中国物理B

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Mei symmetry of Tzénoff equations of holonomic system

郑世旺, 贾利群, 余宏生

2006 (7): 1399-1402. doi: 10.1088/1009-1963/15/7/001

摘要 ( 1536 )

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The Mei symmetry of Tzénoff equations under the infinitesimal transformations of groups is studied in this paper. The definition and the criterion equations of the symmetry are given. If the symmetry is a Noether symmetry, then the Noether conserved quantity of the Tzénoff equations can be obtained by the Mei symmetry.

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A unified symmetry of nonholonomic mechanical systems in phase space

王鹏, 方建会, 丁宁, 张鹏玉

2006 (7): 1403-1406. doi: 10.1088/1009-1963/15/7/002

摘要 ( 1725 )

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In this paper, we have studied the unified symmetry of a nonholonomic mechanical system in phase space. The definition and the criterion of a unified symmetry of the nonholonomic mechanical system in phase space are given under general infinitesimal transformations of groups in which time is variable. The Noether conserved quantity, the generalized Hojman conserved quantity and the Mei conserved quantity are obtained from the unified symmetry. An example is given to illustrate the application of the results.

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On the linearization of the coupled Harry－Dym soliton hierarchy

陈金兵, 耿献国

2006 (7): 1407-1413. doi: 10.1088/1009-1963/15/7/003

摘要 ( 1523 )

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This paper is devoted to the study of the underlying linearities of the coupled Harry--Dym (cHD) soliton hierarchy, including the well-known cHD equation. Resorting to the nonlinearization of Lax pairs, a family of finite-dimensional Hamiltonian systems associated with soliton equations are presented, constituting the decomposition of the cHD soliton hierarchy. After suitably introducing the Abel--Jacobi coordinates on a Riemann surface, the cHD soliton hierarchy can be ultimately reduced to linear superpositions, expressed by the Abel--Jacobi variables.

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An exact solution of Fisher equation and its stability

段文山, 杨红娟, 石玉仁

2006 (7): 1414-1417. doi: 10.1088/1009-1963/15/7/004

摘要 ( 1793 )

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In this paper, the Fisher equation is analysed. One of its travelling wave solution is obtained by comparing it with KdV--Burgers (KdVB) equation. Its amplitude, width and speed are investigated. The instability for the higher order disturbances to the solution of the Fisher equation is also studied.

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Secure quantum dialogue based on single-photon

计新, 张寿

2006 (7): 1418-1420. doi: 10.1088/1009-1963/15/7/005

摘要 ( 1593 )

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In this paper a quantum dialogue scheme is proposed by using N batches of single photons. The same secret message is encoded on each batch of single photons by the sender with two different unitary operations, and then the N batches of single photons are sent to the receiver. After eavesdropping check, the message is encoded on the one remaining batch by the receiver. It is shown that the intercept-and-resend attack and coupling auxiliary modes attack can be resisted more efficiently, because the photons are sent only once in our quantum dialogue scheme.

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Scheme for sharing classical information via tripartite entangled states

薛正远, 易佑民, 曹卓良

2006 (7): 1421-1424. doi: 10.1088/1009-1963/15/7/006

摘要 ( 1722 )

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We investigate schemes for quantum secret sharing and quantum dense coding via tripartite entangled states. We present a scheme for sharing classical information via entanglement swapping using two tripartite entangled GHZ states. In order to throw light upon the security affairs of the quantum dense coding protocol, we also suggest a secure quantum dense coding scheme via W state by analogy with the theory of sharing information among involved users.

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The quantum tunnelling radiation of Schwarzschild de Sitter black hole with a global monopole

陈德友, 蒋青权, 李慧玲, 杨树政

2006 (7): 1425-1429. doi: 10.1088/1009-1963/15/7/007

摘要 ( 1499 )

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Applying Parikh's quantum tunnelling method, this paper has studied the quantum tunnelling radiation of Schwarzschild de Sitter black hole with a global monopole. The result shows that the tunnelling rates at the event horizon and the cosmological horizon are related to Bekenstein--Hawking entropy and the derived radiation spectrum is not precisely thermal when considering energy conservation and self-gravitation interaction.

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Restudy of the stability problem of the Schwarzschild black hole

田贵花, 王世坤, 赵峥

2006 (7): 1430-1434. doi: 10.1088/1009-1963/15/7/008

摘要 ( 1696 )

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The stability of the Schwarzschild black hole is restudied in the Painlevé coordinates. Using the Painlevé time coordinate to define the initial time, we reconsider the odd perturbation and find that the Schwarzschild black hole in the Painlevé coordinates is unstable. The Painlevé metric in this paper corresponds to the white-hole-connected region of the Schwarzschild black hole (r>2m) and the odd perturbation may be regarded as the angular perturbation. Therefore, the white-hole-connected region of the Schwarzschild black hole is unstable with respect to the rotating perturbation.

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Steady-state analysis of a bistable system subject to a coloured multiplicative noise and a white additive noise with coloured cross-correlated noises

王参军, 陈世波, 梅冬成

2006 (7): 1435-1440. doi: 10.1088/1009-1963/15/7/009

摘要 ( 1623 )

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The steady-state properties of a bistable system are investigated when both the multiplicative noise and the coupling between additive and multiplicative noises are coloured with different values of noise correlation times \tau_1 and \tau_2. After introducing a dimensionless parameter R(R=\alpha/D, D is the intensity of the multiplicative noise and \alpha is the intensity of the additive noise), and performing the numerical computations, we find the following points: (1) For the case of R>1, \lambda (the intensity of correlation between additive and multiplicative noises),\tau_{1} and \tau_{2} can induce the stationary probability distribution (SPD) transition from bimodal to unimodal in structure, but for the cases of R\leq1, the bimodal structure is preserved; (2) \alpha can also induce the SPD transition from bimodal to unimodal in structure; (3) the bimodal structure of the SPD exhibits a symmetrical structure as D increases.

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A lattice Bhatnagar--Gross--Krook model for a class of the generalized Burgers equations

余晓美, 施保昌

2006 (7): 1441-1449. doi: 10.1088/1009-1963/15/7/010

摘要 ( 1594 )

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A new lattice Bhatnagar--Gross--Krook (LBGK) model for a class of the generalized Burgers equations is proposed. It is a general LBGK model for nonlinear Burgers equations with source term in arbitrary dimensional space. The linear stability of the model is also studied. The model is numerically tested for three problems in different dimensional space, and the numerical results are compared with either analytic solutions or numerical results obtained by other methods. Satisfactory results are obtained by the numerical simulations.

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Singularly perturbed solution of a sea--air oscillator model for the ENSO

莫嘉琪, 王辉, 林万涛

2006 (7): 1450-1453. doi: 10.1088/1009-1963/15/7/011

摘要 ( 1535 )

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A time delay equation for the sea--air oscillator model is studied. The aim is to create an asymptotic solving method of nonlinear equation for the El Ni\tilde{\rm n}o--Southern Oscillation model. And based on a class of oscillators of the model, employing the method of ENSO singular perturbation, the asymptotic solution of corresponding problem is obtained. It is proven from the results that the method of singular perturbation can be used for analysing the sea surface temperature anomaly in the equatorial eastern Pacific of the atmosphere--ocean oscillation for ENSO model.

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An observer based asymptotic trajectory control using a scalar state for chaotic systems

禹东川, 夏临华, 王冬青

2006 (7): 1454-1459. doi: 10.1088/1009-1963/15/7/012

摘要 ( 1536 )

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A state-observer based full-state asymptotic trajectory control (OFSTC) method requiring a scalar state is presented to asymptotically drive all the states of chaotic systems to arbitrary desired trajectories. It is no surprise that OFSTC can obtain good tracking performance as desired due to using a state-observer. Significantly OFSTC requires only a scalar state of chaotic systems. A sinusoidal wave and two chaotic variables were taken as illustrative tracking trajectories to validate that using OFSTC can make all the states of a unified chaotic system track the desired trajectories with high tracking accuracy and in a finite time. It is noted that this is the first time that the state-observer of chaotic systems is designed on the basis of Kharitonov's Theorem.

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Evaluating the dynamical coupling between spatiotemporally chaotic signals via an information theory approach

肖方红, 郭少华, 胡元太

2006 (7): 1460-1463. doi: 10.1088/1009-1963/15/7/013

摘要 ( 1705 )

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An information-theoretic measure is introduced for evaluating the dynamical coupling of spatiotemporally chaotic signals produced by extended systems. The measure of the one-way coupled map lattices and the one-dimensional, homogeneous, diffusively coupled map lattices is computed with the symbolic analysis method. The numerical results show that the information measure is applicable to determining the dynamical coupling between two directly coupled or indirectly coupled chaotic signals.

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Nonlinear dynamics in sliding processes:the single-particle case

袁晓平, 陈宏斌, 郑志刚

2006 (7): 1464-1470. doi: 10.1088/1009-1963/15/7/014

摘要 ( 1420 )

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Dynamical behaviours of the motion of particles in a periodic potential under a constant driving velocity by a spring at one end are explored. In the stationary case, the stable equilibrium position of the particle experiences an elasticity instability transition. When the driving velocity is nonzero, depending on the elasticity coefficient and the pulling velocity, the system exhibits complicated and interesting dynamics, such as periodic and chaotic motions. The results obtained here may shed light on studies of dynamical processes in sliding friction.

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The CA model for traffic-flow at the grade roundabout crossing

陈瑞熊, 白克钊, 刘慕仁

2006 (7): 1471-1476. doi: 10.1088/1009-1963/15/7/015

摘要 ( 1876 )

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The cellular automaton model is suggested to describe the traffic-flow at the grade roundabout crossing. After the simulation with computer, the fundamental properties of this model have been revealed. Analysing this kind of road structure, this paper transforms the grade roundabout crossing with inner-roundabout-lane and outer-roundabout-lane into a configuration with many bottlenecks. Because of the self-organization, the traffic flow remains unblocked under a certain vehicle density. Some results of the simulation are close to the actual design parameter.

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Influence of strong magnetic field on β decay in the crusts of neutron stars

张洁, 刘门全, 罗志全

2006 (7): 1477-1480. doi: 10.1088/1009-1963/15/7/016

摘要 ( 1883 )

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βdecay in the strong magnetic field of the crusts of neutron stars is analysed by an improved method. The reactions ⁶⁷ Ni(β^-)⁶⁷ Cu and ⁶² Mn\beta ^-⁶² Fe are investigated as examples. The results show that a weak magnetic field has little effect on βdecay but a strong magnetic field (B>10¹²G) increases β decay rates obviously. The conclusion derived may be crucial to the research of late evolution of neutron stars and nucleosynthesis in r-process.

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Isoscaling of projectile-like fragments

钟晨, 马余刚, 方德清, 蔡翔舟, 陈金根, 沈文庆, 田文栋, 王鲲, 魏义彬, 陈金辉, 郭威, 马春旺, 马国亮, 苏前敏, 颜庭志, 左嘉旭

2006 (7): 1481-1485. doi: 10.1088/1009-1963/15/7/017

摘要 ( 1925 )

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In this paper, the isotopic and isotonic distributions of projectile fragmentation products have been simulated by a modified statistical abrasion--ablation model and the isoscaling behaviour of projectile-like fragments has been discussed. The isoscaling parameters α and β have been extracted respectively, for hot fragments before evaporation and cold fragments after evaporation. It looks that the evaporation has stronger effect on α than β. For cold fragments, a monotonic increase of α and β with the increase of Z and N is observed. The relation between isoscaling parameter and the change of isospin content is discussed.

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Damaging impacts of energetic charge particles on materials in plasma energy explosive events

邓柏权, 彭利林, 严建成, 罗正明, 陈志

2006 (7): 1486-1491. doi: 10.1088/1009-1963/15/7/018

摘要 ( 1585 )

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To provide some reference data for estimation of the erosion rates and lifetimes of some candidate plasma facing component (PFC) materials in the plasma stored energy explosive events (PSEEE), this paper calculates the sputtering yields of Mo, W and deuterium saturated Li surface bombarded by energetic charged particles by a new sputtering physics description method based on bipartition model of charge particle transport theory. The comparisons with Monte Carlo data of TRIM code and experimental results are made. The dependences of maximum energy deposition, particle and energy reflection coefficients on the incident energy of energetic runaway electrons impinging on the different material surfaces are also calculated. Results may be useful for estimating the lifetime of PFC and analysing the impurity contamination extent, especially in the PSEEE for high power density and with high plasma current fusion reactor.

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An ingenious approach of determining hydrogen isotope solubilities, diffusivities and permeabilities in GWHER-1 stainless steel

陈志, 邓柏权, 彭利林, 冯开明, 杜家驹, 毛鸥

2006 (7): 1492-1496. doi: 10.1088/1009-1963/15/7/019

摘要 ( 1354 )

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Coherent population transfer in Rydberg potassium atom by a single frequency-chirped laser pulse

张现周, 马巧枝, 李小红

2006 (7): 1497-1501. doi: 10.1088/1009-1963/15/7/020

摘要 ( 1573 )

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By using the time-dependent multilevel approach, we have calculated the coherent population transfer among the quantum states of potassium atom by a single frequency-chirped laser pulse. The results show that the population can be efficiently transferred to a target state and be trapped there by using an `intuitive' or a `counter-intuitive' frequency sweep laser pulse in the case of `narrowband' frequency-chirped laser pulse. It is also found that a pair of sequential `broadband' frequency-chirped laser pulses can efficiently transfer population from one ground state of the \La atom to the other one.

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Theoretical simulations of emission spectra of Fe⁷⁺ and Fe⁸⁺

曾交龙, 王雁桂, 赵刚, 袁建民

2006 (7): 1502-1510. doi: 10.1088/1009-1963/15/7/021

摘要 ( 1627 )

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The energy levels, oscillator strengths, spontaneous radiative decay rates, and electron impact collision strengths are calculated for Fe VIII and Fe IX using the recently developed flexible atomic code (FAC). These atomic data are used to analyse the emission spectra of both laboratory and astrophysical plasmas. The {\it n}f--3d emission lines have been simulated for Fe VIII and Fe IX in a wavelength range of 6--14 nm. For Fe VIII, the predicted relative intensities of lines are insensitive to temperature. For Fe IX, however, the intensity ratios are very sensitive to temperature, implying that the information of temperature in the experiment can be inferred. Detailed line analyses have also been carried out in a wavelength range of 60--80 nm for Fe VIII, where the solar ultraviolet measurements of emitted radiation spectrometer records a large number of spectra. More lines can be identified with the aid of present atomic data. A complete dataset is available electronically from http://www.astrnomy.csdb.cn/EIE/.

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Cluster-assisted generation of multi-charged ions in nanosecond laser ionization of pulsed hydrogen sulfide beam at 1064 and 532nm

牛冬梅, 李海洋, 罗晓琳, 梁峰, 程爽, 李安林

2006 (7): 1511-1516. doi: 10.1088/1009-1963/15/7/022

摘要 ( 1687 )

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The multi-charged sulfur ions of S^q= (q\le 6) have been generated when hydrogen sulfide cluster beams are irradiated by a nanosecond laser of 1064 and 532,nm with an intensity of 10¹⁰\sim 10¹²W1\cdotcm^-2. S⁶⁺ is the dominant multi-charged species at 1064nm, while S⁴⁺, S³⁺ and S²⁺ ions are the main multi-charged species at 532nm. A three-step model (i.e., multiphoton ionization triggering, inverse bremsstrahlung heating, electron collision ionizing) is proposed to explain the generation of these multi-charged ions at the laser intensity stated above. The high ionization level of the clusters and the increasing charge state of the ion products with increasing laser wavelength are supposed mainly due to the rate-limiting step, i.e., electron heating by absorption energy from the laser field via inverse bremsstrahlung, which is proportional to \lambda ², \lambda being the laser wavelength.

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Spin polarization effect for Fe₂ molecule

阎世英, 朱正和

2006 (7): 1517-1521. doi: 10.1088/1009-1963/15/7/023

摘要 ( 1539 )

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This paper uses the density functional theory (DFT)(B3p86) of Gaussian03 to optimize the structure of Fe₂ molecule. The result shows that the ground state for Fe₂ molecule is a 9-multiple state, which shows spin polarization effect of Fe₂ molecule of transition metal elements for the first time. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions with higher energy states. So, that the ground state for Fe₂ molecule is a 9-multiple state is indicative of the spin polarization effect of Fe₂ molecule of transition metal elements. That is, there exist 8 parallel spin electrons. The non-conjugated electron is greatest in number. These electrons occupy different spacious tracks, so that the energy of the Fe₂ molecule is minimized. It can be concluded that the effect of parallel spin of the Fe₂ molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell--Sorbie potential functions with the parameters for the ground state and other states of Fe₂ molecule are derived. Dissociation energy D_e for the ground state of Fe₂ molecule is 2.8586ev, equilibrium bond length R_e is 0.2124nm, vibration frequency \omega _e is 336.38,cm^-1. Its force constants f₂, f₃,and f₄ are 1.8615aJ\cdotnm^-2, --8.6704aJ\cdotnm^-3, 29.1676aJ\cdotnm^-4 respectively. The other spectroscopic data for the ground state of Fe₂ molecule \omega_e \chi_e, B_e, \alpha_e are 1.5461,cm^-1, 0.1339,cm^-1,7.3428×10^-4,cm^-1 respectively.

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Diode end-pumped self-Q-switched and mode-locked Nd,Cr:YAG /KTP green laser

杜仕峰, 王素梅, 张东香, 冯宝华, 张春雨, 张玲, 张治国, 张世文

2006 (7): 1522-1525. doi: 10.1088/1009-1963/15/7/024

摘要 ( 1586 )

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We first experimentally demonstrate a laser-diode end-pumped self-Q-switched and mode-locked Nd,Cr:YAG green laser with a KTP crystal as the intra-cavity frequency doubler. The device produces an average output power of 680 mW at 532 nm. The corresponding pulse width of the Q-switched envelope of the green laser is 170±20 ns. The mode-locked pulses have a repetition rate of approximately 183 MHz and the average pulse duration is estimated to be around sub-nanosecond. It is found that the intra-cavity frequency doubling greatly improves the modulation depth and stability of the mode-locked pulses within the Q-switched envelope.

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The viscoelasticity of lipid shell and the hysteresis of subharmonic in liquid containing microbubbles

龚燕君, 章东, 龚秀芬, 谭开彬, 刘政

2006 (7): 1526-1531. doi: 10.1088/1009-1963/15/7/025

摘要 ( 1559 )

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The viscoelasticity and subharmonic generation of a kind of lipid ultrasound contrast agent are investigated. Based on the measurement of the sound attenuation spectrum, the viscoelasticity of the lipid shell is estimated by use of an optimization method. Shear modulus G_S=10MPa and shear viscosity \mu _S=1.49N\cdotS/m² are obtained. The nonlinear oscillation of the encapsulated microbubble is studied with Church's model theoretically and experimentally. Especially, the dependence of subharmonic on the incident acoustic pressure is studied. The results reveal that the development of the subharmonic undergoes three stages, i.e. occurrence, growth and saturation, and that hysteresis appears in descending ramp insonation.

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Stability of tokamak plasmas with internal transport barriers against high n ideal magnetohydrodynamic ballooning mode

石秉仁, 曲文孝

2006 (7): 1532-1538. doi: 10.1088/1009-1963/15/7/026

摘要 ( 1524 )

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A ballooning mode equation for tokamak plasma, with the toroidicity and the Shafranov shift effects included, is derived for a shift circular flux tokamak configuration. Using this equation, the stability of the plasma configuration with an internal transport barrier (ITB) against the high n (the toroidal mode number) ideal magnetohydrodynamic (MHD) ballooning mode is analysed. It is shown that both the toroidicity and the Shafranov shift effects are stabilizing. In the ITB region, these effects give rise to a low shear stable channel between the first and the second stability regions. Out of the ITB region towards the plasma edge, the stabilizing effect of the Shafranov shift causes the unstable zone to be significantly narrowed.

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Initial transient process in a simple helical flux compression generator

杨显俊

2006 (7): 1539-1543. doi: 10.1088/1009-1963/15/7/027

摘要 ( 1308 )

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An analytical scheme on the initial transient process in a simple helical flux compression generator, which includes the distributions of both the magnetic field in the hollow of an armature and the conducting current density in the stator, is developed by means of a diffusion equation. A relationship between frequency of the conducting current, root of the characteristic function of Bessel equation and decay time in the armature is given. The skin depth in the helical stator is calculated and is compared with the approximate one which is widely used in the calculation of magnetic diffusion. Our analytical results are helpful to understanding the mechanism of the loss of magnetic flux in both the armature and stator and to suggesting an optimal design for improving performance of the helical flux compression generator.

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Development of a new atmospheric pressure cold plasma jet generator and application in sterilization

程诚, 刘鹏, 徐蕾, 张力叶, 詹如娟, 张文锐

2006 (7): 1544-1548. doi: 10.1088/1009-1963/15/7/028

摘要 ( 1791 )

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This paper reports that a new plasma generator at atmospheric pressure, which is composed of two homocentric cylindrical all-metal tubes, successfully generates a cold plasma jet. The inside tube electrode is connected to ground, the outside tube electrode is connected to a high-voltage power supply, and a dielectric layer is covered on the outside tube electrode. When the reactor is operated by low-frequency (6 kHz--20 kHz) AC supply in atmospheric pressure and argon is steadily fed as a discharge gas through inside tube electrode, a cold plasma jet is blown out into air and the plasma gas temperature is only 25--30℃. The electric character of the discharge is studied by using digital real-time oscilloscope (TDS 200-Series), and the discharge is capacitive. Preliminary results are presented on the decontamination of E.colis bacteria and Bacillus subtilis bacteria by this plasma jet, and an optical emission analysis of the plasma jet is presented in this paper. The ozone concentration generated by the plasma jet is 1.0×10¹⁶cm^-3 which is acquired by using the ultraviolet absorption spectroscopy.

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A comparative study of the structure and crystallization of bulk metallic amorphous rod Pr₆₀Ni₃₀Al₁₀ and melt-spun metallic amorphous ribbon Al₈₇Ni₁₀Pr₃

孟庆格, 李建国, 周建坤

2006 (7): 1549-1557. doi: 10.1088/1009-1963/15/7/029

摘要 ( 1587 )

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Pr-based bulk metallic amorphous (BMA) rods (Pr₆₀Ni₃₀Al₁₀) and Al-based amorphous ribbons (Al₈₇Ni₁₀Pr₃) have been prepared by using copper mould casting and single roller melt-spun techniques, respectively. Thermal parameters deduced from differential scanning calorimeter (DSC) indicate that the glass-forming ability (GFA) of Pr\xj{60}Ni\xj{30}Al\xj{10} BMA rod is far higher than that of Al₈₇Ni₁₀Pr₃ ribbon. A comparative study about the differences in structure between the two kinds of glass-forming alloys, superheated viscosity and crystallization are also made. Compared with the amorphous alloy Al₈₇Ni₁₀Pr₃, the BMA alloy Pr₆₀Ni₃₀Al₁₀ shows high thermal stability and large viscosity, small diffusivity at the same superheated temperatures. The results of x-Ray diffraction (XRD) and transmission electron microscope (TEM) show the pronounced difference in structure between the two amorphous alloys. Together with crystallization results, the main structure compositions of the amorphous samples are confirmed. It seems that the higher the GFA, the more topological type clusters in the Pr--Ni--Al amorphous alloys, the GFAs of the present glass-forming alloys are closely related to their structures.

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Observation of MWCNTs with low-energy electron point source microscope

于洁, 柏鑫, 张兆祥, 张耿民, 郭等柱, 薛增泉

2006 (7): 1558-1562. doi: 10.1088/1009-1963/15/7/030

摘要 ( 1483 )

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The low-energy electron point source (LEEPS) microscope, which creates enlarged projection images with low-energy field emission electron beams, can be used to observe the projection image of nano-scale samples and to characterize the coherence of the field emission beam. In this paper we report the design and test operation performance of a home-made LEEPS microscope. Multi-walled carbon nanotubes (MWCNTs) synthesized by the CVD method were observed by LEEPS microscope using a conventional tungsten tip, and projection images with the magnification of up to 10₄ was obtained. The resolution of the acquired images is \sim10 nm. A higher resolution and a larger magnification can be expected when the AC magnetic field inside the equipment is shielded and the vibration of the instrument reduced.

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Length dependence of linear and nonlinear optical properties of finite-length BN(5,0) nanotube

蓝尤钊, 吴东升, 黄淑萍, 沈娟, 李飞飞, 程文旦

2006 (7): 1563-1569. doi: 10.1088/1009-1963/15/7/031

摘要 ( 1559 )

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In this paper, we investigate the length dependence of linear and nonlinear optical properties of finite-length BN nanotubes. The recently predicted smallest BN(5,0) nanotube with configuration stabilization is selected as an example. The energy gap and optical gap show the obvious length dependence with the increase of nanotube length. When the length reaches about 24 {\AA}, the energy gap will saturate at about 3.2 eV, which agrees well with the corrected quasi-particle energy gap. The third-order polarizabilities increase with the increase of tube length. Two-photon allowed excited states have significant contributions to the third-order polarizabilities of BN(5,0) nanotube.

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A velocity-difference-separation model for car-following theory

李志鹏, 刘允才

2006 (7): 1570-1576. doi: 10.1088/1009-1963/15/7/032

摘要 ( 1337 )

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We introduce a velocity-difference-separation model that modifies the previous models in the literature. The improvement of this new model over the previous ones lies in that it not only theoretically retains many strong points of the previous ones, but also performs more realistically than others in the dynamical evolution of congestion. Furthermore, the proposed model is investigated with analytic and numerical methods, with the finding that it can demonstrate some complex physical features observed in real traffic such as the existence of three phases: free flow, synchronized flow, and wide moving jam; sudden flow drop in flow-density plane; and traffic hysteresis in transition between the free and the synchronized flow.

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Spontaneous U(1) symmetry breaking and Bose--Einstein condensation

钱锋, 黄洪斌, 齐观晓, 沈才康

2006 (7): 1577-1579. doi: 10.1088/1009-1963/15/7/033

摘要 ( 1662 )

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Based on Bogoliubov's truncated Hamiltonian H_B for a weakly interacting Bose system, and adding a U(1) symmetry breaking term $\sqrt{V}(\lambda a₀+\lambda^*a₀⁺) to H_B, we show by using the coherent state theory and the mean-field approximation rather than the c-number approximations, that the Bose--Einstein condensation(BEC) occurs if and only if the U(1) symmetry of the system is spontaneously broken. The real ground state energy and the justification of the Bogoliubov c-number substitution are given by solving the Schr\"{o}dinger eigenvalue equation and using the self-consistent condition.

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Surface rumpling of cubic CaTiO₃ from density functional theory

杨鲲, 王春雷, 李吉超, 张超, 吴清早, 张艳飞, 尹娜, 刘雪燕

2006 (7): 1580-1584. doi: 10.1088/1009-1963/15/7/034

摘要 ( 1650 )

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In this paper, the structure of cubic CaTiO₃ (001) surfaces with CaO and TiO₂ terminations has been studied from density functional calculations. It has been found that the Ca atom has the largest relaxation for both kinds of terminations, and the rumpling of the CaO-terminated surface is much larger than that of TiO₂-terminated surface. Also we have found that the metal atom relaxes much more prominently than the O atom does in each layer. The CaO-terminated surface is slightly more energetically favourable than the TiO₂-terminated surface from the analysis of the calculated surface energy.

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First principles study on the structural,electronic and optical properties of diluted magnetic semiconductors Zn_1-xCo_xX (X=S, Se, Te)

欧阳楚英, 熊志华, 欧阳企振, 刘国栋, 叶志清, 雷敏生

2006 (7): 1585-1590. doi: 10.1088/1009-1963/15/7/035

摘要 ( 1762 )

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The electronic and optical properties of zincblende ZnX(X=S, Se, Te) and ZnX:Co are studied from density functional theory (DFT) based first principles calculations. The local crystal structure changes around the Co atoms in the lattice are studied after Co atoms are doped. It is shown that the Co-doped materials have smaller lattice constant (about 0.6%--0.9%). This is mainly due to the shortened Co--X bond length. The (partial) density of states (DOS) is calculated and differences between the pure and doped materials are studied. Results show that for the Co-doped materials, the valence bands are moving upward due to the existence of Co 3d electron states while the conductance bands are moving downward due to the reduced lattice constants. This results in the narrowed band gap of the doped materials. The complex dielectric indices and the absorption coefficients are calculated to examine the influences of the Co atoms on the optical properties. Results show that for the Co-doped materials, the absorption peaks in the high wavelength region are not as sharp and distinct as the undoped materials, and the absorption ranges are extended to even higher wavelength region.

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The influence of hole shape on enhancing transmission through subwavelength hole arrays

孙梅, 刘荣鹃, 李志远, 程丙英, 张道中, 杨海方, 金爱子

2006 (7): 1591-1594. doi: 10.1088/1009-1963/15/7/036

摘要 ( 1558 )

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The extraordinary light transmission through a 200-nm thick gold film when passing through different subwavelength hole arrays is observed experimentally. The sample is fabricated by electron beam lithography and reactive ion etching system. A comparison between light transmissions shows that the hole shape changing from rectangular to diamond strongly affects the transmission intensity although both structures possess the same lattice constant of 600,nm. Moreover, the position of the transmission maximum undergoes a spectral red-shift of about 63,nm. Numerical simulations by using a transfer matrix method reproduce the observed transmission spectrum quite well.

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The rotational anisotropies in the ferromagnetism/antiferromagnetism 1/ antiferromagnetism 2 exchange bias structures

胡经国, StampsRL

2006 (7): 1595-1601. doi: 10.1088/1009-1963/15/7/037

摘要 ( 1472 )

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The rotational anisotropies in the exchange bias structures of ferromagnetism/antiferromagnetism 1/antiferromagnetism 2 are studied in this paper. Based on the model, in which the antiferromagnetism is treated with an Ising mean field theory and the rotational anisotropy is assumed to be related to the field created by the moment induced on the antiferromagnetic layer next to the ferromagnetic layer, we can explain why in experiments for ferromagnetism (FM)/antiferromagntism 1 (AFM1)/antiferromagnetism 2 (AFM2) systems the thickness-dependent rotational anisotropy value is non-monotonic, i.e. it reaches a minimum for this system at a specific thickness of the first antiferromagnetic layer and exhibits oscillatory behaviour. In addition, we find that the temperature-dependent rotational anisotropy value is in good agreement with the experimental result.

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Monte carlo simulation of magnetization and coercivity of free magnetic clusters

黄志高, 陈志高, 蒋丽钦, 叶晴莹, 吴青云

2006 (7): 1602-1610. doi: 10.1088/1009-1963/15/7/038

摘要 ( 1491 )

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Based on Monte Carlo method, the oscillatory behaviour of the average magnetic moment as a function of the cluster sizes and the temperature dependences of magnetic moment with different sizes have been studied. It is found that the oscillations superimposed on the decreasing moment are associated with not only the geometrical structure effects but also the thermal fluctuation. The hystereses and thermal coercivities for free clusters with zero and finite uniaxial anisotropies have been calculated. The simulated thermal dependence of the coercivity is consistent with the experimental result, but does not fit the T^α law in the whole temperature range. It is evident that an easy magnetization direction and an anisotropy resulting from the spin configurations exist in the free clusters with the pure exchange interaction, which is also proved by the natural angle and energy distribution of clusters. A systematic theoretical analysis is also made to establish the relationship between natural angle and coercivity.

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Diffuse dielectric anomaly of (Na_0.5K_0.5Bi)_0.5TiO₃ crystal at high temperature

赵明磊, 仪修杰, 王春雷, 王矜奉, 张家良

2006 (7): 1611-1614. doi: 10.1088/1009-1963/15/7/039

摘要 ( 1675 )

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This paper investigates the dielectric properties of (Na_0.5K_0.5Bi)_0.5TiO₃ crystal at intermediate frequencies (1kHz \le f \le 1MHz) in the temperature range of 30--560℃. A pronounced high-temperature diffuse dielectric anomaly has been observed. This dielectric anomaly is shown to arise from a Debye-like dielectric dispersion that slows down following an Arrhenius law. The activation energy E_r obtained in the fitting process is about 0.69eV. It proposes that the dielectric peak measured at low frequency above 400℃ is not related to the phase transition but to a space-charge relaxation.

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Conical bubble photoluminescence from rhodamine 6G in 1, 2-propanediol

何寿杰, 艾希成, 董丽芳, 陈得应, 王骐, 李雪辰, 张建平, 王龙

2006 (7): 1615-1620. doi: 10.1088/1009-1963/15/7/040

摘要 ( 1571 )

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A modified U-tube conical bubble sonoluminescence device is used to study the conical bubble photoluminescence. The spectra of conical bubble sonoluminescence at different concentrations of rhodamine 6G (Rh6G) solution in 1,2-propanediol have been measured. Results show that the sonoluminescence from the conical bubbles can directly excite Rh6G, which in turn can fluoresce. The light emission of this kind is referred to as conical bubble photoluminescence. The maximum of fluorescence spectral line intensity in the conical bubble photoluminescence has a red shift in relative to that of the standard photo-excited fluorescence, which is due to the higher self-absorption of Rh6G, and the spectral line of conical bubble photoluminescence is broadened in width compared with that of photo-excited fluorescence.

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Critical area computation for real defects and arbitrary conductor shapes

王俊平, 郝跃

2006 (7): 1621-1630. doi: 10.1088/1009-1963/15/7/041

摘要 ( 1310 )

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In current critical area models, it is generally assumed the defect outlines are circular and the conductors to be rectangle or the merger of rectangles. However, real defects and conductors associated with optimal layout design exhibit a great variety of shapes. Based on mathematical morphology, a new critical area model is presented, which can be used to estimate the critical area of short circuit, open circuit and pinhole. Based on the new model, the efficient validity check algorithms are explored to extract critical areas of short circuit, open circuit and pinhole from layouts. The results of experiment on an approximate layout of ${4\times 4}$ shifts register show that the new model predicts the critical areas accurately. These results suggest that the proposed model and algorithm could provide new approaches for yield prediction.

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Absolute stability of the solidification interface in a laser resolidified Zn--2wt.%Cu hypoperitectic alloy

苏云鹏, 林鑫, 王猛, 薛蕾, 黄卫东

2006 (7): 1631-1637. doi: 10.1088/1009-1963/15/7/042

摘要 ( 1294 )

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This paper reports on laser surface remelting experiments performed on a Zn--2wt.%}Cu hypoperitectic alloy by employing a 5kW CW CO₂ laser at scanning velocities between 6 and 1207mm/s. The growth velocities of the microstructures in the laser molten pool were accurately measured. The planar interface structure caused by the high velocity absolute stability was achieved at a growth velocity of 210~mm/s. An implicit expression of the critical solidification velocity for the cellular--planar transition was carried out by nonlinear stability analyses of the planar interface. The results showed a better agreement with the measured critical velocity than that predicted by M--S theory. Cell-free structures were observed throughout the whole molten pool at a scanning velocity of 652~mm/s and the calculated minimum temperature gradient in this molten pool was very close to the critical temperature gradient for high gradient absolute stability (HGAS) of the \eta phase. This indicates that HGAS was successfully achieved in the present experiments.

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Effects of unsymmetrical geometric confinements on depletion interactions in colloidal suspensions

郭纪源, 黄立新, 肖长明

2006 (7): 1638-1644. doi: 10.1088/1009-1963/15/7/043

摘要 ( 1366 )

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The depletion interactions between two large-spheres immersed in a fluid of small spheres under unsymmetrical geometrical confinement are studied through the acceptance ratio method. The numerical results show that no matter whether the volume fraction is large or small, both the depletion potential and depletion force are affected by the presence of the two plates; the closer the two large spheres are to the plate, the larger the effects of the unsymmetrical confinements.

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Method of determining cosmological parameter ranges with samples of candles with an intrinsic distribution

覃一平, 张彬彬, 董云明, 张富文, 李怀珍, 贾兰伟, 毛李胜, 陆睿静, 易庭丰, 崔晓红, 张志彬

2006 (7): 1645-1652. doi: 10.1088/1009-1963/15/7/044

摘要 ( 1302 )

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In this paper, the effect of the intrinsic distribution of cosmological candles is investigated. We find that in the case of a narrow distribution the deviation of the observed modulus of sources from the expected central value can be estimated within a ceratin range. We thus introduce lower and upper limits of X², X _min² and X_max² to estimate cosmological parameters by applying the conventional minimizing X² method. We apply this method to a gamma-ray burst (GRB) sample as well as to a combined sample including this GRB sample and an SN Ia sample. Our analysis shows that: a) in the case of assuming an intrinsic distribution of candles of the GRB sample, the effect of the distribution is obvious and should not be neglected; b) taking into account this effect would lead to a poorer constraint of the cosmological parameter ranges. The analysis suggests that in the attempt of constraining the cosmological model with current GRB samples, the results tend to be worse than was previously anticipated if the mentioned intrinsic distribution does exist.

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