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Chin. Phys. B  
  Chin. Phys. B--2005, Vol.14, No.10
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Exact invariants and adiabatic invariants of Raitzin's canonical equations of motion for a nonlinear nonholonomic mechanical system

Qiao Yong-Fen, Li Ren-Jie, Sun Dan-Na
Chin. Phys. B 2005, 14 (10): 1919 ;  doi: 10.1088/1009-1963/14/10/001
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The exact invariants and the adiabatic invariants of Raitzin's canonical equations of motion for a nonlinear nonholonomic mechanical system are studied. The relations between the invariants and the symmetries of the system are established. Based on the concept of higher-order adiabatic invariant of a mechanical system under the action of a small perturbation, the forms of the exact invariants and adiabatic invariants and the conditions for their existence are proved. Finally, the inverse problem of the perturbation to symmetries of the system is studied and an example is also given to illustrate the application of the results.

Exact solutions for the coupled Klein--Gordon--Schr?dinger equations using the extended F-expansion method

He Hong-Sheng, Chen Jiang, Yang Kong-Qing
Chin. Phys. B 2005, 14 (10): 1926 ;  doi: 10.1088/1009-1963/14/10/002
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The extended F-expansion method or mapping method is used to construct exact solutions for the coupled Klein-Gordon SchrOdinger equations (K-G-S equations) by the aid of the symbolic computation system Mathematica. More solutions in the Jacobi elliptic function form are obtained, including the single Jacobi elliptic function solutions, combined Jacobi elliptic function solutions, rational solutions, triangular solutions,soliton solutions and combined soliton solutions.

Energy levels and states of parabolic cylindrical lens shaped quantum dots

Hou Chun-Feng, Jiang Yong-Yuan, Abdurusul
Chin. Phys. B 2005, 14 (10): 1932 ;  doi: 10.1088/1009-1963/14/10/003
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The parabolic cylindrical lens shaped quantum dot is investigated theoretically. The SchrOdinger equation for an electron confined in this structure is solved in the parabolic cylindrical coordinate system. The wavefunctions for the electron are presented in terms of confluent hypergeometric functions, and the electron energy spectra are also obtained.

Generation of the nonlocal quantum entanglement of three three-level particles by local operations

Jin Xing-Ri, Zhang Ying-Qiao, Jin Zhe, Zhang Shou
Chin. Phys. B 2005, 14 (10): 1936 ;  doi: 10.1088/1009-1963/14/10/004
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We propose a scheme to realize the nonlocal quantum entanglement of three three-level particles by using a three-particle entangled state of three levels as a quantum channel with the aid of some local unitary transformations. This scheme can be directly generalized to the nonlocal quantum entanglement of N three-level particles.

Vibration properties of low-fraction hydrogen in deuterium ices

Wang Yan, Dong Shun-Le
Chin. Phys. B 2005, 14 (10): 1942 ;  doi: 10.1088/1009-1963/14/10/005
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Inelastic incoherent neutron scattering spectra of D2O high-density amorphous (hda) ice, ice-VIII and ice-II mixed with small amount of H2O (<5%) have been measured recently on high-energy transfer spectrometer at Rutherford Appleton Laboratory (UK). The hydrogen atom on D2O ice lattices has three distinguished vibrational modes, two bending at low frequencies and one stretching at high frequencies, and their frequencies are slightly different for different phases of ice. It was found that the lower one of the bending modes is located at \sim 95\,meV for hda-ice, at \sim 95\,meV for ice-VIII and at \sim 96\,meV for ice-II and they are all lower than the value of 104\,meV for ice-Ih. It was also measured that the O-D and O-H covalent bond stretching modes of ice-VIII are at \sim 315 and \sim 425\,meV, ice-II at 307 and \sim $415\,meV, hda-ice at 312 and \sim 418\,meV, respectively. They are significantly higher than the values of ice-Ih at \sim 299 and \sim 406\,meV, respectively.

Three-dimensional ab initio dipole moment surfaces and stretching vibrational band intensities of the XH3 molecules

Liu An-Wen, Hu Shui-Ming, Ding Yun, Zhu Qing-Shi
Chin. Phys. B 2005, 14 (10): 1946 ;  doi: 10.1088/1009-1963/14/10/006
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Stretching vibrational band intensities of XH3 (X=N, Sb) molecules are investigated employing three-dimensional dipole moment surfaces combined with the local mode Hamiltonian model.The dipole moment surfaces of NH3 and SbH3 are calculated with the density functional theory and at the correlated MP2 level,respectively. The calculated band intensities are in good agreement with the available experimental data. The contribution to the band intensities from the different terms in the polynomial expansion of the dipole moments of four group V hydrides (NH3, PH3,AsH3 and SbH3) are discussed. It is concluded that the breakdown of the bond dipole approximation must be considered. The intensity “borrowing” effect due to the wave function mixing among the stretching vibrational states is found to be less significant for the molecules that reach the local mode limit.

Perturbation study via rotational-resolved spectrum in the triplet band d3Δ-a3∏(2, 1) of CO

Xu Chun-Yan, Yang Xiao-Hua, Guo Ying-Chun, Wu Ling, Li Wei, Chen Yang-Qin
Chin. Phys. B 2005, 14 (10): 1954 ;  doi: 10.1088/1009-1963/14/10/007
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The triplet band d3Δ-a3∏ (2, 1) of the CO molecule in the near infrared region of 12350--12850cm-1 has been observed and analysed by taking into account the perturbation interaction between the d3Δ(v = 2) and a3∏ (v = 9) states. The most perturbed lines and most precise perturbation parameters, \alpha2 and \beta2, and electronic perturbation constants,\xi _\e and \eta _\e , for the d3Δ (v= 2) and 3∏ (v = 9) states have been obtained.

The multielectron dissociative ionization dynamics of N2 molecule in intense femtosecond laser fields with arbitrary polarization

Chen Jian-Xin, Gong Qi-Huang
Chin. Phys. B 2005, 14 (10): 1960 ;  doi: 10.1088/1009-1963/14/10/008
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The field-ionization Coulomb explosion model is extended to investigate the multielectron dissociative ionization process of N2 molecule irradiated by an intense femtosecond laser field with an arbitrary polarization. The ionization process of N2 molecule is found to be optimal at the critical internuclear distance Rc=7a.u., which is independent of the laser polarization state, the molecular explosion channel and the angle between the molecular axis and the direction of laser electric field. The kinetic energies of the ion fragments are identical in the cases of linear and circular polarizations at the same incident laser intensity. However,the probability of electron ionization is very sensitive to the above three parameters. At the critical distance Rc=7a.u. the angular dependence of the threshold intensity for the over-the-barrier ionization leads to the geometric alignment of molecules in the case of linear polarization. The threshold intensity in the case of circular polarization is apparently higher than that in the case of linear polarization, which can well explain the significant decrease of ionization in the case of circular polarization. The numerical calculations are compared with the experimental measurements.

Experimental and calculated momentum densities for the complete valence orbitals of the antimicrobial agent diacetyl

Su Guo-Lin, Ren Xue-Guang, Zhang Shu-Feng, Ning Chuan-Gang, Zhou Hui, Li Bin, Li Gui-Qin, Deng Jing-Kang
Chin. Phys. B 2005, 14 (10): 1966 ;  doi: 10.1088/1009-1963/14/10/009
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The first electronic structural study of the complete valence shell binding energy spectra of the antimicrobial agent diacetyl, encompassing both the outer and inner valence regions, is reported. The binding energy spectra as well as the individual orbital momentum profiles have been measured by using a high resolution (e, 2e) electron momentum spectrometer (EMS) at an impact energy of 1200eV plus the binding energy, and using symmetric noncoplanar kinematics. The experimental orbital electron momentum profiles are compared with self-consistent field (SCF) theoretical profiles calculated using the Hartree--Fock approximation and Density Functional theory predictions in the target Kohn-Sham approximation which includes some treatment of correlation via the exchange and correlation potentials with a range of basis sets. The pole strengths of the main ionization peaks from the inner valence orbitals are estimated.

First-principle study of geometries, electronic structures and vibrational spectra of neutral and anionic onion-like [As@Ni12@As20

Liu Hai-Tao, Li Jia-Ming
Chin. Phys. B 2005, 14 (10): 1974 ;  doi: 10.1088/1009-1963/14/10/010
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We present results of first-principle study for both neutral and anionic onion-like [As@Ni12@As20]. The ground-states of singly-charged and doubly-charged anions deviate from ideal Ih symmetrical geometry because of Jahn--Teller effect, whereas the triply-charged singlet and neutral quartet have similar stable geometries of Ih symmetry. The infrared and Raman spectra may provide a way to determine various charge states of this molecule with the same symmetry. Based on our systematical calculations, we suggest additional experimental measurements in order to determine the appropriate functional with great confidence, which should be important in the research for future quantum dot devices.

Optical feedback characteristics in a dual-frequency laser during laser cavity tuning

Liu Gang, Zhang Shu-Lian, Li Yan, Zhu Jun
Chin. Phys. B 2005, 14 (10): 1984 ;  doi: 10.1088/1009-1963/14/10/011
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The optical feedback characteristics in a Zeeman-birefringence dual-frequency laser are studied during the laser cavity tuning in three different kinds of optical feedback conditions: (i) only // -light is fed back; (ii) only ⊥-light is fed back; (iii) both lights are fed back.A compact displacement sensor is designed using the experimental result that there is a nearly 90 degrees phase delay between the two lights' cosine optical feedback signals when both lights are fed back into the laser cavity.The priority order that the two lights' intensity curves appear can be used for direction discrimination. The resolution of the displacement sensor is at least 79 nm, and the sensor can discriminate the target's moving direction easily.

The autocorrelation of speckles in deep Fresnel diffraction region and characterizations of random self-affine fractal surfaces

Teng Shu-Yun, Cheng Chuan-Fu, Liu Man, Gui Wei-Ling, Xu Zhi-Zhan
Chin. Phys. B 2005, 14 (10): 1990 ;  doi: 10.1088/1009-1963/14/10/012
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This paper studies the correlation properties of the speckles in the deep Fresnel diffraction region produced by the scattering of rough self-affine fractal surfaces. The autocorrelation function of the speckle intensities is formulated by the combination of the light scattering theory of Kirchhoff approximation and the principles of speckle statistics. We propose a method for extracting the three surface parameters, i.e.~the roughness w, the lateral correlation length \xi and the roughness exponent \alpha , from the autocorrelation functions of speckles. This method is verified by simulating the speckle intensities and calculating the speckle autocorrelation function. We also find the phenomenon that for rough surfaces with \alpha = 1, the structure of the speckles resembles that of the surface heights, which results from the effect of the peak and the valley parts of the surface, acting as micro-lenses converging and diverging the light waves.

A new distribution scheme of decryption keys used in optical verification system with multiple-wavelength information

Niu Chun-Hui, Zhang Yan, Gu Ben-Yuan
Chin. Phys. B 2005, 14 (10): 1996 ;  doi: 10.1088/1009-1963/14/10/013
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A new distribution scheme of decryption keys used in optical verification systems is proposed. The encryption procedure is digitally implemented with the use of an iteration algorithm in computer. Three target images corresponding to three wavelengths are encoded into three sets of phase-only masks (POMs) by a special distributing method. These three sets of POMs are assigned to three authorized users as the personal identification. A lensless optical system is used as the verification system. In the verification procedure, every two of the three authorized users can pass the verification procedure cooperatively, but only one user cannot do. Numerical simulation shows that the proposed distribution scheme of decryption keys not only can improve the security level of verification system, but also can bring convenience and flexibility for authorized users.

A new photopolymerizable holographic recording material based on acrylamide and N-hydroxymethyl acrylamide

Gong Qiao-Xia, Wang Su-Lian, Huang Ming-Ju, Gan Fu-Xi
Chin. Phys. B 2005, 14 (10): 2004 ;  doi: 10.1088/1009-1963/14/10/014
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new polyvinylalcohol-based photopolymeric holographic recording material has been developed. The recording is obtained by the copolymerization of acrylamide and N-hydroxymethyl acrylamide. Diffraction efficiencies near 50% are obtained with energetic exposure of 80mJ/cm2. N-hydroxymethyl acrylamide can improve the optical quality of the film. With the increase of the concentration of N-hydroxymethyl acrylamide, the flatness of the film increases, scattering reduces and the straight image is clearer with a small distortion. The postexposure effect on the grating is also studied. The diffraction efficiency of grating increases further during postexposure, gradient of monomer exists after exposure.

Quantum entanglement in the system of two two-level atoms interacting with a single-mode vacuum field

Zeng Ke, Fang Mao-Fa
Chin. Phys. B 2005, 14 (10): 2009 ;  doi: 10.1088/1009-1963/14/10/015
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The entanglement properties of the system of two two-level atoms interacting with a single-mode vacuum field are explored. The quantum entanglement between two two-level atoms and a single-mode vacuum field is investigated by using the quantum reduced entropy; the quantum entanglement between two two-level atoms, and that between a single two-level atom and a single-mode vacuum field are studied in terms of the quantum relative entropy. The influences of the atomic dipole--dipole interaction on the quantum entanglement of the system are also discussed. Our results show that three entangled states of two atoms--field, atom--atom, and atom--field can be prepared via two two-level atoms interacting with a single-mode vacuum field.

Resonant propagation of femtosecond laser pulse in DBASVP molecule:one-dimensional asymmetric organic molecule

Zhao Ke, Liu Ji-Cai, Wang Chuan-Kui, Luo Yi
Chin. Phys. B 2005, 14 (10): 2014 ;  doi: 10.1088/1009-1963/14/10/016
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We have investigated the resonant propagation of femtosecond laser pulse in 4-trans-[p-(N, N-Di-n-butylamino)-p-stilbenyl vinyl] pyridine medium with permanent dipole moments. The electronic structures and parameters for the compound have been calculated by using density functional theory. In the optical regime, there is one charge-transfer state, and the molecule can thus be simplified as a two-level system. Both the one- and two-photon transitions occur between the ground and charge-transfer states. The numerical results show that the permanent dipole moments have an obvious effect on the propagation of the ultrashort pulse laser. The ideal self-induced transparency disappears for 2$\pi$ pulse, and second harmonic spectral components occur significantly due to the two-photon absorption process. For the 6\pi pulse, continuum frequency generation is produced and a shorter duration pulse in time domain with 465 as is obtained.

The propagation dynamics of ultraviolet light filament with Rayleigh scattering in air

Zhang Hua
Chin. Phys. B 2005, 14 (10): 2019 ;  doi: 10.1088/1009-1963/14/10/017
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In this paper we present for the first time the effects of Rayleigh scattering on the long distance propagation of ultraviolet (UV) light filament in air based on the stationary analysis. The simulation results show that the effects of Rayleigh scattering on the propagation of UV laser filaments may not be ignored. These influences are slightly dependent on the laser wavelength. We also compare the UV filament propagations at different input powers in the presence and the absence of the Rayleigh scattering and discuss the mechanisms of power loss and beam defocusing. In the absence of Rayleigh scattering, the filament propagation is determined by the oscillating behaviour of the beam size. In the presence of the scattering,the propagation lengths of filament are close to each other at different initial powers and determined by the Rayleigh scattering.

Beam divergence effects on high power optical parametric oscillation

Li Hui-Qing, Geng Ai-Cong, Bo Yong, Wu Ling-An, Cui Da-Fu, Xu Zu-Yan
Chin. Phys. B 2005, 14 (10): 2026 ;  doi: 10.1088/1009-1963/14/10/018
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The beam divergence effects of the input pump laser on a high power nanosecond optical parametric oscillator (OPO) have been numerically simulated.The OPO conversion efficiency is affected due to the angular deviation of real laser beams from ideal phase matching conditions. Our theoretical model is based on the decomposition of the Gaussian beam and assumes each component has a single deviation angle and thus a particular wave vector mismatch. We take into account the variable intensity profile in the spatial and temporal domains of the Gaussian beam, the pump depletion effects for large-signal processes as well as the oscillatory effects of the three waves. Two nonlinear crystals \beta-BaB2O4 (BBO) and LiB3O5 (LBO) have been investigated in detail. The results indicate that the degree of beam divergence strongly influences the maximum pump intensity, optimum crystal length and OPO conversion efficiency. The impact of beam divergence is much more severe in the case of critical phase-matching for BBO than in the case of non-critical phase-matching for LBO. The results provide a way to choose the optimum parameters for a high power ns OPO such as the nonlinear material, the crystal length and the pump intensity, etc. Good agreement is obtained with our experimental results.

Analysis and engineering of coupled cavity waveguides based on coupled-mode theory

Lin Xu-Sheng, Chen Xiong-Wen, Lan Sheng
Chin. Phys. B 2005, 14 (10): 2033 ;  doi: 10.1088/1009-1963/14/10/019
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The analytical expression for the transmission spectra of coupled cavity waveguides (CCWs) in photonic crystals (PCs) is derived based on the coupled-mode theory (CMT). Parameters in the analytical expression can be extracted by simple numerical simulations. We reveal that it is the phase shift between the two adjacent PC defects that uniquely determines the flatness of the impurity bands of CCWs. In addition, it is found that the phase shift also greatly affects the bandwidth of CCWs. Thus, the engineering of the impurity bands of CCWs can be realized through the adjustment of the phase shift. Based on the theoretical results, an interesting phenomenon in which a CCW acts as a single PC defect and its impurity band possesses a Lorentz lineshape is predicted. Very good agreement between the analytical results and the numerical simulations based on transfer matrix method has been achieved.

The measuring of spectral emissivity of object using chaotic optimal algorithm

Yang Chun-Ling, Wang Yu-Ye, Zhao Dong-Yang, Zhao Guo-Liang
Chin. Phys. B 2005, 14 (10): 2041 ;  doi: 10.1088/1009-1963/14/10/020
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There exist a considerable variety of factors affecting the spectral emissivity of an object. The authors have designed an improved combined neural network emissivity model, which can identify the continuous spectral emissivity and true temperature of any object only based on the measured brightness temperature data. In order to improve the accuracy of approximate calculations, the local minimum problem in the algorithm must be solved.Therefore, the authors design an optimal algorithm, i.e. a hybrid chaotic optimal algorithm, in which the chaos is used to roughly seek for the parameters involved in the model, and then a second seek for them is performed using the steepest descent. The modelling of emissivity settles the problems in assumptive models in multi-spectral theory.

Numerical simulation for separation of multi-phase immiscible fluids in porous media

Wu Bai-Zhi, Xu You-Sheng, Liu Yang, Huang Guo-Xiang
Chin. Phys. B 2005, 14 (10): 2046 ;  doi: 10.1088/1009-1963/14/10/021
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Based on a lattice Boltzmann method and general principles of porous flow, a numerical technique is presented for analysing the separation of multi-phase immiscible fluids in porous media. The total body force acting on fluid particles is modified by adding relative permeability in Nithiarasu's expression with an additional surface tension term. As a test of this model, we simulate the phase separation for the case of two immiscible fluids. The numerical results show that the two coupling relative permeability coefficients K12 and K21 have the same magnitude, so the linear flux-forcing relationships satisfy Onsager reciprocity. Phase separation phenomenon is shown with the time evolution of density distribution and bears a strong similarity to the results obtained from other numerical models and the flows in sands. At the same time, the dynamical rules in this model are local, therefore it can be run on massively parallel computers with well computational efficiency.

The instability of electrostatic wave in a magnetized dusty plasma with nonadiabatic dust charge fluctuation

Zhang Li-Ping, Xue Ju-Kui
Chin. Phys. B 2005, 14 (10): 2052 ;  doi: 10.1088/1009-1963/14/10/022
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The effects of external magnetized field and nonadiabatic dust charge fluctuation on instability of wave incorporating the nonthermally distributed ions and the temperatures of ion and dust in dusty plasmas are investigated. A linear dispersion relation is obtained. The numerical results show that the external magnetized field, fast ions and nonadiabatic dust charge fluctuation have strong influence on the frequency and the damping of wave.

Study of sawtooth oscillations on the HT-7 tokamak using 2D tomography of soft x-ray signal

Ma Tian-Peng, Hu Li-Qun, Wan Bao-Nian, Ruan Huai-Lin, Gao Xiang, Zhen Xiang-Jun, Zhou Li-Wu, Sun You-Wen, Chen Zhong-Yong, Lin Shi-Yao, Kong Wei
Chin. Phys. B 2005, 14 (10): 2061 ;  doi: 10.1088/1009-1963/14/10/023
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It is the first time so far as we know that two arrays of multi-channel soft x-ray detectors are used to generate two-dimensional (2D) images of sawtooth oscillation on the HT-7 tokamak using the Fourier--Bessel harmonic reconstruction method, and using the singular value ecomposition to analyse the data from soft x-ray cameras. By these two arrays, 2D image reconstruction of soft x-ray emissivity can be obtained without assumption of plasma rigid rotation.Tomographic reconstruction of the m=1 mode structure is obtained during the precursor oscillation of the sawtooth crash. The crescent-shaped mode structure appearing on the contour map of the soft x-ray emissivity is consistent with the quasi-interchange mode. The characteristics of the m=1/n=1 mode structure observed in the soft x-ray tomography are as follows:the magnetic surface is made up of the crescent-shaped ``hot core'' and the circular ``cold bubble''. The structure of the magnetic surface rotates in the direction of the electron diamagnetic drift and the rotation frequency is the oscillation frequency of soft x-ray signals.

Growth of aligned single-walled carbon nanotubes under ac electric fields through floating catalyst chemical vapour deposition

Dou Xin-Yuan, Zhou Zhen-Ping, Tan Ping-Heng, Zhou Jian-Jun, Song Li, Sun Lian-Feng, Jiang Peng, Liu Li-Feng, Zhao Xiao-Wei, Luo Shu-Dong, Zhang Zeng-Xing, Liu Dong-Fang, Wang Jian-Xiong, Gao Yan, Zhou
Chin. Phys. B 2005, 14 (10): 2068 ;  doi: 10.1088/1009-1963/14/10/024
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Through floating catalyst chemical vapour deposition(CVD) method,well-aligned isolated single-walled carbon nanotubes (SWCNTs) and their bundles were deposited on the metal electrodes patterned on the SiO2/Si surface under ac electric fields at relatively low temperature(280℃). It was indicated that SWCNTs were effectively aligned under ac electric fields after they had just grown in the furnace.The time for a SWCNT to be aligned in the electric field and the effect of gas flow were estimated. Polarized Raman scattering was performed to characterize the aligned structure of SWCNTs. This method would be very useful for the controlled fabrication and preparation of SWCNTs in practical applications.

Pressure dissociation of dense hydrogen

Chen Qi-Feng, Cai Ling-Cang, Chen Dong-Quan, Jing Fu-Qian
Chin. Phys. B 2005, 14 (10): 2077 ;  doi: 10.1088/1009-1963/14/10/025
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The self-consistent fluid variational model (SFVM) has been used to describe the pressure dissociation of dense hydrogen at high temperatures. This paper focuses on a mixture of hydrogen atoms and molecules and is devoted to the study of the phenomenon of pressure dissociation at finite temperatures. The equation of state and dissociation degree have been calculated from the free energy functions in the range of temperature 2000--10,000K and density 0.02--1.0g/cm2, which can be compared with other approaches and experiments. The pressure dissociation is found to occur in higher density range, while temperature dissociation is a more gradual effect.

Adsorption and diffusion of Si adatom near single-layer steps on Si surface

Zhu Xiao-Yan, Huang Yan
Chin. Phys. B 2005, 14 (10): 2083 ;  doi: 10.1088/1009-1963/14/10/026
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By use of the empirical tight-binding (ETB) method, the adsorption and diffusion behaviours of single silicon adatom on the reconstructed Si(100) surface with single-layer steps are simulated. The adsorption energies around the SA step, nonrebonded SB step, rebonded Sm B step, and rough SB step with a kink structure are specially mapped out in this paper,from which the favourable binding sites and several possible diffusion paths are achieved. Because of the rebonded and kink structures, the SB step is more suitable for the attachment of Si adatom than the SA step or defective surface.

The 1/f noise in multiwalled carbon nanotubes

Kong Wen-Jie, Lü Li, Zhang Dian-Lin, Pan Zheng-Wei
Chin. Phys. B 2005, 14 (10): 2090 ;  doi: 10.1088/1009-1963/14/10/027
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The $1/f$ noise in multiwalled carbon nanotubes bundles has been investigated between the frequency range of 0.1 to 30 Hz. At room temperature the noise spectrum is standard 1/f, and its level is proportional to the square of the bias voltage. With decreasing temperature the noise level also decreases. At 4.2 K the noise level follows a non-monotonic dependence against the bias voltage, showing a peak at a certain bias voltage, meanwhile its frequency dependence also deviates from the 1/f trend. This anomalous behaviour is discussed within the picture of environmental quantum fluctuation of charge transport in the samples.

Ac response of a coupled double quantum dot

Xu Jie, Shangguan W. Z., Zhan Shi-Chang
Chin. Phys. B 2005, 14 (10): 2093 ;  doi: 10.1088/1009-1963/14/10/028
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The effect of phase-breaking process on the ac response of a coupled double quantum dot is studied in this paper based on the nonequilibrium Green function formalism. A general expression is derived for the ac current in the presence of electron--phonon interaction. The ac conductance is numerically computed and the results are compared with those in [Anatram M P and Datta S 1995 Phys. Rev. B 51 7632]. Our results reveal that the inter-dot electron tunnelling interplays with that between dots and electron reservoirs, and contributes prominently to the ac current when inter-dot tunnelling coupling is much larger than the tunnelling coupling between dots and electron reservoirs. In addition, the phase-breaking process is found to have a significant effect on the ac transport through the coupled double dot.

Quantum spin transport through Aharonov--Bohm ring with a tangent magnetic field

Li Zhi-Jian
Chin. Phys. B 2005, 14 (10): 2100 ;  doi: 10.1088/1009-1963/14/10/029
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Quantum spin transport in a mesoscopic Aharonov--Bohm ring with two leads subject to a magnetic field with circular configuration is investigated by means of one-dimensional quantum waveguide theory.Within the framework of Landauer--B\"{u}ttiker formalism, the polarization direction of transmitted electrons can be controlled either by the AB magnetic flux or by the tangent magnetic field. In particular, the spin flips can be induced by hopping the AB magnetic flux or the tangent field.

Magnetism of Zr atomic wires

Zhu Zhi-Li, Wang Jian-Tao, Jia Jin-Feng, Xue Qi-Kun, Wang Ding-Sheng
Chin. Phys. B 2005, 14 (10): 2106 ;  doi: 10.1088/1009-1963/14/10/030
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By using the full-potential linearized augmented plane wave method to perform ab initio total energy calculations, we have explored magnetic ordering in one-dimensional Zr wires. The result shows that Zr can form linear, or dimerized, or zigzag wires, and the magnetic properties strongly depend on their geometric structures.The linear and zigzag wires exhibit ferromagnetic ground states at the equilibrium bonding distance, while the dimerized wire, despite its higher stability than that of the linear one,exhibits nonmagnetic ground states. The most stable geometry is shown to be the zigzag wire with a magnetic moment of 0.26 \mu _B per atom.

Stochastic resonance and nonequilibrium dynamic phase transition of Ising spin system driven by a joint external field

Shao Yuan-Zhi, Zhong Wei-Rong, Lin Guang-Ming, Li Jian-Can
Chin. Phys. B 2005, 14 (10): 2110 ;  doi: 10.1088/1009-1963/14/10/031
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The dynamic response and stochastic resonance of a kinetic Ising spin system (ISS) subject to the joint action of an external field of weak sinusoidal modulation and stochastic white-noise are studied by solving the mean-field equation of motion based on Glauber dynamics. The periodically driven stochastic ISS shows that the characteristic stochastic resonance as well as nonequilibrium dynamic phase transition (NDPT) occurs when the frequency \textit{$\omega $} and amplitude $h_{0}$ of driving field, the temperature $t$ of the system and noise intensity $D$ are all specifically in accordance with each other in quantity. There exist in the system two typical dynamic phases, referred to as dynamic disordered paramagnetic and ordered ferromagnetic phases respectively, corresponding to a zero- and a unit-dynamic order parameter. The NDPT boundary surface of the system which separates the dynamic paramagnetic phase from the dynamic ferromagnetic phase in the 3D parameter space of $h_{0}$-$t$-$D$ is also investigated. An interesting dynamical ferromagnetic phase with an intermediate order parameter of 0.66 is revealed for the first time in the ISS subject to the perturbation of a joint determinant and tochastic field. The intermediate order dynamical ferromagnetic phase is dynamically metastable in nature and owns a peculiar characteristic in its stability as well as the response to external driving field as compared with a fully order dynamic ferromagnetic phase.

Effect of Cu doping on the magnetic and electrical properties of n=2 Ruddlesden--Popper manganates

Si Ji-Wei, Cao Qing-Qi, Gu Ben-Xi, Du You-Wei
Chin. Phys. B 2005, 14 (10): 2117 ;  doi: 10.1088/1009-1963/14/10/032
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A series of polycrystalline Cu-doped $n$=2 Ruddlesden--Popper manganates La$_{1.2}$Sr$_{1.8}$Cu$_{x}$Mn$_{(2-x)}$O$_{7}$ ($x$=0, 0.04, 0.13) were synthesized by the solid state reaction method. The effect of Cu doping on the magnetic and transport properties has been studied. It is found that Cu substitution for Mn greatly affects the magnetic and electrical properties of the parent phase La_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$. With the increase of Cu content, the system undergoes a transition from long-range ferromagnetic order to the spin glass state and further to an antiferromagnetic order. A little of Cu dopant can lead to the samples showing semiconductor or insulator behaviour in the whole observed temperature range while the parent phase has a metal--insulator transition.These samples show colossal magnetoresistance at low temperatures and the value of it decreases with increasing Cu content.

Effect of composition on the crystallographic texture and magnetic properties of the Sm(Co,Fe,Cu,Zr)z ribbons prepared by simple processing

Rong Chuan-Bing, He Shu-Li, Chen Ren-Jie, Zhang Hong-Wei, Shen Bao-Gen
Chin. Phys. B 2005, 14 (10): 2122 ;  doi: 10.1088/1009-1963/14/10/033
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Sm(Co_balFe_yCu_xZr_w)_z ribbons have been prepared by melt spinning at a low wheel velocity followed by short-time aging and slow cooling the as-spun ribbons from 850 to 400℃. It is found that the composition can significantly influence the degree of crystallographic texture of the ribbons. The 1:7 phase of the as-spun ribbons is segregated into 1:5 and 2:17 phases by the simple processing procedure. However, the crystallographic texture is still preserved in the ribbons after precipitation hardening. (BH)_{\rm max} about 86kJ/m^{3} can be obtained in the Sm(Co, Fe, Cu, Zr)_{z} ribbons by the adjustment of composition.

Crystal field analysis of the magnetic properties of RFe11Ti and RFe11TiH (R=Sm, Tb, Ho)

Su Gang, Yan Yu, Xu Shu-Wei, Du Xiao-Bo, Jin Han-Min, Wang Xiang-Qun
Chin. Phys. B 2005, 14 (10): 2127 ;  doi: 10.1088/1009-1963/14/10/034
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The crystalline-electric-field parameters A_nm for RFe_11Ti and RFe_{11}TiH (R=Sm,Tb,Ho) are evaluated by fitting calculations to the magnetization curves measured on the single crystals or on magnetically aligned powder samples at 4.2K and higher temperatures. Interstitial hydrogen atom in RFe_11Ti has been found to have a significant effect on crystalline-electric-field parameters A_nm. By using the parameters of exchange field 2\textit\mu _BH_ex estimated from inelastic neutron scattering experiments and the fitted A_nm, the calculations can reproduce the experimental curves well.

Photoluminescence characteristics of GaN:Si

Feng Qian, Gong Xin, Zhang Xiao-Ju, Hao Yue
Chin. Phys. B 2005, 14 (10): 2133 ;  doi: 10.1088/1009-1963/14/10/035
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Both the electrical and optical properties are studied of the GaN:Si films with carrier concentrations ranging from 10$^{17}$cm$^{-3}$ to 10$^{19}$cm$^{-3}$.The results indicate that the increase in slope of carrier concentration starts to slow down when the flow rate of SiH$_{4}$ is larger than 6.38\mu $mol/min, which is attributed to the amphoteric character of Si. At the same time, the photoluminescence results show that the FWHM of UV is widened, which can be interpreted quantitatively with a semi-classic model. Furthermore, the intensity ratio between the yellow and the UV luminescences reduces monotonically with Si dopants increasing.

Ultrafast carrier dynamics in purified and as-grown single-walled carbon nanotube films

Long Yong-Bing, Song Li, Zhang Chun-Yu, Wang Li, Fu Pan-Ming, Zhang Zhi-Guo, Xie Si-Shen, Wang Guo-Ping
Chin. Phys. B 2005, 14 (10): 2137 ;  doi: 10.1088/1009-1963/14/10/036
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Ultrafast time-resolved optical transmissions in purified and as-grown single-walled carbon nanotube films are measured at a temperature of 200K.The signal of the purified sample shows a crossover from photobleaching to photoabsorption. The former and the latter are interpreted as the state filling and the red shift of the $\pi$-plasmon, respectively. The signal of the as-grown sample can be perfectly fitted by a single-exponential with a time constant of 232fs. The disappearance of the negative component in the as-grown sample is attributed to the charge transfer between the semiconducting nanotubes and the impurities.

Photoluminescence study on Eu-implanted GaN

Zhang Chun-Guang, Bian Liu-Fang, Chen Wei-De
Chin. Phys. B 2005, 14 (10): 2141 ;  doi: 10.1088/1009-1963/14/10/037
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The photoluminescence (PL) properties of Eu-implanted GaN thin films are studied. The experimental results show that the PL intensity is seriously affected by ion implantation conditions. The PL efficiency increases exponentially with annealing temperature increasing up to a maximum temperature of 1050℃. Moreover, the PL intensity for the sample implanted along the channelling direction is nearly twice more than that observed from the sample implanted along the random direction. The thermal quenching of PL intensity from 10K to 300K for sample annealed at 1050℃ is only 42.7%.

Photoluminescence and transmission spectra of nanocrystalline GaAs1-xSbx embedded in silica films

Liu Fa-Min, Zhang Li-De, Li Guo-Hua
Chin. Phys. B 2005, 14 (10): 2145 ;  doi: 10.1088/1009-1963/14/10/038
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The composite films of the nanocrystalline GaAs1-xSbx--SiO2 have been successfully deposited on glass and GaSb substrates by radio frequency magnetron co-sputtering. The 10K photoluminescence (PL) properties of the nanocrystalline GaAs1-xSbx indicated that the PL peaks of the GaAs1-xSbx nanocrystals follow the quantum confinement model very closely. Optical transmittance spectra showed that there is a large blue shift of optical absorption edge in nanocrystalline GaAs1-xSbx--SiO2 composite films, as compared with that of the corresponding bulk semiconductor,which is due to the quantum confinement effect.
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