In addition, a comparison of the small-signal gain of this structure with a conventional round helix is made. The presented analysis will be useful for the design of the TWT with a rectangular helix circuit.

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Investigation of composite electromagnetic scattering from ship-like target on the randomly rough sea surface using FDTD method Li Juan, Guo Li-Xin, Zeng Hao, Han Xu-Biao 2009, 18 (7):  2757-2763.  doi: 10.1088/1674-1056/18/7/022 Abstract ( 0 )   PDF (282KB) ([an error occurred while processing this directive])   Composite electromagnetic scattering from a two-dimensional (2D) ship-like target on a one-dimensional sea surface is investigated by using the finite-difference time-domain (FDTD) method. A uniaxial perfectly matched layer is adopted for truncation of FDTD lattices. The FDTD updated equations can be used for the total computation domain by choosing the uniaxial parameters properly. To validate the proposed numerical technique, a 2D infinitely long cylinder over the sea surface is taken into account first. The variation of angular distribution of the scattering changing with incident angle is calculated. The results show good agreement with the conventional moment method. Finally, the influence of the incident angle, the polarization, and the size of the ship-like target on the composite scattering coefficient is discussed in detail.

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A new method of aperture synthetizing in digital holography Zhang Qing-Sheng, Lü Xiao-Xu, Yu Qing-Ting, Liu Gan-Yong 2009, 18 (7):  2764-2768.  doi: 10.1088/1674-1056/18/7/023 Abstract ( 0 )   PDF (1155KB) ([an error occurred while processing this directive])   This paper proposes a new method of aperture synthetizing in digital holography based on the principle of holography. In the new method aperture synthetizing is achieved by reconstructing each sub-hologram respectively, firstly, moving each reconstructed wave field referred to the benchmark reconstructed wave field according to the relationship between spacial motion and frequency shift, and finally splicing them by using superposition. Two different recording ways, using plane wave to record and using spherical wave to record, are analyzed, and their moving formula is deduced, too. Simulation and experiment are done. The results show that in comparison with the traditional method of aperture synthetizing in digital holography, the new method can decrease calculation and save reconstructed time obviously which has better applicability.

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Correcting dynamic residual aberrations of conformal optical systems using AO technology Li Yan, Li Lin, Huang Yi-Fan, Du Bao-Lin 2009, 18 (7):  2769-2773.  doi: 10.1088/1674-1056/18/7/024 Abstract ( 0 )   PDF (242KB) ([an error occurred while processing this directive])   This paper analyses the dynamic residual aberrations of a conformal optical system and introduces adaptive optics (AO) correction technology to this system. The image sharpening AO system is chosen as the correction scheme. Communication between MATLAB and Code V is established via ActiveX technique in computer simulation. The SPGD algorithm is operated at seven zoom positions to calculate the optimized surface shape of the deformable mirror. After comparison of performance of the corrected system with the baseline system, AO technology is proved to be a good way of correcting the dynamic residual aberration in conformal optical design.

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Study on the design and Zernike aberrations of a segmented mirror telescope Jiang Zhen-Yu, Li Lin, Huang Yi-Fan 2009, 18 (7):  2774-2778.  doi: 10.1088/1674-1056/18/7/025 Abstract ( 0 )   PDF (1567KB) ([an error occurred while processing this directive])   The segmented mirror telescope is widely used. The aberrations of segmented mirror systems are different from single mirror systems. This paper uses the Fourier optics theory to analyse the Zernike aberrations of segmented mirror systems. It concludes that the Zernike aberrations of segmented mirror systems obey the linearity theorem. The design of a segmented space telescope and segmented schemes are discussed, and its optical model is constructed. The computer simulation experiment is performed with this optical model to verify the suppositions. The experimental results confirm the correctness of the model.

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Fractional Fourier transform of Lorentz beams Zhou Guo-Quan 2009, 18 (7):  2779-2784.  doi: 10.1088/1674-1056/18/7/026 Abstract ( 0 )   PDF (1416KB) ([an error occurred while processing this directive])   This paper introduces Lorentz beams to describe certain laser sources that produce highly divergent fields. The fractional Fourier transform (FRFT) is applied to treat the propagation of Lorentz beams. Based on the definition of convolution and the convolution theorem of the Fourier transform, an analytical expression for a Lorentz beam passing through a FRFT system has been derived. By using the derived formula, the properties of a Lorentz beam in the FRFT plane are illustrated numerically.

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The transmission enhancement of a THz pulse through an Ag/Ag2O layer detected by terahertz time-domain spectroscopy Chen Hua, and Wang Li 2009, 18 (7):  2785-2787.  doi: 10.1088/1674-1056/18/7/027 Abstract ( 0 )   PDF (896KB) ([an error occurred while processing this directive])   This paper reports a new way to detect the enhanced transmission of a THz electromagnetic wave through an Ag/Ag2O layer by THz-TDS (time-domain spectroscopy). As the THz beam illuminates the sub-wavelength Ag particles gained by Ag2O thermal decomposition, the evanescent wave is generated. The evanescent wave is coupled by a 500μ m-GaAs substrate, which attaches behind the Ag/Ag2O layer, and then it transmits to the far field to be detected. The experimental results indicate that the transmitting amplitude is enhanced, as well as the frequent shifting and spectra broadening.

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Dispersion effect in optical microscopy systems with a supersphere solid immersion lens Zhang Yao-Ju, Zhuang You-Yi 2009, 18 (7):  2788-2793.  doi: 10.1088/1674-1056/18/7/028 Abstract ( 0 )   PDF (605KB) ([an error occurred while processing this directive])   This paper studies the dispersion effect of the supersphere solid immersion lens (SIL) on a near field optical microscopy system by using the vector diffraction theory. Results show that when a real non-monochromatic beam illuminates a supersphere SIL microscopy, the dispersion effect of the SIL has an important influence on the image quality. As the wavelength bandwidth of the non-monochromatic beam increases, the size of the focused spot increases and its intensity decreases in near-field microscopy systems with a supersphere SIL.

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Quantum entanglement between the two-mode fields and atomic entropy squeezing in the system of a moving atom interacting with two-mode entangled coherent field Zou Yan, Li Yong-Ping 2009, 18 (7):  2794-2800.  doi: 10.1088/1674-1056/18/7/029 Abstract ( 0 )   PDF (233KB) ([an error occurred while processing this directive])   This paper investigates the entropy squeezing of a moving two-level atom interacting with the two-mode entangled coherent field via two-photon transition by using an entropic uncertainty relation and the degree of entanglement between the two-mode fields by using quantum relative entropy. The results obtained from numerical calculation indicate that the squeezed period, the duration of entropy squeezing and the maximal squeezing can be controlled by appropriately choosing the intensity of the light field, the atomic motion and the field-mode structure. The atomic motion leads to the periodic recovery of the initial maximal degree of entanglement between the two-mode fields. Moreover, there exists a corresponding relation between the time evolution properties of the atomic entropy squeezing and those of the entanglement between the two-mode fields.

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A dual-loop Sagnac interferometer Ma Hai-Qiang, Zhao Jian-Ling, Wu Ling-An 2009, 18 (7):  2801-2805.  doi: 10.1088/1674-1056/18/7/030 Abstract ( 0 )   PDF (161KB) ([an error occurred while processing this directive])   A new type of all-fibre Sagnac interferometer composed of two loops is proposed and analysed in detail. It can be used with a very long transmission line while maintaining excellent performance characteristics due to the automatic compensation of any birefringence effects in the trunk fibre. Preliminary experiments at 1310~nm wavelength with a 70~km long trunk fibre demonstrated an interference visibility as high as 98%, indicating that this scheme has promising potential applications.

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Influence of spherical aberrations on fundamental mode beam quality under different laser resonators Xiang Zhen, Hu Miao, Ge Jian-Hong, Zhao Zhi-Gang, Wang Sha, Liu Chong, Chen Jun 2009, 18 (7):  2806-2815.  doi: 10.1088/1674-1056/18/7/031 Abstract ( 0 )   PDF (773KB) ([an error occurred while processing this directive])   Spherical aberrations of the thermal lens of the active media are severe when solid state lasers are strongly pumped. The fundamental mode profile deteriorates due to the aberrations. Self-consistent modes of a resonator with aberrations are calculated by using the Fox--Li diffraction iterative algorithm. Calculation results show that the aberration induced fundamental mode beam quality deterioration depends greatly on the resonator design. The tolerance of a flat--flat resonator to the aberration coefficient is about 30λ in the middle of stability, where λ is the wavelength of laser beam. But for a dynamically stable resonator, 2λ of spherical aberration will create diffraction loss of more than 40%, if inappropriate design criteria are used. A birefringence compensated laser resonator with two Nd:YAG rods is experimentally studied. The experimental data are in quite good agreement with simulation results.

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Interactions of chirped femtosecond solitonlike pulses Song Li-Jun, Wu Liang, Zhang Yan-Feng, Yang Rong-Cao 2009, 18 (7):  2816-2821.  doi: 10.1088/1674-1056/18/7/032 Abstract ( 0 )   PDF (518KB) ([an error occurred while processing this directive])   This paper studies the interactions between two and more adjacent chirped soliton-like pulses, respectively. The results show that the pulses present strong interactions when the separations between them are smaller than a certain value, and their behaviour is very distinct under different conditions, such as a different number of pulses or different initial separations between them. Furthermore, we also study the suppression of these interactions and obtain very good effects by using different initial amplitude ratios.

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Gaussian solitons in nonlocal media: variational analysis Shen Ming, Xi Ning, Kong Qian, Ge Li-Juan, Shi Jie-Long, Wang Qi 2009, 18 (7):  2822-2827.  doi: 10.1088/1674-1056/18/7/033 Abstract ( 0 )   PDF (289KB) ([an error occurred while processing this directive])   Exact solutions of Gaussian solitons in nonlinear media with a Gaussian nonlocal response are obtained. Using the variational approach, we obtain the approximate solutions of such solitons when the degree of the nonlocality is arbitrary. Specifically, we study the conditions for Gaussian solitons that propagate in weakly and highly nonlocal media. We also compare the variational result with the known exact solutions for weakly and highly nonlocal media.

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Concentration dependent nonlinear refraction in chloroaluminum phthalocyanine/ethanol solution Yang Jun-Yi, Song Ying-Lin, Gu Ji-Hua 2009, 18 (7):  2828-2834.  doi: 10.1088/1674-1056/18/7/034 Abstract ( 0 )   PDF (235KB) ([an error occurred while processing this directive])   Nonlinear refractive properties of chloroaluminum phthalocyanine (CAP) in ethanol solution are studied using the Z-scan technique with picosecond (ps) and nanosecond (ns) laser pulses at a wavelength of 532 nm. A transition from self-focusing to self-defocusing in CAP solution excited by 10 ns pulses is observed during the decrease of its concentration. This transition is due to co-existing excited-state refraction and transient thermal lensing effects. The experimental results are described very well using the rate-equation model and the theory of transient thermal refraction in liquids. The refractive cross sections of the excited-state are also obtained.

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Investigation on the effect of beam divergence angle upon output waveform based on stimulated Brillouin scattering optical limiting Hasi Wu-Li-Ji, Lu Huan-Huan, Gong Sheng, Fu Mei-Ling, Lü Zhi-Wei, Lin Dian-Yang, He Wei-Ming 2009, 18 (7):  2835-2838.  doi: 10.1088/1674-1056/18/7/035 Abstract ( 0 )   PDF (382KB) ([an error occurred while processing this directive])   This paper investigates the effect of beam divergence angle on output waveform based on stimulated Brillouin scattering optical limiting. Output waveforms in the case of different pump divergence angles are numerically simulated, and validated in a Nd:YAG seed-injected laser system. The results indicate that a small pump divergence angle can lead to good interaction between pump and Stokes, and a platform can be easily realized in the transmitted waveform. In contrast, a peak followed by the platform appears when the divergence angle becomes large.

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Temporal behaviour of open-circuit photovoltaic solitons Zhang Mei-Zhi, Lu Ke-Qing, Cheng Guang-Hua, Li Ke-Hao, Zhang Yi-Qi, Zhang Yu-Hong, Zhang Yan-Peng 2009, 18 (7):  2839-2845.  doi: 10.1088/1674-1056/18/7/036 Abstract ( 0 )   PDF (1440KB) ([an error occurred while processing this directive])   Based on the time-dependent band-transport model in a photorefractive medium, dark open-circuit photovoltaic (PV) solitons are investigated both theoretically and experimentally. Compared with those of the time-independent models, our theoretical results revealed that quasi-steady-state and steady-state PV solitons can both be obtained. Our results also revealed that when r < 1 (r is the normalized intensity at infinity), the full width at half maximum (FWHM) of solitons decreases monotonically to a constant value; when r > 1, however, the FWHM of solitons first decreases to a minimum before it increases to a constant value. Moreover, the FWHM of steady solitons decreases with increasing intensity ratio for r < 1, and increases with increasing intensity ratio for r > 1. We further observed dark PV solitons in experiments, and recorded their evolution. These results indicated that steady solitons can be observed at low optical power, while quasi-steady-state solitons can only be generated at higher optical power. Good agreement is found between theory and experiment.

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Investigation of pump-wavelength dependence of terahertz-wave parametric oscillator based on LiNbO3 Sun Bo, Liu Jin-Song, Li En-Bang, Yao Jian-Quan 2009, 18 (7):  2846-2852.  doi: 10.1088/1674-1056/18/7/037 Abstract ( 0 )   PDF (972KB) ([an error occurred while processing this directive])   This paper investigates the performances of terahertz-wave parametric oscillators (TPOs) based on the LiNbO3 crystal at different pump wavelengths. The calculated results show that TPO characteristics, including the frequency tuning range, the THz-wave gain and the stability of THz-wave output direction based on the Si-prism coupler, can be significantly improved by using a short-wavelength pump. It also demonstrates that a long-wavelength-pump allows the employment of a short TPO cavity due to an enlarged phase-matching angle, that is, an increased angular separation between the pump and oscillated Stokes beams under the THz-wave generation at a specific frequency. The study provides an useful guide and a theoretical basis for the further improvement of TPO systems.

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Variational solutions for Hermite--Gaussian solitons in nonlocal nonlinear media Bai Dong-Feng, Huang Chang-Chun, He Jun-Feng, Wang Yi 2009, 18 (7):  2853-2857.  doi: 10.1088/1674-1056/18/7/038 Abstract ( 0 )   PDF (331KB) ([an error occurred while processing this directive])   The physical features exhibited by Hermite--Gaussian (HG) beams propagating in nonlocal nonlinear media with Gaussian-shaped response are discussed with an approximate variational method. Using direct numerical simulations, we find that the beam properties in the normalized system are different with the change of the degree of nonlocality. It is shown that initial HG profiles break up into several individual beams with propagation when the degree of nonlocality α is small. HG beams can propagate stably when α is large enough.

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The photosensitive effect of Ce on the precipitation of Ag nanoparticles induced by femtosecond laser in silicate glass Dai Ye, Qiu Jian-Rong 2009, 18 (7):  2858-2863.  doi: 10.1088/1674-1056/18/7/039 Abstract ( 0 )   PDF (1167KB) ([an error occurred while processing this directive])   This paper studies the photosensitive effect of cerium oxide on the precipitation of Ag nanoparticles after femtosecond laser irradiating into silicate glass and successive annealing. Spectroscopy analysis and diffraction efficiency measurements show that the introduction of cerium oxide may increase the concentration of Ag atoms in the femtosecond laser-irradiated regions resulting from the photoreduction reaction Ce3+ + Ag+ \to Ce3+ + Ag0 via multiphoton excitation. These results promote the aggregation of Ag nanoparticles during the annealing process. It is also found that different concentrations of cerium oxide may influence the Ag nanoparticle precipitation in the corresponding glass.

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The design of a photonic crystal filter in the terahertz range Zhao Xing-Xing, Zhu Qiao-Fen, Zhang Yan 2009, 18 (7):  2864-2867.  doi: 10.1088/1674-1056/18/7/040 Abstract ( 0 )   PDF (309KB) ([an error occurred while processing this directive])   One-dimensional photonic crystal structures for multiple channeled filtering and polarization selective filtering in the terahertz (THz) range are studied theoretically. The design of aperiodic photonic quantum-well (APQW) structures for multiple channeled filtering and different polarization filtering at arbitrary preassigned frequencies are achieved by using the simulated annealing algorithm with a special merit function. The parameters of these filters can be expediently controlled and the transmission characters are polarization dependent. Numerical simulations show that the designed APQWs can meet the desired specification well.

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Application of sampled grating to control the lasing wavelength in complex-coupled DFB laser Wang Huan, Zhu Hong-Liang, Jia Ling-Hui, Chen Xiang-Fei, Kong Duan-Hua, Wang Lie-Song, Zhang Wei, Zhao Ling-Juan, Wang Wei 2009, 18 (7):  2868-2872.  doi: 10.1088/1674-1056/18/7/041 Abstract ( 0 )   PDF (1362KB) ([an error occurred while processing this directive])   This paper reports that the complex-coupled distributed feedback laser with the sampled grating has been designed and fabricated. The +1st order reflection of the sampled grating is utilized for laser single mode operation, which is 1.5387~μ m in the experiment. The typical threshold current of the device is 30~mA, and the optical output power is about 10~mW at the injection current of 100~mA.

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Modified KdV equation for solitary Rossby waves with β effect in barotropic fluids Song Jian, Yang Lian-Gui 2009, 18 (7):  2873-2877.  doi: 10.1088/1674-1056/18/7/042 Abstract ( 0 )   PDF (152KB) ([an error occurred while processing this directive])   This paper uses the weakly nonlinear method and perturbation method to deal with the quasi-geostrophic vorticity equation, and the modified Korteweg-de Vries(mKdV) equations describing the evolution of the amplitude of solitary Rossby waves as the change of Rossby parameter β(y) with latitude y is obtained.

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Lattice Boltzmann simulation of behaviour of particles moving in blood vessels under the rolling massage Yi Hou-Hui, Yang Xiao-Feng, Wang Cai-Feng, Li Hua-Bing 2009, 18 (7):  2878-2884.  doi: 10.1088/1674-1056/18/7/043 Abstract ( 0 )   PDF (269KB) ([an error occurred while processing this directive])   The rolling massage is one of the most important manipulations in Chinese massage, which is expected to eliminate many diseases. Here, the effect of the rolling massage on a pair of particles moving in blood vessels under rolling massage manipulation is studied by the lattice Boltzmann simulation. The simulated results show that the motion of each particle is considerably modified by the rolling massage, and it depends on the relative rolling velocity, the rolling depth, and the distance between particle position and rolling position. Both particles' translational average velocities increase almost linearly as the rolling velocity increases, and obey the same law. The increment of the average relative angular velocity for the leading particle is smaller than that of the trailing one. The result is helpful for understanding the mechanism of the massage and to further develop the rolling techniques.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Calculating the dielectric anisotropy of nematic liquid crystals: a reinvestigation of the Maier--Meier theory Zhang Ran, He Jun, Peng Zeng-Hui, Xuan Li 2009, 18 (7):  2885-2892.  doi: 10.1088/1674-1056/18/7/044 Abstract ( 0 )   PDF (338KB) ([an error occurred while processing this directive])   This paper investigates the average dielectric permittivity (\overline ε ) in the Maier--Meier theory for calculating the dielectric anisotropy (Δε) of nematic liquid crystals. For the reason that \overline ε of nematics has the same expression as the dielectric permittivity of the isotropic state, the Onsager equation for isotropic dielectric was used to calculate it. The computed \overline ε shows reasonable agreement with the results of the numerical methods used in the literature. Molecular parameters, such as the polarizability and its anisotropy, the dipole moment and its angle with the molecular long axis, were taken from semi-empirical quantum chemistry (MOCPAC/AM1) modeling. The calculated values of Δε according to the Maier--Meier equation are in good agreement with the experimental results for the investigated compounds having different core structures and polar substituents.

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Floating-zone growth and property characterizations of high-quality La2-xSrxCuO4 superconductor crystals Shen Xiao-Li, Li Zheng-Cai, Shen Cai-Xia, Lu Wei, Dong Xiao-Li, Zhou Fang, Zhao Zhong-Xian 2009, 18 (7):  2893-2897.  doi: 10.1088/1674-1056/18/7/045 Abstract ( 0 )   PDF (1189KB) ([an error occurred while processing this directive])   We have grown underdoped (x = 0.11, 0.12) and optimally doped (x = 0.16) La2-xSrxCuO4 single crystals by the traveling-solvent floating-zone technique. In order to prepare good quality cuprate crystals, we have made much effort to optimize the preparation procedures. For example, we haveadopted the sol--gel route to prepare a highly fine and homogeneous La2-xSrxCuO4 precursor powder for fabricating a very dense ceramic feed rod used for the floating-zone growth, and we have also used quite a slow growth rate. The high quality of the grown crystals has been verified by double-crystal x-ray rocking curves, with the full-width-at-half-maximum being only 113--150 arcseconds, which are the best data reported so far for La2-xSrxCuO4 crystals. The superconducting critical temperatures of the grown crystals are 30, 31 and 38.5~K for x = 0.11, 0.12 and 0.16 samples, respectively, according to magnetic measurements.

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Theoretical study of a melting curve for tin Xi Feng, Cai Ling-Cang 2009, 18 (7):  2898-2900.  doi: 10.1088/1674-1056/18/7/046 Abstract ( 0 )   PDF (152KB) ([an error occurred while processing this directive])   The melting curve of Sn has been calculated using the dislocation-mediated melting model with the `zone-linking method'. The results are in good agreement with the experimental data. According to our calculation, the melting temperature of γ -Sn at zero pressure is about 436~K obtained by the extrapolation of the method from the triple point of Sn. The results show that this calculation method is better than other theoretical methods for predicting the melting curve of polymorphic material Sn.

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A novel approach to topological defects in a vector order parameter system Ren Ji-Rong, Rong Shu-Jun, Zhu Tao 2009, 18 (7):  2901-2904.  doi: 10.1088/1674-1056/18/7/047 Abstract ( 0 )   PDF (156KB) ([an error occurred while processing this directive])   Based on Duan's topological current theory, we propose a novel approach to study the topological properties of topological defects in a two-dimensional complex vector order parameter system. This method shows explicitly the fine topological structure of defects. The branch processes of defects in the vector order parameter system have also been investigated with this method.

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On the core structure and mobility of the <100>{010} and <100>{011} dislocations in B2 structure YAg and YCu Wu Xiao-Zhi, Wang Shao-Feng, Liu Rui-Ping 2009, 18 (7):  2905-2911.  doi: 10.1088/1674-1056/18/7/048 Abstract ( 0 )   PDF (221KB) ([an error occurred while processing this directive])   Dislocations are thought to be the principal mechanism of high ductility of the novel B2 structure intermetallic compounds YAg and YCu. In this paper, the edge dislocation core structures of two primary slip systems <100>{010} and <100>{01\overline{1}} for YAg and YCu are presented theoretically within the lattice theory of dislocation. The governing dislocation equation is a nonlinear integro-differential equation and the variational method is applied to solve the equation. Peierls stresses for <100>{010} and <100>{01\overline{1}} slip systems are calculated taking into consideration the contribution of the elastic strain energy. The core width and Peierls stress of a typical transition-metal aluminide NiAl is also reported for the purpose of verification and comparison. The Peierls stress of NiAl obtained here is in agreement with numerical results, which verifies the correctness of the results obtained for YAg and YCu. Peierls stresses of the <100>{01\overline{1}} slip system are smaller than those of <100>{010} for the same intermetallic compounds originating from the smaller unstable stacking fault energy. The obvious high unstable stacking fault energy of NiAl results in a larger Peierls stress than those of YAg and YCu although they have the same B2 structure. The results show that the core structure and Peierls stress depend monotonically on the unstable stacking fault energy.

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Degraded model of radiation-induced acceptor defects for GaN-based high electron mobility transistors (HEMTs) Fan Long, Hao Yue, Zhao Yuan-Fu, Zhang Jin-Cheng, Gao Zhi-Yuan, Li Pei-Xian 2009, 18 (7):  2912-2919.  doi: 10.1088/1674-1056/18/7/049 Abstract ( 0 )   PDF (275KB) ([an error occurred while processing this directive])   Using depletion approximation theory and introducing acceptor defects which can characterize radiation induced deep-level defects in AlGaN/GaN heterostructures, we set up a radiation damage model of AlGaN/GaN high electron mobility transistor (HEMT) to separately simulate the effects of several main radiation damage mechanisms and the complete radiation damage effect simultaneously considering the degradation in mobility. Our calculated results, consistent with the experimental results, indicate that thin AlGaN barrier layer, high Al content and high doping concentration are favourable for restraining the shifts of threshold voltage in the AlGaN/GaN HEMT; when the acceptor concentration induced is less than 1014cm-3, the shifts in threshold voltage are not obvious; only when the acceptor concentration induced is higher than 1016cm-3, will the shifts of threshold voltage remarkably increase; the increase of threshold voltage, resulting from radiation induced acceptor, mainly contributes to the degradation in drain saturation current of the current--voltage (I--V) characteristic, but has no effect on the transconductance in the saturation area.

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Thermal stability of silicon nanowires: atomistic simulation study Liu Wen-Liang, Zhang Kai-Wang, Zhong Jian-Xin 2009, 18 (7):  2920-2924.  doi: 10.1088/1674-1056/18/7/050 Abstract ( 0 )   PDF (536KB) ([an error occurred while processing this directive])   Using the Stillinger--Weber (SW) potential model, we investigate the thermal stability of pristine silicon nanowires based on classical molecular dynamics (MD) simulations. We explore the structural evolutions and the Lindemann indices of silicon nanowires at different temperatures in order to unveil atomic-level melting behaviour of silicon nanowires. The simulation results show that silicon nanowires with surface reconstructions have higher thermal stability than those without surface reconstructions, and that silicon nanowires with perpendicular dimmer rows on the two (100) surfaces have somewhat higher thermal stability than nanowires with parallel dimmer rows on the two (100) surfaces. Furthermore, the melting temperature of silicon nanowires increases as their diameter increases and reaches a saturation value close to the melting temperature of bulk silicon. The value of the Lindemann index for melting silicon nanowires is 0.037.

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Nanoporous AlN particles production from a solid-state metathesis reaction Yan Guo-Jun, Chen Guang-De, Wu Ye-Long 2009, 18 (7):  2925-2927.  doi: 10.1088/1674-1056/18/7/051 Abstract ( 0 )   PDF (1329KB) ([an error occurred while processing this directive])   This paper reports that nanoporous AlN particles are synthesized from solid-state metathesis reactions using AlCl3 and Mg3N2 as reactants. The samples are characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction, high-resolution transmission electron microscopy (HRTEM), ultraviolet--visible (UV--vis) absorption spectroscopy and Raman spectroscopy. The results show that samples with walls 10 nm in thickness and pores between 10 nm and 100 nm in diameter were produced successfully from these reactions, and their band gap and vibration modes agree with those of AlN bulk crystal.

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

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Phonon spectra of La0.5Ca2MnO3 Cao Xian-Sheng, Chen Chang-Le 2009, 18 (7):  2928-2932.  doi: 10.1088/1674-1056/18/7/052 Abstract ( 0 )   PDF (198KB) ([an error occurred while processing this directive])   This paper presents a microscopic theory to explain different Raman modes of La0.5Ca0.5MnO3 based on the electronic Hamiltonian of the Kondo lattice model, which adds phonon interaction to the hybridization between the conduction electrons of the system and the l-electrons. The spectral density is calculated by the Green function technique of Zubarev at zero wave vector and in the low temperature limit. It finds that there are three Raman-active modes and the spectral densities of these modes are substantially influenced by model parameters such as the position of l-level (εJT), the effective electron--phonon coupling strength (g) and the hybridization parameter (v). Finally, the intensity changes of those peaks are investigated.

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Atomic and electronic structures of montmorillonite in soft rock He Man-Chao, Fang Zhi-Jie, Zhang Ping 2009, 18 (7):  2933-2937.  doi: 10.1088/1674-1056/18/7/053 Abstract ( 0 )   PDF (1288KB) ([an error occurred while processing this directive])   Montmorillonite is a kind of clay mineral which often causes large deformation in soft-rock tunnel engineering and thus brings about safety problems in practice. To deal with these engineering safety problems, the physical and chemical properties of montmorillonite should be studied from basic viewpoints. We study the atomic and electronic structures of montmorillonite by using density-functional theory within the local-density approximation (LDA). The results of calculation show that Al--O bond lengths are longer than Si--O bond lengths. It is found that both the valence band maximum (VBM) and the conduction band minimum (CBM) of montmorillonite are at point Γ, and the calculated direct band gap of montmorillonite is 5.35~eV. We show that the chemical bonding between cations and oxygen anions in montmorillonite is mainly ionic, accompanied as well by a minor covalent component. It is pointed out that the VBM and CBM of montmorillonite consist of oxygen 2p and cation s states, respectively. Our calculated results help to understand the chemical and physical properties of montmorillonite, and are expected to be a guide for solving the problem of large deformation of soft-rock tunnels.

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Electronic and optical properties of the zinc-blende structured LiZnN under pressure Chang Jing, Lan Jun-Qing, Ai Qiong, Chen Xiang-Rong 2009, 18 (7):  2938-2944.  doi: 10.1088/1674-1056/18/7/054 Abstract ( 0 )   PDF (367KB) ([an error occurred while processing this directive])   The electronic and optical properties of the cubic zinc-blende (ZB) structured filled tetrahedral semiconductor α-LiZnN under pressure are investigated by using \textit{ab initio} plane wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The electronic band structure and the density of state under pressure are systematically described. The basic optical constants, including the reflection and absorption spectra, the energy-loss function, the complex refractive index and the dielectric function, are calculated and analysed at different external pressures. Our results suggested that the ZB α-LiZnN is transparent in the partially ultra-violet to the visible light region, and it seems that the transparency is hardly affected by the pressure.

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Electronic structure and optical properties of Nb-doped Sr2TiO4 by density function theory calculation Yun Jiang-Ni, Zhang Zhi-Yong 2009, 18 (7):  2945-2952.  doi: 10.1088/1674-1056/18/7/055 Abstract ( 0 )   PDF (1486KB) ([an error occurred while processing this directive])   This paper investigates the effect of Nb doping on the electronic structure and optical properties of Sr2TiO4 by the first-principles calculation of plane wave ultra-soft pseudo-potential based on density functional theory (DFT). The calculated results reveal that due to the electron doping, the Fermi level shifts into conduction bands(CBs) for Sr2NbxTi1-xO4 with x=0.125 and the system shows n-type degenerate semiconductor features. Sr2TiO4 exhibits optical anisotropy in its main crystal axes, and the c-axis shows the most suitable crystal growth direction for obtaining a wide transparent region. The optical transmittance is higher than 90% in the visible range for Sr2Nb0.125Ti0.875O4.

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First-principles study on magnetism of different dimensional Ru systems Zhu Qiu-Xiang, Pang Hua, Li Fa-Shen 2009, 18 (7):  2953-2960.  doi: 10.1088/1674-1056/18/7/056 Abstract ( 0 )   PDF (278KB) ([an error occurred while processing this directive])   The magnetism, the magnetocrystalline anisotropy and the optical properties of the monolayer and atomic chain of 4d transition-metal Ru are investigated by using the full-potential linearized-augmented-plane-wave method in a generalized gradient approximation. The magnetic moments are 1.039~μ _B/atom and 1.130~μB/atom for the monolayer and atomic chain, respectively. Both systems have large magnetocrystalline anisotropy energy (MAE). The magnetic easy axis is normal to the monolayer and perpendicular to the chain axis in the atomic chain. The optical properties of the two low-dimensional Ru systems are investigated by calculating the complex optical conductivity tensor. Both systems exhibit anisotropy in photoconductivity, especially for the atomic chain. The physical origins of MAE and photoconductivity are studied based on electronic structures. It is found that the changes in crystal field caused by different symmetry-breaking mechanisms in the two low-dimensional Ru systems result in MAE through spin--orbit coupling, while the anisotropy in photoconductivity mainly comes from the crystallographic anisotropy.

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Effect of interchain coupling on a biexciton in organic polymers Gao Kun, Xie Shi-Jie, Li Yuan, Yin Sun, Liu De-Sheng, Zhao Xian 2009, 18 (7):  2961-2966.  doi: 10.1088/1674-1056/18/7/057 Abstract ( 0 )   PDF (201KB) ([an error occurred while processing this directive])   The effect of interchain coupling on the formation and the stability of a biexciton is studied in poly (p-phenylene vinylene) chains in the framework of the tight-binding approach. We obtain an intrachain exciton and biexciton as well as an interchain exciton and biexciton through a double-photon excitation. It is found that a biexciton is energetically favourable to two single excitons even when there exists an interchain coupling. There is a turnover value t⊥C of the interchain coupling for the formation of a biexciton, beyond which two excitons are combined into one biexciton. The binding energy of a biexciton is calculated to decrease with the increase of interchain coupling, which indicates that a biexciton is relatively stable in polymers with a weak interchain coupling. The conclusion is consistent with the experimental observations. In addition, a suggestion about how to improve the yielding efficiency or the formation of biexcitons in actual applications is given.

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Effect of local structure on electron paramagnetic resonance spectra for trigonal [Cr(H2O)6]3+coordination complex in the sulfate alums series: a ligand field theory study Li Yan-Fang, Kuang Xiao-Yu, Gao Ming-Liang, Zhao Ya-Ru, Wang Huai-Qian 2009, 18 (7):  2967-2974.  doi: 10.1088/1674-1056/18/7/058 Abstract ( 0 )   PDF (855KB) ([an error occurred while processing this directive])   A simple theoretical method is introduced for studying the interrelation between electronic and molecular structures. By diagonalizing the 120× 120 complete energy matrices, the relationships between zero-field splitting (ZFS) parameter D and local distortion parameter Δθ for Cr3+ ions doped, separately, in α- and β- alums are investigated. Our results indicate that there exists an approximately linear relationship between D and Δθ in a temperature range 4.2--297~K and the signs of D and Δθ are opposite to each other. Moreover, in order to understand the contribution of spin--orbit coupling coefficient ζ to ZFS parameter D, the relation between D and ζ is also discussed.

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Analytical solution of the Boltzmann--Poisson equation and its application to MIS tunneling junctions Zhang Li-Zhi, Wang Zheng-Chuan 2009, 18 (7):  2975-2980.  doi: 10.1088/1674-1056/18/7/059 Abstract ( 0 )   PDF (208KB) ([an error occurred while processing this directive])   In order to consider quantum transport under the influence of an electron--electron (e--e) interaction in a mesoscopic conductor, the Boltzmann equation and Poisson equation are investigated jointly. The analytical expressions of the distribution function for the Boltzmann equation and the self-consistent average potential concerned with e--e interaction are obtained, and the dielectric function appearing in the self-consistent average potential is naturally generalized beyond the Thomas--Fermi approximation. Then we apply these results to the tunneling junctions of a metal--insulator--semiconductor (MIS) in which the electrons are accumulated near the interface of the semiconductor, and we find that the e--e interaction plays an important role in the transport procedure of this system. The electronic density, electric current as well as screening Coulombic potential in this case are studied, and we reveal the time and position dependence of these physical quantities explicitly affected by the e--e interaction.

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Dissipationless spin-Hall current contribution in the extrinsic spin-Hall effect Yan Yu-Zhen, Li Hui-Wu, Hu Liang-Bin 2009, 18 (7):  2981-2987.  doi: 10.1088/1674-1056/18/7/060 Abstract ( 0 )   PDF (182KB) ([an error occurred while processing this directive])   This paper shows that a substantial amount of dissipationless spin-Hall current contribution may exist in the extrinsic spin-Hall effect, which originates from the spin-orbit coupling induced by the applied external electric field itself that drives the extrinsic spin-Hall effect in a nonmagnetic semiconductor (or metal). By assuming that the impurity density is in a moderate range such that the total scattering potential due to all randomly distributed impurities is a smooth function of the space coordinate, it is shown that this dissipationless contribution shall be of the same orders of magnitude as the usual extrinsic contribution from spin-orbit dependent impurity scatterings (or may even be larger than the latter one). The theoretical results obtained are in good agreement with recent relevant experimental results.

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Infrared studies of oxygen-related complexes in electron-irradiated Cz-Si Chen Gui-Feng, Yan Wen-Bo, Chen Hong-Jian, Cui Hui-Ying, Li Yang-Xian 2009, 18 (7):  2988-2991.  doi: 10.1088/1674-1056/18/7/061 Abstract ( 0 )   PDF (190KB) ([an error occurred while processing this directive])   This paper investigates the infrared absorption spectra of oxygen-related complexes in silicon crystals irradiated with electron (1.5~MeV) at 360~K. Two groups of samples with low [Oi]=6.9× 1017~cm-3 and high [ Oi]=1.06× 1018~cm-3 were used. We found that the concentration of the VO pairs have different behaviour to the annealing temperature in different concentration of oxygen specimen, it is hardly changed in the higher concentration of oxygen specimen. It was also found that the concentration of VO2 in lower concentration of oxygen specimen gets to maximum at 450~℃ and then dissapears at 500~℃, accompanied with the appearing of VO3. For both kinds of specimens, the concentration of VO3 reachs to maximum at 550~℃ and does not disappear completely at 600~℃.

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First-principles study of structrural and corrected band properties of wurtzite Zn1-xCdxO and Zn1-xMgxO systems Wang Zhi-Jun, Li Shou-Chun, Wang Lian-Yuan, Liu Zhen 2009, 18 (7):  2992-2997.  doi: 10.1088/1674-1056/18/7/062 Abstract ( 0 )   PDF (450KB) ([an error occurred while processing this directive])   A first-principles method based on density functional theory (DFT), a generalized gradient approximation (GGA), and a projector-augmented wave (PAW) are used to study the structual and band properties of wurtzite Zn1-xCdxO and Zn1-xMgxO (0\leqq x\leqq 1) ternary alloys. By taking into account all of the possible structures, the band gaps of Zn1-xCdxO and Zn1-xMgxO alloys are corrected and compared with experimental data.

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Degradation mechanism of two-dimensional electron gas density in high Al-content AlGaN/GaN heterostructures Zhang Jin-Cheng, Zheng Peng-Tian, Zhang Juan, Xu Zhi-Hao, Hao Yue 2009, 18 (7):  2998-3001.  doi: 10.1088/1674-1056/18/7/063 Abstract ( 0 )   PDF (1804KB) ([an error occurred while processing this directive])   This paper finds that the two-dimensional electron gas density in high Al-content AlGaN/GaN heterostructures exhibits an obvious time-dependent degradation after the epitaxial growth. The degradation mechanism was investigated in depth using Hall effect measurements, high resolution x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy. The results reveal that the formation of surface oxide is the main reason for the degradation, and the surface oxidation always occurs within the surface hexagonal defects for high Al-content AlGaN/GaN heterostructures.

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Air-stable ambipolar organic field effect transistors with heterojunction of pentacene and N,N'-bis(4-trifluoromethylben-zyl)perylene-3,4,9,10-tetracarboxylic diimide Li Jian-Feng, Chang Wen-Li, Ou Gu-Ping, Zhang Fu-Jia 2009, 18 (7):  3002-3007.  doi: 10.1088/1674-1056/18/7/064 Abstract ( 0 )   PDF (1577KB) ([an error occurred while processing this directive])   Fabrication of ambipolar organic field-effect transistors (OFETs) is essential for the achievement of an organic complementary logic circuit. Ambipolar transports in OFETs with heterojunction structures are realized. We select pentacene as a P-type material and N,N'-bis(4-trifluoromethylben-zyl)perylene-3,4,9,10-tetracarboxylic diimide (PTCDI-TFB) as a n-type material in the active layer of the OFETs. The field-effect transistor shows highly air-stable ambipolar characteristics with a field-effect hole mobility of 0.18~cm2/(V.s) and field-effect electron mobility of 0.031~cm2/(V.s). Furthermore the mobility only slightly decreases after being exposed to air and remains stable even for exposure to air for more than 60 days. The high electron affinity of PTCDI-TFB and the octadecyltrichlorosilane (OTS) self-assembly monolayer between the SiO2 gate dielectric and the organic active layer result in the observed air-stable characteristics of OFETs with high mobility. The results demonstrate that using the OTS as a modified gate insulator layer and using high electron affinity semiconductor materials are two effective methods to fabricate OFETs with air-stable characteristics and high mobility.

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Effect of strain on geometric and electronic structures of graphene on Ru(0001) surface Sun Jia-Tao, Du Shi-Xuan, Xiao Wen-De, Hu Hao, Zhang Yu-Yang, Li Guo, Gao Hong-Jun 2009, 18 (7):  3008-3013.  doi: 10.1088/1674-1056/18/7/065 Abstract ( 0 )   PDF (3240KB) ([an error occurred while processing this directive])   The atomic and electronic structures of a graphene monolayer on a Ru(0001) surface under compressive strain are investigated by using first-principles calculations. Three models of graphene monolayers with different carbon periodicities due to the lattice mismatch are proposed in the presence and the absence of the Ru(0001) substrate separately. Considering the strain induced by the lattice mismatch, we optimize the atomic structures and investigate the electronic properties of the graphene. Our calculation results show that the graphene layers turn into periodic corrugations and there exist strong chemical bonds in the interface between the graphene N×N superlattice and the substrate. The strain does not induce significant changes in electronic structure. Furthermore, the results calculated in the local density approximation (LDA) are compared with those obtained in the generalized gradient approximation (GGA), showing that the LDA results are more reasonable than the GGA results when only two substrate layers are used in calculation.

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The improvement of Al2O3/AlGaN/GaN MISHEMT performance by N2 plasma pretreatment Feng Qian, Tian Yuan, Bi Zhi-Wei, Yue Yuan-Zheng, Ni Jin-Yu, Zhang Jin-Cheng, Hao Yue, Yang Lin-An 2009, 18 (7):  3014-3017.  doi: 10.1088/1674-1056/18/7/066 Abstract ( 0 )   PDF (714KB) ([an error occurred while processing this directive])   This paper discusses the effect of N2 plasma treatment before dielectric deposition on the electrical performance of a Al2O3/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT), with Al2O3 deposited by atomic layer deposition. The results indicated that the gate leakage was decreased two orders of magnitude after the Al2O3/AlGaN interface was pretreated by N2 plasma. Furthermore, effects of N2 plasma pretreatment on the electrical properties of the AlGaN/Al2O1-x interface were investigated by x-ray photoelectron spectroscopy measurements and the interface quality between Al2O3 and AlGaN film was improved.

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Experimental and numerical analysis of the multi-recessed gate structure for microwave silicon carbide power MESFETs Deng Xiao-Chuan, Feng Zhen, Zhang Bo, Li Zhao-Ji, Li Liang, Pan Hong-Shu 2009, 18 (7):  3018-3023.  doi: 10.1088/1674-1056/18/7/067 Abstract ( 0 )   PDF (2279KB) ([an error occurred while processing this directive])   This paper reports that multi-recessed gate 4H-SiC MESFETs (metal semiconductor filed effect transistors) with a gate periphery of 5-mm are fabricated and characterized. The multi-recessed region under the gate terminal is applied to improve the gate--drain breakdown voltage and to alleviate the trapping induced instabilities by moving the current path away from the surface of the device. The experimental results demonstrate that microwave output power density, power gain and power-added efficiency for multi-finger 5-mm gate periphery SiC MESFETs with multi-recessed gate structure are about 29%, 1.1dB and 7% higher than those of conventional devices fabricated in this work using the same process.

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Synthesis and electrical characterization of tungsten oxide nanowires Huang Rui, Zhu Jing, Yu Rong 2009, 18 (7):  3024-3030.  doi: 10.1088/1674-1056/18/7/068 Abstract ( 0 )   PDF (7121KB) ([an error occurred while processing this directive])   Tungsten oxide nanowires of diameters ranging from 7 to 200~nm are prepared on a tungsten rod substrate by using the chemical vapour deposition (CVD) method with vapour--solid (VS) mechanism. Tin powders are used to control oxygen concentration in the furnace, thereby assisting the growth of the tungsten oxide nanowires. The grown tungsten oxide nanowires are determined to be of crystalline W18O49. I--V curves are measured by an \textit{in situ} transmission electron microscope (TEM) to investigate the electrical properties of the nanowires. All of the I--V curves observed are symmetric, which reveals that the tungsten oxide nanowires are semiconducting. Quantitative analyses of the experimental I--V curves by using a metal--semiconductor--metal (MSM) model give some intrinsic parameters of the tungsten oxide nanowires, such as the carrier concentration, the carrier mobility and the conductivity.

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Successive phase transformation in ferromagnetic shape memory alloys Co37Ni34Al39 melt-spun ribbons Meng Fan-Bin, Guo Hong-Jun, Liu Guo-Dong, Liu He-Yan, Dai Xue-Fang, Luo Hong-Zhi, Li Yang-Xian, Chen Jing-Lan, Wu Guang-Heng 2009, 18 (7):  3031-3034.  doi: 10.1088/1674-1056/18/7/069 Abstract ( 0 )   PDF (502KB) ([an error occurred while processing this directive])   The martensitic transformation in Co37Ni34Al29 ribbon is characterized in detail by means of in-situ thermostatic x-ray diffraction and magnetic measurements. The results show a structural transition from the body-centred cubic to martensite with a tetragonal structure during cooling. Comparison between the results of the diffraction intensity with the magnetic susceptibility measurements indicates that the martensitic transformation takes place in several different steps during cooling from 273 to 163~K. During heating from 313 to 873~K, the peak width becomes very wide and the intensity turns very low. The γ-phase (face-centred cubic structure) emerges and increases gradually with temperature increasing from 873 to 1073~K.

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Effect of cobalt on the magnetoresistance characteristics of rare-earth doped manganites Jiang Kuo, Gong Sheng-Kai 2009, 18 (7):  3035-3039.  doi: 10.1088/1674-1056/18/7/070 Abstract ( 0 )   PDF (194KB) ([an error occurred while processing this directive])   The effect of cobalt-doping on the magnetic, transport and magnetoresistance characteristics of La1-xSrxMnO3 was investigated. The results show that the magnetoelectric property of rare-earth doped manganites is greatly affected by substitution of Co for Mn sites. The Curie temperature as well as the magnetic moment decreases with the increase of doping concentration, and the samples exhibit obvious characteristics of the spin glass state. Moreover, the magnetoresistance is evidently modulated by doping concentration, and the relevant temperature dependence is also suppressed. In addition, low-temperature magnetoresistance is significantly promoted as doping concentration increases, which renders a value of approximately 50% in the temperature range of 5--200~K and varies within 12.5%. It can be attributed to the effect of spin scattering, induced by cobalt doping, on the itinerant electrons of Mn ions, thus introducing a spin-disorder region into the ferromagnetic region of double-exchange interaction between neighbouring Mn3+ and Mn 3+ ions.

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A fabrication and magnetic properties study on Al doped Zn0.99Co0.01O dilution ferromagnetic semiconductors Yu Zhou, Li Xiang, Long Xue, Cheng Xing-Wang, Liu Ying, Cao Chuan-Bao 2009, 18 (7):  3040-3043.  doi: 10.1088/1674-1056/18/7/071 Abstract ( 0 )   PDF (1281KB) ([an error occurred while processing this directive])   This paper reports that a chemical method is employed to synthesize Co and Al co-doped ZnO, namely, Zn0.99-xCo0.01AlxO dilution semiconductors with the nominal composition of x=0, 0.005 and 0.02. Structural, magnetic and optical properties of the produced samples are studied. The results indicate that samples sintered in air under the temperatures of 500~℃ show a single wurtzite ZnO structure and the ferromagnetism decreases with the increase of Al. Photoluminescence spectra of different Al-doped samples indicate that increasing Al concentration in Zn0.99-xCo0.01AlxO results in a decrease of Zni, which resembles the trend of the ferromagnetic property of the corresponding samples. Therefore, it is deduced that the ferromagnetism observed in the studied samples originates from the interstitial defect of zinc (Zni ) in the lattice of Co-doped ZnO.

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A comparison of silicon oxide and nitride as host matrices on the photoluminescence from Er+ ions Ding Wu-Chang, Liu Yan, Zhang Yun, Guo Jian-Chuan, Zuo Yu-Hua, Cheng Bu-Wen, Yu Jin-Zhong, Wang Qi-Ming 2009, 18 (7):  3044-3048.  doi: 10.1088/1674-1056/18/7/072 Abstract ( 0 )   PDF (176KB) ([an error occurred while processing this directive])   This paper compares the properties of silicon oxide and nitride as host matrices for Er ions. Erbium-doped silicon nitride films were deposited by a plasma-enhanced chemical-vapour deposition system. After deposition, the films were implanted with Er3+ at different doses. Er-doped thermal grown silicon oxide films were prepared at the same time as references. Photoluminescence features of Er3+ were inspected systematically. It is found that silicon nitride films are suitable for high concentration doping and the thermal quenching effect is not severe. However, a very high annealing temperature up to 1200~℃ is needed to optically activate Er3+, which may be the main obstacle to impede the application of Er-doped silicon nitride.

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Cavity design and linear analysis of 225 GHz frequency-quadrupling gyroklystron Liu Di-Wei, Yuan Xue-Song, Yan Yang, Liu Sheng-Gang 2009, 18 (7):  3049-3053.  doi: 10.1088/1674-1056/18/7/073 Abstract ( 0 )   PDF (270KB) ([an error occurred while processing this directive])   This paper considers the frequency-quadrupling three-cavity gyroklystrons with successive frequency-doubling in each cavity. The cavities of 225~GHz frequency-quadrupling gyroklystron are designed with the scattering matrices method and the possible operating mode are discussed. With the point-gap theory, the starting currents of the possible operating modes and the potential parasitic modes in the output cavity are calculated. The optimal operating mode is proposed under consideration of the mode competition and the power capacity of the cavity.

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Influence of lateral size on dielectric properties of ferroelectric thin films with structure transition zones Zhou Jing, Lü Tian-Quan, Xie Wen-Guang, Cao Wen-Wu 2009, 18 (7):  3054-3060.  doi: 10.1088/1674-1056/18/7/074 Abstract ( 0 )   PDF (275KB) ([an error occurred while processing this directive])   By taking into account structural transition zones near the lateral and thickness direction edges, this paper uses a modified transverse Ising model to study dielectric properties of a finite size ferroelectric thin film in the framework of the mean-field approximation. The results indicate that the influence of the lateral size on the dielectric susceptibility cannot be neglected and lateral structural transition zones could be a crucial factor that improves the mean susceptibility of the fixed size film.

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Studies on organic binders with high infrared transparency Fu Cheng-Wu, Zhou Hao-Shen, Chen Ming-Qing 2009, 18 (7):  3061-3065.  doi: 10.1088/1674-1056/18/7/075 Abstract ( 0 )   PDF (315KB) ([an error occurred while processing this directive])   This paper reports that two kinds of polymers with high infrared transparency and good mechanical and physical properties have been prepared. An internal standard method is used to evaluate the infrared transparency of the binders. The physical and mechanical properties of the binders are measured according to corresponding standards. The results show the absorbance of polymer A in 8--14~μ m range is 26% that of the ethylene-vinyl acetate copolymer (EVA), and polymer B is 9% that of the EVA correspondingly. The film of polymer A shows good flexibility of above 1~mm, a hardness of grade 1, and adhesion of grade 2. The film of polymer B shows good flexibility of above 1~mm, a hardness of grade 1, and adhesion of grade 1.

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An effective scatter correction method based on single scatter simulation for a 3D whole-body PET scanner Gao Fei, Yamada Ryoko, Watanabe Mitsuo, Liu Hua-Feng 2009, 18 (7):  3066-3072.  doi: 10.1088/1674-1056/18/7/076 Abstract ( 0 )   PDF (532KB) ([an error occurred while processing this directive])   Hamamatsu SHR74000 is a newly designed full three-dimensional (3D) whole body positron emission tomography (PET) scanner with small crystal size and large field of view (FOV). With the improvement of sensitivity, the scatter events increase significantly at the same time, especially for large objects. Monte Carlo simulations help us to understand the scatter phenomena and provide good references for scatter correction. In this paper, we introduce an effective scatter correction method based on single scatter simulation for the new PET scanner, which accounts for the full 3D scatter correction. With the results from Monte Carlo simulations, we implement a new scale method with special concentration on scatter events from outside the axial FOV and multiple scatter events. The effects of scatter correction are investigated and evaluated by phantom experiments; the results show good improvements in quantitative accuracy and contrast of the images, even for large objects.

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The dissociation pathways of N2+ in intense femtosecond laser fields Chen De-Ying, Zhang Sheng, Xia Yuan-Qin 2009, 18 (7):  3073-3078.  doi: 10.1088/1674-1056/18/7/077 Abstract ( 0 )   PDF (361KB) ([an error occurred while processing this directive])   Using a neutral N2 beam as target, this paper studies the dissociation of N2+ in intense femtosecond laser fields (45~fs, ～ 1× 1016~W/cm2) at the laser wavelength of 800 nm based on the time-of-flight mass spectra of N+ fragment ions. The angular distributions of N+ and the laser power dependence of N+ yielded from different dissociation pathways show that the dissociation mechanisms mainly proceed through the couplings between the metastable states (A, B and C) and the upper excited states of N2+. A coupling model of light-dressed potential energy curves of N2+ is used to interpret the kinetic energy release of N+.

CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Thermal stability of Mg2Si epitaxial film formed on Si(111) substrate by solid phase reaction Wang Xi-Na, Wang Yong, Zou Jin, Zhang Tian-Chong, Mei Zeng-Xia, Guo Yang, Xue Qi-Kun, Du Xiao-Long, Zhang Xiao-Na, Han Xiao-Dong, Zhang Ze 2009, 18 (7):  3079-3083.  doi: 10.1088/1674-1056/18/7/078 Abstract ( 0 )   PDF (1708KB) ([an error occurred while processing this directive])   A single crystalline Mg2Si film was formed by solid phase reaction (SPR) of a Si(111) substrate with an Mg overlayer capped with an oxide layer(s), which was enhanced by post annealing from room temperature to 100~℃ in a molecular beam epitaxy (MBE) system. The thermal stability of the Mg2Si film was then systematically investigated by post annealing in an oxygen-radical ambient at 300~℃, 450~℃ and 650~℃, respectively. The Mg2Si film stayed stable until the annealing temperature reached 450~℃ then it transformed into amorphous MgOx attributed to the decomposition of Mg2Si and the oxidization of dissociated Mg.

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Synthesis and high temperature thermoelectric transport properties of Si-based type-I clathrates Deng Shu-Kang, Tang Xin-Feng, Tang Run-Sheng 2009, 18 (7):  3084-3089.  doi: 10.1088/1674-1056/18/7/079 Abstract ( 0 )   PDF (212KB) ([an error occurred while processing this directive])   N-type Si-based type-I clathrates with different Ga content were synthesized by combining the solid-state reaction method, melting method and spark plasma sintering (SPS) method. The effects of Ga composition on high temperature thermoelectric transport properties were investigated. The results show that at room temperature, the carrier concentration decreases, while the carrier mobility increases slightly with increasing Ga content. The Seebeck coefficient increases with increasing Ga content. Among all the samples, Ba7.93Ga17.13Si28.72 exhibits higher Seebeck coefficient than the others and reaches -135~μ V.K-1 at 1000 K. The sample prepared by this method exhibits very high electrical conductivity, and reaches 1.95× 105S.m-1 for Ba8.01Ga16.61Si28.93 at room temperature. The thermal conductivity of all samples is almost temperature independent in the temperature range of 300--1000~K, indicating the behaviour of a typical metal. The maximum {ZT} value of 0.75 is obtained at 1000~K for the compound Ba7.93Ga17.13Si28.72.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Numerical method of studying nonlinear interactions between long waves and multiple short waves Xie Tao, Kuang Hai-Lan, William Perrie, Zou Guang-Hui, Nan Cheng-Feng, He Chao, Shen Tao, Chen Wei 2009, 18 (7):  3090-3098.  doi: 10.1088/1674-1056/18/7/080 Abstract ( 0 )   PDF (295KB) ([an error occurred while processing this directive])   Although the nonlinear interactions between a single short gravity wave and a long wave can be solved analytically, the solution is less tractable in more general cases involving multiple short waves. In this work we present a numerical method of studying nonlinear interactions between a long wave and multiple short harmonic waves in infinitely deep water. Specifically, this method is applied to the calculation of the temporal and spatial evolutions of the surface elevations in which a given long wave interacts with several short harmonic waves. Another important application of our method is to quantitatively analyse the nonlinear interactions between an arbitrary short wave train and another short wave train. From simulation results, we obtain that the mechanism for the nonlinear interactions between one short wave train and another short wave train (expressed as wave train 2) leads to the energy focusing of the other short wave train (expressed as wave train 3). This mechanism occurs on wave components with a narrow frequency bandwidth, whose frequencies are near that of wave train 3.