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2009年, 第18卷, 第4期　刊出日期：2009-04-20 上一期    下一期

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Topological structure of Gauss--Bonnet--Chern theorem and p-branes 田苗, 张欣会, 段一士 2009 (4):  1301-1305.  doi: 10.1088/1674-1056/18/4/001 摘要 ( 1916 )   PDF(187KB) ( 958 )   By making use of the φ-mapping topological current theory, this paper shows that the Gauss--Bonnet--Chern density (the Euler--Poincaré characteristic χ(M) density) can be expressed in terms of a smooth vector field φ and take the form of δ(φ), which means that only the zeros of φ contribute to χ(M). This is the elementary fact of the Hopf theorem. Furthermore, it presents that a new topological tensor current of \tilde {p}-branes can be derived from the Gauss--Bonnet--Chern density. Using this topological current, it obtains the generalized Nambu action for multi \tilde p-branes. 相关文章 | 计量指标

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Effect of incubation period on epidemic spreading in complex networks 黄炜, 姜锐, 胡茂彬, 吴清松 2009 (4):  1306-1311.  doi: 10.1088/1674-1056/18/4/002 摘要 ( 1761 )   PDF(462KB) ( 805 )   We study the effect of incubation period on epidemic spreading in the Barabasi--Albert scale-free network and the Watts--Strogatz small world network by using a Suspectable-Incubated-Infected-Suspectable model. Our analytical investigations show that the epidemic threshold is independent of incubation period in both networks, which is verified by our large-scale simulation results. We also investigate the effect of incubation period on the epidemic dynamics in a supercritical regime. It is found that with the increase of incubation period Ω , a damped oscillation evolution of ρT(the ratio of persons in incubated state) appears and the time needed to reach a saturation value increases. Moreover, the steady value of ρT increases and approaches to an asymptotic constant with the value of {\it\Omega} increasing. As a result, the infected ratio ρI decreases with the increase of Ω according to a power law. 相关文章 | 计量指标

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A generalized Mei conserved quantity and Mei symmetry of Birkhoff system 王鹏, 方建会, 王先明 2009 (4):  1312-1315.  doi: 10.1088/1674-1056/18/4/003 摘要 ( 1588 )   PDF(138KB) ( 867 )   This paper studies a new conserved quantity which can be called generalized Mei conserved quantity and directly deduced by Mei symmetry of Birkhoff system. The conditions under which the Mei symmetry can directly lead to generalized Mei conserved quantity and the form of generalized Mei conserved quantity are given. An example is given to illustrate the application of the results. 相关文章 | 计量指标

GENERAL

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Coupled flexural-torsional vibration band gap in periodic beam including warping effect 方剑宇, 郁殿龙, 韩小云, 蔡力 2009 (4):  1316-1321.  doi: 10.1088/1674-1056/18/4/004 摘要 ( 1722 )   PDF(1514KB) ( 1162 )   The propagation of coupled flexural-torsional vibration in the periodic beam including warping effect is investigated with the transfer matrix theory. The band structures of the periodic beam, both including warping effect and ignoring warping effect, are obtained. The frequency response function of the finite periodic beams is simulated with finite element method, which shows large vibration attenuation in the frequency range of the gap as expected. The effect of warping stiffness on the band structure is studied and it is concluded that substantial error can be produced in high frequency range if the effect is ignored. The result including warping effect agrees quite well with the simulated result. 相关文章 | 计量指标

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Lattice models of traffic flow considering drivers' delay in response 祝会兵 2009 (4):  1322-1327.  doi: 10.1088/1674-1056/18/4/005 摘要 ( 1810 )   PDF(169KB) ( 925 )   This paper proposes two lattice traffic models by taking into account the drivers' delay in response. The lattice versions of the hydrodynamic model are described by the differential-difference equation and difference-difference equation, respectively. The stability conditions for the two models are obtained by using the linear stability theory. The modified KdV equation near the critical point is derived to describe the traffic jam by using the reductive perturbation method, and the kink--antikink soliton solutions related to the traffic density waves are obtained. The results show that the drivers' delay in sensing headway plays an important role in jamming transition. 相关文章 | 计量指标

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Two-mode excited entangled coherent states and their entanglement properties 周冬林, 匡乐满 2009 (4):  1328-1332.  doi: 10.1088/1674-1056/18/4/006 摘要 ( 1780 )   PDF(113KB) ( 825 )   This paper introduces two types of two-mode excited entangled coherent states (TMEECSs) |Ψ±(α,m,n)>, studies their entanglement characteristics, and investigates the influence of photon excitations on quantum entanglement. It shows that for the state |Ψ+(α,m,m)> the two-mode photon excitations affect seriously entanglement character while the state |Ψ-(α,m,m)> is always a maximally entangled state, and shows how such states can be produced by using cavity quantum electrodynamics and quantum measurements. It finds that the entanglement amount of the TMEECSs is larger than that of the single-mode excited entangled coherent states with the same photon excitation number. 相关文章 | 计量指标

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Participant attack on quantum secret sharing based on entanglement swapping 宋婷婷, 张劼, 高飞, 温巧燕, 朱甫臣 2009 (4):  1333-1337.  doi: 10.1088/1674-1056/18/4/007 摘要 ( 2298 )   PDF(107KB) ( 949 )   The security of quantum secret sharing based on entanglement swapping is revisited and a participant attack is presented. In this attack two dishonest agents together can illegally recover the secret quantum state without the help of any other controller, and it will not be detected by any other users. Furthermore, by modifying the distribution process of particles and adding a detection step after each distribution process, we propose an improved protocol which can resist this kind of attack. 相关文章 | 计量指标

GENERAL

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Bipartite entanglement of a two-qubit system with anisotropic couplings under nonuniform magnetic fields 秦猛, 田东平 2009 (4):  1338-1341.  doi: 10.1088/1674-1056/18/4/008 摘要 ( 1518 )   PDF(166KB) ( 728 )   This paper investigates bipartite entanglement of a two-qubit system with anisotropic couplings under an inhomogeneous magnetic field. This work is mainly to investigate the characteristics of a Heisenberg XYZ chain and obtains some meaningful results. By the concept of negativity, it finds that the inhomogeneity of magnetic field may induce entanglement and the critical magnetic field is independent of Jz. The inhomogeneous magnetic field can increase the value of critical magnetic field Bc. It also finds that the magnetic field not only suppresses the entanglement but also can induce it to revival for some time. 相关文章 | 计量指标

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Proof of the insecurity of quantum secret sharing based on the Smolin bound entangled states 於亚飞, 张智明 2009 (4):  1342-1345.  doi: 10.1088/1674-1056/18/4/009 摘要 ( 1697 )   PDF(102KB) ( 712 )   This paper reconsiders carefully the possibility of using the Smolin bound entangled states as the carrier for sharing quantum secret. It finds that the process of quantum secret sharing based on Smolin states has insecurity though the Smolin state was reported to violate maximally the two-setting Bell-inequality. The general proof is given. 相关文章 | 计量指标

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Macroscopic inequivalent entanglement witness in Heisenberg spin chain 张婷, 陈平形, 李承祖 2009 (4):  1346-1351.  doi: 10.1088/1674-1056/18/4/010 摘要 ( 1545 )   PDF(134KB) ( 653 )   Motivated by the wise idea of entanglement witness (EW), we present an inequivalent entanglement witness (IEEW) that can analogously classify certain eigenstates entangled in inequivalent ways under stochastic local operations and classical communication (SLOCC) in the Heisenberg spin chain. Since the IEEW is the absolute value of magnetization | M| that is a macroscopically measurable quantity, our conclusions provide a macroscopic method to detect inequivalent entanglement between microscopic spins, on the one hand, and clearly show that inequivalent entanglement can yield different macroscopic effects, on the other hand. 相关文章 | 计量指标

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Quantum logic gates with two-level trapped ions beyond Lamb--Dicke limit 郑小娟, 罗益民, 蔡建武 2009 (4):  1352-1356.  doi: 10.1088/1674-1056/18/4/011 摘要 ( 1444 )   PDF(139KB) ( 627 )   In the system with two two-level ions confined in a linear trap, this paper presents a simple scheme to realize the quantum phase gate (QPG) and the swap gate beyond the Lamb--Dicke (LD) limit. These two-qubit quantum logic gates only involve the internal states of two trapped ions. The scheme does not use the vibrational mode as the data bus and only requires a single resonant interaction of the ions with the lasers. Neither the LD approximation nor the auxiliary atomic level is needed in the proposed scheme. Thus the scheme is simple and the interaction time is very short, which is important in view of decoherence. The experimental feasibility for achieving this scheme is also discussed. 相关文章 | 计量指标

GENERAL

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Properties on the distant distribution of entanglement for arbitrary two-qubit pure states via noisy quantum channels 王琼, 李际新, 曾浩生 2009 (4):  1357-1361.  doi: 10.1088/1674-1056/18/4/012 摘要 ( 1494 )   PDF(97KB) ( 601 )   This paper investigates the change of entanglement for transmitting an arbitrarily entangled two-qubit pure state via one of three typical kinds of noisy quantum channels: amplitude damping quantum channel, phase damping quantum channel and depolarizing quantum channel. It finds, in all these three cases, that the output distant entanglement (measured by concurrence) reduces proportionately with respect to its initial amount, and the decaying ratio is determined only by the noisy characteristics of quantum channels and independent of the form of initial input state. 相关文章 | 计量指标

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An exact inflationary solution in the chaotic model with non-minimal coupling 刘雄伟, 杨树政, 陈世武, 林恺 2009 (4):  1362-1366.  doi: 10.1088/1674-1056/18/4/013 摘要 ( 1446 )   PDF(120KB) ( 583 )   This paper presents a new exact inflationary solution to the non-minimally coupled scalar field. The inflation is driven by the evolution of a scalar field with inflation potential V(φ ) = (λ/ 4)φ4+ b1 φ2+ b2 + b3 φ-2 + b4 φ-4. The spectral index of the scalar density fluctuations ns is consistent with the result of WMAP3 (Wilkinson Microwave Anisotropy Probe 3) for λCDM (Lambda-Cold Dark Matter). This model relaxes the constraint to the quartic coupling constant. And it can enter smoothly into a radiation-dominated stage when inflation ends. 相关文章 | 计量指标

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Chirality-asymmetry force between ɑ-quartz and copper block 胡永红, 徐庆, 刘中柱 2009 (4):  1367-1372.  doi: 10.1088/1674-1056/18/4/014 摘要 ( 1469 )   PDF(341KB) ( 543 )   The chirality-asymmetry macroscopic force mediated by light pseudoscalar particles between α -quartz and some achiral matter is studied. If this force between achiral source mass and α -quartz with some chirality is attractive, it will become repulsive when the chirality of the α -quartz crystal is changed. According to the tested limits of the coupling constant gs gp /\hbar c< 1.5× 10-24 at the Compton wavelength λ = 10-3 m, the force (F) between a 0.08× 0.08× 0.002 m3 block of α -quartz and a 0.08× 0.08× 0.01 m3 copper block with a separation being 0.5× 10-3 \mbox{m} in between, is estimated from the published data at less than 4.64× 10-24 N, i.e. F < 4.64× 10-24 N. 相关文章 | 计量指标

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Fluctuations and pseudo long range dependence in network flows: A non-stationary Poisson process model 陈煜东, 李力, 张毅, 胡坚明 2009 (4):  1373-1379.  doi: 10.1088/1674-1056/18/4/015 摘要 ( 1444 )   PDF(252KB) ( 572 )   In the study of complex networks (systems), the scaling phenomenon of flow fluctuations refers to a certain power-law between the mean flux (activity) < Fi> of the i-th node and its variance σi as Fi ∝ <Fiα. Such scaling laws are found to be prevalent both in natural and man-made network systems, but the understanding of their origins still remains limited. This paper proposes a non-stationary Poisson process model to give an analytical explanation of the non-universal scaling phenomenon: the exponent α varies between 1/2 and 1 depending on the size of sampling time window and the relative strength of the external/internal driven forces of the systems. The crossover behaviour and the relation of fluctuation scaling with pseudo long range dependence are also accounted for by the model. Numerical experiments show that the proposed model can recover the multi-scaling phenomenon. 相关文章 | 计量指标

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Nonextensive and extensive thermostatistic properties of Fermi systems trapped in different external potentials 黄志福, 欧聪杰, 陈金灿 2009 (4):  1380-1388.  doi: 10.1088/1674-1056/18/4/016 摘要 ( 1601 )   PDF(417KB) ( 606 )   The thermostatistic properties of a q-generalized Fermi system trapped in a generic power-law potential are studied, based on the generalized statistic distribution derived from the Tsallis entropy. The total number of particles, the total energy, and the heat capacity at constant volume of the system are derived. The thermostatistic characteristics of the system are discussed in detail. It is found that the thermostatistic properties of such a system depend closely on parameter q, dimensional number of the space, kinetic characteristics of particles and shapes of the external potential, and the external potential has a great influence on the thermostatistic properties of the system. Moreover, it is shown that the results obtained here are very general and can be used to unify the description of the nonextensive and extensive thermostatistic properties of a class of Fermi systems trapped in different external potentials so that the important conclusions of many typical Fermi systems in the literature may be directly derived from the present paper. 相关文章 | 计量指标

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Stochastic resonance in a single-mode laser driven by quadratic pump noise and amplitude-modulated signal 张莉 2009 (4):  1389-1393.  doi: 10.1088/1674-1056/18/4/017 摘要 ( 1587 )   PDF(176KB) ( 693 )   This paper investigates the phenomenon of stochastic resonance in a single-mode laser driven by quadratic pump noise and amplitude-modulated signal. A new linear approximation approach is advanced to calculate the signal-to-noise ratio. In the linear approximation only the drift term is linearized, the multiplicative noise term is unchangeable. It is found that there appears not only the standard form of stochastic resonance but also the broad sense of stochastic resonance, especially stochastic multiresonance appears in the curve of signal-to-noise ratio as a function of coupling strength λ between the real and imaginary parts of the pump noise. 相关文章 | 计量指标

GENERAL

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A new hyperchaos system and its circuit simulation by EWB 周平, 曹玉霞, 程雪峰 2009 (4):  1394-1398.  doi: 10.1088/1674-1056/18/4/018 摘要 ( 1930 )   PDF(1351KB) ( 1058 )   This paper reports a new hyperchaotic system evolved from the three-dimensional Lü chaotic system. The Lyapunov exponents spectrum and the bifurcation diagram of this new hyperchaotic system are obtained. Hyperchaotic attractor, periodic orbit and chaotic attractor are obtained by computer simulation. A circuit is designed to realize this new hyperchaotic system by electronic workbench. 相关文章 | 计量指标

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Controlling chaos in permanent magnet synchronous motor based on finite-time stability theory 韦笃取, 张波 2009 (4):  1399-1403.  doi: 10.1088/1674-1056/18/4/019 摘要 ( 1707 )   PDF(682KB) ( 1820 )   This paper reports that the performance of permanent magnet synchronous motor (PMSM) degrades due to chaos when its systemic parameters fall into a certain area. To control the undesirable chaos in PMSM, a nonlinear controller, which is simple and easy to be constructed, is presented to achieve finite-time chaos control based on the finite-time stability theory. Computer simulation results show that the proposed controller is very effective. The obtained results may help to maintain the industrial servo driven system's security operation. 相关文章 | 计量指标

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Synchronization of time-delay chaotic systems on small-world networks with delayed coupling 祁伟, 汪映海 2009 (4):  1404-1408.  doi: 10.1088/1674-1056/18/4/020 摘要 ( 2060 )   PDF(603KB) ( 800 )   By using the well-known Ikeda model as the node dynamics, this paper studies synchronization of time-delay systems on small-world networks where the connections between units involve time delays. It shows that, in contrast with the undelayed case, networks with delays can actually synchronize more easily. Specifically, for randomly distributed delays, time-delayed mutual coupling suppresses the chaotic behaviour by stabilizing a fixed point that is unstable for the uncoupled dynamical system. 相关文章 | 计量指标

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A diode laser spectrometer at 634nm and absolute frequency measurements using optical frequency comb 伊林, 袁杰, 齐向晖, 陈文兰, 周大伟, 周通, 周小计, 陈徐宗 2009 (4):  1409-1412.  doi: 10.1088/1674-1056/18/4/021 摘要 ( 1602 )   PDF(545KB) ( 756 )   This paper reports that two identical external-cavity-diode-laser (ECDL) based spectrometers are constructed at 634 nm referencing on the hyperfine B-X transition R(80)8-4 of 127I2. The lasers are stabilized on the Doppler-free absorption signals using the third-harmonic detection technique. The instability of the stabilized laser is measured to be 2.8×10-12 (after 1000 s) by counting the beat note between the two lasers. The absolute optical frequency of the transition is, for the first time, determined to be 472851936189.5 kHz by using an optical frequency comb referenced on the microwave caesium atomic clock. The uncertainty of the measurement is less than 4.9 kHz. 相关文章 | 计量指标

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Analysis of prompt fission neutron spectrum and multiplicity for 237Np(n, f) in the frame of multi-modal Los Alamos model 郑娜, 丁毅, 钟春来, 陈金象, 樊铁栓 2009 (4):  1413-1420.  doi: 10.1088/1674-1056/18/4/022 摘要 ( 1307 )   PDF(269KB) ( 632 )   The improved version of Los Alamos model with the multi-modal fission approach is used to analyse the prompt fission neutron spectrum and multiplicity for the neutron-induced fission of 237Np. The spectra of neutrons emitted from fragments for the three most dominant fission modes (standard I, standard II and superlong) are calculated separately and the total spectrum is synthesized. The multi-modal parameters contained in the spectrum model are determined on the basis of experimental data of fission fragment mass distributions. The calculated total prompt fission neutron spectrum and multiplicity are better agreement with the experimental data than those obtained from the conventional treatment of the Los Alamos model. 相关文章 | 计量指标

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Determination of the stellar reaction rate for 12C(ɑ, γ)16O: using a new expression with the reaction mechanism 徐毅, 徐望, 马余刚, 蔡翔舟, 陈金根, 范功涛, 樊广伟, 郭威, 罗文, 潘强岩, 沈文庆, 杨利峰 2009 (4):  1421-1427.  doi: 10.1088/1674-1056/18/4/023 摘要 ( 1250 )   PDF(376KB) ( 607 )   The astrophysical reaction rate of 12C(α, γ)16O plays a key role in massive star evolution. However, this reaction rate and its uncertainties have not been well determined yet, especially at T9=0.2. The existing results even disagree with each other to a certain extent. In this paper, the E1, E2 and total (E1+E2) 12C(α,γ)16O reaction rates are calculated in the temperature range from T9=0.3 to 2 according to all the available cross section data. A new analytic expression of the 12C(α,γ)16O reaction rate is brought forward based on the reaction mechanism. In this expression, each part embodies the underlying physics of the reaction. Unlike previous works, some physical parameters are chosen from experimental results directly, instead of all the parameters obtained from fitting. These parameters in the new expression, with their 3∑gma fit errors, are obtained from fit to our calculated reaction rate from T9=0.3 to 2. Using the fit results, the analytic expression of 12C(α,γ)16O reaction rate is extrapolated down to T9=0.05 based on the underlying physics. The 12C(α,γ)16O reaction rate at T9=0.2 is (8.78\pm1.52)×1015 cm3s-1mol-1. Some comparisons and discussions about our new 12C(α, γ)16O reaction rate are presented, and the contributions of the reaction rate correspond to the different part of reaction mechanism are given. The agreements of the reaction rate below T9=2 between our results and previous works indicate that our results are reliable, and they could be included in the astrophysical reaction rate network. Furthermore, we believe our method to investigate the 12C(α,γ)16O reaction rate is reasonable, and this method can also be employed to study the reaction rate of other astrophysical reactions. Finally, a new constraint of the supernovae production factor of some isotopes are illustrated according to our 12C(α,γ)16O reaction rates. 相关文章 | 计量指标

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Measurement of anomalous nuclear reaction in deuterium-loaded metal 蒋崧生, 李井怀, 汪建清, 何明, 武绍勇, 张红涛, 姚顺和, 赵永刚 2009 (4):  1428-1435.  doi: 10.1088/1674-1056/18/4/024 摘要 ( 1550 )   PDF(242KB) ( 617 )   This paper reports on an experiment for testing natural nuclear fusion at low temperature searching for evidence of the origin of 3He from natural nuclear fusion in deep Earth. The experiment was carried out using deuterium-loaded titanium foil samples and powder sample. Detection of charged particle was carried out using a low-level charged particle spectrometer. An Al foil was used as an energy absorber for identification of charged particle. Although the counting rate is very low in the experiment, the emission of energetic particle from the sample is observed and the particle is identified as a proton having energy about 2.8 MeV after exiting the titanium sample. This work provides a positive result for the emission of charged particle in the deuterium-loaded titanium foil samples at low temperature, but a negative result for the deuterium-loaded titanium powder sample. The average reaction yield is deduced to be (0.46±0.08) protons/h for the foil samples. With the suggestion that the proton originates from d--d reaction, we calculate the reaction rate for d--d reaction, and the obtained result is 1.4× 10-24 fusion/d--d\cdot sec. The negative result of the deuterium-loaded titanium powder sample suggests that the reaction yield might be correlated with the density or microscopic variables of deuterium-loaded titanium materials. The negative result also indicates that d--d reaction catalysed by μ-meson from cosmic ray can be excluded in the samples in this experiment. 相关文章 | 计量指标

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Structures, stabilities and magnetic moment of small copper-nickel clusters 冯翠菊, 薛永红, 张晓燕, 张晓春 2009 (4):  1436-1442.  doi: 10.1088/1674-1056/18/4/025 摘要 ( 1525 )   PDF(1235KB) ( 929 )   This paper obtains the lowest-energy geometric structures and the electronic and magnetic properties of small CuNiN clusters by using all-electron density functional theory. The calculated results reveal that the Cu atom prefers to occupy the apical site when N ≤ 9 and for the clusters with N=10, the Cu atom starts to encapsulate in the cage. The CuNi7} and CuNi9 are magic clusters. The magnetism correlates closely with the symmetry of the clusters. For these clusters, the charge tends to transfer from the nickel atoms to the copper atoms. It finds that the doping of Cu atom decreases the stability of pure NiN clusters. 相关文章 | 计量指标

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Studies of K-shell x-ray energy shifts induced by MeV/u heavy ions 宋张勇, 杨治虎, 邵剑雄, 崔莹, 张红强, 阮芳芳, 杜鹃, 高志民, 于得洋, 陈熙萌, 蔡晓红 2009 (4):  1443-1450.  doi: 10.1088/1674-1056/18/4/026 摘要 ( 1573 )   PDF(197KB) ( 666 )   This paper reports that the K x-ray spectra of the thin target 47Ag, 48Cd, 49In and 50Sn were measured by an HPGe semi-conductor detector in collisions with 84.5~MeV 6C4+ ions. Our experiment revealed the Kα x-ray energy shifts were not obvious and the Kβ1 x-ray energy shifts were about 90～110~eV. The simple model of Burch \emph{et al} has been previously used to calculate the K x-ray energy shifts due to an additional vacancy in 2p orbit. The present work extends the model of Burch to calculate the x-ray energy shifts of multiple ionized atoms induced by heavy ions with kinetic energy of MeV/u. In addition to our experimental results, many other experimental results are compared with the calculated values by using the model. 相关文章 | 计量指标

ATOMIC AND MOLECULAR PHYSICS

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Variation of photoabsorption cross section of atomic silver from isolated to condensed conditions 马晓光, 龚玉兵, 曲照军 2009 (4):  1451-1457.  doi: 10.1088/1674-1056/18/4/027 摘要 ( 1461 )   PDF(1028KB) ( 580 )   The influence of the local-field on the photoabsorption cross section of the atomic silver is studied in detail by using the Clausius--Mossotti (CM) model and the Onsager model separately. The variations of the photoabsorption cross section of atomic silver with number density and radius of the environmental interaction cavity are studied systematically by using more general expressions for the photoabsorption cross sections, proposed by Sun et al recently. It has proved to be reasonable to model the optical response properties of bulky material by coupling the property of isolated atom with the environmental effects in the present work. 相关文章 | 计量指标

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Phase-dependent quantum interference between different pathways in bichromatic harmonic generation 蔡俊, 王黎明, 乔豪学 2009 (4):  1458-1462.  doi: 10.1088/1674-1056/18/4/028 摘要 ( 1585 )   PDF(550KB) ( 663 )   This paper studies the harmonic generation of the hydrogen atom subjected to a collinear bichromatic laser field by numerically solving the time-dependent Schr?dinger equation using the split-operator pseudo-spectral method. By adding a frequency variation to the additional field, the contributions of different pathways to particular order harmonic generation can be isolated. The quantum interference pattern between harmonic pathways, which influences the harmonic intensity, is found to be either constructive or destructive with respect to different relative phase of the two field components. Detailed description of up to the 35th-order harmonics and the harmonic pathways for a wide range of field parameters is presented. 相关文章 | 计量指标

ATOMIC AND MOLECULAR PHYSICS

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Ultrafast multiplex CARS investigation of vibrational characteristics in chloroform and PMMA 王英惠, 彭亚晶, 何兴, 宋云飞, 杨延强 2009 (4):  1463-1468.  doi: 10.1088/1674-1056/18/4/029 摘要 ( 1481 )   PDF(1240KB) ( 730 )   This paper demonstrates the femtosecond time-resolved coherent anti-Stokes Raman scattering by using folded BOXCARS geometry where an ultrashort broadband coherent white light continuum was used as Stokes pulse, and carries out the non-contact detection at long distance. The CARS signal is so easy to be detected that it can be seen even by nude eye. The C--H bonds of chloroform or PMMA were detected and the vibration modes belonging to the side chain and the main chain in PMMA were also compared. Their vibrational characteristics involved decay process and quantum beating were discussed. This modified CARS experimental technique could make up the deficiency of traditional CARS technique. 相关文章 | 计量指标

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Tunable phase-stabilized infrared parametric laser source 张春梅, 王建良, 尉鹏飞, 宋立伟, 李闯, 金哲中, 冷雨欣 2009 (4):  1469-1472.  doi: 10.1088/1674-1056/18/4/030 摘要 ( 1457 )   PDF(700KB) ( 796 )   This paper reports that the tunable self-phase-stabilized infrared laser pulses have been generated from a two-stage optical parametric amplifier. With an 800 nm pump source, the output idler pulses are tunable from 1.3 μm to 2.3 μm, and the maximum output energy of the idler pulses is higher than 1 mJ at 1.6 μm by using 6 mJ pump laser. A carrier-envelope phase fluctuation of ～ 0.15 rad (rms) for the idler pulses is measured for longer than one hour by using a home build f-to-2f interferometer. 相关文章 | 计量指标

ATOMIC AND MOLECULAR PHYSICS

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Quantum-mechanical analysis of pulse reconstruction for a narrow bandwidth attosecond x-ray pulse 葛愉成 2009 (4):  1473-1478.  doi: 10.1088/1674-1056/18/4/031 摘要 ( 1408 )   PDF(279KB) ( 595 )   The photoelectron energy spectra (PESs) excited by narrow bandwidth attosecond x-ray pulses in the presence of a few-cycle laser are quantum-mechanically calculated. Transfer equations are used to reconstruct the detailed temporal structure of an attosecond x-ray pulse directly from a measured PES. Theoretical analysis shows that the temporal uncertainties of the pulse reconstruction depend on the x-ray bandwidth. The procedure of pulse reconstruction is direct and simple without making any previous pulse assumption, data fitting analysis and time-resolved measurement of PESs. The temporal measurement range is half of a laser optical cycle. 相关文章 | 计量指标

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Time-dependent theoretical approach to the influence of laser fields on the resonance enhanced multi-photon ionization of SH radical 岳大光, 郑晓云, 刘浩, 王春兴, 孟庆田 2009 (4):  1479-1485.  doi: 10.1088/1674-1056/18/4/032 摘要 ( 1320 )   PDF(238KB) ( 515 )   This paper reports that the (2+1) resonance enhanced multi-photon ionization spectra of SH radical in external fields are simulated using the split-operator scheme of time-dependent wave-packet method. Two ionic states, i.e.~a1Δ and b1∑+, are involved in the simulation. It gives the simulated photoelectron spectra, the population in each electronic state, as well as the projection of the wave-packet in each electronic state on different vibrational states. These results show that the so-called four-state model can represent the experimental results well. 相关文章 | 计量指标

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Calculation of the elastic collision properties of Na and Li atoms at ultracold temperature 张计才, 张莹, 杜丙阁, 孙金锋 2009 (4):  1486-1490.  doi: 10.1088/1674-1056/18/4/033 摘要 ( 1353 )   PDF(145KB) ( 593 )   This paper firstly reports a theoretical study of elastic scattering properties in a mixture of 23Na and 7Li atoms at cold and ultracold temperatures in detail. Based on the new constructed accurate singlet X1∑g+ and the triplet a3∑u+ states interatomic potentials for 23Na7Li mixture, it calculates the scattering lengths and the effective ranges by three computational methods, and obtains good agreements. Using the mass scaling method, it also calculates 23Na6Li scattering lengths and s-wave and total elastic cross sections, whose rich resonance structures were found and interpreted in terms of quasibound diatomic levels trapped behind a centrifugal barrier. 相关文章 | 计量指标

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An ab initio study of niobium (n = 2--11) clusters: structure, stability and magnetism 任凤竹, 王渊旭, 张光彪, 魏书克, 罗有华 2009 (4):  1491-1497.  doi: 10.1088/1674-1056/18/4/034 摘要 ( 1522 )   PDF(861KB) ( 820 )   The ground-state configurations of the Nbn (n= 2--11) clusters are studied through the first-principles calculations. It is found that niobium clusters (n= 2--11) tend to form compact structures with low symmetry. The clusters with 4, 8 and 10 atoms are found to be magic and have relatively large highest occupied--lowest unoccupied molecular orbital (HOMO-LUMO) gaps. The Nbn clusters possess low magnetic moments, which exhibit an odd-even oscillational character. The analyses of calculated electronic density and population of the lowest-energy niobium clusters for n= 2, 3, 5, 7, 9, 11 show that the total magnetic moments of Nbn originate mainly from a few Nb atoms with longer spacings between them in most cases, while they are located on two Nb atoms for n= 2, 3, 5. The total magnetic moments come mainly from the 4d local moments but with the exception of the Nb5 cluster. 相关文章 | 计量指标

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Analysis of femtosecond laser ionization/dissociation of olyatomic molecule C6H10O from one-colour pump—probe measurement 胡飞飞, 周胜鹏, 胡湛, 金明星, 张栋栋, 吴迪, 成西会, 姜殿武, 丁大军 2009 (4):  1498-1502.  doi: 10.1088/1674-1056/18/4/035 摘要 ( 1349 )   PDF(172KB) ( 645 )   This paper reports that a one-colour fs pump--probe measurement has been carried out for studying photoionization/photodissociation of cyclohexanone (C6H10O) in intense laser field. Two of the fragments from cyclohexanone, C2H3+ and C3}H3+, are studied under 800 nm laser pump--probe and the results obtained show similar time evolutions. It proposes a feasible model for analysing the experimental observations of the one-colour {fs} pump--probe measurement. The results demonstrate that as an intermediate product, the excited molecular parent ions play a very important role in photionization/photodissociation processes in intense laser field. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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Hybrid method for investigation of electromagnetic scattering from conducting target above the randomly rough surface 王蕊, 郭立新, 麻军, 吴振森 2009 (4):  1503-1511.  doi: 10.1088/1674-1056/18/4/036 摘要 ( 1280 )   PDF(726KB) ( 885 )   A current based hybrid method (HM) is proposed which combines the method of moment (MOM) with the Kirchhoff approximation (KA) for the analysis of scattering interaction between a two-dimensional (2D) infinitely long conducting target with arbitrary cross section and a one-dimensional (1D) Gaussian rough surface. The electromagnetic scattering region in the HM is split into KA region and MOM region. The electric field integral equation (EFIE) in MOM region (target) is derived, the computational time of the HM depends mainly on the number of unknowns of the target. The bistatic scattering coefficient for the infinitely long cylinder above the rough surface with Gaussian roughness spectrum is calculated, and the numerical results are compared and verified with those obtained by the conventional MOM, which shows the high efficiency of the HM. Finally, the influence of the size, location of the target, the rms height and correlation length of the rough surface on the bistatic scattering coefficient with different polarizations is discussed in detail. 相关文章 | 计量指标

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Single-mode photon number measurement for the squeezed two-mode number state 许雪芬, 朱士群 2009 (4):  1512-1516.  doi: 10.1088/1674-1056/18/4/037 摘要 ( 1406 )   PDF(106KB) ( 496 )   Based on the fact that a two-mode squeezed number state is a two-variable Hermite polynomial excitation of the two-mode squeezed vacuum state, the result of one-mode l-photon measurement for the two-mode squeezed number state $S_2|m,n\rangle$ is discussed. It is found that a remaining field-mode simultaneously collapses into a number state $|n-m+l\rangle$ with the coefficient being a Jacobi polynomial of n, m and l, which manifestly exhibits the entanglement between the two modes, i.e. it depends on the number-difference between the two modes. The second mode collapses into an excited coherent state when the first mode is measured as a coherent state. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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Entropy squeezing for a two-level atom in two-mode Raman coupled model with intrinsic decoherence 张剑, 邵彬, 邹健 2009 (4):  1517-1527.  doi: 10.1088/1674-1056/18/4/038 摘要 ( 1437 )   PDF(323KB) ( 703 )   In this paper, we investigate the entropy squeezing for a two-level atom interacting with two quantized fields through Raman coupling. We obtain the dynamical evolution of the total system under the influence of intrinsic decoherence when the two quantized fields are prepared in a two-mode squeezing vacuum state initially. The effects of the field squeezing factor, the two-level atomic transition frequency, the second field frequency and the intrinsic decoherence on the entropy squeezing are discussed. Without intrinsic decoherence, the increase of field squeezing factor can break the entropy squeezing. The two-level atomic transition frequency changes only the period of oscillation but not the strength of entropy squeezing. The influence of the second field frequency is complicated. With the intrinsic decoherence taken into consideration, the results show that the stronger the intrinsic decoherence is, the more quickly the entropy squeezing will disappear. The increase of the atomic transition frequency can hasten the disappearance of entropy squeezing. 相关文章 | 计量指标

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Ultraslow optical solitons in tunnel-coupled double semiconductor quantum well 陈爱喜, 徐彦秋, 邓黎, 周素云 2009 (4):  1528-1533.  doi: 10.1088/1674-1056/18/4/039 摘要 ( 1470 )   PDF(448KB) ( 565 )   This paper investigates the nonlinear evolution of the pulse probe field in an asymmetric coupled-quantum well driven coherently by a pulse probe field and two controlled fields. This study shows that, by choosing appropriate physical parameters, self-modulation can precisely balance group velocity dispersion in the investigated system, leading to the formation of ultraslow optical solitons of the probe field. The proposed scheme may lead to the development of the controlled technique of optical buffers and optical delay lines. 相关文章 | 计量指标

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Normal ordering and antinormal ordering of the operator ( fQ+gP)n and some of their applications 孟祥国, 王继锁, 梁宝龙 2009 (4):  1534-1541.  doi: 10.1088/1674-1056/18/4/040 摘要 ( 1342 )   PDF(141KB) ( 470 )   In this paper by virtue of the technique of integration within an ordered product (IWOP) of operators and the intermediate coordinate-momentum representation in quantum optics, we derive the normal ordering and antinormal ordering products of the operator ( fQ+gP)n when n is an arbitrary integer. These products are very useful in calculating their matrix elements and expectation values and obtaining some useful mathematical formulae. Finally, the applications of some new identities are given. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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Kinetic analysis of the factors limiting the output power of the Ne--CuBr UV laser 毛邦宁, 潘佰良, 陈立, 王亚娟, 姚志欣 2009 (4):  1542-1546.  doi: 10.1088/1674-1056/18/4/041 摘要 ( 1407 )   PDF(500KB) ( 608 )   The parametric optimization of the Ne--CuBr UV laser excited by longitudinal pulsed discharge is analysed by using a self-consistent kinetic model. Consistent characteristics of the optimization process are obtained by comparing with the experimental results. Simulation results show that neon ions come into being along with considerable depletion of the ground-state copper atoms. And the optimization of the discharge tube diameter is the tradeoff between the specific output photon density and the total active volume. Both the optimal neon gas pressure and the optimal reservoir temperature result from the balance between the neon ion density and the ground-state copper atom density to arrive at a maximum of their product. 相关文章 | 计量指标

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Theoretical analysis and experimental research on thermal focal length of a YVO4/Nd:YVO4 composite crystal 周城 2009 (4):  1547-1552.  doi: 10.1088/1674-1056/18/4/042 摘要 ( 1388 )   PDF(579KB) ( 1051 )   This paper investigates the temperature field distribution and thermal focal length within a laser diode array (LDA) end-pumped YVO4/Nd:YVO4 rectangular composite crystal. A general expression of the temperature field distribution within the Nd:YVO4 rectangular crystal was obtained by analysing the characteristics of the Nd:YVO4 crystal and solving the Poisson equation with boundary conditions. The temperature field distributions in the Nd:YVO4 rectangular crystal for the YVO4/Nd:YVO4 composite crystal and the Nd:YVO4 single crystal are researched respectively. Calculating the thermal focal length within the Nd:YVO4 rectangular crystal was done by an analysis of the additional optical path differences (OPD) caused by heat, which was very identical with experimental results in this paper. Research results show that the maximum relative temperature on the rear face of the Nd:YVO4 crystal in the composite crystal is 150 K and the thermal focal length is 35.7 mm when the output power of the LDA is 22 W. In the same circumstances, the experimental value of the thermal focal length is 37.4 mm. So the relative error between the theoretical analysis and the experimental result is only 4.5%. With the same conditions, the thermal focal length of the Nd:YVO4 single crystal is 18.5 mm. So the relative rate of the thermal focal length between the YVO4/Nd:YVO4 crystal and the Nd:YVO4 crystal is 93%. So, the thermal stability of the output power and the beam quality of the YVO4/Nd:YVO4 laser is more advantageous than the laser with Nd:YVO4 single crystal. 相关文章 | 计量指标

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Analysis of thermal conductivity in tree-like branched networks 寇建龙, 陆杭军, 吴锋民, 许友生 2009 (4):  1553-1559.  doi: 10.1088/1674-1056/18/4/043 摘要 ( 1475 )   PDF(880KB) ( 803 )   Asymmetric tree-like branched networks are explored by geometric algorithms. Based on the network, an analysis of the thermal conductivity is presented. The relationship between effective thermal conductivity and geometric structures is obtained by using the thermal-electrical analogy technique. In all studied cases, a clear behaviour is observed, where angle (δ ,θ ) among parent branching extended lines, branches and parameter of the geometric structures have stronger effects on the effective thermal conductivity. When the angle δ is fixed, the optical diameter ratio β* is dependent on angle θ . Moreover, γ and m are not related to β * . The longer the branch is, the smaller the effective thermal conductivity will be. It is also found that when the angle θ < δ / 2, the higher the iteration m is, the lower the thermal conductivity will be and it tends to zero, otherwise, it is bigger than zero. When the diameter ratio β 1< 0.707 and angle δ is bigger, the optimal k of the perfect ratio increases with the increase of the angle δ ; when β 1> 0.707, the optimal k decreases. In addition, the effective thermal conductivity is always less than that of single channel material. The present results also show that the effective thermal conductivity of the asymmetric tree-like branched networks does not obey Murray's law. 相关文章 | 计量指标

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Monte Carlo simulations of biaxial structure in thin hybrid nematic film based upon spatially anisotropic pair potential 张志东, 常春蕊, 马东来 2009 (4):  1560-1563.  doi: 10.1088/1674-1056/18/4/044 摘要 ( 1300 )   PDF(142KB) ( 508 )   Hybrid nematic films have been studied by Monte Carlo simulations using a lattice spin model, in which the pair potential is spatially anisotropic and dependent on elastic constants of liquid crystals. We confirm in the thin hybrid nematic film the existence of a biaxially nonbent structure and the structure transition from the biaxial to the bent-director structure, which is similar to the result obtained using the Lebwohl--Lasher model. However, the step-like director's profile, characteristic for the biaxial structure, is spatially asymmetric in the film because the pair potential leads to K1 ≠ K3. We estimate the upper cell thickness to be 69 spin layers, in which the biaxial structure can be found. 相关文章 | 计量指标

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Shielding effect and emission criterion of a screw dislocation near an interfacial blunt crack 宋豪鹏, 方棋洪, 刘又文 2009 (4):  1564-1569.  doi: 10.1088/1674-1056/18/4/045 摘要 ( 1365 )   PDF(306KB) ( 584 )   Shielding effect and emission criterion of a screw dislocation near an interfacial blunt crack are dealt with in this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for complex potentials and stress fields due to a screw dislocation located near the interfacial blunt crack. The stress intensity factor on the crack tips and the critical stress intensity factor for dislocation emission are also calculated. The influence of the orientation of the dislocation and the morphology of the blunt crack as well as the material elastic dissimilarity on the shielding effect and the emission criterion is discussed in detail. The results show that positive screw dislocations can reduce the stress intensity factor of the interfacial blunt crack tip (shielding effect). The shielding effect increases with the increase of the shear modulus of the lower half-plane, but it decreases with the increase of the dislocation azimuth angle. The critical loads at infinity for dislocation emission increases with the increase of emission angle and curvature radius of blunt crack tip, and the most probable angle for screw dislocation emission is zero. The present solutions contain previous results as special cases. 相关文章 | 计量指标

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Ultra-thin a-SiNx protective overcoats for hard disks and read/write heads 丁万昱, 徐军, 陆文琪, 邓新绿, 董闯 2009 (4):  1570-1573.  doi: 10.1088/1674-1056/18/4/046 摘要 ( 1650 )   PDF(723KB) ( 1701 )   This paper reports that amorphous silicon nitride (a-SiNx) overcoats were deposited at room temperature by microwave ECR plasma enhanced unbalanced magnetron sputtering. The 2 nm a-SiNx overcoat has better anti-corrosion properties than that of reference a-CNx overcoats (2--4.5 nm). The superior anti-corrosion performance is attributed to its stoichiometric bond structure, where 94.8% Si atoms form Si--N asymmetric stretching vibration bonds. The N/Si ratio is 1.33 as in the stoichiometry of Si3N4 and corresponds to the highest hardness of 25.0 GPa. The surface is atomically smooth with RMS <0.2 nm. The ultra-thin a-SiNx overcoats are promising for hard disks and read/write heads protective coatings. 相关文章 | 计量指标

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

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Ab initio study on phase transition and magnetism of BiFeO3 under pressure 冯宏剑, 刘发民 2009 (4):  1574-1577.  doi: 10.1088/1674-1056/18/4/047 摘要 ( 1832 )   PDF(140KB) ( 953 )   In this paper the first-principles calculations within local spin density approximation (LSDA)+U show that BiFeO3 experiences a mixed phase state with P4mm structure being the intermediate phase before the pressure of phase transition is reached. The critical pressure for the insulator--metal transition (IMT) is found to be about 50 GPa. A pressure induced crossover of high-spin states and low-spin states is observed close to the IMT pressure in R3c structure. The LSDA+U calculations account well for the mechanism of the IMT and crossover of spin states predicted in recent experiment (Ref.[1]). 相关文章 | 计量指标

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Ground state energy of excitons in quantum dot treated variationally via Hylleraas-like wavefunction 2009 (4):  1578-1585.  doi: 10.1088/1674-1056/18/4/048 摘要 ( 1527 )   PDF(213KB) ( 661 )   In this work, the effects of quantum confinement on the ground state energy of a correlated electron--hole pair in a spherical and in a disc-like quantum dot have been investigated as a function of quantum dot size. Under parabolic confinement potential and within effective mass approximation Ritz's variational method is applied to Hylleraas-like trial wavefunction. An efficient method for reducing the main effort of the calculation of terms like $r^k_{\rm eh}\exp(-\lambda r_{\rm eh})$ is introduced. The main contribution of the present work is the introduction of integral transforms which provide the calculation of expectation value of energy and the related matrix elements to be done analytically over single-particle coordinates instead of Hylleraas coordinates. 相关文章 | 计量指标

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Investigations of the electron paramagnetic resonance parameters and the tetragonal local structure for (VCl6)4- coordination complex in MCl:V2+ (M=Na, K, Rb) systems 祁林, 邝小渝, 柴瑞鹏, 段美玲, 张彩霞 2009 (4):  1586-1593.  doi: 10.1088/1674-1056/18/4/049 摘要 ( 1418 )   PDF(257KB) ( 498 )   By simulating the electron paramagnetic resonance (EPR) and optical spectra on the basis of the 120× 120 complete energy matrix, this paper determines the local lattice structure parameters R1 and R2 for MCl:V2+ (M=Na, K, Rb) systems at 77 K, 195 K and RT (room temperature 295 K or 302 K), respectively. The theoretical results indicate that there exists a compressed distortion in MCl:V2+ systems. Meanwhile, it finds that the structure parameters R1 , R2 and |Δ R |(= R1 - R2 ) increase with the rising temperature. Subsequently, from the analysis it concludes that the relation of EPR parameter D vs. Δ R is approximately linear. Finally, the effects of orbital reduction factor k on the g factors for the three systems have been discussed. 相关文章 | 计量指标

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The research on suspended ZnO nanowire field-effect transistor 黎明, 张海英, 郭常新, 徐静波, 付晓君 2009 (4):  1594-1597.  doi: 10.1088/1674-1056/18/4/050 摘要 ( 1548 )   PDF(394KB) ( 715 )   This paper reports that a novel type of suspended ZnO nanowire field-effect transistors (FETs) were successfully fabricated using a photolithography process, and their electrical properties were characterized by I--V measurements. Single-crystalline ZnO nanowires were synthesized by a hydrothermal method, they were used as a suspended ZnO nanowire channel of back-gate field-effect transistors (FET). The fabricated suspended nanowire FETs showed a p-channel depletion mode, exhibited high on--off current ratio of ～105. When VDS=2.5 V, the peak transconductances of the suspended FETs were 0.396 μS, the oxide capacitance was found to be 1.547 fF, the pinch-off voltage VTH was about 0.6 V, the electron mobility was on average 50.17 cm2/Vs. The resistivity of the ZnO nanowire channel was estimated to be 0.96× 102Ω cm at VGS = 0 V. These characteristics revealed that the suspended nanowire FET fabricated by the photolithography process had excellent performance. Better contacts between the ZnO nanowire and metal electrodes could be improved through annealing and metal deposition using a focused ion beam. 相关文章 | 计量指标

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

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Frequency selective surface structure optimized by genetic algorithm 卢俊, 汪剑波, 孙贯成 2009 (4):  1598-1600.  doi: 10.1088/1674-1056/18/4/051 摘要 ( 1691 )   PDF(389KB) ( 827 )   Frequency selective surface (FSS) is a two-dimensional periodic structure which has prominent characteristics of bandpass or bandblock when interacting with electromagnetic waves. In this paper, the thickness, the dielectric constant, the element graph and the arrangement periodicity of an FSS medium are investigated by Genetic Algorithm (GA) when an electromagnetic wave is incident on the FSS at a wide angle, and an optimized FSS structure and transmission characteristics are obtained. The results show that the optimized structure has better stability in relation to incident angle of electromagnetic wave and preserves the stability of centre frequency even at an incident angle as large as 80°, thereby laying the foundation for the application of FSS to curved surfaces at wide angles. 相关文章 | 计量指标

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High-electric-field-stress-induced degradation of SiN passivated AlGaN/GaN high electron mobility transistors 谷文萍, 段焕涛, 倪金玉, 郝跃, 张进城, 冯倩, 马晓华 2009 (4):  1601-1608.  doi: 10.1088/1674-1056/18/4/052 摘要 ( 1635 )   PDF(1865KB) ( 1038 )   AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated by employing SiN passivation, this paper investigates the degradation due to the high-electric-field stress. After the stress, a recoverable degradation has been found, consisting of the decrease of saturation drain current IDsat, maximal transconductance gm, and the positive shift of threshold voltage VTH at high drain-source voltage VDS. The high-electric-field stress degrades the electric characteristics of AlGaN/GaN HEMTs because the high field increases the electron trapping at the surface and in AlGaN barrier layer. The SiN passivation of AlGaN/GaN HEMTs decreases the surface trapping and 2DEG depletion a little during the high-electric-field stress. After the hot carrier stress with VDS=20 V and VGS=0 V applied to the device for 104 sec, the SiN passivation decreases the stress-induced degradation of IDsat from 36% to 30%. Both on-state and pulse-state stresses produce comparative decrease of IDsat, which shows that although the passivation is effective in suppressing electron trapping in surface states, it does not protect the device from high-electric-field degradation in nature. So passivation in conjunction with other technological solutions like cap layer, prepassivation surface treatments, or field-plate gate to weaken high-electric-field degradation should be adopted. 相关文章 | 计量指标

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

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Localized states of flattened quantum elliptic rings and their optical properties 司徒树平 2009 (4):  1609-1613.  doi: 10.1088/1674-1056/18/4/053 摘要 ( 1365 )   PDF(586KB) ( 476 )   A flattened elliptic ring containing an electron is studied. The emphasis is placed on clarifying the effect of the flattening. The localized states are classified into four types according to their inherent nodes. When the ring becomes more flattened, the total probability of dipole absorption of each state is found to be reduced. Furthermore, each spectral line of absorption is found to shift towards red and may split into a few lines, and these lines as a whole become more diffusive. 相关文章 | 计量指标

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The leakage current mechanisms in the Schottky diode with a thin Al layer insertion between Al0.245Ga0.755N/GaN heterostructure and Ni/Au Schottky contact 刘芳, 王涛, 沈波, 黄森, 林芳, 马楠, 许福军, 王鹏, 姚建铨 2009 (4):  1614-1617.  doi: 10.1088/1674-1056/18/4/054 摘要 ( 1483 )   PDF(171KB) ( 832 )   This paper investigates the behaviour of the reverse-bias leakage current of the Schottky diode with a thin Al inserting layer inserted between Al0.245Ga0.755N/GaN heterostructure and Ni/Au Schottky contact in the temperature range of 25--350 °C. It compares with the Schottky diode without Aluminium inserting layer. The experimental results show that in the Schottky diode with Al layer the minimum point of I--V curve drifts to the minus voltage, and with the increase of temperature increasing, the minimum point of I--V curve returns the 0 point. The temperature dependence of gate-leakage currents in the novelty diode and the traditional diode are studied. The results show that the Al inserting layer introduces interface states between metal and Al0.245Ga0.755N. Aluminium reacted with oxygen formed Al2O3 insulator layer which suppresses the trap tunnelling current and the trend of thermionic field emission current. The reliability of the diode at the high temperature is improved by inserting a thin Al layer. 相关文章 | 计量指标

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Thermal annealing behaviour of Al/Ni/Au multilayer on n-GaN Schottky contacts 刘芳, 王涛, 沈波, 黄森, 林芳, 马楠, 许福军, 王鹏, 姚建铨 2009 (4):  1618-1621.  doi: 10.1088/1674-1056/18/4/055 摘要 ( 1581 )   PDF(334KB) ( 775 )   Recently GaN-based high electron mobility transistors (HEMTs) have revealed the superior properties of a high breakdown field and high electron saturation velocity. Reduction of the gate leakage current is one of the key issues to be solved for their further improvement. This paper reports that an Al layer as thin as 3 nm was inserted between the conventional Ni/Au Schottky contact and n-GaN epilayers, and the Schottky behaviour of Al/Ni/Au contact was investigated under various annealing conditions by current--voltage (I--V) measurements. A non-linear fitting method was used to extract the contact parameters from the I--V characteristic curves. Experimental results indicate that reduction of the gate leakage current by as much as four orders of magnitude was successfully recorded by thermal annealing. And high quality Schottky contact with a barrier height of 0.875 eV and the lowest reverse-bias leakage current, respectively, can be obtained under 12 min annealing at 450°C in N2 ambience. 相关文章 | 计量指标

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

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Conductance switching mechanism of Rose Bengal organic thin films in ambient conditions 蔡莉, 郭海明, 朱熙, 杜世萱, 时东霞, 高鸿钧 2009 (4):  1622-1626.  doi: 10.1088/1674-1056/18/4/056 摘要 ( 1422 )   PDF(460KB) ( 494 )   The molecular thin films of Rose Bengal (RB) embedded in polymethyl methacrylate matrix are fabricated by using the spin-coating technique. The macroscopic current--voltage (I--V) characterization of the film shows that the RB molecule has two conductance switching states with a high ON/OFF ratio in ambient conditions. The infrared spectra indicate that intermolecular hydrogen bonds can form in the RB thin films after their hydrolysis in air. With the first-principles calculations, we demonstrate that the hydrogen bonds will be destroyed in concomitance with the conformational change when the RB molecule switches to its high-conductance state after applying a voltage. 相关文章 | 计量指标

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Numerical model of multilayer organic light-emitting devices 胡玥, 饶海波 2009 (4):  1627-1630.  doi: 10.1088/1674-1056/18/4/057 摘要 ( 1600 )   PDF(277KB) ( 1931 )   A numerical model of multilayer organic light-emitting devices is presented in this article. This model is based on the drift-diffusion equations which include charge injection, transport, space charge effects, trapping, heterojunction interface and recombination process. The device structure in the simulation is ITO/CuPc (20 nm)/NPD (40 nm)/Alq3 (60 nm)/LiF/Al. There are two heterojunctions which should be dealt with in the simulation. The I--V characteristics, carrier distribution and recombination rate of a device are calculated. The simulation results and measured data are in good agreement. 相关文章 | 计量指标

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Study on reaction mechanism of YBa2Cu3O7-x film by TFA-MOD process 丁发柱, 吕旭东, 古宏伟, 李弢, 曹江利 2009 (4):  1631-1636.  doi: 10.1088/1674-1056/18/4/058 摘要 ( 1582 )   PDF(1621KB) ( 766 )   This paper systematically investigates the intermediate phases of YBa2Cu3O7-x (YBCO) film prepared by metalorganic deposition method using trifluoroacetates (TFA-MOD). According to x-ray diffraction and Raman analyses, the precursor film decomposed in a mixture of BaF2, Y2O3 and CuO after the pyrolysis process. Then these intermediate phases converted into tetragonal YBa2Cu3O6.5 at about 725 °C. The influence of water vapour pressure on the YBa2Cu3O7-x film growth on LaAlO3 single-crystal substrates was also studied. The films prepared at low water vapour pressures (40--140 hPa) showed poor electrical performance due to the a-axis grain structure and impurity phases. However, the films prepared at 190 hPa exhibited the highest critical temperature of 90 K and the highest Jc of 3.8 MA/cm2, which was attributed to the formation of a purer YBCO phase and stronger biaxial texture. 相关文章 | 计量指标

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Raman scattering studies on manganese ion-implanted GaN 徐大庆, 张义门, 张玉明, 李培咸, 王超 2009 (4):  1637-1642.  doi: 10.1088/1674-1056/18/4/059 摘要 ( 1645 )   PDF(198KB) ( 632 )   This paper reports that the Raman spectra have been recorded on the metal-organic chemical vapour deposition epitaxially grown GaN before and after the Mn ions implanted. Several Raman defect modes have emerged from the implanted samples. The structures around 182 cm-1 modes are attributed to the disorder-activated Raman scattering, whereas the 361 cm-1 and 660 cm-1 peaks are assigned to nitrogen vacancy-related defect scattering. One additional peak at 280 cm-1 is attributed to the vibrational mode of gallium vacancy-related defects and/or to disorder activated Raman scattering. A Raman-scattering study of lattice recovery is also presented by rapid thermal annealing at different temperatures between 700 °C and 1050 °C on Mn implanted GaN epilayers. The behaviour of peak-shape change and full width at half maximum (FWHM) of the A1(LO) (733 cm-1) and EH2 (566 cm-1) Raman modes are explained on the basis of implantation-induced lattice damage in GaN epilayers. 相关文章 | 计量指标

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Investigation of fabrication and hetero-epitaxy relationship of CoCrPt thin films grown on CrW underlayer 李松田, 刘曦, 史文魁, 曹江伟, 魏福林, 韦丹 2009 (4):  1643-1646.  doi: 10.1088/1674-1056/18/4/060 摘要 ( 1374 )   PDF(140KB) ( 548 )   This paper reports that longitudinally oriented CoCrPt thin films with Cr85W15 underlayer and CoCr intermediate layer for use of giant magnetoresistance heads were fabricated by magnetron sputtering. Without CoCr intermediate layer, CoCrPt layer deposited directly on Cr85W15 underlayer which has a dominant (200) texture exhibits unexpected (10\bar {1}1) texture. After introducing CoCr intermediate layer, the CoCrPt layer shifts into (11\bar {2}0) texture. This article studies the crystallographic hetero-epitaxy relationship between magnetic layer and underlayer in order to understand the appearance of CoCrPt (10\bar {1}1) texture on (200) textured Cr underlayer and the influence of CoCr intermediate layer on the inducement of CoCrPt (11\bar {2}0) texture. The CoCr intermediate layer plays a crucial role in controlling the microstructure and consequently the magnetic properties of the overlying magnetic layer. 相关文章 | 计量指标

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

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First principles study on the magnetocrystalline anisotropy of Fe--Ga magnetostrictive alloys 郑蕾, 蒋成保, 尚家香, 徐惠彬 2009 (4):  1647-1652.  doi: 10.1088/1674-1056/18/4/061 摘要 ( 1657 )   PDF(306KB) ( 908 )   This paper investigates the electronic structure and magnetocrystalline anisotropy of Fe--Ga magnetostrictive material by means of the full potential-linearized augmented plane-wave method within the generalized gradient approximation. The 3d-orbit splitting of Fe atoms in D03, B2-like and L12 crystalline structures of Fe--Ga is calculated with consideration of the crystal field as well as the spin--orbit coupling effect. Because of the frozen orbital angular momenta of the 3d-orbit for Fe atoms in Fe--Ga magnetostrictive alloys and the spin--orbit coupling, the distribution of the electron cloud is not isotropic, which leads to the anisotropy of exchange interaction between the different atoms. A method on estimating the magnetocrystalline anisotropy of Fe--Ga alloys by means of calculating orbit-projected density of states for Fe atoms is performed. The anisotropic distribution of the electron cloud of Fe atoms in these three crystalline structures of Fe--Ga is studied based on the above method showing the highest magnetic anisotropy for B2-like structure. This qualitative method comes closer to physical reality with a vivid physical view, which can evaluate the anisotropy of electron cloud for 3d transition atoms directly. The calculated results are in good agreement with both the previous theoretical computation and the tested value on the magnetic anisotropy constant, which confirms that the electron cloud anisotropy of Fe atoms could well characterize the magnetocrystalline anisotropy of Fe--Ga magnetostrictive material. 相关文章 | 计量指标

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Microwave left-handed composite material made of slim ferrite rods and metallic wires 徐芳, 白洋, 乔利杰, 赵宏杰, 周济 2009 (4):  1653-1657.  doi: 10.1088/1674-1056/18/4/062 摘要 ( 1527 )   PDF(888KB) ( 703 )   This paper reports on experimental study of the microwave properties of a composite material consisting of ferrite and copper wires. It finds that the slim ferrite rods can modify the magnetic field distribution through their anisotropy, so that the ferrite's negative influence on the copper wires' plasma will be reduced. Left-handed properties are observed even in the specimen with close stuck ferrite rods and copper wires. 相关文章 | 计量指标

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Combined effect of the transition layer and interfacial coupling on the properties of ferroelectric bilayer film 孙普男, 崔莲, 吕天全 2009 (4):  1658-664.  doi: 10.1088/1674-1056/18/4/063 摘要 ( 1506 )   PDF(989KB) ( 626 )   Within the framework of modified Ginzburg--Landau--Devonshire phenomenological theory, a ferroelectric bilayer film with a transition layer within each constituent film and an interfacial coupling between two materials has been studied. Properties including the Curie temperature and the spontaneous polarization of a bilayer film composed of two equally thick ferroelectric constituent films are discussed. The results show that the combined effect of the transition layer and the interfacial coupling plays an important role in explaining the interesting behaviour of ferroelectric multilayer structures consisting of two ferroelectric materials. 相关文章 | 计量指标

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

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Potts-Ising model for simulation of polarization switching in polycrystalline ferroelectrics 张艳飞, 王春雷, 赵明磊, 李吉超, 张睿智 2009 (4):  1665-1668.  doi: 10.1088/1674-1056/18/4/064 摘要 ( 1500 )   PDF(435KB) ( 619 )   This paper proposes a scheme based on the Potts and Ising models for simulating polarization switching of polycrystalline ferroelectrics using the Monte Carlo method. The polycrystalline texture with different average grain size is produced from the Potts model. Then Ising model is implemented in the polycrystalline texture to produce the domain pattern and hysteresis loop. The domain patterns and hysteresis loops have been obtained for polycrystalline texture with different average grain size. From the results of domain pattern evolution process under an applied electric field using this scheme, an extended domain, which covers more than one grain with polarization aligned roughly in the same direction, has been observed during the polarization reversal. This scheme can well reproduce the basic properties of polycrystalline ferroelectrics and is a valuable tool for exploring the physical properties of polycrystalline ferroelectrics. 相关文章 | 计量指标

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Spontaneous formation of single crystal ZnO nanohelices 武祥, 蔡伟, 曲凤玉 2009 (4):  1669-1673.  doi: 10.1088/1674-1056/18/4/065 摘要 ( 1276 )   PDF(1611KB) ( 611 )   This paper reports a novel helix-like ZnO nanostructure with several tens of nanometres in thickness synthesized on a gold-coated Si substrate by thermal evaporation of zinc sulfide powder at 1020°C. Transmission electron microscope characterization shows that as-synthesized ZnO nanohelices extend along [01\bar 11] direction and the axial direction of the helix is along [0001] direction. A catalyst-intervened dislocation-induced growth mechanism has been suggested to explain the formation of the helix-like ZnO nanostructures. This study opens a new route to construct helix-like ZnO nanostructures by different evaporation sources. 相关文章 | 计量指标

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The study of a new n/p tunnel recombination junction and its application in a-Si:H/μc-Si:H tandem solar cells 李贵君, 侯国付, 韩晓艳, 袁育洁, 魏长春, 孙建, 赵颖, 耿新华 2009 (4):  1674-1678.  doi: 10.1088/1674-1056/18/4/066 摘要 ( 1555 )   PDF(185KB) ( 931 )   This paper reports that a double N layer (a-Si:H/μc-Si:H) is used to substitute the single microcrystalline silicon n layer (n-μc-Si:H) in n/p tunnel recombination junction between subcells in a-Si:H/μc-Si:H tandem solar cells. The electrical transport and optical properties of these tunnel recombination junctions are investigated by current--voltage measurement and transmission measurement. The new n/p tunnel recombination junction shows a better ohmic contact. In addition, the n/p interface is exposed to the air to examine the effect of oxidation on the tunnel recombination junction performance. The open circuit voltage and FF of a-Si:H/μc-Si:H tandem solar cell are all improved and the current leakage of the subcells can be effectively prevented efficiently when the new n/p junction is implemented as tunnel recombination junction. 相关文章 | 计量指标

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A comparative study of YBa2Cu3O7-δ/YSZ bilayer films deposited on silicon-on-insulator substrates with and without HF pretreatment 王萍, 李洁, 陈莺飞, 李绍, 王佳, 解廷月, 郑东宁 2009 (4):  1679-1683.  doi: 10.1088/1674-1056/18/4/067 摘要 ( 1539 )   PDF(552KB) ( 524 )   Highly epitaxial YBa2Cu3O7 - δ (YBCO) and yttria-stabilized zirconia (YSZ) bilayer thin films have been deposited on silicon-on-insulator (SOI) substrates by using in situ pulsed laser deposition (PLD) technique. In the experiment, the native amorphous SiO2 layers on some of the SOI substrates are removed by dipping them in a 10% HF solution for 15 s. Comparing several qualities of films grown on substrates with or without HF pretreatment, such as thin film crystallinity, general surface roughness, temperature dependence of resistance, surface morphology, as well as average crack spacing and crack width, naturally leads to the conclusion that preserving the native SiO2 layer on the surface of the SOI substrate can not only simplify the experimental process but can also achieve fairly high quality YSZ and YBCO thin films. 相关文章 | 计量指标

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Structural statistical properties of knotted proteins 王向红, 沈瑜, 章林溪 2009 (4):  1684-1690.  doi: 10.1088/1674-1056/18/4/068 摘要 ( 1245 )   PDF(231KB) ( 609 )   The composition and residue--residue interactions of knotted proteins, compared with those of other proteins, can provide considerable insight into the driver of the knots in proteins. In this paper, we calculate the probabilities of 20 amino acids in 273 knotted entries from the Protein Data Bank (PDB). The collection of 273 entries contains all knotted structures in the PDB, and it is not a subset. With an appropriate value of Rc, the numbers of all residue--residue contacts are counted in all 273 knotted structures. To make an accurate comparison, we count up to 9000 other entries from the PDB as well, and these entries spread over all sorts. In knotted structures, Leu occupies a maximal proportion of 9.62% among all 20 amino acids, and Leu, Phe, Trp, Gly, His, Gln, Asp, Lys and Pro may all play a more important role. Also, we analyse the effects of amino acid residues on the long-range contacts. We observe a larger average number of long-range contacts in the knotted structures than that in other ones, implying their important role in achieving the knots. Accordingly, the average number of short-range contacts becomes small when the structure becomes knotted because it depends mainly on the short-haul sequence of amino acids to form the short-range contact. In addition, the shape distribution of knotted proteins and the contrast with the other proteins are also presented. A comparison shows that the knots may make structures more globular because the average shape factor is 0.059 for the knotted proteins, which is only about 1/3 of the average shape factor for the other proteins. 相关文章 | 计量指标

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The effect of anisotropic surface tension on the morphological stability of planar interface during directional solidification 陈明文, 兰曼, 袁琳, 王玉燕, 王自东, 徐鉴君 2009 (4):  1691-1699.  doi: 10.1088/1674-1056/18/4/069 摘要 ( 1413 )   PDF(371KB) ( 636 )   This paper considers the effect of the anisotropic surface tension on the morphological stability of the planar interface during directional solidification. When the expression exhibiting the four-fold symmetry is included, the modified absolute stability criterion is obtained by employing the multi-variable expansion method. The linear stability analysis reveals that for the given temperature gradient, as the anisotropic surface tension parameter increases, the stability zone tends to decrease. 相关文章 | 计量指标

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Evolution analysis of the states of the EZ model 陈清华, 丁义明, 董洪光 2009 (4):  1700-1706.  doi: 10.1088/1674-1056/18/4/070 摘要 ( 1243 )   PDF(187KB) ( 483 )   Based on suitable choice of states, this paper studies the stability of the equilibrium state of the EZ model by regarding the evolution of the EZ model as a Markov chain and by showing that the Markov chain is ergodic. The Markov analysis is applied to the EZ model with small number of agents, the exact equilibrium state for N = 5 and numerical results for N=18 are obtained. 相关文章 | 计量指标

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Interference phase of mass neutrino in CM space--time 陈霞, 王永久 2009 (4):  1707-1710.  doi: 10.1088/1674-1056/18/4/071 摘要 ( 1430 )   PDF(142KB) ( 503 )   In the gravitational field of central mass with electric and magnetic charges and magnetic moment (CM space-time), this paper calculates the interference phase of mass neutrino along geodesic in the radial direction, and discusses the contribution of the electric and magnetic charges and magnetic moment of the central mass to the phase. 相关文章 | 计量指标

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Observational constraints on the accelerating universe in the framework of a 5D bounce cosmological model 吕剑波, 徐立昕, 刘墨林, 桂元星 2009 (4):  1711-1720.  doi: 10.1088/1674-1056/18/4/072 摘要 ( 1526 )   PDF(475KB) ( 525 )   In the framework of a five-dimensional (5D) bounce cosmological model, a useful function f(z) is obtained by giving a concrete expression of deceleration parameter q(z)=q1+{q2}/{1+ln (1+ z)}. Then using the obtained Hubble parameter H(z) according to the function f(z), we constrain the accelerating universe from recent cosmic observations: the 192 ESSENCE SNe Ia and the 9 observational H(z) data. The best fitting values of transition redshift zT and current deceleration parameter q0 are given as zT= 0.65-0.120.25 and q0 = - 0.76-0.15+0.15 (1σ). Furthermore, in the 5D bounce model it can be seen that the evolution of equation of state (EOS) for dark energy wde can cross over -1 at about z=0.23 and the current value w0de= - 1.15<- 1. On the other hand, by giving a concrete expression of model-independent EOS of dark energy wde, in the 5D bounce model we obtain the best fitting values zT= 0.660.08+0.11 and q0 = - 0.690.10+0.10 (1σ) from the recently observed data: the 192 ESSENCE SNe Ia, the observational H(z) data, the 3-year Wilkinson Microwave Anisotropy Probe (WMAP), the Sloan Digital Sky Survey (SDSS) baryon acoustic peak and the x-ray gas mass fraction in clusters. 相关文章 | 计量指标