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Chin. Phys. B  
  Chin. Phys. B--2004, Vol.13, No.8
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GENERAL

A type of multi-component integrable hierarchy

Zhang Yu-Feng, Zhang Yu-Sen
Chin. Phys., 2004, 13 (8): 1183-1186 doi: 10.1088/1009-1963/13/8/001
Full Text: [PDF 89 KB] (Downloads:378)
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A new isospectral problem is established by constructing a simple interesting loop algebra. A commutation operation of the loop algebra is as straightforward as the loop algebra ?_1. It follows that a type of multi-component integrable hierarchy is obtained. This can be used as a general method.

Lie symmetry and Mei symmetry of a rotational relativistic system in phase space

Li Hong, Fang Jian-Hui
Chin. Phys., 2004, 13 (8): 1187-1190 doi: 10.1088/1009-1963/13/8/002
Full Text: [PDF 140 KB] (Downloads:454)
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The Lie symmetry and the Mei symmetry of a rotational relativistic system in phase space are studied. The definition, criterion and conserved quantity of the Lie symmetry and the Mei symmetry of a rotational relativistic system in phase space are given. The relation between the Lie symmetry and the Mei symmetry is found. An example is given to illustrate the application of the result.

Vertically forced surface wave in weakly viscous fluids bounded in a circular cylindrical vessel

Jian Yong-Jun, E Xue-Quan
Chin. Phys., 2004, 13 (8): 1191-1200 doi: 10.1088/1009-1963/13/8/003
Full Text: [PDF 1693 KB] (Downloads:848)
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Two-time scale perturbation expansions were developed in weakly viscous fluids to investigate surface wave motions by linearizing the Navier-Stokes equation in a circular cylindrical vessel which is subject to a vertical oscillation. The fluid field was divided into an outer potential flow region and an inner boundary layer region. A linear amplitude equation of slowly varying complex amplitude, which incorporates a damping term and external excitation, was derived for the weakly viscid fluids. The condition for the appearance of stable surface waves was obtained and the critical curve was determined. In addition, an analytical expression for the damping coefficient was determined and the relationship between damping and other related parameters (such as viscosity, forced amplitude, forced frequency and the depth of fluid, etc.) was presented. Finally, the influence both of the surface tension and the weak viscosity on the mode formation was described by comparing theoretical and experimental results. The results show that when the forcing frequency is low, the viscosity of the fluid is prominent for the mode selection. However, when the forcing frequency is high, the surface tension of the fluid is prominent.

Stochastic resonance in a bistable system with coloured correlation between additive and multiplicative noise

Luo Xiao-Qin, Zhu Shi-Qun
Chin. Phys., 2004, 13 (8): 1201-1209 doi: 10.1088/1009-1963/13/8/004
Full Text: [PDF 366 KB] (Downloads:496)
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The phenomenon of stochastic resonance (SR) in a bistable nonlinear system with coupling between additive and multiplicative noises is investigated when the correlation between two noise terms is coloured. It is found that the signal-to-noise ratio (SNR) of the system is affected not only by the coupling strength λ between two noise terms, but also by the noise correlation time τ. The SNR is changed from a single peak, to two peaks with a dip, and then to a monotonically decreasing function with noise strength. The dependence of the SR on the initial conditions is entirely caused by the coupling strength λ between two noise terms.

Chaotifying a linear time-invariant system by the state feedback controller and sawtooth function

Wei Rong, Wang Xing-Yu
Chin. Phys., 2004, 13 (8): 1210-1214 doi: 10.1088/1009-1963/13/8/005
Full Text: [PDF 208 KB] (Downloads:297)
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Another algorithm for chaotification of any given linear time-invariant discrete-time systems is presented. The new chaotification algorithm uses the decentralized control and the continuous sawtooth function, which can generate discrete chaos with an arbitrarily desired amplitude bound. Based on the Marotto theorem, we mathematically prove that the controlled system is chaotic in the sense of Li and Yorke. Finally, a simple example is used to illustrate the effectiveness of the proposed theory and method.

Synchronization of chaotic erbium-doped fibre lasers and its application in secure communication

Zhang Sheng-Hai, Shen Ke
Chin. Phys., 2004, 13 (8): 1215-1220 doi: 10.1088/1009-1963/13/8/006
Full Text: [PDF 443 KB] (Downloads:557)
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We have investigated the synchronization of chaotic dual-ring erbium-doped fibre lasers using the delay feedback-injection scheme. Numerical simulation shows that two chaotic dual-ring erbium-doped fibre lasers can be well synchronized if the strengths of delay feedback and injection are suitable. Even though the effects of the noises and the difference between the two lasers are considered, the twins can still reach good synchronization. Secure communication could be realized using the scheme of message-masking based on the synchronization of the chaotic dual-ring erbium-doped fibre lasers.

Global synchronization of Chua's chaotic delay network by using linear matrix inequality

Li Zhi, Shi Song-Jiao
Chin. Phys., 2004, 13 (8): 1221-1225 doi: 10.1088/1009-1963/13/8/007
Full Text: [PDF 186 KB] (Downloads:387)
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Global synchronization of Chua's chaotic dynamical networks with coupling delays is investigated in this paper. Unlike other approaches, where only local results were obtained, the network is found to be not linearized in this paper. Instead, the global synchronization is obtained by using the linear matrix inequality theory. Moreover, some quite simple linear-state-error feedback controllers for global synchronization are derived, which can be easily constructed based on the minimum eigenvalue of the coupling matrix. A simulation of Chua's chaotic network with global coupling delays in nodes is finally given, which is used to verify the theoretical results of the proposed global synchronization scheme.

Basic properties of an rf SQUID involving two Josephson junctions connected in series

Mao Bo, Tan Zhong-Kui, Meng Shu-Chao, Dai Yuan-Dong, Wang Fu-Ren
Chin. Phys., 2004, 13 (8): 1226-1229 doi: 10.1088/1009-1963/13/8/008
Full Text: [PDF 190 KB] (Downloads:386)
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We have studied the basic characteristics of a radio frequency superconducting quantum interference device (rf SQUID) involving two Josephson junctions connected in series, the case for the widely used grain boundary junction (GBJ) rf SQUID. It is found that the SQUID properties are determined mainly by the weaker junction when the critical current of the weaker junction is much lower than that of the other junction. Otherwise, the effect of the other junction is not negligible. We also find that only when the hysteresis parameter β is less than 1-α, where α is the critical current ratio of the two junctions, will the SQUID operate in the nonhysteretic mode.
NUCLEAR PHYSICS

Isospin and F-spin symmetry structure in low-lying levels of 4850Cr isotopes

Falih H. Al-Khudair, Long Gui-Lu
Chin. Phys., 2004, 13 (8): 1230-1238 doi: 10.1088/1009-1963/13/8/009
Full Text: [PDF 279 KB] (Downloads:352)
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The low-energy level structure and electromagnetic transitions of {}^{48,50}Cr nuclei have been studied using the interacting boson model with isospin (IBM-3). A sequence of isospin excitation bands with isospin T=T_z, T_z+1 and T_z+2 has been assigned, and compared with available data. According to this study, the 2^+_3 and 2^+_2 states are the lowest mixed symmetry states in {}^{48}Cr and {}^{50}Cr, respectively. In particular, the present calculations suggest that a combination of isospin and F-spin excitation can explain the structure in these nuclei. The transition probabilities between the levels are analysed in terms of isoscalar and isovector decompositions which reveal the detailed nature of the energy levels. The results obtained are in good agreement with recent experimental data.

Production of helium projectile fragments in {16O-emulsion interactions at 4.5 A GeV/c

Zhang Dong-Hai, Li Zhen-Yu, Li Jun-Sheng, Wu Feng-Juan
Chin. Phys., 2004, 13 (8): 1239-1245 doi: 10.1088/1009-1963/13/8/010
Full Text: [PDF 229 KB] (Downloads:531)
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The measurements of partial production cross sections of the multiple helium projectile fragments emitted at 4.5 A GeV/c {}^{16}O-Em interactions are reported. We have studied the production rate of helium projectile fragments due to fragmentation of {}^{16}O ions and compared it with that obtained from different projectiles at various energies. The dependence of on the mass number of the incident beams is formulated. The multiplicity distributions of the helium fragments produced in {}^{16}O-Em interactions at different energies exhibit Koba-Nielson-Olesen (KNO) scaling. The correlation of helium projectile fragments and target fragments is also investigated and it is found that the average of target fragments is increased with the decrease of the number of helium fragments in peripheral interactions.
CLASSICAL AREAS OF PHENOMENOLOGY

Resonator insensitive investigation to thermal lens for end-pumped lasers

Gong Chuan-Bo, Chen Chang-Shui, Song Qiu-Ming, Zhu Ling
Chin. Phys., 2004, 13 (8): 1263-1268 doi: 10.1088/1009-1963/13/8/014
Full Text: [PDF 195 KB] (Downloads:322)
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Optical pumping of solid-state lasers induces a thermal lens effect in the laser crystal; this thermal effect determines the beam properties. In this paper, the focal length of the thermal lens is calculated, and resonator parameter (g_1 g_2) is obtained, which is insensitive to thermal distortions when the product of the resonator parameters (g_1, g_2) equals 1/2. By using our calculated results, we get the fundamental transverse mode laser output with optic-optic conversion of 48.6%, and slope efficiency of 56.3%.

A new class of quantum states generated by m-fold application of Bogoliubov's transformation

Wu Wei, Wu Ling-An, Xin Zong-Zheng
Chin. Phys., 2004, 13 (8): 1269-1275 doi: 10.1088/1009-1963/13/8/015
Full Text: [PDF 618 KB] (Downloads:312)
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By applying higher powers of the Bogoliubov transformation operator b^{\dagger }=ν^*a+μ^*a^{\dagger } to the two-photon coherent states (or minimum uncertainty squeezed states) we construct a new type of quantum state which we call the generalized excited two-photon coherent states. Analytic expressions for the quantum statistical properties are derived, and through numerical computation the phase space quasi-probability distributions are found. These states can exhibit highly nonclassical behaviour depending on the degree of excitation m and other parameters. For particular values of two parameters λ and ρ, these generalized states reduce to other classes of coherent states formerly reported. Our theory thus presents a much broader approach to these types of quantum states.

Influence of atomic motion on the population and dipole squeezing of a cascade three-level atom in cavity field

Zhu Ai-Dong, Zhang Shou
Chin. Phys., 2004, 13 (8): 1276-1282 doi: 10.1088/1009-1963/13/8/016
Full Text: [PDF 353 KB] (Downloads:368)
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The dynamical property of a cascade three-level atom is investigated in the condition of atomic motion. The influence of atomic motion on the population and dipole squeezing is discussed. The results show that atomic motion makes the amplitude of atomic population be steady and increasing the parameter εp which denotes the atomic motion and the structure of field mode can shorten the period of collapse-revivals. By choosing an appropriate parameter εp, we can obtain a dipole squeezed atom of long standing.

Optical ballast and adaptive dynamic stable resonator

Zhang Guang-Yin, Jiao Zhi-Yong, Guo Shu-Guang, Zhang Xiao-Hua, Gu Xue-Wen, Yan Cai-Fan, Wu Ding-Er, Song Feng
Chin. Phys., 2004, 13 (8): 1283-1286 doi: 10.1088/1009-1963/13/8/017
Full Text: [PDF 201 KB] (Downloads:235)
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In this paper a new concept of ‘optical ballast' is put forward. Optical ballast is a kind of device that can be used to decrease the variation and fluctuation of the propagation characteristics of light beams caused by the disturbance of refractive index of the medium. To illustrate the idea clearly and concretely, a fully adaptive dynamic stable solid-state laser resonator is presented as application example of optical ballast.

Nonlinear optical properties of 75TeO2-20Nb2O5-5ZnO glasses doped with CeO2

Zhang Shi-An, Sun Zhen-Rong, Wang Yu-Fei, Zeng He-Ping, Wang Zu-Geng, Lin Jian, Huang Wen-Hai, Xu Zhi-Zhan, Li Ru-Xin
Chin. Phys., 2004, 13 (8): 1287-1290 doi: 10.1088/1009-1963/13/8/018
Full Text: [PDF 195 KB] (Downloads:423)
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Nonlinear optical properties of 75TeO_2-20Nb_2O_5-5ZnO glasses doped with CeO_2 have been investigated with a self-diffracted time-resolved degenerate four-wave mixing (DFWM) technique at different excitation intensities and lattice temperatures. The DFWM signal exhibits three peaks at higher excitation intensities, where a main peak appears at zero delay time and two rather weak side peaks are located symmetrically at the negative and positive time delay. Due to destructive interferences between the fifth- and third-order polarizations, the line-shape of the main peak around the zero time delay evolves from single peak into a double-peak structure with increasing excitation intensity. Two side peaks emerge at the positive and negative time delay and gradually intensify with increasing excitation intensity or lattice temperature, and their positions are independent of the pulse duration, temperature and excitation intensity, which are attributed to the many-body Coulomb interaction.

General demonstration of principal states of polarization and real-time monitoring of polarization mode dispersion in optical fibres

Dong Hui, Wu Chong-Qing, Fu Song-Nian
Chin. Phys., 2004, 13 (8): 1291-1295 doi: 10.1088/1009-1963/13/8/019
Full Text: [PDF 263 KB] (Downloads:348)
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We investigated the general properties of polarization effects in optical fibres and demonstrated the existence of so-called principal states of polarization (PSP), which mean the fixed points in mathematics, in different polarization effects, such as birefringence and polarization mode dispersion, by using fixed point theory. Furthermore, a time evolution vector is defined to describe the time evolution of polarization state in optical fibres, which is used to investigate the time evolution of polarization mode dispersion vector (PDV), including differential group delay and PSP. The experimental results of real-time monitoring of PDV by using this method are reported. To our knowledge, this is the first report on monitoring PSP evolution in optical fibres.
ATOMIC AND MOLECULAR PHYSICS

Oscillator strengths for 2 {2P-n 2D transitions of lithium-like systems with Z=11 to 20

Hu Mu-Hong, Wang Zhi-Wen
Chin. Phys., 2004, 13 (8): 1246-1250 doi: 10.1088/1009-1963/13/8/011
Full Text: [PDF 169 KB] (Downloads:329)
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The dipole-length, velocity and acceleration absorption oscillator strengths for the 1s^22p-1s^2nd(3≤n≤9) transitions of the lithium-like systems with Z=11 to 20 are calculated using the energies and the multiconfiguration interaction wavefunctions obtained from a full core plus correlation method. The agreement between the f-values calculated from the length, velocity and acceleration formulae is excellent. Our results agree closely with the experimental data available in the literature. Combining these discrete oscillator strengths with the single-channel quantum defect theory, the discrete oscillator strengths for the transitions from 1s^22p state to highly excited states (n≥10) and the oscillator strength densities corresponding to the bound-free transitions are obtained.

Variation of the absorption and dispersion profiles in a ladder-four-level system

Li Yong-Fang, Sun Jian-Feng, Niu Yue-Ping
Chin. Phys., 2004, 13 (8): 1251-1258 doi: 10.1088/1009-1963/13/8/012
Full Text: [PDF 246 KB] (Downloads:263)
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A theoretical research on the variation of the absorption and dispersion profiles and population distribution of each level in a ladder-four-level system driven by two coherent fields has been made. Whether the variation occurs or not depends on the effect of quantum interference, the detuning of the upper coherent field and the separation of the two intermediate levels. A dressed-state analysis is introduced to explain the numerical results.

Intermolecular interaction potentials of methane-argon complex calculated using LDA approaches

Bai Yu-Lin, Chen Xiang-Rong, Zhou Xiao-Lin, Yang Xiang-Dong, Wang Hai-Yan
Chin. Phys., 2004, 13 (8): 1259-1262 doi: 10.1088/1009-1963/13/8/013
Full Text: [PDF 204 KB] (Downloads:300)
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The intermolecular interaction potential for methane-argon complex is calculated by local density approximation (LDA) approaches. The calculated potential has a minimum when the intermolecular distance of methane-argon complex is 6.75 a.u.; the corresponding depth of the potential is 0.0163eV which has good agreement with experimental data. We also have made a nonlinear fitting of our results for the Lennard-Jones (12-6) potential function and obtain that V(R)=143794365.332/R^{12}-3032.093 / R^6 (R in a.u. and V(R) in eV).
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Theory of electromagnetic wave propagation in a plasma-filled corrugate waveguide immersed in a finite magnetized field

Li Wei, Gao Hong, Gong Ma-Li, Liu Sheng-Gang
Chin. Phys., 2004, 13 (8): 1296-1301 doi: 10.1088/1009-1963/13/8/020
Full Text: [PDF 249 KB] (Downloads:458)
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The linear theory of electromagnetic radiation from a high-power backward-wave-oscillator (BWO), travelling-wave-tube (TWT) with plasma-filled, sinusoidally corrugate waveguide driven by an intense relativistic electron beam (IREB) has been derived and analysed numerically. A general dispersion relation is presented for analysing a plasma-filled corrugate waveguide immersed in magnetized plasma in this paper. It is shown that the linear theory developed here is in good agreement with the previous work.

Particle simulation on electron acceleration process by the laser ponderomotive force in inhomogeneous underdense plasma layers

Cao Li-Hua, Yu Wei, Xu Han, Liu Zhan-Jun, Zheng Chun-Yang, Li Bin
Chin. Phys., 2004, 13 (8): 1302-1308 doi: 10.1088/1009-1963/13/8/021
Full Text: [PDF 253 KB] (Downloads:396)
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The mechanism of electron ponderomotive acceleration due to increasing group velocity of laser pulse in inhomogeneous underdense plasma layers is studied by two-dimensional relativistic parallel particle-in-cell code. The electrons within the laser pulse move with it and can be strongly accelerated ponderomotively when the duration of laser pulse is much shorter than the duration of optimum condition for acceleration in the wake. The extra energy gain can be attributed to the change of laser group velocity. More high energy electrons are generated in the plasma layer with descending density profile than that with ascending density profile. The process and character of electron acceleration in three kinds of underdense plasma layers are presented and compared.

Properties of TiN coating on 45# steel for inner surface modification by grid-enhanced plasma source ion implantation method

Zhang Gu-Ling, Wang Jiu-Li, Liu Yuan-Fu, Liu Chi-Zi, Yang Si-Ze
Chin. Phys., 2004, 13 (8): 1309-1314 doi: 10.1088/1009-1963/13/8/022
Full Text: [PDF 320 KB] (Downloads:346)
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Using a new inner surface modification method named GEPSII (grid-enhanced plasma source ion implantation), which is designed for inner surface modification of tubular work pieces, we successfully produced polycrystalline TiN coating on 0.45% C steel (45^# steel) samples. Compared with the uncoated 45^# steel sample, the electrochemical corrosion test on the coated 45^# steel samples presents evident improvement in their corrosion resistance. Two implanted voltages, direct current (-2kV) and pulsed negative voltage (-10kV), are applied on the substrates. It is shown that the direct current implantation is more effective than the pulsed implantation in the surface corrosion resistance. AES depth profile shows that coating thickness is about tens of nanometres. The preferred orientations expressed by peaks at (111) and (200) can be seen clearly in XRD patterns.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Grain size and its distribution in NiTi thin films sputter-deposited on heated substrates

Li Yong-Hua, Meng Fan-Ling, Qiu Deng-Li, Wang Yi, Zheng Wei-Tao, Wang Yu-Ming
Chin. Phys., 2004, 13 (8): 1315-1319 doi: 10.1088/1009-1963/13/8/023
Full Text: [PDF 2398 KB] (Downloads:344)
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Grain size and its distribution in NiTi thin films sputter-deposited on a heated substrate have been investigated using the small angle x-ray scattering technique. The crystalline particles have a small size and are distributed over a small range of sizes for the films grown at substrate temperatures 370 and 420℃. The results show that the sizes of crystalline particles are about the same. From the x-ray diffraction profiles, the sizes of crystalline particles obtained were 2.40nm and 2.81nm at substrate temperatures of 350 and 420℃, respectively. The morphology of NiTi thin films deposited at different substrate temperatures has been studied by atomic force microscopy. The root mean square roughness calculated for the film deposited at ambient temperature and 420℃ are 1.42 and 2.75nm, respectively.

Adhesion elastic contact and hysteresis effect

Wei Zheng, Zhao Ya-Pu
Chin. Phys., 2004, 13 (8): 1320-1325 doi: 10.1088/1009-1963/13/8/024
Full Text: [PDF 235 KB] (Downloads:501)
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In this paper, we study the relationship between the pull-off force and the transition parameter (or Tabor number) as well as the variation of the pull-off radius with the transition parameter in the adhesion elastic contact. Hysteresis models are presented to describe the contact radius as a function of external loads in loading and unloading processes. Among these models, we verified the hysteresis model from Johnson-Kendall-Roberts theory, based on which the calculated results are in good agreement with experimental ones.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Investigation of photoelectron temporal characteristics in silver halide microcrystals using the microwave absorption technique

Yang Shao-Peng, Fu Guang-Sheng, Dai Xiu-Hong, Dong Guo-Yi, Li Xiao-Wei, Han Li
Chin. Phys., 2004, 13 (8): 1326-1329 doi: 10.1088/1009-1963/13/8/025
Full Text: [PDF 166 KB] (Downloads:499)
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The free photoelectron lifetime reflects to a large extent the latent image formation efficiency and sensitivity of silver halide material. The microwave absorption dielectric-spectrum technique enables measurement of the photoelectron decay process of silver halide emulsion exposed to 35ps laser pulse. For T-grain AgBr emulsion, the relationship between exciting energy and photoelectron action has been obtained, and the influence of iodide dopants on photoelectron lifetime was measured and analysed. The photoelectron lifetime of dye-sensitized AgBr emulsion with tabular grains is shorter than that with cubic grains, and the latent image formation efficiency of the former is higher than the latter.

Preparation of transparent conductive ZnO:Tb films and their photoluminescence properties

Fang Ze-Bo, Tan Yong-Sheng, Liu Xue-Qin, Yang Ying-Hu, Wang Yin-Yue
Chin. Phys., 2004, 13 (8): 1330-1333 doi: 10.1088/1009-1963/13/8/026
Full Text: [PDF 196 KB] (Downloads:419)
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Tb-doped Zinc oxide (ZnO:Tb) films were prepared by RF reactive magnetron sputtering of a Zn target with some Tb-chips attached. The results show that the appropriate Tb ions incorporated into ZnO films can improve the structural and electrical properties of ZnO films. Photoluminescence (PL) measurements show that the characteristic emission lines correspond to the intra-4f^n-shell transitions in Tb^{3+} ions at room temperature. Under the optimal conditions, the ZnO:Tb films were prepared with the lowest resistivity (ρ) of 9.34×10^{ -4}Ωcm, transmittance over 80% at the visible region and the strong blue emission.

Temperature dependence of Hall electron density of GaN-based heterostructures

Zhang Jin-Feng, Zhang Jin-Cheng, Hao Yue
Chin. Phys., 2004, 13 (8): 1334-1338 doi: 10.1088/1009-1963/13/8/027
Full Text: [PDF 201 KB] (Downloads:349)
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The theoretic calculation and analysis of the temperature dependence of Hall electron density of a sample AlGaN/GaN heterostructure has been carried out in the temperature range from 77 to 300K. The densities of the two-dimensional electron gas and the bulk electrons are solved by self-consistent calculation of one-dimensional Schr?dinger and Poisson equations at different temperatures, which allow for the variation of energy gap and structure strain, and are used for evaluation of the temperature dependence of Hall electron density. The calculated Hall electron density agrees with the measured one quite well with the appropriate bulk mobility data. Analysis revealed that for the temperature range considered, even in the heterostructures with a small bulk conductance the factors that determine the Hall mobility and electron density could be of different sources, and not just the two-dimensional electron gas as generally supposed.

Transport characteristics of Rabi oscillations in the two-band superlattices

Duan Su-Qing, Wu Bin-Yi, Wang Zhi-Gang, Zhao Xian-Geng
Chin. Phys., 2004, 13 (8): 1339-1343 doi: 10.1088/1009-1963/13/8/028
Full Text: [PDF 185 KB] (Downloads:302)
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We investigated the transport characteristics of Rabi oscillations, by using numerical methods, within a two-band tight-binding model driven by dc-ac electric fields. We found that Rabi oscillations make the long-time average current a sharply change, i.e. the current have resonant peaks appearing. Rabi oscillations are destroyed by dephasing; these peaks are the signatures of Rabi oscillations on the current response. The strong interband coupling will change the conditions of Rabi oscillations and, correspondingly, changes the places where the current resonant peaks appear.

Change in the magnetic ground state of LaFe11.4Al1.6 compound by the substitution of Mn for Fe

Wang Fang, Chen Yuan-Fu, Wang Guang-Jun, Sun Ji-Rong, Shen Bao-Gen
Chin. Phys., 2004, 13 (8): 1344-1347 doi: 10.1088/1009-1963/13/8/029
Full Text: [PDF 239 KB] (Downloads:335)
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The structure and magnetic properties of La(Fe_{1-x}Mn_x)_{11.4}Al_{1.6} (0≤x≤0.25)compounds have been studied. The NaZn_{13}-type structure is preserved and the lattice parameter increases linearly with increasing the Mn concentration. The magnetic ground state changes from the antiferromagnetic to the spin-glass or the cluster-glass state by the substitution of Mn for Fe. Furthermore, a field-induced transition from cluster glass to ferromagnet is found for the samples with x=0.05 and 0.10.

Magnetic properties of composites of Tb0.28Dy0.72Fe2 and polyvinylidene fluoride

Cai Ning, Zhai Jun-Yi, Shi Zhan, Lin Yuan-Hua, Nan Ce-Wen
Chin. Phys., 2004, 13 (8): 1348-1352 doi: 10.1088/1009-1963/13/8/030
Full Text: [PDF 4146 KB] (Downloads:359)
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Bi-ferroic particulate composites with Tb_{0.28}Dy_{0.72}Fe_2 (Terfenol-D) particles randomly dispersed in ferroelectric polyvinylidene fluoride matrix prepared by a simple hot-pressing procedure were investigated. With increasing concentration of Terfenol-D, the magnetic susceptibility, saturation magnetization and initial permeability of the composites increases. The dependence of the effective magnetostriction on applied bias for the composites is similar to that for bulk Terfenol-D, but the effective magnetostriction strongly depends on the volume fraction of Terfenol-D. The observed behaviour of the composite is reasonably described by using effective medium theories.

Relationship between the magnetic field distribution and attractive force of single-domain YBCO bulk under different field cooling processes

Yang Wan-Min, Zhou Lian, Feng Yong, Zhang Ping-Xiang, R. Nicolsky
Chin. Phys., 2004, 13 (8): 1353-1357 doi: 10.1088/1009-1963/13/8/031
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The levitation forces under different field cooling states were measured at 77K by changing the field cooling distance Z_{fc} between a YBCO bulk and a permanent magnet. It is found that the relationship between the absolute maximum attractive force (Z_{maf}) and the corresponding gap distance (Z_{maf}) to F_{maf} can be well described by exponential laws as a function of Z_{fc}, which allow us to predict these values according to Z_{fc}. It is also found that the distance between the Z_{0fa} (gap distance corresponding to the zero force) and Z_{maf} in the ascending process is a constant value, which is closely related to the constant reduction factor of the axial component of flux density along the axial line of the magnet if Z_{maf}-Z_{0fa} is a constant value. These results are very interesting for fundamental research and helpful in practical designing and applications.

Effect of magnetic field of light on refractive index

Zhang Tao
Chin. Phys., 2004, 13 (8): 1358-1364 doi: 10.1088/1009-1963/13/8/032
Full Text: [PDF 238 KB] (Downloads:481)
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Light refraction in a medium results from energy exchange between the medium and the magnetic field of the light. Formulas of refractive index, that is, the ratio of light speed in vacuum to light speed in the medium, were derived with the inductor model of electron cloud and the law of energy conservation. Refractive indices of several media were calculated using the formulas derived, and the calculated results are in agreement with the results measured. The anisotropy and the nonlinearity of the refractive index are explained with the theory described in this work.

Structural evolution of a-Si:H/SiO2 multilayers upon step by step thermal annealing

Mei Jia-Xin, Xu Jun, Ma Zhong-Yuan, Zhu-Da, Sui Yan-Ping, Li Wei, Li Xin, Rui Yun-Jun, Huang Xin-Fan, Chen Kun-Ji
Chin. Phys., 2004, 13 (8): 1365-1369 doi: 10.1088/1009-1963/13/8/033
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a-Si:H/SiO_2 multilayers were prepared by alternatively changing plasma enhanced chemical vapour deposition of a-Si:H layers and in situ plasma oxidation process. Subsequently, as-grown samples were annealed at temperatures from 350℃ to 1100℃ in N_2 ambient with an increment of 100℃. The evolution of bonding configurations and structures with annealing treatments was systematically investigated by Fourier-transform infrared spectroscopy. The peak position of Si-O stretching vibration of SiO_2 layers shift to 1087cm^{-1} after annealing at 1100℃, which demonstrates that the SiO_2 films fabricated by plasma oxidation after high temperature annealing can have similar properties to the thermal grown ones. A Si-O vibration from interfacial SiO_x was identified: the value x was found to increase as increasing the annealing temperature, which is ascribed to the cooperation of hydrogen effusion and reordering of the oxygen bond in SiO_x networks. The H-related bonds were observed in the form of H-Si-O_3 and H-Si-Si_{3-n}O_n (n=1-2) configurations, which are supposed to be present in SiO_2 and interfacial SiO_x layers, respectively. The H atoms bonded in different bonding configurations effuse at different temperatures due to their different desorption energies.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

The variability of BL Lac 3C 66A

Su Cheng-Yue
Chin. Phys., 2004, 13 (8): 1375-1376 doi: 10.1088/1009-1963/13/8/035
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It is now known that there are supermassive black holes at the centre of a galaxy, surrounded by an accretion disc. The black hole-jet-accretion disc model plays an important role in the explanation of the observational properties of active galactic nuclei. BL Lacertae objects form a subclass of blazars; they are monitored through electromagnetic wave bands. During the OJ-94 project, 3C 66A was observed as a comparison object of OJ287 and found to display a possible 65-day period in the V light curve. In this paper, we show that the instability of an accretion disc surrounding a massive central black hole (2.5×10^{7}M_⊙) may explain this period in 3C 66A.
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