Chin. Phys. B
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CN 11-5639/O4
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Chin. Phys. B  
  Chin. Phys. B--2004, Vol.13, No.6
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GENERAL

Study of the electric field and wall voltage in a high pressure ac-PDP cell by laser induced fluorescence spectroscopy

Zhou Yan, K. W. Whang, J. H. Yang, D. C. Jeong, C. H. Ha, Y. W. Choi
Chin. Phys., 2004, 13 (6): 789-793 doi: 10.1088/1009-1963/13/6/001
Full Text: [PDF 235 KB] (Downloads:367)
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The electric field in a surface discharge type ac-PDP cell with He or He/Xe(0.1%) mixture has been measured over a wide range of pressure (5-50 kPa) using laser induced fluorescence detection. The wall voltage was estimated from the measured electric field. The Stark manifolds of triplet atomic helium Rydberg state (2s^3S) with principal quantum numbers (n=8 and 9) have been used to measure the electric field, as the lifetime of 2s^3S is longer than the single atomic helium Rydberg state (2s^1S) in high pressure discharge. Comparison of the Stark manifolds between the n=9 and n=8 shows that the measurement accuracy of electric field can be increased by 10%. The maximum electric field strength during discharge and the wall voltage at the end of pulse decreases with the increase of pressure. The comparison of He and He/Xe(0.1%) discharge at 13 kPa showed that He/Xe gas mixture discharge can accumulate more wall charge on MgO surface and the electric field was somewhat higher than those of pure helium discharge during pulse off period under the same discharge conditions.

The Schr?dinger equation for a Kirchhoff elastic rod with noncircular cross section

Xue Yun, Liu Yan-Zhu, Chen Li-Qun
Chin. Phys., 2004, 13 (6): 794-797 doi: 10.1088/1009-1963/13/6/002
Full Text: [PDF 150 KB] (Downloads:1840)
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The extended Schr?dinger equation for the Kirchhoff elastic rod with noncircular cross section is derived using the concept of complex rigidity. As a mathematical model of supercoiled DNA, the Schr?dinger equation for the rod with circular cross section is a special case of the equation derived in this paper. In the twistless case of the rod when the principal axes of the cross section are coincident with the Frenet coordinates of the centreline, the Schr?dinger equation is transformed to the Duffing equation. The equilibrium and stability of the twistless rod are discussed, and a bifurcation phenomenon is presented.

General Jacobian elliptic function expansion method and its applications

Zhu Jia-Min, Ma Zheng-Yi, Fang Jian-Ping, Zheng Chun-Long, Zhang Jie-Fang
Chin. Phys., 2004, 13 (6): 798-804 doi: 10.1088/1009-1963/13/6/003
Full Text: [PDF 390 KB] (Downloads:441)
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An extended Jacobian elliptic function expansion method is presented and successfully applied to the nonlinear Schr?dinger (NLS) equation and Zakharov equation. We obtain some new solutions besides Fu et al's results. The results show that our method is more powerful to construct Jacobian elliptic function and can be applied to other nonlinear physics systems.

Periodic solutions of nonlinear Schr?dinger type equations

Liu Guan-Ting, Fan Tian-You
Chin. Phys., 2004, 13 (6): 805-810 doi: 10.1088/1009-1963/13/6/004
Full Text: [PDF 162 KB] (Downloads:336)
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By using the solutions of an auxiliary elliptic equation, a direct algebraic method is proposed to construct the exact solutions of nonlinear Schr?dinger type equations. It is shown that many exact periodic solutions of some nonlinear Schr?dinger type equations are explicitly obtained with the aid of symbolic computation, including corresponding envelope solitary and shock wave solutions.

Exact solutions for nonlinear Schr?dinger equation in phase space: applications to Bose-Einstein condensate

Lu Jun
Chin. Phys., 2004, 13 (6): 811-816 doi: 10.1088/1009-1963/13/6/005
Full Text: [PDF 169 KB] (Downloads:414)
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The stationary-state nonlinear Schr?dinger equation, which models the dilute-gas Bose-Einstein condensate, is introduced within the framework of the quantum phase-space representation established by Torres-Vega and Frederick. The exact solutions of equation are obtained in the phase space, by means of the wave-mechanics method. The eigenfunctions in position and momentum spaces are obtained through the ‘Fourier-like' projection transformation from the phase space eigenfunctions. The eigenfunction with a hypersecant part is discussed as an example.

Experimental realization of information transmission between not-directly-coupled spins on NMR quantum computers

Wei Da-Xiu, Luo Jun, Yang Xiao-Dong, Sun Xian-Ping, Zeng Xi-Zhi, Liu Mai-Li, Ding Shang-Wu, Zhan Ming-Sheng
Chin. Phys., 2004, 13 (6): 817-823 doi: 10.1088/1009-1963/13/6/006
Full Text: [PDF 669 KB] (Downloads:328)
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This paper presents a simple scheme for information transmission between two non-directly interactive qubits in an n-qubit system. An example has been realized on a three-qubit nuclear magnetic resonance (NMR) spectrometer quantum computer. The experimental result successfully demonstrates that the feasible measure can also be extended to other quantum logical gates, or other quantum algorithms, where some qubits have no direct interactions in a multi-qubit system.

Euclidean non-vacuum wormholes in Brans-Dicke theory

Lu Hui-Qing, Ji Pei-Yong, Pan Peng-Peng
Chin. Phys., 2004, 13 (6): 824-827 doi: 10.1088/1009-1963/13/6/007
Full Text: [PDF 165 KB] (Downloads:285)
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The Brans-Dicke theory is investigated in which the Pauli metric is identified to be a physical spacetime metric. The solutions of a wormhole are obtained in Brans-Dicke theory with a relativistic radiation field for ω>-3/2. However, it is found that one cannot construct a wormhole in the presence of a 3-form axion field.

The dynamical feature of transition of a Hamiltonian system to a dissipative system

Zhang Guang-Cai, Zhang Hong-Jun
Chin. Phys., 2004, 13 (6): 828-835 doi: 10.1088/1009-1963/13/6/008
Full Text: [PDF 1862 KB] (Downloads:311)
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The mechanism of generation and annihilation of attractors during transition from a Hamiltonian system to a dissipative system is studied numerically using the dissipative standard map. The transient process related to the formation of attracting basins of periodic attractors is studied by discussing the evolution of the KAM tori of the standard map. The result shows that as damping increases, attractors are mainly generated from elliptic orbits of the Hamiltonian system and annihilated by colliding with unstable periodic orbits originating from the corresponding hyperbolic orbits of the Hamiltonian system. The transient process also exhibits the general feature of bifurcation.
NUCLEAR PHYSICS

Electromagnetic dissociation of 3.7 A GeV 16O in nuclear emulsion

Li Jun-Sheng, Zhang Dong-Hai, Li Zhen-Yu, Wu Feng-Juan
Chin. Phys., 2004, 13 (6): 836-844 doi: 10.1088/1009-1963/13/6/009
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The electromagnetic dissociation (ED) of 3.7 A GeV {}^{16}O in nuclear emulsion is investigated with high statistics. It is found that the electromagnetically dissociated cross section increases with increasing beam energy, the charge distribution of projectile fragments is the same as the results at 60 and 200 A GeV, and the production probability of projectile fragments with charge 3≤Z≤5 is less than that of the other projectile fragments. These results can be well explained by use of Weizsacker and Williams method for calculating the ED contributions. The percentile abundance of various decay modes for ED at 3.7 A GeV is close to the result at 60 and 200 A GeV, but it is different from the result at 14.6 A GeV. The ED of 3.7 A GeV is mainly caused by the giant dipole and quadrupole resonance of E1 and E2, which can be qualitatively explained by the multiplicity distribution of projectile proton in ED. The multiplicity distribution of the α fragments in ED and nuclear events have different functional forms. This difference may be a consequence of the different reaction mechanism involved.
CLASSICAL AREAS OF PHENOMENOLOGY

A birefringent cavity He-Ne laser and optical feedback

Liu Gang, Zhang Shu-Lian, Li Yan, Zhu Jun
Chin. Phys., 2004, 13 (6): 855-859 doi: 10.1088/1009-1963/13/6/012
Full Text: [PDF 223 KB] (Downloads:373)
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Strong modes competition makes only one of o-light and e-light oscillate in a birefringent dual-frequency laser when the angle between the crystalline axis and the laser beam is nearly zero. When the oscillated mode is in a different part of the gain curve, the detected intensity curves of o-light and e-light are quite different in the existence of optical feedback. The curves are divided into five cases. Three cases of the experimental results can be used for direction discrimination. The polarization characteristics of the birefringent cavity He-Ne laser are also discussed without optical feedback.

Superposition of Fock states via adiabatic passage in a coupled four-level atom-cavity system

Gong Shang-Qing, Jin Shi-Qi, Li Ru-Xin, Zheng Zhen-Xun, Xu Zhi-Zhan
Chin. Phys., 2004, 13 (6): 860-864 doi: 10.1088/1009-1963/13/6/013
Full Text: [PDF 183 KB] (Downloads:316)
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We have investigated the behaviour of an atom-cavity system via a stimulated Raman adiabatic passage technique in a four-level system, in which two dark states are present. We find, because of the coherent control field, that a superposition of Fock states can be prepared, even when the cavity is initially not in its vacuum state. This method provides a way to generate arbitrary quantum states of a cavity field.

Realization of adiabatic population transfer in a three-level system by using LR Hermitian invariants theory

Zhao Hua, Gao Ying-Fang, Liang Jiu-Qing
Chin. Phys., 2004, 13 (6): 865-870 doi: 10.1088/1009-1963/13/6/014
Full Text: [PDF 181 KB] (Downloads:357)
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We have studied the population transfer in a three-state system driven by laser beams in terms of the theory of Lewis-Riesenfeld Hermitian invariants for explicitly time-dependent Hamiltonian. The exact solutions obtained allow us to recover two existing schemes producing complete population transfer in the literature, i.e. the π-pulse and stimulated Raman adiabatic passage methods in our unified description. We present a strict formulation of adiabatic conditions and a more accurate expression of the π-pulse method according to the exact time-evolution of state vector.

Theoretical and experimental investigations of quasi-continuous wave diode array side-pumped Yb:YAG slab laser

Wu Hai-Sheng, Yan Ping, Gong Ma-Li, Liu Qiang
Chin. Phys., 2004, 13 (6): 871-876 doi: 10.1088/1009-1963/13/6/015
Full Text: [PDF 510 KB] (Downloads:364)
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An analytical model of quasi-continuous wave (quasi-CW) diode array side-pumped slab laser for Yb:YAG oscillator in long-pulse free-running has been developed based on the CW model. In this model we first introduce a new parameter, pump pulse width, and make the model available for use in the quasi-CW model. We also give an analytical equation of laser delay time to calculate the laser pulse width. A detailed model is also presented for a new structure laser design, taking account of the geometry of Yb:YAG slab. A quasi-CW diode array side-pumped Yb:YAG slab laser is investigated theoretically and experimentally. Experiments yield a quasi-CW output energy up to 20.36 mJ with the laser pulse width of 654.55 μs at 1049 nm when the diode arrays operate at 25 Hz and 1 ms pulse width. The crystal dimensions are 3 mm×8 mm×1 mm and the doping density is 10 at.%. The experimental results are in good agreement with the predictions of the theoretical model.

Evolution of sum-chirp in polarization multiplexed communication system

Wang Jing, Wang Zhen-Li
Chin. Phys., 2004, 13 (6): 877-881 doi: 10.1088/1009-1963/13/6/016
Full Text: [PDF 237 KB] (Downloads:308)
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The evolution of sum-chirp for an initially chirped Gaussian pulse is studied in the polarization multiplexed communication system, with fibre attenuation considered. The sum-chirp is found to have the character of saturation. Its value appears different along the two different polarization axes, determined by the incidence polarization angle. We also find that sum-chirp is dominated by the initial chirp at a short distance, and by the cross-phase modulation effect at long distance. And it is influenced apparently by a wavevector mismatch parameter below 10 ps/km. Further, its saturation results from the effective distance determined by fibre attenuation.

All-optical NOT and XOR logic operation at 2.5 Gb/s based on semiconductor optical amplifier loop mirror

Wang Ying, Zhang Xin-Liang, Huang De-Xiu
Chin. Phys., 2004, 13 (6): 882-886 doi: 10.1088/1009-1963/13/6/017
Full Text: [PDF 216 KB] (Downloads:351)
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All-optical XOR and NOT logic operations based on semiconductor optical amplifier loop mirror (SLALOM) are simultaneously demonstrated theoretically and experimentally. Based on a segmented semiconductor optical amplifier model, the all-optical logic operation process is simulated theoretically. In an experimental study, 2.5 Gb/s all-optical XOR operation was achieved in the output port of SLALOM, while all-optical NOT operation was achieved in the input port through a circulator at the same time.
ATOMIC AND MOLECULAR PHYSICS

Radiative lifetimes of Rydberg 6pnd J=2 states of Pb I by multichannel quantum defect theory

Dai Zhen-Wen, Jiang Hong-Mei, Sun Gui-Juan, Jiang Zhan-Kui
Chin. Phys., 2004, 13 (6): 845-849 doi: 10.1088/1009-1963/13/6/010
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Energy levels of the odd-parity 6pnd J=2 Rydberg states of Pb I are analysed by the multichannel quantum defect theory (MQDT) in the frame of a five-channel three-limit calculation model. With optimal MQDT parameters, channel admixture coefficients are obtained and used to calculate the theoretical lifetimes of the levels by comparing to the previously measured lifetimes. The predicted lifetimes for higher-lying Rydberg states are given and discussed. These predicted lifetimes are very different from those obtained by the four-channel two-limit model previously used, which means that introduction of the additional interacting channel is important for studying the 6pnd J=2 Rydberg states of Pb I.

Dielectronic recombination rate coefficient for Cu-like Au50 ion

Yang Tian-Li, Jiang Gang, Zhu Zheng-He
Chin. Phys., 2004, 13 (6): 850-854 doi: 10.1088/1009-1963/13/6/011
Full Text: [PDF 186 KB] (Downloads:273)
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The rate coefficients α^{DR} of dielectronic recombination (DR) for Cu-like Au^{50+} ion collided with the incident free electron are calculated based on the quasi-relativistic multi-configuration Hartree-Fock theory. The results clearly show that the α^{DR} of all recombination channels exhibits resonance characters with electron temperature. At lower temperatures, the recombination for electrons caused by 4s excitation is dominant through outer electron radiative transitions among the intermediate doubly excited autoionizing levels, in which the most components come from 3d^{10}5pns states, whereas with increasing electron temperature, DR caused by 3d excitation turns out to be dominant, and the contribution from the 3d^94s4fnf state to the total rate coefficient of electron 3d is the largest with α^{DR}=1.15×10^{- 11} cm^3·s^{-1} at an electron temperature of T_e=0.35 keV. Under this condition, there exists a strong competition between the two types of recombination channels.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Sawtooth-like electron density oscillations under laser blow-off and lower hybrid current drive in HL-1M tokamak

Jiao Yi-Ming, Zhou Yan, Deng Zhong-Chao, Gao Qing-Di
Chin. Phys., 2004, 13 (6): 887-890 doi: 10.1088/1009-1963/13/6/018
Full Text: [PDF 185 KB] (Downloads:366)
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By using of a six-channel HCN laser interferometer, the sawtooth-like density oscillations without being exhibited in the ohmic phase plasma have been observed during lower hybrid current drive (LHCD) discharges in the HL-1M device. There are often accompanied by injected impurity with laser blow-off. Analyses show that this kind of density sawtooth-like oscillation comes from the mutual effect of LHCD and impurity. An available mechanism is the loss of superthermal electrons by the magnetic perturbation, which is caused by the crash of the central accumulated impurities.

Emission spectra simulation of calcium plasmas in non-local thermodynamic equilibrium

Liang Gui-Yun, Bian Xia, Zhao Gang
Chin. Phys., 2004, 13 (6): 891-897 doi: 10.1088/1009-1963/13/6/019
Full Text: [PDF 220 KB] (Downloads:342)
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We use previous high-quality experimental spectra to test the accuracy of atomic data and the validity of the collisional-radiative (CR) model used in this paper. The synthetic spectrum with electron temperature log T_e(K)=6.745 and electron density n_e=6.0×10^{13}cm^{-3}, which almost reproduces the experimental spectra, is presented. Nearly all the features of the experimental spectra were identified. The results of the CR modelling for the emission spectra of calcium plasmas all agree well with the measured spectral line intensities within the experimental error for most of the lines. Furthermore, we make the electron temperature diagnostic through the synthetic spectrum and population fractions of every ionization state as a function of charge state at different electron temperatures, as well as the electron density diagnostic through the intensity ratios of two lines of Be-like calcium and three lines of C-like calcium. A good agreement between the calculated values and the measured ones is found.

Study of electron temperature gradient instability in toroidal plasmas with negative magnetic shear

Jian Guang-De, Dong Jia-Qi
Chin. Phys., 2004, 13 (6): 898-904 doi: 10.1088/1009-1963/13/6/020
Full Text: [PDF 237 KB] (Downloads:336)
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Electron temperature gradient driven instability in toroidal plasmas with negative magnetic shear is studied. Full electron kinetics is considered, and the behaviours of the modes and corresponding turbulent transport in the parameter regimes close to the instability threshold are emphasized. Growing and damped modes are both investigated. The singular points of the integrand are disposed of, and the fitting formulae for the critical gradient are given. The theoretical results are shown to be close to the experimental observations.

Chirping and spreading of ultrashort laser pulses in underdense plasmas

Zhang Qiu-Ju, Sheng Zheng-Ming, Zhang Jie
Chin. Phys., 2004, 13 (6): 905-912 doi: 10.1088/1009-1963/13/6/021
Full Text: [PDF 323 KB] (Downloads:342)
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A linear theory on the propagation of ultrashort pulses including only a few cycles in underdense plasmas is presented. It is shown that the dispersion in plasmas causes severe distortions in the pulse shape, including pulse chirping and spreading. The analytical calculations coincide very well with those obtained by particle-in-cell (PIC) simulations. The upper limit of the peak amplitude of the pulses, above which the linear theory breaks down due to the setting in of nonlinear effects of both the relativistic electron-mass increase and ponderomotive force, is also examined by PIC simulations. At certain high amplitudes, it is found that the ultrashort laser pulses can propagate like solitons.

Sterilization of E. coli bacterium with an atmospheric pressure surface barrier discharge

Xu Lei, Zhang Rui, Liu Peng, Ding Li-Li, Zhan Ru-Juan
Chin. Phys., 2004, 13 (6): 913-917 doi: 10.1088/1009-1963/13/6/022
Full Text: [PDF 3702 KB] (Downloads:408)
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The atmospheric pressure surface barrier discharge (APSBD) in air has been used in killing Escherichia coli (E. coli). There is almost no bacterial colony in the sample after treatment by discharge plasma for 2 min. A diagnostic technique based on mass spectrum has been applied to the discharge gas and the mechanism of killing is discussed. Ozone and monatomic oxide are considered to be the major antimicrobial active species. There is almost no harmful by-product. The experiment proves that APSBD plasma is a very simple, effective and innocuous tool for sterilization.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Crystallographic and magnetic structures of Pr6Fe13Ge studied by powder neutron diffraction

Wang Fang-Wei, Zhang Pan-Lin, Shen Bao-Gen, Yan Qi-Wei
Chin. Phys., 2004, 13 (6): 918-923 doi: 10.1088/1009-1963/13/6/023
Full Text: [PDF 299 KB] (Downloads:352)
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Crystallographic and magnetic structures of Pr_6Fe_{13}Ge have been investigated by high-resolution powder neutron diffraction in the temperature range of 10-300 K. The magnetic structure consists of ferromagnetic Pr_6Fe_{13} slabs that alternate antiferromagnetically, along c, with the next Pr_6Fe_{13} slab separated by a non-magnetic Ge layer. The magnetic moments lie within the ab-planes. The propagation vector of this structure is k=(001) with respect to the conventional reciprocal lattice of the I-centred structure. However, the temperature-dependence of neutron-scattering intensity of the (110) Bragg peak, very similar to the temperature-dependent magnetization measured by SQUID magnetometer, indicates that a small c-axis ferromagnetic component should be added to the above antiferromagnetic model.

The physical property tensors of one-dimensional quasicrystals

Li Cui-Lian, Liu You-Yan
Chin. Phys., 2004, 13 (6): 924-931 doi: 10.1088/1009-1963/13/6/024
Full Text: [PDF 182 KB] (Downloads:477)
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According to the group representation theory, we derive the character formulae of representation-matrices of the physical property tensors for the one-dimensional (1D) quasicrystals. Based on this, we have calculated the numbers of independent components of representation-matrices for thermal expansion coefficient tensors, piezoelectric coefficient tensors and elastic constant tensors under 31 point-groups for the 1D quasicrystals. Moreover, we have deduced the particular matrix forms of these tensors under the 31 point-groups. This is an important complement of quasicrystal physical property.

Chemisorption of Fe on Au-passivated Si(001) surface

Wei Shu-Yi, Wang Jian-Guang, Ma Li, Xia Cong-Xin, Yan Yu-Li
Chin. Phys., 2004, 13 (6): 932-937 doi: 10.1088/1009-1963/13/6/025
Full Text: [PDF 214 KB] (Downloads:353)
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The chemisorption of one monolayer of Fe atoms on a Au-passivated Si(001) surface is studied by using the self-consistent tight-binding linear muffin-tin orbital method. The Fe adatom chemisorption on an ideal Si(001) surface is also considered for comparison. The chemisorption energy and layer projected density of states for a monolayer of Fe atoms on Au-passivated Si(001) surface are calculated and compared with that of the Fe atoms on an ideal Si(001) surface. The charge transfer is investigated. It is found that the most stable position is at the fourfold hollow site for the adsorbed Fe atoms, which might sit below the Au surface. Therefore there will be a Au-Fe mixed layer at the Fe/Au-Si(100) interface. It is found that the adsorbed Fe atoms cannot sit below the Si surface, indicating that a buffer layer of Au atoms may hinder the intermixing of Fe atoms and Si atoms at the Fe/Au-Si(001) interface effectively, which is in agreement with the experimental results.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Spin current in double quantum dot

Zhao Hua, Zhang Guo-Feng, Yin Wen, Liang Jiu-Qing
Chin. Phys., 2004, 13 (6): 938-941 doi: 10.1088/1009-1963/13/6/026
Full Text: [PDF 155 KB] (Downloads:368)
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We have studied the dynamical behaviours of two electrons confined in a double quantum dot driven by rotating magnetic fields in terms of the theory of Lewis-Riesenfeld Hermitian invariants for the explicitly time-dependent Hamiltonian. The coherent spin oscillations in the dot provide a generation source for spin current. Exact solutions obtained allow us to investigate the dynamical properties of the spin localization for various initial localized states.

Effects of a donor on the bond property of quantum-dot molecules

Wang Li-Min, Luo Ying, Ma Ben-Kun, Duan Su-Qing, Zhao Xian-Geng
Chin. Phys., 2004, 13 (6): 942-947 doi: 10.1088/1009-1963/13/6/027
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Within the framework of effective mass approximation, we have calculated the electronic structure of the two laterally coupled quantum dots with a donor by the finite element method. The calculated results show that the bond states of quantum-dot molecules are quite sensitive to the donor positions. By varying the donor position, the transition from covalent to ionic bond state is realized for some electronic states. Some extreme cases are also discussed for comparison.

A novel technique for predicting ionizing radiation effects of commercial MOS devices

Zhang Guo-Qiang, Guo Qi, Erkin, Lu Wu, Ren Di-Yuan
Chin. Phys., 2004, 13 (6): 948-953 doi: 10.1088/1009-1963/13/6/028
Full Text: [PDF 182 KB] (Downloads:372)
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A nondestructive selection technique for predicting ionizing radiation effects of commercial metal-oxide-semiconductor (MOS) devices has been put forward. The basic principle and application details of this technique have been discussed. Practical application for the 54HC04 and 54HC08 circuits has shown that the predicted radiation-sensitive parameters such as threshold voltage, static power supply current and radiation failure total dose are consistent with the experimental results obtained only by measuring original electrical parameters. It is important and necessary to choose suitable information parameters. This novel technique can be used for initial radiation selection of some commercial MOS devices.

Observation of the current-voltage plateau-like structure of resonant tunnelling diode with prewells under different magnetic fields

Zhang Xiao-Xin, Zeng Yi-Ping, Qiu Zhi-Jun, Wang Bao-Qiang, Zhu Zhan-Ping
Chin. Phys., 2004, 13 (6): 954-957 doi: 10.1088/1009-1963/13/6/029
Full Text: [PDF 164 KB] (Downloads:322)
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We have grown resonant tunnelling diodes (RTDs) with different sized emitter prewells and without a prewell. The current-voltage (I-V) characteristics of them in different magnetic fields were investigated. Two important phenomena were observed. First, a high magnetic field can destroy the plateau-like structure in the I-V curves of the RTD. This phenomenon is ascribed to the fact that the high magnetic field will demolish the coupling between the energy level in the main quantum well and that in the emitter quantum well or in the prewell. Secondly, the existence and size of the prewell are also important factors influencing the plateau-like structure.

Phase separation and abnormal transport behaviours in La0.7-xGdxSr0.3MnO3 system

Liu Ning, Tong Wei, Zhang Yu-Heng
Chin. Phys., 2004, 13 (6): 958-967 doi: 10.1088/1009-1963/13/6/030
Full Text: [PDF 409 KB] (Downloads:351)
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The magnetic and transport behaviours of the La_{0.7-x}Gd_xSr_{0.3}MnO_3 (0≤x≤0.70) system are investigated. The experimental results indicate that with increasing Gd doping content, the magnetism of the system changes from the long-range ferromagnetic order state to the cluster-spin glass state, then to the antiferromagnetic (AFM) state. It is interesting that the phase separation appears at x=0.30 and 0.40 and disappears for x≥0.50 where the AFM state occurs. At high doping content, the transport behaviours exhibit abnormality, e.g. there are two temperature ranges in which the ρ-T curves can be well fitted by a variable-range hopping (VRH) model. We suggest that the VRH does not come from the hopping of carriers between clusters, but from the different magnetic backgrounds in the clusters.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Quantum statistical entropy for Kerr-de Sitter black hole

Zhang Li-Chun, Wu Yue-Qin, Zhao Ren
Chin. Phys., 2004, 13 (6): 974-978 doi: 10.1088/1009-1963/13/6/032
Full Text: [PDF 163 KB] (Downloads:359)
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Improving the membrane model by which the entropy of the black hole is studied, we study the entropy of the black hole in the non-thermal equilibrium state. To give the problem stated here widespread meaning, we discuss the (n+2)-dimensional de Sitter spacetime. Through discussion, we obtain that the black hole's entropy which contains two horizons (a black hole's horizon and a cosmological horizon) in the non-thermal equilibrium state comprises the entropy corresponding to the black hole's horizon and the entropy corresponding to the cosmological horizon. Furthermore, the entropy of the black hole is a natural property of the black hole. The entropy is irrelevant to the radiation field out of the horizon. This deepens the understanding of the relationship between black hole's entropy and horizon's area. A way to study the bosonic and fermionic entropy of the black hole in high non-thermal equilibrium spacetime is given.
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