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2008年, 第17卷, 第6期　刊出日期：2008-06-20 上一期    下一期

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A field method for integrating the equations of motion of mechanico--electrical coupling dynamical systems 傅景礼, 徐树山, 翁玉权 2008 (6):  1939-1945.  doi: 10.1088/1674-1056/17/6/001 摘要 ( 1812 )   PDF(328KB) ( 683 )   A field method for integrating the equations of motion for mechanico--electrical coupling dynamical systems is studied. Two examples in mechanico--electrical engineering are given to illustrate this method. 相关文章 | 计量指标

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Existence and asymptotic estimates of periodic solutions of a sea--air oscillator model of decadal variations in subtropical cells and equatorial Pacific SST 李晓静 2008 (6):  1946-1950.  doi: 10.1088/1674-1056/17/6/002 摘要 ( 1863 )   PDF(160KB) ( 555 )   This paper studies a time delay equation for sea--air oscillator model. The existence and asymptotic estimates of periodic solutions of corresponding problem are obtained by employing the technique of upper and lower solution, and by using the continuation theorem of coincidence degree theory. 相关文章 | 计量指标

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Synchronization of coupled logistic maps on random community networks 冯存芳, 许新建, 吴枝喜, 汪映海 2008 (6):  1951-1956.  doi: 10.1088/1674-1056/17/6/003 摘要 ( 1711 )   PDF(214KB) ( 693 )   The collective synchronization of a system of coupled logistic maps on random community networks is investigated. It is found that the synchronizability of the community network is affected by two factors when the size of the network and the number of connections are fixed. One is the number of communities denoted by the parameter $m$, and the other is the ratio $\sigma$ of the connection probability $p$ of each pair of nodes within each community to the connection probability $q$ of each pair of nodes among different communities. Theoretical analysis and numerical results indicate that larger $m$ and smaller $\sigma$ are the key to the enhancement of network synchronizability. We also testify synchronous properties of the system by analysing the largest Lyapunov exponents of the system. 相关文章 | 计量指标

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Perturbation to Mei symmetry and Mei adiabatic invariants for mechanical systems in phase space 张明江, 方建会, 张小妮, 路凯 2008 (6):  1957-1961.  doi: 10.1088/1674-1056/17/6/004 摘要 ( 1811 )   PDF(143KB) ( 664 )   For a perturbed mechanical system in phase space, considering ${\tilde{{\rm d}}}/{ {{\rm d}t}}$ in the structure equation and process of proof including infinitesimal parameter $\varepsilon $ obviously, this paper studies the perturbation to Mei symmetry and adiabatic invariants. Firstly, the exact invariant induced directly from the Mei symmetry of the system without perturbation is given. Secondly, based on the concept of high-order adiabatic invariant, the determining equations of the perturbation to Mei symmetry are established, the condition of existence of the Mei adiabatic invariant led by the perturbation to Mei symmetry is obtained, and its form is presented. Lastly, an example is given to illustrate the application of the results. 相关文章 | 计量指标

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New conserved quantities of Noether--Mei symmetry of mechanical system in phase space 方建会, 刘仰魁, 张小妮 2008 (6):  1962-1966.  doi: 10.1088/1674-1056/17/6/005 摘要 ( 1778 )   PDF(138KB) ( 576 )   This paper studies two new types of conserved quantities deduced by Noether--Mei symmetry of mechanical system in phase space. The definition and criterion of Noether--Mei symmetry for the system are given. A coordination function is introduced, and the conditions under which the Noether--Mei symmetry leads to the two types of conserved quantities and the forms of the two types of conserved quantities are obtained. An illustrative example is given. The coordination function can be selected according to the demand for finding the gauge function, and the choice of the coordination function has multiformity, so more conserved quantities deduced from Noether--Mei symmetry of mechanical system can be obtained. 相关文章 | 计量指标

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Perturbation to Lie symmetry and another type of Hojman adiabatic invariants for Birkhoffian systems 丁宁, 方建会, 陈相霞 2008 (6):  1967-1971.  doi: 10.1088/1674-1056/17/6/006 摘要 ( 1793 )   PDF(147KB) ( 731 )   The perturbation to Lie symmetry and another type of Hojman adiabatic invariants induced from the perturbation to Lie symmetry for Birkhoffian systems are studied. The exact invariants of Lie symmetry for the system without perturbation are given. Based on the concept of adiabatic invariant, the perturbation to Lie symmetry is discussed and another new type of Hojman adiabatic invariants that have the different form from that in [{\em Acta Phys. Sin.} {\bf 55} 3833] for the perturbed system are obtained. 相关文章 | 计量指标

GENERAL

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Generation of multipartite entangled states by cavity QED 张英杰, 任廷琦, 夏云杰 2008 (6):  1972-1978.  doi: 10.1088/1674-1056/17/6/007 摘要 ( 1507 )   PDF(169KB) ( 661 )   We propose the methods of generating multipartite entanglement by considering the interaction of a system of $N$ two-level atoms in $M$ cavities of high quality factor with a strong classical driving field. It is shown that, with the cavity detuning, the applied driving field detuning and vacuum Rabi coupling, we can produce an entangled coherent state in two single-mode cavities and generate the entangled coherent cluster states in two bimodal vacuum cavities. Tuning these parameters also allows us to acquire the anti-Jaynes--Cummings (AJC) interaction, with which we can generate the maximally two-photon entangled states, and the two-atom and the two-photon entangled cluster states. 相关文章 | 计量指标

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Generation of various multiatom entangled graph states via resonant interactions 董萍, 章礼华, 曹卓良 2008 (6):  1979-1984.  doi: 10.1088/1674-1056/17/6/008 摘要 ( 1539 )   PDF(330KB) ( 495 )   In this paper, a scheme for generating various multiatom entangled graph states via resonant interactions is proposed. We investigate the generation of various four-atom graph states first in the ideal case and then in the case in which the cavity decay and atomic spontaneous emission are taken into consideration in the process of interaction. More importantly, we improve the possible distortion of the graph states coming from cavity decay and atomic spontaneous emission by performing appropriate unitary transforms on atoms. The generation of multiatom entangled graph states is very important for constructing quantum one-way computer in a fault-tolerant manner. The resonant interaction time is very short, which is important in the sense of decoherence. Our scheme is easy and feasible within the reach of current experimental technology. 相关文章 | 计量指标

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Resonant frequencies of massless scalar field in rotating black-brane spacetime 荆继良, 潘启沅 2008 (6):  1985-1989.  doi: 10.1088/1674-1056/17/6/009 摘要 ( 1395 )   PDF(168KB) ( 480 )   This paper investigates the resonant frequencies of the massless scalar field in the near extremal Kerr-like black-brane spacetime. It is shown that the different angular quantum number will present different resonant frequencies. It is also shown that the real part of the resonant frequencies increases as the compact dimensions parameter $\mu_i$ increases, but the magnitude of the imaginary part decreases as $\mu_i$ increases. 相关文章 | 计量指标

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Noise composed of multiplication of two dichotomous noises 李静辉 2008 (6):  1990-1997.  doi: 10.1088/1674-1056/17/6/010 摘要 ( 1523 )   PDF(314KB) ( 603 )   In this paper, we introduce a noise which is composed of multiplication of two dichotomous noises, and derive the probability density and the statistical properties of this noise. The obtained results can help study the resonant activation phenomenon, the phenomenon of stochastic resonance, the transport of particles, and the nonequilibrium (phase) transition for the systems driven by this noise. 相关文章 | 计量指标

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Time series prediction using wavelet process neural network 丁刚, 钟诗胜, 李洋 2008 (6):  1998-2003.  doi: 10.1088/1674-1056/17/6/011 摘要 ( 1617 )   PDF(482KB) ( 790 )   In the real world, the inputs of many complicated systems are time-varying functions or processes. In order to predict the outputs of these systems with high speed and accuracy, this paper proposes a time series prediction model based on the wavelet process neural network, and develops the corresponding learning algorithm based on the expansion of the orthogonal basis functions. The effectiveness of the proposed time series prediction model and its learning algorithm is proved by the Mackey--Glass time series prediction, and the comparative prediction results indicate that the proposed time series prediction model based on the wavelet process neural network seems to perform well and appears suitable for using as a good tool to predict the highly complex nonlinear time series. 相关文章 | 计量指标

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Study on phase synchronization of stochastic chaotic system 杨晓丽, 徐伟 2008 (6):  2004-2009.  doi: 10.1088/1674-1056/17/6/012 摘要 ( 1678 )   PDF(866KB) ( 597 )   This paper detects and characterizes the diverse roles played by bounded noise in chaotic phase synchronization (CPS) of weakly coupled nonlinear stochastic systems. Analysis of a paradigmatic model of two bidirectional coupled three-level food chains is carried out by various statistical measures such as Shannon entropy and mutual information. The results indicate that inside the synchronous regime, CPS is considerably reduced under the influence of bounded noise; near the onset of phase synchronization, temporal phase locking is diversely changed with the increase of noise, i.e., either weak or strong noise also degrades the degree of CPS, while intermediate noise enhances CPS remarkably, and an optimal noise intensity is detected that maximizes the enhancement. 相关文章 | 计量指标

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Radiation-induced resistance oscillation and instability in GaAS/AlGaAS heterostructure under transverse magnetic fields 杨癸, 涂必红, 李国辉, 赵宏伟, 周世平 2008 (6):  2010-2017.  doi: 10.1088/1674-1056/17/6/013 摘要 ( 1553 )   PDF(274KB) ( 638 )   This paper studies dynamics of a modulation-doped GaAs/AlGaAs heterostructure under transverse magnetic fields and microwave radiations. It finds that negative differential conductivity, due to the real-space electron transfer and delayed dielectric relaxation of the interface potential barrier, can lead to complex behaviours when a relatively small magnetic field is applied. Quasiperiodicity, frequency-locking and the routes from period-doubling to chaos are found. Under a large magnetic field, however, two time-independent homogeneous steady states exist; and the longitudinal resistance of the system shows an interesting oscillation with period tuned by the ratio of microwave radiation frequency $\omega$ to the cyclotron frequency $\omega_{\rm c}$ and local minima at $\omega/\omega_{\rm c}={\rm integer}+1/4$. 相关文章 | 计量指标

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Fractional Fourier transform of Cantor sets: further numerical study 高穹, 廖天河, 崔远峰 2008 (6):  2018-2022.  doi: 10.1088/1674-1056/17/6/014 摘要 ( 1577 )   PDF(452KB) ( 904 )   This paper is a further work of the authors' paper published previously (Liao T H and Gao Q 2005 {\it Chin. Phys. Lett.} {\bf 22} 2316). The amplitudes of fractional Fourier transform of Cantor sets are analysed from the viewpoint of multifractal by wavelet transform maxima method (WTMM). An integral operation is carried out before the application of WTMM, such that the function obtained can be considered as the perturbed devil staircase. Also, wavelets with large number of vanishing moments are used, which makes the complete singularity spectrum more accessible. The validity of multifractal formalism is guaranteed by restricting parameter $q$ to a proper range, so that the phenomenon of multifractal phase transition can be explained reasonably. Particularly, the method of determining the range of parameter $q$ in the above paper is developed to be more operational and rigorous. 相关文章 | 计量指标

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Ground state for CH2 and symmetry for methane decomposition 张莉, 罗文浪, 阮文, 蒋刚, 朱正和 2008 (6):  2023-2026.  doi: 10.1088/1674-1056/17/6/015 摘要 ( 1652 )   PDF(148KB) ( 723 )   Using the different level of methods B3P86, BLYP、B3PW91, HF, QCISD、CASSCF (4,4) and MP2 with the various basis functions 6-311G**, D95, cc--pVTZ and DGDZVP, the calculations of this paper confirm that the ground state is $\tilde {X}{ }^3B_1 $ with $C_{2v} $ group for CH$_{2}$. Furthermore, the three kinds of theoretical methods, i.e. B3P86、CCSD(T, MP4) and G2 with the same basis set cc-pVTZ only are used to recalculate the zero-point energy revision which are modified by scaling factor 0.989 for the high level based on the virial theorem, and also with the correction for basis set superposition error. These results are also contrary to $\tilde {X}{ }^3\Si _{\rm g} ^ - $ for the ground state of CH$_{2}$ in reference. Based on the atomic and molecular reaction statics, this paper proves that the decomposition type (1) i.e. CH$_{4}\to $CH$_{2}$+H$_{2}$, is forbidden and the decomposition type (2) i.e. CH$_{4} \to $CH$_{3}$+H is allowed for CH$_{4}$. This is similar to the decomposition of SiH$_{4}$. 相关文章 | 计量指标

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Relativistic multichannel treatment of autoionization Rydberg series of 4s2 nf(n=4--23)Jπ=(7/2)0 for scandium 贾凤东, 王京阳, 钟志萍 2008 (6):  2027-2032.  doi: 10.1088/1674-1056/17/6/016 摘要 ( 1633 )   PDF(268KB) ( 588 )   Based on relativistic multichannel theory, this paper calculates the energy levels of autoionization Rydberg series 4s2 nf(n=4-23)Jπ =(7/2)0 of scandium at different levels of approximation within the framework of multichannel quantum defect theory. The present results show that the dipole polarizations play an important role. Considering the dynamical dipole polarization effects, this paper finds that the difference between calculated and experimental quantum defects for the 4s2nf(n=4-23)Jπ =(7/2)0 series is generally about 0.01--0.03. Furthermore, the reason that 4s216f is obscured in experimental spectra is suggested to be the interaction with the neighbouring resonance state converged to 3d2(1G4 ) of Sc+. 相关文章 | 计量指标

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Theoretical study on decay of the 4d core-excited states of Cs III 丁晓彬, 董晨钟, Stephan Fritzsche 2008 (6):  2033-2039.  doi: 10.1088/1674-1056/17/6/017 摘要 ( 1545 )   PDF(200KB) ( 589 )   In a recent XUV photoabsorption spectrum of Cs III ions by Cummings and O'Sullivan [2001 {\em J. Phys.} B {\bf 34} 199], rather large linewidths were found for the ${\rm 4d}^{\,9} {\rm 5s}^2 {\rm 5p}^6 \,- \,{\rm 4d}^{\,10} {\rm 5s}^2 {\rm 5p}^5$ transition which are quite in disagreement with corresponding quasi-relativistic multiconfiguration Hartree--Fock (MCHF) calculation. In the present work, a detailed multiconfiguration Dirac-Fock study has been carried out to explore this discrepancy. Owing to the detailed consideration of electron correlation effects, some 'forbidden' Auger decay channels, such as ${\rm 4d}^{\,10} {\rm 5s}^2 {\rm 5p}^3 {\rm 5d} $ and ${\rm 4d}^{\,10} {\rm 5s}^0 {\rm 5p}^6 $, would become `open'. As a result, remarkable improvement of the linewidths has been obtained in our calculation. Furthermore, the theoretical Auger spectrum of the ${\rm 4d}^{\,9} {\rm 5s}^2 {\rm 5p}^6$ core-excited states of Cs III ions is given in the present work. 相关文章 | 计量指标

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The splitting of low-lying or low excited states for hydride molecules (cations) of the third period under spin-orbit coupling 李桂霞, 高涛, 张云光 2008 (6):  2040-2047.  doi: 10.1088/1674-1056/17/6/018 摘要 ( 1785 )   PDF(178KB) ( 626 )   This paper reports that the splitting of potential energy curves for the low-lying or low excited states for hydride molecules (cations) (MgH, AlH+, SiH, PH+, SH,ClH+ of the third period under Spin-Orbit Coupling has been calculated by using the Spin-Orbit Multi-Configuration Quasi-Degenerate Perturbation Theory (SO-MCQDPT) method. Then, spectroscopic constants of the split states have been derived from the Murrell--Sorbie function. The calculated dissociation energies for the spectrum branch terms have been given, respectively. The spectroscopic constants and dissociation energies for the spectrum branch terms are given for the first time in this paper. 相关文章 | 计量指标

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Accurate studies of dissociation energies and vibrational energies on alkali metals 刘秀英, 孙卫国, 樊群超 2008 (6):  2048-2061.  doi: 10.1088/1674-1056/17/6/019 摘要 ( 1430 )   PDF(235KB) ( 641 )   This paper studies full vibrational spectra {\{}$E_\upsilon ${\}} and molecular dissociation energies $D_\e$ by using conventional least-squares (LS) fitting and an algebraic method (AM) proposed recently for 10 diatomic electronic states of ${ }^7$Li$_2 $, Na$_2$, NaK and NaLi molecules based on some known experimental vibrational energies in a subset [$E_\upsilon ^{\exp t} $] respectively. Studies show that: (1) although both the full AM spectrum {\{}$E_\upsilon ^{\rm AM} ${\}} and the LS spectrum {\{}$E_\upsilon ^{\rm LS} ${\}} can reproduce the known experimental energies in [$E_\upsilon ^{\exp t} $], the {\{}$E_\upsilon ^{\rm AM} ${\}} is superior to the {\{}$E_\upsilon ^{\rm LS} ${\}} in that the high-lying AM vibrational energies which may not be available experimentally have better or much better accuracy than those LS counterparts in {\{}$E_\upsilon ^{\rm LS} ${\}}, and so is the AM dissociation energy $D_\e^{\rm AM} $; (2) the main source of the errors in the data obtained by using the LS fitting is that the fitting which is just a pure mathematical process does not use any physical criteria that must be satisfied by the full vibrational spectrum, while the AM method does. This study suggests that when fitting or solving a physical equation using a set of source data, it is important not only to apply a proper mathematical tool, but also to use correct physical criteria which measure the physical properties of the data, kick out those data having bigger errors, and impose conditional convergence on the numerical process. 相关文章 | 计量指标

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Observation of single neutral atoms in a large-magnetic-gradient vapour-cell magneto-optical trap 王婧, 何军, 邱英, 杨保东, 赵江艳, 张天才, 王军民 2008 (6):  2062-2065.  doi: 10.1088/1674-1056/17/6/020 摘要 ( 1650 )   PDF(366KB) ( 764 )   Single caesium atoms in a large-magnetic-gradient vapour-cell magneto-optical trap have been identified. The trapping of individual atoms is marked by the steps in fluorescence signal corresponding to the capture or loss of single atoms. The typical magnetic gradient is about 29\,mT/cm, which evidently reduces the capture rate of magneto-optical trap. 相关文章 | 计量指标

ATOMIC AND MOLECULAR PHYSICS

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Anomalous aggregation growth of palladium nanosphere with SPR band in visible range 肖从文, 申承民, 徐梽川, 杨天中, 高鸿钧 2008 (6):  2066-2071.  doi: 10.1088/1674-1056/17/6/021 摘要 ( 1604 )   PDF(7313KB) ( 590 )   The morphology and properties of nanostructures are significantly influenced by the chemical coordination during their growth procedure. Using small molecule N-vinyl pyrolidone as stabilizer, this paper introduces a new strategy for synthesis of palladium nanospheres, which has a novel surface plasmon resonance band in the visible range. An aggregation growth mode was observed in the growth process. More specifically, the growth rate increases with increasing concentration of stabilizer. The absorption in visible region suggests new optical applications for these Pd nanospheres, such as photocatalysis, photothermal heating and surface enhanced Raman scattering. 相关文章 | 计量指标

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Use of photoelectron laser phase determination method for attosecond measurements with quantum-mechanical calculations 葛愉成 2008 (6):  2072-2077.  doi: 10.1088/1674-1056/17/6/022 摘要 ( 1493 )   PDF(808KB) ( 590 )   This paper calculates quantum-mechanically the photoelectron energy spectra excited by attosecond x-rays in the presence of a few-cycle laser. A photoelectron laser phase determination method is used for precise measurements of the pulse natural properties of x-ray intensity and the instantaneous frequency profiles. As a direct procedure without any previous pulse profile assumptions and time-resolved measurements as well as data fitting analysis, this method can be used to improve the time resolutions of attosecond timing and measurements with metrological precision. The measurement range is half of a laser optical cycle. 相关文章 | 计量指标

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The differential interference angle in collisional quantum interference on rotational energy transfer 王伟丽, 苗刚, 陈跃辉, 唐丹, 马凤才 2008 (6):  2078-2084.  doi: 10.1088/1674-1056/17/6/023 摘要 ( 1385 )   PDF(370KB) ( 486 )   Collisional quantum interference (CQI) in the intramolecular rotational energy transfer was observed in experiment by Sha and co-workers.$^{[1]}$ The interference angle, which measuring the degree of the coherence, were measured in the experiment of the static cell. Based on the first Born approximation of time dependent perturbation theory, taking into accounts the anisotropic Lennard-Jones interaction potentials, this paper describes the theoretical model of CQI in intramolecular rotational energy transfer in an atom--diatom collision system. In the model, the differential interference angle for the experiment of the molecular beam is calculated, the changing tendencies of the differential interference angle with the impact parameter and collision partners are obtained. This theoretical model is important for understanding or performing this kind of experiments. 相关文章 | 计量指标

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The structure and the analytical potential energy function of NH2 (X2B1) 刘玉芳, 蒋利娟, 马恒, 孙金锋 2008 (6):  2085-2089.  doi: 10.1088/1674-1056/17/6/024 摘要 ( 1539 )   PDF(601KB) ( 628 )   This paper reports that the equilibrium structure of NH2 has been optimized at the QCISD/6-311++G (3df, 3pd) level. The ground-state NH2 has a bent (C2v, $X2B1 structure with an angle of 103.05820. The geometrical structure is in good agreement with the other calculational and experimental results. The harmonic frequencies and the force constants have also been calculated. Based on the group theory and the principle of microscopic reversibility, the dissociation limits of NH2(C2v, X2B1 have been derived. The potential energy surface of NH2(X2B1 is reasonable. The contour lines are constructed, the structure and energy of NH2 reappear on the potential energy surface. 相关文章 | 计量指标

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Elastic scattering of two H(2Sg) and N(4Su) atoms at low temperatures and accurate spectroscopic parameters of NH (X3∑-) radical 施德恒, 张金平, 孙金锋, 朱遵略, 刘玉芳, 杨向东 2008 (6):  2090-2096.  doi: 10.1088/1674-1056/17/6/025 摘要 ( 1637 )   PDF(218KB) ( 675 )   This paper reports that the interaction potential for the X3\Si- state of NH radical is constructed at the CCSD(T)/ cc-PV6Z level of theory. Using this potential, this paper calculates the spectroscopic parameters ($D_{\e}$, $R_{\e}$, \textit{$\omega $}$_{\e}$, \textit{$\omega $}$_{\e}$\textit{$\chi $}$_{\e}$, \textit{$\alpha $}$_{\e}$ and $B_{\e})$ and their values are of 3.578\,eV, 0.10368\,nm, 3286.833\,cm-1, 78.433\,cm-1, 0.6469\,cm-1 and 16.6735\,cm-1, respectively, which are in excellent agreement with the experiments. Then the total of 14 vibrational states has been found when $J$=0 by solving the radial Schr\"{o}dinger equation of nuclear motion. For each vibrational state, the vibrational manifolds are reported for the first time. And last, the total cross sections, s-wave, p-wave and d-wave cross sections are computed for the elastic collisions between two ground-state atoms (hydrogen and nitrogen) at low temperatures. It finds that the total elastic cross sections are dominated by s-wave scattering when the collision energy is below 10-6a.u. The pronounced shape resonance is found at energy of 6.1$\times $10-6a.u. Calculations have shown that the shape resonance comes from the p-wave contributions. 相关文章 | 计量指标

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Close coupling calculations for excitation partial cross sections in Ne--HF collisions 余春日 2008 (6):  2097-2102.  doi: 10.1088/1674-1056/17/6/026 摘要 ( 1471 )   PDF(215KB) ( 646 )   This paper reports that an exact quantum close coupling calculation is carried out for rotational excitation in Ne--HF collisions on the available anisotropic potential. Partial cross sections are obtained separately at the incident energies of 48.35, 75, 120 and 150\,meV. The reliability of the results is demonstrated by comparison with previously published theoretical findings. Based on the calculations, the effect of the potential energy surface on the excitation partial cross sections is discussed in detail. 相关文章 | 计量指标

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Additivity rule for electron--molecule total cross section calculations at 50--5000eV: a new geometrical approach 施德恒, 孙金锋, 朱遵略, 刘玉芳 2008 (6):  2103-2109.  doi: 10.1088/1674-1056/17/6/027 摘要 ( 1403 )   PDF(187KB) ( 721 )   Taking into consideration the changes of the geometric shielding effect in a molecule as the energy of incident electrons varies, this paper presents an empirical fraction, which depends on the energy of incident electrons, the target's molecular dimension and the atomic and electronic numbers in the molecule. Using this empirical fraction, it proposes a new formulation of the additivity rule. Employing the new additivity rule, it calculates the total cross sections of electron scattering by C$_{2}$H$_{4}$, C$_{6}$H$_{6}$, C$_{6}$H$_{14}$ and C$_{8}$H$_{18}$ over the energy range from 50 to 5000\,eV. In order to exclude the calculation deviations caused by solving the radial Schr\"{o}dinger equation of electron scattering by atoms, here the atomic cross sections are derived from the experimental total cross section results of simple molecules (H$_{2}$, O$_{2}$, CO) via the inversion algorithm. The quantitative total cross sections are compared with those obtained by experiments and other theories, and good agreement is obtained over a wide energy range, even at energy of several tens of eV. 相关文章 | 计量指标

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Density functional study on structural and electronic properties of bimetallic gold--yttrium clusters: comparison with pure gold and yttrium clusters 毛华平, 王红艳, 盛勇 2008 (6):  2110-2115.  doi: 10.1088/1674-1056/17/6/028 摘要 ( 1519 )   PDF(616KB) ( 934 )   Employing first-principles methods, based on the density functional theory, this paper investigates the ground state geometric and electronic properties of pure gold clusters, pure yttrium clusters and gold clusters doped each with one yttrium atom. It is shown that the average bond lengths in the Au$_{n - 1}$Y($n \le $9) bimetallic clusters are shorter than those in the corresponding pure gold and yttrium clusters. The most stable isomers of the yttrium-doped gold clusters tend to equally delocalize valence s, p and d electrons of the constituent atoms over the entire structure. The Y atom has maximum number of neighbouring Au atom, which tends to be energetically favourable in the lowest-energy equilibrium structures, because the Au--Y bond is stronger than the Au-Au bond. The three-dimensional isomers of Au$_{n - 1}$Y structures are found in an early appearance starting at $n$=5 (Au$_{4}$Y). Calculated vertical ionization potential and electron affinities as a function of the cluster size show odd-even oscillatory behaviour, and resemble pure gold clusters. However, one of the most striking feature of pure yttrium clusters is the absence of odd-even alternation, in agreement with mass spectrometric observations. The HOMO--LUMO gap of Au$_{3}$Y is the biggest in all the doped Au$_{n - 1}$Y($n \le $9) bimetallic clusters. 相关文章 | 计量指标

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A density functional theoretical investigation of RhSin(n=1--6) clusters 任兆玉, 侯 茹, 郭平, 高继开, 杜恭贺, 文振翼 2008 (6):  2116-2123.  doi: 10.1088/1674-1056/17/6/029 摘要 ( 1489 )   PDF(597KB) ( 634 )   This paper computationally investigates the RhSi$_{n}(n=1$--$6)$ clusters by using a density functional approach. Geometry optimizations of the RhSi$_{n}(n=1$--$6)$ clusters are carried out at the B3LYP level employing LanL2DZ basis sets. It presents and discusses the equilibrium geometries of the RhSi$_{n}(n=1$--$6)$ clusters as well as the corresponding averaged binding energies, fragmentation energies, natural populations, magnetic properties, and the energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Theoretical results show that the most stable RhSi$_{n}(n=1$--$6)$ isomers keep an analogous framework of the corresponding Si$_{n + 1 }$ clusters, the RhSi$_{3}$ is the most stable cluster in RhSi$_{n}(n=1$--$6)$ isomers. Furthermore, the charges of the lowest-energy RhSi$_{n}(n=1$--$6)$ clusters transfer mainly from Si atom to Rh atom. Meanwhile, the magnetic moments of the RhSi$_{n}(n=1$--$6)$ arises from the 4d orbits of Rh atom. Finally, compared with the Si$_{n+1}$ cluster, the chemical stability RhSi$_{n}$ clusters are universally improved. 相关文章 | 计量指标

ATOMIC AND MOLECULAR PHYSICS

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Effect of laser spot size on fusion neutron yield in laser--deuterium cluster interactions 陈光龙, 卢海洋, 王成, 刘建胜, 李儒新, 倪国权, 徐至展 2008 (6):  2124-2129.  doi: 10.1088/1674-1056/17/6/030 摘要 ( 1515 )   PDF(455KB) ( 605 )   The effect of the laser spot size on the neutron yield of table-top nuclear fusion from explosions of a femtosecond intense laser pulse heated deuterium clusters is investigated by using a simplified model, in which the cluster size distribution and the energy attenuation of the laser as it propagates through the cluster jet are taken into account. It has been found that there exists a proper laser spot size for the maximum fusion neutron yield for a given laser pulse and a specific deuterium gas cluster jet. The proper spot size, which is dependent on the laser parameters and the cluster jet parameters, has been calculated and compared with the available experimental data. A reasonable agreement between the calculated results and the published experimental results is found. 相关文章 | 计量指标

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Micro thermal shear stress sensor based on vacuum anodic bonding and bulk-micromachining 易亮, 欧毅, 石莎莉, 马瑾, 陈大鹏, 叶甜春 2008 (6):  2130-2136.  doi: 10.1088/1674-1056/17/6/031 摘要 ( 1484 )   PDF(1525KB) ( 509 )   This paper describes a micro thermal shear stress sensor with a cavity underneath, based on vacuum anodic bonding and bulk micromachined technology. A Ti/Pt alloy strip, 2$\mu $m$\times $100$\mu $m, is deposited on the top of a thin silicon nitride diaphragm and functioned as the thermal sensor element. By using vacuum anodic bonding and bulk-si anisotropic wet etching process instead of the sacrificial-layer technique, a cavity, functioned as the adiabatic vacuum chamber, 200$\mu $m$\times $200$\mu $m$^{ }\times $400$\mu $m, is placed between the silicon nitride diaphragm and glass (Corning 7740). This method totally avoid adhesion problem which is a major issue of the sacrificial-layer technique. 相关文章 | 计量指标

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The entanglement of two dipole--dipole coupled atoms interacting with a thermal field via a two-photon process 廖湘萍, 方卯发, 蔡建武, 郑小娟 2008 (6):  2137-2142.  doi: 10.1088/1674-1056/17/6/032 摘要 ( 1724 )   PDF(420KB) ( 701 )   This paper studies entanglement between two dipole--dipole coupled atoms interacting with a thermal field via a two-photon process. It shows that the entanglement is dependent on the mean photon number of the thermal field and the dipole--dipole interaction. The results also show that the atom--atom entanglement through the two-photon process is larger than that through the one-photon process and a remarkable amount of entanglement between the atoms still remains at certain times even for a very highly noisy thermal field. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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Generation of entangled coherent states for two cavity modes via resonant interaction with a V-type three-level atom 郑仕标 2008 (6):  2143-2146.  doi: 10.1088/1674-1056/17/6/033 摘要 ( 1554 )   PDF(139KB) ( 574 )   This paper proposes a scheme for the generation of entangled coherent states for two cavity modes. In the scheme a V-type three-level atom is sent through a two-mode cavity filled with a coherent field. After the atom--cavity interaction and detection of the atomic state the cavity modes may evolve to a superposition of two-mode coherent states. As the scheme is based on resonant atom--cavity interaction, the required interaction time is short, which is important in view of the decoherence. Moreover, additional classical pulses are unnecessary before and after the atom--cavity interaction. 相关文章 | 计量指标

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Spectral feature with sub-natural linewidth due to quantum interference in a four-level system 杨丽君, 张连水, 庄仲红, 郭庆林, 傅广生 2008 (6):  2147-2151.  doi: 10.1088/1674-1056/17/6/034 摘要 ( 1519 )   PDF(407KB) ( 693 )   This paper studies the narrow spectral feature appearing in a four-level system coupled by two strong coherent fields and probed by a weak laser field. The linewidth is examined as a function of the Rabi frequencies of coupling fields, and the result is explained by using the dressed-state formalism. 相关文章 | 计量指标

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Two-hertz-linewidth Nd:YAG lasers at 1064nm stabilized to vertically mounted ultra-stable cavities 蒋燕义, 毕志毅, 徐信业, 马龙生 2008 (6):  2152-2155.  doi: 10.1088/1674-1056/17/6/035 摘要 ( 1792 )   PDF(160KB) ( 816 )   Two Nd:YAG lasers operating at 1064\,nm are separately servo-locked to two vertically mounted ultra-stable cavities. The optical heterodyne beat between two cavity-stabilized lasers shows that the linewidth of each laser reaches 2\,Hz and the average frequency drift reduces to less than 1\,Hz/s. 相关文章 | 计量指标

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Laser-induced pattern formation from homogeneous polyisoprene solutions 林殿阳, 黎明, 王淑杰, 吕志伟 2008 (6):  2156-2159.  doi: 10.1088/1674-1056/17/6/036 摘要 ( 1568 )   PDF(658KB) ( 591 )   This paper reports that the pattern formation in homogeneous solutions of polyisoprene in toluene saturated with C$_{60}$ induced by a continuous-wave visible laser is observed experimentally. The transmitted beam patterns change with the increase of the laser irradiation time. In the initial phase, the patterns with concentric ring-shaped structure are formed. In the end, the patterns become speckle-shaped. The incubation time of the transmitted beam widening is inversely proportional to the laser power density and solution concentration. The pattern formation results from the optical-field-induced refractive index changes in the solutions, but the mechanism of optical-field-induced refractive index changes in the polymer solutions needs to be further studied. 相关文章 | 计量指标

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Slowly moving matter--wave gap soliton propagation in weak random nonlinear potential 张铭锐, 张永亮, 蒋寻涯, 资剑 2008 (6):  2160-2169.  doi: 10.1088/1674-1056/17/6/037 摘要 ( 1368 )   PDF(1003KB) ( 497 )   We systematically investigate the motion of slowly moving matter--wave gap solitons in a nonlinear potential, produced by the weak random spatial variation of the atomic scattering length. With the weak randomness, we construct an effective-particle theory to study the motion of gap solitons. Based on the effective-particle theory, the effect of the randomness on gap solitons is obtained, and the motion of gap solitons is finally solved. Moreover, the analytic results for the general behaviours of gap soliton motion, such as the ensemble-average speed and the reflection probability depending on the weak randomness are obtained. We find that with the increase of the random strength the ensemble-average speed of gap solitons decreases slowly where the reduction is proportional to the variance of the weak randomness, and the reflection probability becomes larger. The theoretical results are in good agreement with the numerical simulations based on the Gross--Pitaevskii equation. 相关文章 | 计量指标

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Enhanced optical nonlinear absorption of graded Au--TiO2 composite films 刘莉, 苏雄睿 2008 (6):  2170-2174.  doi: 10.1088/1674-1056/17/6/038 摘要 ( 1383 )   PDF(313KB) ( 640 )   This paper reports that single-layer and graded Au--TiO$_{2}$ granular composite films with Au atom content 15{\%}--66{\%} were prepared by using reactive co-sputtering technique. The third-order optical nonlinearity of single-layer and graded composite films was investigated by using s- and p-polarized $Z$-scans in femtosecond time scale. The nonlinear absorption coefficient \textit{$\beta $}$_{\rm eff}$ of single-layer Au--TiO$_{2}$ films is measured to be --2.3$\times $10$^{3}-$0.76$\times $10$^{3}$ cm/GW with Au atom content 15{\%}--66{\%}. The \textit{$\beta $}$_{\rm eff}$ value of the 10-layer Au--TiO$_{2}$ graded film is enhanced to be --2.1$\times $10$^{4}$cm/GW calculated from p-polarized $Z$-scans, which is about ten times the maximum \textit{$\beta $}$_{\rm eff}$ of single-layer films. Broadened response in the wavelength region 730--860\,nm of the enhanced optical nonlinearity of graded Au--TiO$_{2}$ composite films was also investigated. 相关文章 | 计量指标

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Molecular dynamics study of ice structural evolution 王燕, 董顺乐 2008 (6):  2175-2179.  doi: 10.1088/1674-1056/17/6/039 摘要 ( 1625 )   PDF(233KB) ( 623 )   Molecular dynamics simulation is employed to study the structural evolution of low density amorphous ice during its compression from one atmosphere to 2.5\,GPa. Calculated results show that high density amorphous ice is formed at an intermediate pressure of $\sim $1.0\,GPa; the O--O--O bond angle ranges from 83$^{\circ}$ to 113$^{\circ}$, and the O--H$\cdots$O bond is bent from 112$^{\circ}$ to 160$^{\circ}$. Very high density amorphous ice is obtained by quenching to 80\,K and decompressing the ice to ambient pressure from 160\,K/1.3\,GPa or 160\,K/1.7\,GPa; and the next-nearest O--O length is found to be 0.310\,nm, just 0.035\,nm beyond the nearest O--O distance of 0.275\,nm. 相关文章 | 计量指标

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Synthesis of large-scale GaN nanowires by ammoniating Ga2O3 films on Co layer deposited on Si(111) substrates 秦丽霞, 薛成山, 庄惠照, 杨兆柱, 陈金华, 李红 2008 (6):  2180-2183.  doi: 10.1088/1674-1056/17/6/040 摘要 ( 1474 )   PDF(4544KB) ( 634 )   A mass of GaN nanowires has been successfully synthesized on Si(111) substrates by magnetron sputtering through ammoniating Ga2O3/Co films at 950\du. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscope and Fourier transformed infrared spectra are used to characterize the samples. The results demonstrate that the nanowires are of single-crystal GaN with a hexagonal wurtzite structure and possess relatively smooth surfaces. The growth mechanism of GaN nanowires is also discussed. 相关文章 | 计量指标

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Synthesis and characterization of axially periodic Zn2SnO4 dendritic nanostructures 沈俊, 葛炳辉, 褚卫国, 罗述东, 张增星, 刘东方, 刘利峰, 马文君, 任彦, 向彦娟, 王超英, 王刚, 周维亚 2008 (6):  2184-2190.  doi: 10.1088/1674-1056/17/6/041 摘要 ( 1713 )   PDF(7735KB) ( 607 )   Zn2SnO4 (ZTO) nanowires with a unique dendritic nanostructure were synthesized via a simple one-step thermal evaporation and condensation process. The morphology and microstructure of the ZTO nanodendrite have been investigated by means of field emission scanning electron microscopy (SEM), x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). SEM observation revealed the formation of branched nanostructures and showed that each branch exhibited a unique periodic structure formed by a row of overlaid rhombohedra of ZTO nanocrystals along the axis of the nanobranch. HRTEM studies displayed that the branches grew homoepitaxially as single-crystalline nanowires from the ZTO nanowire backbone. A possible growth model of the branched ZTO nanowires is discussed. To successfully prepare branched structures would provide an opportunity for both fundamental research and practical applications, such as three-dimensional nanoelectronics, and opto-electronic nanodevices. 相关文章 | 计量指标

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Organic molecules modified palladium nanowires arrays prepared by high temperature liquid phase reduction 申承民, 杨天中, 肖从文, 张怀若, 田继发, 鲍丽宏, 李晨, 李建奇, 高鸿钧 2008 (6):  2191-2196.  doi: 10.1088/1674-1056/17/6/042 摘要 ( 1649 )   PDF(4899KB) ( 526 )   This paper reports high temperature liquid phase synthesis of Pd nanowires using chemically modified porous anodic aluminium oxide as template. In this synthesis process, oleic acid is used to modify the inner wall of the pores and Pd$^{2 + }$ complex with oleylamine is filled into the channel of the template. The complex is then reduced to give oleylamine-capped Pd nanowires. This paper suggests that oleic acid can improve the environment of inner wall of the pores, leading to the formation of uniform Pd nanowires. The synthetic process can be extended to make other types of nanowires. 相关文章 | 计量指标

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Oxidation of silicon surface with atomic oxygen radical anions 王莲, 宋崇富, 孙剑秋, 侯莹, 李晓光, 李全新 2008 (6):  2197-2203.  doi: 10.1088/1674-1056/17/6/043 摘要 ( 1736 )   PDF(507KB) ( 620 )   The surface oxidation of silicon (Si) wafers by atomic oxygen radical anions (O- anions) and the preparation of metal--oxide--semiconductor (MOS) capacitors on the O--oxidized Si substrates have been examined for the first time. The O- anions are generated from a recently developed O- storage-emission material of [Ca24Al28O64]4+.4O- (C12A7-O- for short). After it has been irradiated by an O- anion beam (0.5\mu A/cm2) at 3000C for 1--10 hours, the Si wafer achieves an oxide layer with a thickness ranging from 8 to 32nm. X-ray photoelectron spectroscopy (XPS) results reveal that the oxide layer is of a mixture of SiO2, Si2O3, and Si2O distributed in different oxidation depths. The features of the MOS capacitor of x/Si> are investigated by measuring capacitance-voltage (C-V) and current-voltage (I-V) curves. The oxide charge density is about 6.0 \times 1011cm2 derived from the C-V curves. The leakage current density is in the order of 10-6A/cm2 below 4MV/cm, obtained from the $I-V$ curves. The O- anions formed by present method would have potential applications to the oxidation and the surface-modification of materials together with the preparation of semiconductor devices. 相关文章 | 计量指标

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Magnetic and electrical properties of zincblende CrAs 陈鹏, Takamura K 2008 (6):  2204-2207.  doi: 10.1088/1674-1056/17/6/044 摘要 ( 1487 )   PDF(996KB) ( 600 )   This paper reports that 9\,nm zincblende CrAs is grown by molecular-beam epitaxy on InAs buffer layer. The zb-CrAs shows ferromagnetism at room temperature and the total magnetic moment $3.09\pm 0.15\,\mu_{\rm B}$ per CrAs unit. The temperature dependence of zb-CrAs resistance $R$ shows metallic behaviour. 相关文章 | 计量指标

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

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First-principles calculation of transport property in nano-devices under an external magnetic field 陈竞哲, 张进, 韩汝珊 2008 (6):  2208-2215.  doi: 10.1088/1674-1056/17/6/045 摘要 ( 1726 )   PDF(407KB) ( 571 )   The mesoscopic quantum interference phenomenon (QIP) can be observed and behaves as the oscillation of conductance in nano-devices when the external magnetic field changes. Excluding the factor of impurities or defects, specific QIP is determined by the sample geometry. We have improved a first-principles method based on the matrix Green's function and the density functional theory to simulate the transport behaviour of such systems under a magnetic field. We have studied two kinds of QIP: universal conductance fluctuation (UCF) and Aharonov--Bohm effect (A--B effect). We find that the amplitude of UCF is much smaller than the previous theoretical prediction. We have discussed the origin of difference and concluded that due to the failure of ergodic hypothesis, the ensemble statistics is not applicable, and the conductance fluctuation is determined by the flux-dependent density of states (DOSs). We have also studied the relation between the UCF and the structure of sample. For a specific structure, an atomic circle, the A--B effect is observed and the origin of the oscillation is also discussed. 相关文章 | 计量指标

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First-principles calculations for elastic properties of rutile TiO2 under pressure 朱俊, 于景新, 王艳菊, 陈向荣, 经福谦 2008 (6):  2216-2221.  doi: 10.1088/1674-1056/17/6/046 摘要 ( 1724 )   PDF(197KB) ( 1062 )   This paper studies the equilibrium structure parameters and the dependences of the elastic properties on pressure for rutile TiO$_{2}$ by using the Cambridge Serial Total Energy Package (CASTEP) program in the frame of density functional theory. The obtained equilibrium structure parameters, bulk modulus $B_{0}$ and its pressure derivative $B'_{0}$ are in good agreement with experiments and the theoretical results. The six independent elastic constants of rutile TiO$_{2}$ under pressure are theoretically investigated for the first time. It is found that, as pressure increases, the elastic constants $C_{11}$,$ C_{33}$, $C_{66}$, $C_{12}$ and $C_{13}$ increase, the variation of elastic constant $C_{44}$ is not obvious and the anisotropy will weaken. 相关文章 | 计量指标

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Electronic structure and optical properties of LiXH3 and XLiH3 (X=Be, B or C) 伞晓娇, 何志, 马琰铭, 崔田, 刘冰冰, 邹广田 2008 (6):  2222-2228.  doi: 10.1088/1674-1056/17/6/047 摘要 ( 1640 )   PDF(1326KB) ( 718 )   The equilibrium lattice constant, the cohesive energy and the electronic properties of light metal hydrides LiXH3 and XLiH3 (X=Be, B or C) with perovskite lattice structures have been investigated by using the pseudopotential plane-wave method. Large energy gap of LiBeH3 indicates that it is insulating, but other investigated hydrides are metallic. The pressure-induced metallization of LiBeH3 is found at about 120GPa, which is attributed to the increase of Be-p electrons with pressure. The electronegativity of the p electrons of X atom is responsible for the metallicity of the investigated LiXH3 hydrides, but the electronegativity of the s electrons of X atom plays an important role in the metallicity of the investigated XLiH3 hydrides. In order to deeply understand the investigated hydrides, their optical properties have also been investigated. The optical absorption of either LiBeH3 or BeLiH3 has a strong peak at about 5eV, showing that their optical responses are qualitatively similar. It is also found that the optical responses of other investigated hydrides are stronger than those of LiBeH3 and BeLiH3 in lower energy ranges, especially in the case of CLiH3. 相关文章 | 计量指标

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Quasiparticle density of states of 2H-NbSe2 single crystals revealed by low-temperature specific heat measurements according to a two-component model 闫静, 单磊, 王越, 肖志力, 闻海虎 2008 (6):  2229-2235.  doi: 10.1088/1674-1056/17/6/048 摘要 ( 1488 )   PDF(277KB) ( 689 )   Low-temperature specific heat in a dichalcogenide superconductor 2H-NbSe2 is measured in various magnetic fields. It is found that the specific heat can be described very well by a simple model concerning two components corresponding to vortex normal core and ambient superconducting region, separately. For calculating the specific heat outside the vortex core region, we use the Bardeen--Cooper--Schrieffer (BCS) formalism under the assumption of a narrow distribution of the superconducting gaps. The field-dependent vortex core size in the mixed state of 2H-NbSe2, determined by using this model, can explain the nonlinear field dependence of specific heat coefficient $\gamma(H)$, which is in good agreement with the previous experimental results and more formal calculations. With the high-temperature specific heat data, we can find that, in the multi-band superconductor 2H-NbSe2, the recovered density of states (or Fermi surface) below Tc under a magnetic field seems not to be gapped again by the charge density wave (CDW) gap, which suggests that the superconducting gap and the CDW gap may open on different Fermi surface sheets. 相关文章 | 计量指标

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The ground-state lifetime of polaron in a parabolic quantum dot 于毅夫, 肖景林, 尹辑文, 王子武 2008 (6):  2236-2239.  doi: 10.1088/1674-1056/17/6/049 摘要 ( 1698 )   PDF(391KB) ( 703 )   This paper reports that the ground-state energy of polaron was obtained with strong electron-LO-phonon coupling by using a variational method of the Pekar type in a parabolic quantum dot. Quantum transition is occurred in the quantum system due to the electron--phonon interaction and the influence of temperature. That is the polaron transit from the ground-state to the first-excited state after absorbing a LO-phonon and it causes the change of the polaron lifetime. Numerical calculations are performed and the results illustrate that the ground-state lifetime of the polaron will increase with increasing the ground-state energy of polaron and decrease with increasing the electron-LO-phonon coupling strength, the confinement length of the quantum dot and the temperature. 相关文章 | 计量指标

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Preparation of p-type ZnO:(Al, N) by a combination of sol--gel and ion-implantation techniques 薛书文, 祖小涛, 邵乐喜, 袁兆林, 向霞, 邓宏 2008 (6):  2240-2244.  doi: 10.1088/1674-1056/17/6/050 摘要 ( 1646 )   PDF(605KB) ( 754 )   We report the preparation of p-type ZnO thin films on (0001) sapphire substrates by a combination of sol--gel and ion-implantation techniques. The results of the Hall-effect measurements carried out at room temperature indicate that the N-implanted ZnO:Al films annealed at 600\du\ have converted to p-type conduction with a hole concentration of $1.6\times1018cm-3, a hole mobility of 3.67cm2/V.s and a minimum resistivity of 4.80cm.\Omega$. Ion-beam induced damage recovery has been investigated by x-ray diffraction (XRD), photoluminescence (PL) and optical transmittance measurements. Results show that diffraction peaks and PL intensities are decreased by N ion implantation, but they nearly recover after annealing at 600\du. Our results demonstrate a promising approach to fabricate p-type ZnO at a low cost. 相关文章 | 计量指标

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Temperature dependence of biaxial strain and its influence on phonon and band gap of GaN thin film 徐宏妍, 菅傲群, 薛晨阳, 陈阳, 张斌珍, 张文栋, 张志国, 冯震 2008 (6):  2245-2250.  doi: 10.1088/1674-1056/17/6/051 摘要 ( 1482 )   PDF(223KB) ( 825 )   Hexagonal GaN epilayer grown on sapphire substrate by metal organic chemical vapour deposition (MOCVD) is studied using Raman scattering and photoluminescence in a temperature range from 100\,K to 873\,K. The model of strain (stress) induced by the different lattice parameters and thermal coefficients of epilayer and substrate as a function of temperature is set up. The frequency and the linewidth of $E_2^{\rm high}$ mode in a GaN layer are modelled by a theory with considering the thermal expansion of the lattice, a symmetric decay of the optical phonons, and the strain (stress) in the layer. The temperature-dependent energy shift of free exciton A is determined by using Varshni empirical relation, and the effect of strain (stress) is also investigated. We find that the strain in the film leads to a decreasing shift of the phonon frequency and an about 10meV-increasing shift of the energy in a temperature range from 100\,K to 823\,K. 相关文章 | 计量指标

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Anisotropic electrical conductivity,phase transition and thermal hysteresis of a charge-transfer salt dibutylammonium bis-7,7,8,8-tetracyanoquinodimethane DBA(TCNQ)2 龙云泽, 陈兆甲, 彭海琳, 刘忠范 2008 (6):  2251-2256.  doi: 10.1088/1674-1056/17/6/052 摘要 ( 1602 )   PDF(1423KB) ( 764 )   This paper reports that a charge-transfer salt dibutylammonium bis-7,7,8,8-tetracyanoquinodimethane [DBA (TCNQ)2] has been prepared. The temperature dependences of the DC electrical conductivity of the DBA (TCNQ)2 single crystal measured along the crystallographic a, b, and c axes are reported. The crystal shows semiconducting behaviour and the room-temperature conductivities are highly anisotropic (\sigmaa = 3.63\times 10-4S/cm, \sigmab= 2.84$\times 10-6S/cm, and \sigmac = 1.82\times 10-5S/cm). Particularly, a sharp semiconductor to semiconductor transition has been observed around 270 K on the resistivity curves measured under cooling and heating. In addition, thermal hysteresis phenomena on conductivity and differential scanning calorimetry curves are also reported. 相关文章 | 计量指标

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Excitation of surface plasmons at the boundary of overdense plasma 王亮, 曹金祥, 王艳, 牛田野, 刘磊, 吕铀 2008 (6):  2257-2262.  doi: 10.1088/1674-1056/17/6/053 摘要 ( 1511 )   PDF(673KB) ( 674 )   The excitation of surface plasmons (SPs) with a strip grating at the boundary of an unmagnetized overdense plasma has been investigated theoretically and experimentally. An incident electromagnetic radiation was p-polarized at the frequency of 5GHz. Experiments showed that when the plasma density was four times higher than the critical density with the grating present, and the SPs could be excited at the boundary of the overdense plasma. Contribution of the glass layer in the formation of the SP dispersion relation was examined. When the incident electromagnetic radiation was coupled into SPs the coupling order with the effective permittivity was simulated qualitatively. We find that the existence of SPs at the boundary of overdense plasma indicates that the reflection coefficient of the incident electromagnetic radiation reaches its minimum and even becomes total absorption. In this work the plasma density was diagnosed by a Langmuir double probe. 相关文章 | 计量指标

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Influence of shape anisotropy on microwave complex permeability in carbonyl iron flakes/epoxy resin composites 温福昇, 乔亮, 周栋, 左文亮, 伊海波, 李发伸 2008 (6):  2263-2267.  doi: 10.1088/1674-1056/17/6/054 摘要 ( 1490 )   PDF(1387KB) ( 970 )   To explore the mechanism of carbonyl iron flake composites for microwave complex permeability, this paper investigates the feature of the flakes. The shape anisotropy was certified by the results of the magnetization hysteresis loops and the M\"{o}ssbauer spectra. Furthermore, the shape anisotropy was used to explain the origin of composite microwave performance, and the calculated results agree with the experiment. It is believed that the shape anisotropy dominates microwave complex permeability, and the natural resonance plays main role in flake. 相关文章 | 计量指标

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Magnetocaloric effect in Gd6Co1.67Si3 compound with a second-order phase transition 沈俊, 李养贤, 董巧燕, 王芳, 孙继荣 2008 (6):  2268-2271.  doi: 10.1088/1674-1056/17/6/055 摘要 ( 1430 )   PDF(784KB) ( 588 )   The magnetic properties and the magnetic entropy change \Delta S have been investigated for Gd6Co1.67Si3 compounds with a second-order phase transition. The saturation moment at 5K and the Curie temperature TC are 38.1\muB and 298K, respectively. The \Delta S originates from a reversible second-order magnetic transition around TC and its value reaches 5.2J/kg.K for a magnetic field change from 0 to 5T. The refrigerant capacity (RC) of Gd6Co1.67Si3 are calculated by using the methods given in Refs.[12] and [21], respectively, for a field change of 0--5T and its values are 310 and 440\,J/kg, which is larger than those of some magnetocaloric materials with a first-order phase transition. 相关文章 | 计量指标

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Effect of thermal-annealing on the magnetoresistance of manganite-based junctions 谢燕武, 沈保根, 孙继荣 2008 (6):  2272-2276.  doi: 10.1088/1674-1056/17/6/056 摘要 ( 1993 )   PDF(873KB) ( 555 )   Thermal-annealing has been widely used in modulating the oxygen content of manganites. In this work, we have studied the effect of annealing on the transport properties and magnetoresistance of junctions composed of a La0.9Ca0.1MnO3 + \delta film and a Nb-doped SrTiO3 substrate. We have demonstrated that the magnetoresistance of junctions is strongly dependent on the annealing conditions: From the junction annealed-in-air to the junction annealed-in-vacuum, the magnetoresistance near 0-V bias can vary from \sim --60% to \sim 0. A possible mechanism accounting for this phenomenon is discussed. 相关文章 | 计量指标

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Generalization of iterative perturbation theory and coherent potential approximation (ITP+CPA) to double exchange model with orbital degeneracy 刘自信, 文生辉, 李明 2008 (6):  2277-2280.  doi: 10.1088/1674-1056/17/6/057 摘要 ( 1619 )   PDF(298KB) ( 795 )   A combination of the iterative perturbation theory (ITP) of the dynamical mean field theory (DMFT) and coherent-potential approximation (CPA) is generalized to the double exchange model with orbital degeneracy. The Hubbard interaction and the off-diagonal components for the hopping matrix $t_{ij}^{mn} (m \ne n)$ are considered in our calculation of spectrum and optical conductivity. The numerical results show that the effects of the non-diagonal hopping matrix elements are important. 相关文章 | 计量指标

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Magnetic domain structures of precipitation-hardened SmCo 2:17-type sintered magnets: Heat treatment effect 李岫梅, 方以坤, 郭朝晖, 刘涛, 郭永权, 李卫, 韩宝善 2008 (6):  2281-2287.  doi: 10.1088/1674-1056/17/6/058 摘要 ( 1448 )   PDF(6544KB) ( 875 )   The typical magnetic domains of Sm(CobalFe0.25Cu0.07Zr0.02)7.4 magnets quenched through various heat-treatment steps have been revealed by using magnetic force microscopy (MFM). For the specimens in which the nominal c-axis is perpendicular to the imaging plane, the domain configurations change from plate-like for the as-sintered magnet to corrugation and spike-like for the homogenized one, and then to a coarse and finally to a finer domain structure when isothermally aged at 830\du\ and then annealed at 400\du. However, only plate-like domains can be detected on the surfaces with the nominal c-axis parallel to the imaging plane. The finer domain (so-called interaction domain) is a characteristic magnetic domain pattern of the Sm--Co 2:17-type magnets with high coercivities. Domain walls in a zigzag shape are revealed by means of MFM in final bulk Sm--Co 2:17-type sintered magnets. 相关文章 | 计量指标

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Detection of microarray protein biomolecules by oblique-incidence reflectivity difference technique without labelling agents 张洪艳, 陆珩, 李巍, 梁汝强, 金奎娟, 周岳亮, 阮康成, 杨国桢 2008 (6):  2288-2291.  doi: 10.1088/1674-1056/17/6/059 摘要 ( 1592 )   PDF(944KB) ( 379 )   This paper reports that the detection to the protein in microarray format is carried out by oblique-incidence reflectivity difference (OI--RD) analysis without any labelling agents. The OI--RD intensities not only depend on the protein structure, but also vary with the protein concentration. The results indicate that this method should have potential application in detection of biochemical processes. The high throughout and in situ detection can be achieved by this method with further improving of the experimental system. 相关文章 | 计量指标

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Electrical and deep levels characteristics of ZnO/Si heterostructure by MOCVD deposition 刘磁辉, 刘秉策, 付竹西 2008 (6):  2292-2296.  doi: 10.1088/1674-1056/17/6/060 摘要 ( 1631 )   PDF(199KB) ( 705 )   ZnO films have been prepared on p-type Si substrates by metal-organic chemical vapour deposition (MOCVD) at different total gas flow rates. The current versus voltage and temperature ($I-V-T$) characteristics, the deep-level transient spectroscopy (DLTS) and the photoluminescence (PL) spectra of the samples were measured. DLTS shows two deep-level centres of $E_1$ ($E_{\rm C}$--0.13$\pm $0.02\,eV) and $E_2$ ($E_{\rm C}$--0.43$\pm $0.05\,eV) in sample 1202a, which has a ZnO/p-Si heterostructure. A deep level at $E_{\rm C}$--0.13$\pm $0.01\,eV was also obtained from the $I-T$ characteristics. It was considered to be the same as $E_1$ obtained from DLTS measurement. The emission related to this deep level center was detected by PL spectra. In addition, the energy location and the relative trap density of $E_1$ was varied when the total gas flow rate was changed. 相关文章 | 计量指标

8000 CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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The synchronization of FitzHugh--Nagumo neuron network coupled by gap junction 展永, 张素花, 赵同军, 安海龙, 张振东, 韩英荣, 柳辉, 张玉红 2008 (6):  2297-2303.  doi: 10.1088/1674-1056/17/6/061 摘要 ( 1487 )   PDF(171KB) ( 434 )   It is well known that the strong coupling can synchronize a network of nonlinear oscillators. Synchronization provides the basis of the remarkable computational performance of the brain. In this paper the FitzHugh--Nagumo neuron network is constructed. The dependence of the synchronization on the coupling strength, the noise intensity and the size of the neuron network has been discussed. The results indicate that the coupling among neurons works to improve the synchronization, and noise increases the neuron random dynamics and the local fluctuations; the larger the size of network, the worse the synchronization. The dependence of the synchronization on the strength of the electric synapse coupling and chemical synapse coupling has also been discussed, which proves that electric synapse coupling can enhance the synchronization of the neuron network largely. 相关文章 | 计量指标

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A phase analysis of vorticity vectors associated with tropical convection 崔晓鹏 2008 (6):  2304-2310.  doi: 10.1088/1674-1056/17/6/062 摘要 ( 1639 )   PDF(599KB) ( 669 )   Three new vorticity vectors have been proposed by Gao {\em et al} to study the two-dimensional tropical convection. In the present paper, phase relations between surface rain rate and the vorticity vectors are analysed with the calculations of lag correlation coefficients based on hourly zonally-averaged mass-integrated cloud-resolving simulation data. The cloud-resolving model is integrated with the vertical velocity, zonal wind, horizontal thermal and moisture advections, and sea surface temperature observed and derived from tropical ocean global atmosphere -- coupled ocean atmosphere response experiment (TOGA-COARE) for 10 days. Maximum local increase of the vertical component of the convective vorticity vector leads maximum surface rain rate by 2 hours mainly due to the interaction between vorticity and zonal gradient of ice heating. While maximum local increase of the vertical component of the moist vorticity vector leads maximum surface rain rate by 2 hours mainly because of the interaction between zonal specific humidity gradient and zonal buoyancy gradient. And the maximum local decrease of the zonal component of the dynamic vorticity vector leads maximum surface rain rate by 2 hours mainly due to the interactions between vorticity and vertical pressure gradient as well as vorticity and buoyancy. 相关文章 | 计量指标

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Detection and attribution of abrupt climate changes in the last one hundred years 张 文, 万仕全 2008 (6):  2311-2316.  doi: 10.1088/1674-1056/17/6/063 摘要 ( 1611 )   PDF(183KB) ( 550 )   Based on physical backgrounds, the four time series of the Guliya (Tibetan plateau) ice core (GIC) \textit{$\delta $}$^{18}$O, and three natural factors, i.e. the rotation rate of earth, sunspots, and El Nino--Southern Oscillation (ENSO) signals, are decomposed into two hierarchies, i.e. more and less than 10-year hierarchies respectively, and then the running $t$-test is used to reanalyse the data before and after filtering with the purpose of investigating the contribution of natural factors to the abrupt climate changes in the last one hundred years. The results show that the GIC \textit{$\delta $}$^{18}$O evolved with a quasi-period of 7--9 years, and the abrupt climate changes in the early 1960s and in the period from the end of the 1970s to the beginning of the 1980s resulted from the joint effect of the two hierarchies, in other words, the two interdecadal abrupt changes of climate in the last one hundred years were global. The interannual variations of ENSO and sunspots were the important triggering factors for the abrupt climate changes in the last one hundred years. At the same time, the method of Information Transfer (IT) is employed to estimate the contributions of ENSO signals and sunspots activities to the abrupt climate changes, and it is found that the contribution of the interannual variation of ENSO signals is relatively large. 相关文章 | 计量指标

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Effect of superstrong magnetic fields on thermonuclear reaction rates on the surface of magnetars 刘宏林, 罗志全, 赖祥军, 刘晶晶 2008 (6):  2317-2320.  doi: 10.1088/1674-1056/17/6/064 摘要 ( 1287 )   PDF(158KB) ( 520 )   A simple and efficient screening model for studying the effects of superstrong magnetic fields (such as those of magnetars) on thermonuclear reaction rates on magnetar surfaces is proposed in this paper. The most interesting thermonuclear reactions, including hydrogen burning by the CNO cycle and helium burning by the triple alpha reaction, are investigated on the surface of magnetars. We find that the superstrong magnetic fields can increase the thermonuclear reaction rates by many orders of magnitude. The enhancement may have a dramatic effect on the thermonuclear runaways and bursts on the surfaces of magnetars. 相关文章 | 计量指标

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Hawking radiation from Kerr-Newman-Kasuya black hole via quantum anomalies 何唐梅, 樊军辉, 王永久 2008 (6):  2321-2325.  doi: 10.1088/1674-1056/17/6/065 摘要 ( 1659 )   PDF(164KB) ( 586 )   We have studied the Hawking radiation of the Kerr-Newman-Kasuya black hole via gauge and gravitational anomaly in the dragging coordinates. The fluxes of the electromagnetic current and the energy momentum tensor for each partial wave in two-dimensional field are obtained. 相关文章 | 计量指标