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Chin. Phys. B  
  Chin. Phys. B--2006, Vol.15, No.5
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GENERAL

The Lagrangian and the Lie symmetries of charged particle motion in homogeneous electromagnetic field

Lou Zhi-Mei
Chin. Phys. B 2006, 15 (5): 0891;  doi: 10.1088/1009-1963/15/5/001
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In this paper, a constant of motion of charged particle motion in homogeneous electromagnetic field is derived from Newton's equations and the characteristics of partial differential equation, the related Lagrangian is also given by means of the obtained constant of motion. By discussing the Lie symmetry for this classical system, this paper obtains the general expression of the conserved quantity. It is shown that the conserved quantity is the same as the constant of motion in essence.

Direct method of finding first integral of two-dimensional autonomous systems in polar coordinates

Lou Zhi-Mei, Wang Wen-Long
Chin. Phys. B 2006, 15 (5): 0895;  doi: 10.1088/1009-1963/15/5/002
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A direct method to find the first integral for two-dimensional autonomous system in polar coordinates is suggested. It is shown that if the equation of motion expressed by differential 1-forms for a given autonomous Hamiltonian system is multiplied by a set of multiplicative functions, then the general expression of the first integral can be obtained. An example is given to illustrate the application of the results.

Potential method of integration for solving the equations of mechanical systems

Wu Hui-Bin
Chin. Phys. B 2006, 15 (5): 0899;  doi: 10.1088/1009-1963/15/5/003
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This paper is intended to apply a potential method of integration to solving the equations of holonomic and nonholonomic systems. For a holonomic system, the differential equations of motion can be written as a system of differential equations of first order and its fundamental partial differential equation is solved by using the potential method of integration. For a nonholonomic system, the equations of the corresponding holonomic system are solved by using the method and then the restriction of the nonholonomic constraints on the initial conditions of motion is added.

Unified symmetry of nonholonomic mechanical systems with variable mass

Xia Li-Li, Li Yuan-Cheng, Hou Qi-Bao, Wang Jing
Chin. Phys. B 2006, 15 (5): 0903;  doi: 10.1088/1009-1963/15/5/004
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Based on the total time derivative along the trajectory of the system the definition and the criterion for a unified symmetry of nonholonomic mechanical system with variable mass are presented in this paper. A new conserved quantity, as well as the Noether conserved quantity and the Hojman conserved quantity, deduced from the unified symmetry, are also obtained. An example is given to illustrate the application of the results.

Optimal conclusive teleportation of a d-dimensional two-particle unknown quantum state

Yang Yu-Guang, Wen Qiao-Yan, Zhu Fu-Chen
Chin. Phys. B 2006, 15 (5): 0907;  doi: 10.1088/1009-1963/15/5/005
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A conclusive teleportation protocol of a d-dimensional two-particle unknown quantum state using three d-dimensional particles in an arbitrary pure state is proposed. A sender teleports the unknown state conclusively to a receiver by using the positive operator valued measure(POVM) and introducing an ancillary qudit to perform the generalized Bell basis measurement. We calculate the optimal teleportation fidelity. We also discuss and analyse the reason why the information on the teleported state is lost in the course of the protocol.

Berry phase of coupled two arbitrary spins in a time-varying magnetic field

Xu Chang-Tan, He Ming-Ming, Chen Gang
Chin. Phys. B 2006, 15 (5): 0912;  doi: 10.1088/1009-1963/15/5/006
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In this paper, we investigate the Berry phase of two coupled arbitrary spins driven by a time-varying magnetic field where the Hamiltonian is explicitly time-dependent. Using a technique of time-dependent gauge transform the Berry phase and time-evolution operator are found explicitly in the adiabatic approximation. The general solutions for arbitrary spins are applied to the spin-1/2\ system as an example of explanation.

Teleportation of an unknown bipartite state via non-maximally entangled two-particle state

Cao Hai-Jing, Guo Yan-Qing, Song He-Shan
Chin. Phys. B 2006, 15 (5): 0915;  doi: 10.1088/1009-1963/15/5/007
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In this paper a new scheme for teleporting an unknown entangled state of two particles is proposed. To weaken the requirement for the quantum channel, without loss of generality, two communicators only share a non-maximally entangled two-particle state. Teleportation can be probabilistically realized if sender performs Bell-state measurements and Hadamard transformation and receiver introduces two auxiliary particles, operates C-not operation, single-qubit measurements and appropriate unitary transformations. The probability of successful teleportation is determined by the smaller one among the coefficients' absolute values of the quantum channel.

Semiclassical propagator and van Vleck determinant in a mixed position--momentum space

Yang Guang-Can
Chin. Phys. B 2006, 15 (5): 0919;  doi: 10.1088/1009-1963/15/5/008
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In this paper a semiclassical propagator in a mixed position--momentum space is derived in the formalism of Maslov's multi-dimensional semiclassical theory. The corresponding mixed van Vleck determinant is also given explicitly. The propagator can be used to locally fix semiclassical divergences in singular regions of configuration space. It is shown that when a semiclassical propagator is transformed from one representation to another, its form is invariant.

Scheme for concentration of the unknown GHZ entangled states

Zhang Gang, Yang Ming, Xue Zheng-Yuan, Cao Zhuo-Liang
Chin. Phys. B 2006, 15 (5): 0923;  doi: 10.1088/1009-1963/15/5/009
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We propose two schemes for concentrating unknown nonmaximally tripartite GHZ entangled states via cavity quantum electrodynamics (QED) techniques. The finial pure states obtained from the two schemes are shared by two or three parties. Our schemes only require large-detuned interaction between two driven atoms and the quantized cavity mode, which is insensitive to both the cavity decay and thermal field, thus the schemes are well within current experimental technology.

The properties and geodesics related to the NUT--Taub-like spacetime

Wu Ya-Bo, Zhao Guo-Ming, Deng Xue-Mei, Yang Xiu-Yi, Lü Jian-Bo, Li Song
Chin. Phys. B 2006, 15 (5): 0927;  doi: 10.1088/1009-1963/15/5/010
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Some properties related to the NUT--Taub-like spacetime, such as the surface of infinite red-shift, horizon, singularity and the area of the NUT--Taub-like black hole are discussed. Furthermore, the geodesics in the NUT--Taub-like spacetime are obtained in some special cases. Specifically, the circular orbits for a massive particle are derived, which can reduce to the cases of the Schwarzschild spacetime and the NUT--Taub spacetime when m*=0 and m*\ll M, respectively.

Restrictions on negative energy density for the Dirac field in flat spacetime

Shu Wei-Xing, Yu Hong-Wei, Li Fei, Wu Pu-Xun, Ren Zhong-Zhou
Chin. Phys. B 2006, 15 (5): 0934;  doi: 10.1088/1009-1963/15/5/011
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This paper investigates the quantum Dirac field in n+1-dimensional flat spacetime and derives a lower bound in the form of quantum inequality on the energy density averaged against spacetime sampling functions. The state-independent quantum inequality derived in the present paper is similar to the temporal quantum energy inequality and it is stronger for massive field than for massless one. It also presents the concrete results of the quantum inequality in 2 and 4-dimensional spacetimes.

Single long-polymer translocation through a long pore

Ding Ke-Jian, Cai Dong-Qing, Zhan Fu-Ru, Wu Li-Jun, Wu Yue-Jin, Yu Zeng-Liang
Chin. Phys. B 2006, 15 (5): 0940;  doi: 10.1088/1009-1963/15/5/012
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This paper theoretically studies the free energy and conformational entropy of a long polymer threading a long nanopore (n0/N \ge 0.1) on external electric field. The polymer expanded model is built in this paper, that is, a single long polymer chain with N monomers (each of size a) threading a pore with n0 monomers can be regarded as polymer with N+n_{0} monomers translocating a 2-dimension hole embedded in membrane. A theoretical approach is presented which explicitly takes into account the nucleation theory. Our calculations imply that, the structure of polymer changes more acutely than other situation, while its leading monomer reaches the second vacuum and its end monomer escapes the first vacuum. And it is also shown that the length scale of polymer and pore play a very important role for polymer translocation dynamics. The present model predicts that the translocation time depends on the chemical potential gradient and the property of the solvent on sides of pore to some extent.

Stochastic resonance in a bias linear system with multiplicative and additive noise

Guo Feng, Zhou Yu-Rong, Jiang Shi-Qi, Gu Tian-Xiang
Chin. Phys. B 2006, 15 (5): 0947;  doi: 10.1088/1009-1963/15/5/013
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In this paper, the stochastic resonance in a bias linear system subjected multiplicative and additive dichotomous noise is investigated. Using the linear-response theory and the properties of the dichotomous noise, this paper finds the exact expressions for the first two moments and the signal-to-noise ratio (SNR). It is shown that the SNR is a non-monotonic function of the correlation time of the multiplicative and additive noise, and it varies non-monotonously with the intensity and asymmetry of the multiplicative noise as well as the external field frequency. Moreover, the SNR depends on the system bias, the intensity of the cross noise between the multiplicative and additive noise, and the strength and asymmetry of the additive noise.

Adaptive synchronization of Chua's system with uncertain inputs

Zhang Jian, Xu Hong-Bing, Wang Hou-Jun
Chin. Phys. B 2006, 15 (5): 0953;  doi: 10.1088/1009-1963/15/5/014
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The synchronization of Chua's system, whose inputs include an unknown constant parameter, is studied in this paper. A constructive method is applied to designing an adaptive controller, in which only one variable information of the master system is needed. With the action of control signals, the parameter of the slave system will approach the corresponding unknown parameter in the master system. At the same time, the synchronization errors will also converge to zero asymptotically. Numerical simulations show that the proposed theoretical approach is very effective.

The design and artificial realization of a controller of pulse coupling feedback

Lü Ling, Guo Zhi-An, Luan Ling, Zou Cheng-Ye, Zhao Hong-Yan
Chin. Phys. B 2006, 15 (5): 0958;  doi: 10.1088/1009-1963/15/5/015
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In this paper a controller of pulse coupling feedback (PCF) is designed to control chaotic systems. Control principles and the technique to select the feedback coefficients are introduced. This controller is theoretically studied with a three dimensional (3D) chaotic system. The artificial simulation results show that the chaotic system can be stabilized to different periodic orbits by using the PCF method, and the number of the periodic orbits are 2n× 3mp (n and m are integers). Therefore, this control method is effective and practical.

Hyperchaos evolved from the Liu chaotic system

Wang Fa-Qiang, Liu Chong-Xin
Chin. Phys. B 2006, 15 (5): 0963;  doi: 10.1088/1009-1963/15/5/016
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This paper introduces a new hyperchaotic system by adding an additional state into the third-order Liu chaotic system. Some of its basic dynamical properties, such as the hyperchaotic attractor, Lyapunov exponent, fractal dimension and the hyperchaotic attractor evolving into chaotic, periodic, quasi-periodic dynamical behaviours by varying parameter d are studied briefly. Various attractors are illustrated not only by computer simulation but also by conducting an electronic circuit experiment.

Spatial distribution of electron characteristic in argon rf glow discharges

Zhu Zu-Song, Lin Kui-Xun, Lin Xuan-Ying, Qiu Gui-Ming, Yu Yun-Peng, Luo Yi-Lin
Chin. Phys. B 2006, 15 (5): 0969;  doi: 10.1088/1009-1963/15/5/017
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The spatial distributions of the electron density and the mean electron energy of argon radio frequency (rf) glow discharge plasma in a plasma-enhanced chemical vapour deposition (PECVD) system have been investigated using an established movable Langmuir probe. The results indicate that in the axial direction the electron density tends to peak at midway between the two electrodes while the axial variation trend of mean electron energy is different from that of the electron density, the mean electron energy is high near the electrodes. And the mean electron energy near the cathode is much higher than that near the anode. This article focuses on the radial distribution of electron density and mean electron energy. A proposed theoretical model distribution agrees well with the experimental one: the electron density and the mean electron energy both increase from the centre of the glow to the edge of electrodes. This is useful for better understanding the discharge mechanism and searching for a better deposition condition to improve thin film quality.

A sapphire fibre thermal probe based on fast Fourier transform and phase-lock loop

Wang Yu-Tian, Wang Dong-Sheng, Ge Wen-Qian, Cui Li-Chao
Chin. Phys. B 2006, 15 (5): 0975;  doi: 10.1088/1009-1963/15/5/018
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A sapphire fibre thermal probe with Cr3+ ion-doped end is developed by using the laser heated pedestal growth method. The fluorescence thermal probe offers advantages of compact structure, high performance and ability to withstand high temperature in a detection range from room temperature to 450℃. Based on the fast Fourier transform (FFT), the fluorescence lifetime is obtained from the tangent function of phase angle of the non-zeroth terms in the FFT result. This method has advantages such as quick calculation, high accuracy and immunity to the background noise. This FFT method is compared with other traditional fitting methods, indicating that the standard deviation of the FFT method is about half of that of the Prony method and about 1/6 of that of the log-fit method. And the FFT method is immune to the background noise involved in a signal. So, the FFT method is an excellent way of processing signals. In addition, a phase-lock amplifier can effectively suppress the noise.

OES study of the gas phase during diamond films deposition in high power DC arc plasma jet CVD system

Zhou Zu-Yuan, Chen Guang-Chao, Tang Wei-Zhong, Lü Fan-Xiu
Chin. Phys. B 2006, 15 (5): 0980;  doi: 10.1088/1009-1963/15/5/019
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This paper used optical emission spectroscopy (OES) to study the gas phase in high power DC arc plasma jet chemical vapour deposition (CVD) during diamond films growth processes. The results show that all the deposition parameters (methane concentration, substrate temperature, gas flow rate and ratio of H2/Ar) could strongly influence the gas phase. C2 is found to be the most sensitive radical to deposition parameters among the radicals in gas phase. Spatially resolved OES implies that a relative high concentration of atomic H exists near the substrate surface, which is beneficial for diamond film growth. The relatively high concentrations of C2 and CH are correlated with high deposition rate of diamond. In our high deposition rate system, C2 is presumed to be the main growth radical, and CH is also believed to contribute the diamond deposition.

Selective reflection combined with Fabry--Perot effects from two-level atoms confined between two dielectric walls

Li Yuan-Yuan, Zhou Yu, Zhang Gui-Zhong
Chin. Phys. B 2006, 15 (5): 0985;  doi: 10.1088/1009-1963/15/5/020
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The coefficient of selective reflection at oblique incidence from two-level atoms confined between two dielectric walls is calculated in this paper. It is found to be related to the transient behaviour of atoms after colliding with the wall and the distribution of the field inside the vapour corresponds to L / \lambda , with L the thickness of the film and \lambda the incident wavelength. We find that the sub-Doppler structure is manifest both for normal incidence and small angle oblique incidence. It is feasible to detect the real part of selective reflection in several cases that have not been achieved before.
ATOMIC AND MOLECULAR PHYSICS

Analytic variationally optimized internally orthogonalized modified Laguerre orbitals in accurate atomic configuration interaction calculation

Xiong Zhuang, N C Bacalis
Chin. Phys. B 2006, 15 (5): 0992;  doi: 10.1088/1009-1963/15/5/021
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An analytic configuration interaction method based on variationally optimized internally orthogonalized modified Laguerre orbitals is presented. We have developed the corresponding computer code. For application, we study the 1s2s ^{1}S isoelectronic sequence from helium to neon, and compare with other methods. By taking into account the Eckart upper-bound theorem, we obtained more accurate and more intuitively understandable results than Hartree--Fock and multi-configuration Hartree--Fock reported results.

The splitting of low-lying states for hydroxyl molecule under spin--orbit coupling

Li Gui-Xia, Gao Tao, Chen Dong, Li Yue-Xun, Zhang Yun-Guang, Zhu Zheng-He
Chin. Phys. B 2006, 15 (5): 0998;  doi: 10.1088/1009-1963/15/5/022
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The splitting of potential energy curves for the states $X^{2}\Pi _{3/2}$, $^{2}\Pi _{1/2}$ and $A^{2}\Sigma ^{ +}$ of hydroxyl OH under spin--orbit coupling (SOC) has been calculated by using the SO multi-configuration quasi-degenerate perturbation theory (SO-MCQDPT). Their Murrell--Sorbie (M--S) potential functions have been derived, then, the spectroscopic constants for $X^{2}\Pi _{3/2}$,$^{ 2}\Pi _{1/2}$ and $A^{2}\Sigma ^{ + }$ have been derived from the M--S function. The calculated dissociation energies for the three states are $D_{0}$[OH($X^{2}\Pi _{3/2})$]=34966.632cm$^{-1}$, $D_{0}$[OH($^{2}\Pi _{1/2})$]=34922.802cm$^{-1}$, and $D_{0}$[OH($A^{2}\Sigma ^{ + })$]=17469.794cm$^{-1}$, respectively. The vertical excitation energy $\nu [ {{ }^2\Pi _{1/2} ( {\nu = 0} ) \to {X}{ }^2\Pi _{3/2} ( {\nu = 0} )} ] = 139.6{\rm cm}^{-{\rm 1}}$. All the spectroscopic data for the $X^{2}\Pi _{3/2}$ and $^{2}\Pi _{1/2 }$ are given for the first time except the dissociation energy of $X^{2}\Pi _{3/2}$.

Study of n=2,Δn=0 transition of Be-, B-, C-, N- and O-like sequence in the beam--foil spectrum of titanium

Yang Zhi-Hu, Du Shu-Bin, Zeng Xian-Tang, Song Zhang Yong, Wang You-De, Su Hong
Chin. Phys. B 2006, 15 (5): 01004;  doi: 10.1088/1009-1963/15/5/023
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The foil-excited the spectrum of highly stripped titanium ions between 12--40~nm has been studied. Titanium ions of 80 and 120~MeV were provided by the HI-13 tandem accelerator at the China Institute of Atomic Energy. GIM-957 XUV-VUV monochromator was refocused to get highly-resolved spectra. Our experimental results and the published spectral data of laser-produced plasma show agreement in nearly all cases within \pm 0.03nm. The spectra contained some weak or strong lines previously unclassified. These spectral lines mainly belong to 2s2p^{2 } for TiXVIII, 2p^{3} for TiXVIII, 2s2p^{3} for TiXVII, 2p^{6}4p for Ti XII and 2p^{6}3d for Ti XII transitions.

Mechanical model study of relationship of molecular configuration and multiphase in liquid crystal materials

Ma Heng, Sun Rui-Zhi, Li Zhen-Xin
Chin. Phys. B 2006, 15 (5): 01009;  doi: 10.1088/1009-1963/15/5/024
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A mechanical model of liquid crystals (LCs) is applied to study the polymorphism of homologous series of terphenyl compounds. With a semi-experimental molecular orbit method, we calculate the moment of inertia which represents the rotation state to describe the phase transition temperature obtained from experimental data. We propose a novel explanation of the phase sequence or polymorphism of LC materials using the two key parameters, the moment of inertia and critical rotational velocity. The effect of molecular polarity on the appearance of liquid crystalline is also discussed.

Ab initio calculation of accurate dissociation energy, potential energy curve and dipole moment function for the A1+ state 7LiH molecule

Shi De-Heng, Liu Yu-Fang, Sun Jin-Feng, Yang Xiang-Dong, Zhu Zun-Lue
Chin. Phys. B 2006, 15 (5): 01015;  doi: 10.1088/1009-1963/15/5/025
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The reasonable dissociation limit of the A1+ state $^{7}$LiH molecule is obtained. The accurate dissociation energy and the equilibrium geometry of this state are calculated using a symmetry-adapted-cluster configuration-interaction method in complete active space for the first time. The whole potential energy curve and the dipole moment function for theA1+ state are calculated over a wide internuclear separation range from about 0.1 to 1.4\,nm. The calculated equilibrium geometry and dissociation energy of this potential energy curve are of R_{\e}=0.2487\,nm and D_{\e}=1.064\,eV, respectively. The unusual negative values of the anharmonicity constant and the vibration-rotational coupling constant are of \textit{\omega }_{\e}\textit{\chi }_{\e}=--4.7158cm^{ - 1} and \textit{\alpha }_{\e}=--0.08649cm^{ -1}, respectively. The vertical excitation energy from the ground to the A1+ state is calculated and the value is of 3.613\,eV at 0.15875nm (the equilibrium position of the ground state). The highly anomalous shape of this potential energy curve, which is exceptionally flat over a wide radial range around the equilibrium position, is discussed in detail. The harmonic frequency value of 502.47cm1 about this state is approximately estimated. Careful comparison of the theoretical determinations with those obtained by previous theories about the A1+ state dissociation energy clearly shows that the present calculations are much closer to the experiments than previous theories, thus represents an improvement.
CLASSICAL AREAS OF PHENOMENOLOGY

Direct acceleration of electrons using two crossed Laguerre--Gaussian laser beams in vacuum

Zhao Zhi-Guo, Lü Bai-Da
Chin. Phys. B 2006, 15 (5): 01022;  doi: 10.1088/1009-1963/15/5/026
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The basic physical characteristics of electrons accelerated by two linearly polarized and circularly symmetric crossed Laguerre--Gaussian (LG) laser beams with equal frequency and amplitude in vacuum are studied in detail. The condition, under which electrons can be accelerated effectively, and the energy gain are discussed.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Thomson scattering off a pair (electron--positron) plasma

Zheng Jian
Chin. Phys. B 2006, 15 (5): 01028;  doi: 10.1088/1009-1963/15/5/027
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Thomson scattering off a pair (electron--positron) plasma is theoretically investigated in the collisionless and collisional limits respectively. Our calculations show that the power spectrum of the Thomson scattering off a collisionless pair plasma is just proportional to the velocity distribution function of the particles in the plasma. Collective modes in the plasma do not have any effects on the Thomson scattering spectrum because of the correlation between the negatively- and positively-charged particles. In the collisional limit, the power spectrum of the Thomson scattering presents three spikes: two peaks correspond to two contra-propagating sound waves and one peak corresponds to an entropy wave.

Runaway electrons as a diagnostic of plasma internal magnetic fluctuations

Zheng Yong-Zhen, Ding Xuan-Tong, Li Wen-Zhong
Chin. Phys. B 2006, 15 (5): 01035;  doi: 10.1088/1009-1963/15/5/028
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The transport of runaway electrons in a high-temperature plasma is relatively easy to measure in a steady state experiment and a perturbation experiment, which provides runaway electron diffusion coefficient Dr. This diffusion coefficient is determined by internal magnetic fluctuations, so it can be interpreted in terms of a magnetic fluctuation level. The internal magnetic fluctuation level ($\tilde {b}r/BT is estimated to be about (2--4)×-4 in the HL-1M plasma. The results presented here demonstrate the effectiveness of using runaway electron transport techniques to determine internal magnetic fluctuations. A profile of magnetic fluctuation level in the HL-1M plasma can be estimated from Dr.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Threshold and saturation properties of the field-induced twist cell with two parameters weak anchoring boundaries

Guan Rong-Hua, Sun Yu-Bao
Chin. Phys. B 2006, 15 (5): 01041;  doi: 10.1088/1009-1963/15/5/029
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On the basis of two-parameter formula of weak surface coupling anchoring energy of nematic liquid crystals proposed by Zhao et al recently, the general torque equilibrium equation and boundary conditions of the director have been obtained and the threshold field as well as the saturation field of the field-induced twist cell have been analysed for three kinds of configurations, i.e. homogeneous, splay and Pi cells formed by different rubbing conditions and pretilt angles. The results indicated that the polar anchoring has no effect on the threshold field. It is determined only by the twist anchoring and pretilt angle. But, the polar anchoring and twist anchoring are coupling with each other and have a great influence on the saturation field. The formulae for calculating the threshold field and saturation field are given. These results will be very useful in understanding surface physics and the design of liquid crystal cells.

Effect of solute concentration on the serrated flow in solution-treated Al--4%Cu alloys

Jiang Hui-Feng, Zhang Qing-Chuan, Sun Liang, Wu Xiao-Ping
Chin. Phys. B 2006, 15 (5): 01051;  doi: 10.1088/1009-1963/15/5/030
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In order to compare with annealed Al--4%Cu alloys, the influence of solute concentration on the serrated flow is investigated by solution treatment. In this paper, some dynamic parameters, such as critical time and the ultimate tensile strength are obtained. Moreover, the change of the strain rate range for serrated flow in Al--4%Cu alloys prepared by annealing and quenching heat treatments is reported too. The difference between them is attributed to the increasing solute concentration in the bulk of the solution treated materials.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Kinetics study of ultrafast electron transfer from sensitized dyes to silver halide microcrystals

Yang Shao-Peng, Fan Guo-Zhi, Fan Shan-Shan, Cao Ning, Li Xiao-Wei, Jiang Xiao-Li, Fu Guang-Sheng
Chin. Phys. B 2006, 15 (5): 01055;  doi: 10.1088/1009-1963/15/5/031
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Spectral sensitization micromechanism of cyanine dyes J-aggregate adsorbed on the tabular and cubic AgBr microcrystals with different dye concentrations is studied by using picosecond time-resolved fluorescence spectroscopy, and the dependences of electron transfer and spectral efficiency sensitization on different conditions are analysed in detail. With the steady spectroscopy, the wavelengths of absorption and fluorescence of J-aggregate adsorbed on AgBr microcrystals are found to shift to red relative to dye monomer. The spectrum of fluorescence has a red shift relative to the absorption peak. With the time-resolved fluorescence spectroscopy, the fluorescence decay curves of cyanine dyes J-aggregate adsorbed on the tabular and cubic AgBr grains are found to be fitted well by a double-exponential decay function. The fitting curves consist of a fast and a slow component. Because of the large amplitude of the fast component, this fast decay should be attributable mainly to the electron transfer from J-aggregate of dye to a conduction band of AgBr.

Effects of donor density and temperature on electron systems in AlGaN/AlN/GaN and AlGaN/GaN structures

Zhang Jin-Feng, Wang Chong, Zhang Jin-Cheng, Hao Yue
Chin. Phys. B 2006, 15 (5): 01060;  doi: 10.1088/1009-1963/15/5/032
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It was reported by Shen et al that the two-dimensional electron gas (2DEG) in an AlGaN/AlN/GaN structure showed high density and improved mobility compared with an AlGaN/GaN structure, but the potential of the AlGaN/AlN/GaN structure needs further exploration. By the self-consistent solving of one-dimensional Schr\"{o}dinger--Poisson equations, theoretical investigation is carried out about the effects of donor density (0--1\times 1019cm-3 and temperature (50--500K) on the electron systems in the AlGaN/AlN/GaN and AlGaN/GaN structures. It is found that in the former structure, since the effective \Delta Ec is larger, the efficiency with which the 2DEG absorbs the electrons originating from donor ionization is higher, the resistance to parallel conduction is stronger, and the deterioration of 2DEG mobility is slower as the donor density rises. When temperature rises, the three-dimensional properties of the whole electron system become prominent for both of the structures, but the stability of 2DEG is higher in the former structure, which is also ascribed to the larger effective \Delta Ec. The Capacitance--Voltage (C-V) carrier density profiles at different temperatures are measured for two Schottky diodes on the considered heterostructure samples separately, showing obviously different 2DEG densities. And the temperature-dependent tendency of the experimental curves agrees well with our calculations.

PLE spectra analysis of the sub-structure in the absorption spectra of CdSeS quantum dots

Liu Bing-Can, Pan Xue-Qin, Tian Qiang, Wu Zheng-Long
Chin. Phys. B 2006, 15 (5): 01067;  doi: 10.1088/1009-1963/15/5/033
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The semiconductor CdSeS quantum dots (QDs) embedded in glass are analysed by means of absorption spectra, photoluminescence (PL) spectra and photoluminescence excitation (PLE) spectra. The peaks of absorption spectra shift to lower energies with the size of QD increasing, which obviously shows a quantum-size effect. Using the PLE spectra, the physical origin of the lowest absorption peak is analysed. In PLE spectra, the lowest absorption peak can be deconvoluted into two peaks that stem from the transitions of 1S3/2--1Se and 2S3/2--1Se respectively. The measured energy difference between the two peaks is found to decrease with the size of QD increasing, which agrees well with the theoretical calculation for the two transitions. The luminescence peak of defect states is also analysed by PLE spectra. Two transitions are present in the PLE, which indicates that the transitions of 1S3/2--1Se and 2S3/2--1Se are responsible for the defect states luminescence.

Fabrication and electrical properties of a carbon nanotube quantum dot

Fang Jing-Hai, Liu Li-Wei, Kong Wen-Jie, Cai Jian-Zhen, Lü Li
Chin. Phys. B 2006, 15 (5): 01071;  doi: 10.1088/1009-1963/15/5/034
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Single-walled carbon nanotubes (SWNTs) were synthesized by pyrolyzing methane (CH4) at a temperature of 900℃ on SiO2 substrates pre-coated with iron nano-particles. Electrical contacts were fabricated onto one of the SWNTs by using an electron beam lithography process. Coulomb blockade and single-electron tunnelling characters were found at low temperatures, indicating that the SWNT in-between the electrodes forms a quantum dot. It is found that the Coulomb gap of the quantum dot is about 8.57 meV, and the factor \alpha , which converts the gate voltage to the true electrostatic potential shift, is around 200 for this device.

Electronic spin susceptibility of metallic superconductive nano-particles

Li Feng, Chen Zhi-Qian, Li Qing
Chin. Phys. B 2006, 15 (5): 01075;  doi: 10.1088/1009-1963/15/5/035
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We have observed the thermodynamic properties of metallic superconductive nano-particles in the grand canonical ensemble; and the level distribution and the level correlation between the discrete electronic energy levels are considered in the calculation of the electronic spin susceptibility of the ensemble numerically. The quantum effect, even--odd effect and other special effects existing in the metallic nano-particles are also studied in this article.

Critical properties of XY model on two-dimensional layered magnetic films

Wang Yi, Liu Xiao-Yan, Sun Lei, Zhang Xing, Han Ru-Qi
Chin. Phys. B 2006, 15 (5): 01081;  doi: 10.1088/1009-1963/15/5/036
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Using Monte Carlo simulations, we have investigated the classical $XY$ model on triangular lattices of ultra-thin film structures with middle ferromagnetic layers sandwiched between two antiferromagnetic layers. The internal energy, the specific heat, the chirality and the chiral susceptibility are calculated in order to clarify phase transitions and critical phenomena. From the finite-size scaling analyses, the values of critical exponents are determined. In a range of interaction parameters, we find that the chirality steeply goes up as temperature increases in a temperature range; correspondingly the value of a critical exponent for this change is estimated.

Proton radiation effects on optical constants of Al film reflector

Liu Hai, Wei Qiang, He Shi-Yu, Zhao Dan
Chin. Phys. B 2006, 15 (5): 01086;  doi: 10.1088/1009-1963/15/5/037
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The Al film reflectors can yield a high-reflectance over a broad wavelength region, and have been widely used in the spacecraft optical instruments for high quality optical applications. Under the irradiation of charged particles in the Earth radiation belt, the reflectors could be deteriorated. In order to reveal the deterioration mechanism, the change in optical constants of Al film reflector induced by proton radiation with 60\,keV was studied in an environment of vacuum with heat sink. Experimental results showed that when the radiation damage primarily occurs in the Al reflecting film, the extinction coefficient k will gradually decrease with increasing radiation fluence, which results in the decrease of the energies of reflective light. Therefore, the proton radiation induced an obvious degradation of spectral reflectance in the wavelength region from 200 to 800\,nm on the Al film reflector.

Infrared active phonon modes and ionicity of single crystal MgAl2O4

Bi Cong-Zhi, Ma Ji-Yun, Yan Jun, Fang Xu, Zhao Bai-Ru, Yao Duan-Zheng, Qiu Xiang-Gang
Chin. Phys. B 2006, 15 (5): 01090;  doi: 10.1088/1009-1963/15/5/038
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Near-normal incident infrared reflectivity spectra of (100) MgAl2O4 spinel single crystal have been measured at different temperatures in the frequency region between 50 and 6000cm-1. Eight infrared-active phonon modes are identified, which are fitted with the factorized form of the dielectric function. The dielectric property and optical conductivity of the MgAl2O4 crystal are analysed. From TO/LO splitting, the effective Szigeti charges and Born effective charges at different temperatures are calculated for studying the ionicity and the effect of polarization. Based on the relationship between the (LO--TO)1 splitting, which represents the transverse and longitudinal frequencies splitting of the highest energy phonon band in the reflectivity spectrum, and the ionic-covalent parameter, the four main phonon modes are assigned. MgAl2O4can be considered as a pure ionic crystal and its optical characters do not change with decreasing temperature, so it may be used as a suitable substrate for high-Tc superconducting thin films.

Upconversion properties of Er3+/Yb3+ co-doped TeO2--Nb2O2--Li2O glasses

Su Fang-Ning, Deng Zai-De
Chin. Phys. B 2006, 15 (5): 01096;  doi: 10.1088/1009-1963/15/5/039
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The Er3+/Yb3+ co-doped TeO2--Nb2O5--Li2O glass is prepared by conventional melting method, and its upconversion spectra are measured. The intense green upconversion luminescence upon excitation with a 976nm laser diode is observed with the naked eyes. The dependence of luminescence intensity on the ratio of Yb3+/Er3+ is discussed in detail, and the relationship between the ratio of green luminescence intensity to red luminescence intensity and the ratio of Yb3+/Er3+ is also studied. The luminescence intensity increases with the ratio of Yb3+/Er3+ increasing. The ratio of Yb3+/Er3+ plays a more important role than the concentration of Er3+ in determining the upconversion luminescence intensity. The ratio of green luminescence intensity to red luminescence intensity reaches a maximum when ratio of Yb3+/Er3+ is 3. Thus the glass could be one of the potential candidates for LD pumping solid-state lasers.

Polar interface and surface optical vibration spectra in multi-layer wurtzite quantum wires:transfer matrix method

Zhang Li
Chin. Phys. B 2006, 15 (5): 01101;  doi: 10.1088/1009-1963/15/5/040
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The polar interface optical (IO) and surface optical (SO) phonon modes and the corresponding Fr\"{o}hlich electron--phonon--interaction Hamiltonian in a freestanding multi-layer wurtzite cylindrical quantum wire (QWR) are derived and studied by employing the transfer matrix method in the dielectric continuum approximation and Loudon's uniaxial crystal model. A numerical calculation of a freestanding wurtzite GaN/AlN QWR is performed. The results reveal that for a relatively large azimuthal quantum number m or wave-number kz in the free z-direction, there exist two branches of IO phonon modes localized at the interface, and only one branch of SO mode localized at the surface in the system. The degenerating behaviours of the IO and SO phonon modes in the wurtzite QWR have also been clearly observed for a small kz or m. The limiting frequency properties of the IO and SO modes for large kz and m have been explained reasonably from the mathematical and physical viewpoints. The calculations of electron--phonon coupling functions show that the high-frequency IO phonon branch and SO mode play a more important role in the electron--phonon interaction.
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Repulsive effects in steady axisymmetric fields

Hu Ping-Hui, Wang Yong-Jiu
Chin. Phys. B 2006, 15 (5): 01120;  doi: 10.1088/1009-1963/15/5/043
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In this paper the repulsive effects in the Kerr and Kerr--Newman fields are discussed. The contributions made by all parameters of the fields and test particles to the repulsive effects are also discussed, and the accretive effect on interstellar dust, i.e. the distribution of dust is calculated. The discussion is also carried out on the slow rotation of the Kerr field in which the effect is related to the positions and velocities of the particles and the orientations of their trajectories as well.
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