Table of contents

21 June 2004, Volume 13 Issue 8 Previous issue    Next issue

GENERAL

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A type of multi-component integrable hierarchy Zhang Yu-Feng (张玉峰), Zhang Yu-Sen (张玉森) Chinese Physics, 2004, 13 (8):  1183-1186.  DOI: 10.1088/1009-1963/13/8/001 Abstract ( 1009 )   PDF (89KB) ( 452 )   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 $\tilde{A}_1$. It follows that a type of multi-component integrable hierarchy is obtained. This can be used as a general method.

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Lie symmetry and Mei symmetry of a rotational relativistic system in phase space Li Hong (李红), Fang Jian-Hui (方建会) Chinese Physics, 2004, 13 (8):  1187-1190.  DOI: 10.1088/1009-1963/13/8/002 Abstract ( 1217 )   PDF (140KB) ( 550 )   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.

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Vertically forced surface wave in weakly viscous fluids bounded in a circular cylindrical vessel Jian Yong-Jun (菅永军), E Xue-Quan (鄂学全) Chinese Physics, 2004, 13 (8):  1191-1200.  DOI: 10.1088/1009-1963/13/8/003 Abstract ( 1135 )   PDF (1693KB) ( 968 )   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.

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Stochastic resonance in a bistable system with coloured correlation between additive and multiplicative noise Luo Xiao-Qin (罗晓琴), Zhu Shi-Qun (朱士群) Chinese Physics, 2004, 13 (8):  1201-1209.  DOI: 10.1088/1009-1963/13/8/004 Abstract ( 1339 )   PDF (366KB) ( 670 )   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 $\lambda$ between two noise terms, but also by the noise correlation time $\tau$. 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 $\lambda$ between two noise terms.

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Chaotifying a linear time-invariant system by the state feedback controller and sawtooth function Wei Rong (魏荣), Wang Xing-Yu (王行愚) Chinese Physics, 2004, 13 (8):  1210-1214.  DOI: 10.1088/1009-1963/13/8/005 Abstract ( 1110 )   PDF (208KB) ( 396 )   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.

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Synchronization of chaotic erbium-doped fibre lasers and its application in secure communication Zhang Sheng-Hai (张胜海), Shen Ke (沈柯) Chinese Physics, 2004, 13 (8):  1215-1220.  DOI: 10.1088/1009-1963/13/8/006 Abstract ( 1200 )   PDF (443KB) ( 700 )   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.

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Global synchronization of Chua's chaotic delay network by using linear matrix inequality Li Zhi (李智), Shi Song-Jiao (施颂椒) Chinese Physics, 2004, 13 (8):  1221-1225.  DOI: 10.1088/1009-1963/13/8/007 Abstract ( 1289 )   PDF (186KB) ( 487 )   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.

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Basic properties of an rf SQUID involving two Josephson junctions connected in series Mao Bo (毛博), Tan Zhong-Kui (谭忠魁), Meng Shu-Chao (孟树超), Dai Yuan-Dong (戴远东), Wang Fu-Ren (王福仁) Chinese Physics, 2004, 13 (8):  1226-1229.  DOI: 10.1088/1009-1963/13/8/008 Abstract ( 1289 )   PDF (190KB) ( 567 )   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 $\beta$ is less than $1-\alpha$, where $\alpha$ is the critical current ratio of the two junctions, will the SQUID operate in the nonhysteretic mode.

NUCLEAR PHYSICS

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Isospin and F-spin symmetry structure in low-lying levels of 48,50Cr isotopes Falih H. Al-Khudair (法列), Long Gui-Lu (龙桂鲁) Chinese Physics, 2004, 13 (8):  1230-1238.  DOI: 10.1088/1009-1963/13/8/009 Abstract ( 967 )   PDF (279KB) ( 456 )   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.

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Production of helium projectile fragments in 16O－emulsion interactions at 4.5 A GeV/c Zhang Dong-Hai (张东海), Li Zhen-Yu (李振宇), Li Jun-Sheng (李俊生), Wu Feng-Juan (吴凤娟) Chinese Physics, 2004, 13 (8):  1239-1245.  DOI: 10.1088/1009-1963/13/8/010 Abstract ( 1043 )   PDF (229KB) ( 654 )   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 $< n_{\alpha}>$  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.

ATOMIC AND MOLECULAR PHYSICS

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Oscillator strengths for 2 2P-n 2D transitions of lithium-like systems with Z=11 to 20 Hu Mu-Hong (胡木宏), Wang Zhi-Wen (王治文) Chinese Physics, 2004, 13 (8):  1246-1250.  DOI: 10.1088/1009-1963/13/8/011 Abstract ( 1247 )   PDF (169KB) ( 450 )   The dipole-length, velocity and acceleration absorption oscillator strengths for the 1s$^2$2p－1s$^2$nd(3≤n≤9) transitions of the lithium-like systems with Z=11 to 20 are calculated using the energies and the multiconfiguration interaction wavefunctions obtained from a full core plus correlation method. The agreement between the f-values calculated from the length, velocity and acceleration formulae is excellent. Our results agree closely with the experimental data available in the literature. Combining these discrete oscillator strengths with the single-channel quantum defect theory, the discrete oscillator strengths for the transitions from 1s$^2$2p state to highly excited states (n≥10) and the oscillator strength densities corresponding to the bound-free transitions are obtained.

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Variation of the absorption and dispersion profiles in a ladder-four-level system Li Yong-Fang (李永放), Sun Jian-Feng (孙建锋), Niu Yue-Ping (钮月萍) Chinese Physics, 2004, 13 (8):  1251-1258.  DOI: 10.1088/1009-1963/13/8/012 Abstract ( 1207 )   PDF (246KB) ( 359 )   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.

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Intermolecular interaction potentials of methane－argon complex calculated using LDA approaches Bai Yu-Lin (白玉林), Chen Xiang-Rong (陈向荣), Zhou Xiao-Lin (周晓林), Yang Xiang-Dong (杨向东), Wang Hai-Yan (王海燕) Chinese Physics, 2004, 13 (8):  1259-1262.  DOI: 10.1088/1009-1963/13/8/013 Abstract ( 1316 )   PDF (204KB) ( 401 )   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).

CLASSICAL AREAS OF PHENOMENOLOGY

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Resonator insensitive investigation to thermal lens for end-pumped lasers Gong Chuan-Bo (龚传波), Chen Chang-Shui (陈长水), Song Qiu-Ming (宋秋鸣), Zhu Ling (朱灵) Chinese Physics, 2004, 13 (8):  1263-1268.  DOI: 10.1088/1009-1963/13/8/014 Abstract ( 1323 )   PDF (195KB) ( 419 )   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%.

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A new class of quantum states generated by m-fold application of Bogoliubov's transformation Wu Wei (吴炜), Wu Ling-An (吴令安), Xin Zong-Zheng (辛宗政) Chinese Physics, 2004, 13 (8):  1269-1275.  DOI: 10.1088/1009-1963/13/8/015 Abstract ( 1087 )   PDF (618KB) ( 395 )   By applying higher powers of the Bogoliubov transformation operator $b^{\dagger }=\nu^*a+\mu^*a^{\dagger}$ 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 $\lambda$ and $\rho$, 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.

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Influence of atomic motion on the population and dipole squeezing of a cascade three-level atom in cavity field Zhu Ai-Dong (朱爱东), Zhang Shou (张寿) Chinese Physics, 2004, 13 (8):  1276-1282.  DOI: 10.1088/1009-1963/13/8/016 Abstract ( 1080 )   PDF (353KB) ( 460 )   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.

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Optical ballast and adaptive dynamic stable resonator Zhang Guang-Yin (张光寅), Jiao Zhi-Yong (焦志勇), Guo Shu-Guang (郭曙光), Zhang Xiao-Hua (张晓华), Gu Xue-Wen (顾学文), Yan Cai-Fan (颜彩繁), Wu Ding-Er (武丁二), Song Feng (宋峰) Chinese Physics, 2004, 13 (8):  1283-1286.  DOI: 10.1088/1009-1963/13/8/017 Abstract ( 1110 )   PDF (201KB) ( 355 )   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.

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Nonlinear optical properties of 75TeO2－20Nb2O5－5ZnO glasses doped with CeO2 Zhang Shi-An (张诗按), Sun Zhen-Rong (孙真荣), Wang Yu-Fei (王宇飞), Zeng He-Ping (曾和平), Wang Zu-Geng (王祖赓), Lin Jian (林健), Huang Wen-Hai (黄文旵), Xu Zhi-Zhan (徐至展), Li Ru-Xin (李儒新) Chinese Physics, 2004, 13 (8):  1287-1290.  DOI: 10.1088/1009-1963/13/8/018 Abstract ( 1345 )   PDF (195KB) ( 524 )   Nonlinear optical properties of 75TeO$_2$－20Nb$_2$O$_5$－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.

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General demonstration of principal states of polarization and real-time monitoring of polarization mode dispersion in optical fibres Dong Hui (董晖), Wu Chong-Qing (吴重庆), Fu Song-Nian (付松年) Chinese Physics, 2004, 13 (8):  1291-1295.  DOI: 10.1088/1009-1963/13/8/019 Abstract ( 1253 )   PDF (263KB) ( 472 )   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.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Theory of electromagnetic wave propagation in a plasma-filled corrugate waveguide immersed in a finite magnetized field Li Wei (李伟), Gao Hong (高宏), Gong Ma-Li (巩马理), Liu Sheng-Gang (刘盛纲) Chinese Physics, 2004, 13 (8):  1296-1301.  DOI: 10.1088/1009-1963/13/8/020 Abstract ( 1325 )   PDF (249KB) ( 555 )   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.

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Particle simulation on electron acceleration process by the laser ponderomotive force in inhomogeneous underdense plasma layers Cao Li-Hua (曹莉华), Yu Wei (余玮), Xu Han (徐涵), Liu Zhan-Jun (刘占军), Zheng Chun-Yang (郑春阳), Li Bin (李斌) Chinese Physics, 2004, 13 (8):  1302-1308.  DOI: 10.1088/1009-1963/13/8/021 Abstract ( 1213 )   PDF (253KB) ( 489 )   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.

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Properties of TiN coating on 45# steel for inner surface modification by grid-enhanced plasma source ion implantation method Zhang Gu-Ling (张谷令), Wang Jiu-Li (王久丽), Liu Yuan-Fu (刘元富), Liu Chi-Zi (刘赤子), Yang Si-Ze (杨思泽) Chinese Physics, 2004, 13 (8):  1309-1314.  DOI: 10.1088/1009-1963/13/8/022 Abstract ( 1243 )   PDF (320KB) ( 461 )   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

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Grain size and its distribution in NiTi thin films sputter-deposited on heated substrates Li Yong-Hua (李永华), Meng Fan-Ling (孟繁玲), Qiu Deng-Li (仇登利), Wang Yi (王一), Zheng Wei-Tao (郑伟涛), Wang Yu-Ming (王煜明) Chinese Physics, 2004, 13 (8):  1315-1319.  DOI: 10.1088/1009-1963/13/8/023 Abstract ( 1122 )   PDF (2398KB) ( 456 )   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.

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Adhesion elastic contact and hysteresis effect Wei Zheng (魏征), Zhao Ya-Pu (赵亚溥) Chinese Physics, 2004, 13 (8):  1320-1325.  DOI: 10.1088/1009-1963/13/8/024 Abstract ( 925 )   PDF (235KB) ( 652 )   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

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Investigation of photoelectron temporal characteristics in silver halide microcrystals using the microwave absorption technique Yang Shao-Peng (杨少鹏), Fu Guang-Sheng (傅广生), Dai Xiu-Hong (代秀红), Dong Guo-Yi (董国义), Li Xiao-Wei (李晓苇), Han Li (韩理) Chinese Physics, 2004, 13 (8):  1326-1329.  DOI: 10.1088/1009-1963/13/8/025 Abstract ( 1213 )   PDF (166KB) ( 641 )   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.

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Preparation of transparent conductive ZnO:Tb films and their photoluminescence properties Fang Ze-Bo (方泽波), Tan Yong-Sheng (谭永胜), Liu Xue-Qin (刘雪芹), Yang Ying-Hu (杨映虎), Wang Yin-Yue (王印月) Chinese Physics, 2004, 13 (8):  1330-1333.  DOI: 10.1088/1009-1963/13/8/026 Abstract ( 1226 )   PDF (196KB) ( 579 )   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 ($\rho$) of $9.34\times10^{ -4}$$\Omega$cm, transmittance over 80% at the visible region and the strong blue emission.

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Temperature dependence of Hall electron density of GaN-based heterostructures Zhang Jin-Feng (张金凤), Zhang Jin-Cheng (张进城), Hao Yue (郝跃) Chinese Physics, 2004, 13 (8):  1334-1338.  DOI: 10.1088/1009-1963/13/8/027 Abstract ( 1295 )   PDF (201KB) ( 505 )   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.

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Transport characteristics of Rabi oscillations in the two-band superlattices Duan Su-Qing (段素青), Wu Bin-Yi (吴彬毅), Wang Zhi-Gang (王志刚), Zhao Xian-Geng (赵宪庚) Chinese Physics, 2004, 13 (8):  1339-1343.  DOI: 10.1088/1009-1963/13/8/028 Abstract ( 1192 )   PDF (185KB) ( 410 )   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.

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Change in the magnetic ground state of LaFe11.4Al1.6 compound by the substitution of Mn for Fe Wang Fang (王芳), Chen Yuan-Fu (陈远富), Wang Guang-Jun (王光军), Sun Ji-Rong (孙继荣), Shen Bao-Gen (沈保根) Chinese Physics, 2004, 13 (8):  1344-1347.  DOI: 10.1088/1009-1963/13/8/029 Abstract ( 1196 )   PDF (239KB) ( 431 )   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.

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Magnetic properties of composites of Tb0.28Dy0.72Fe2 and polyvinylidene fluoride Cai Ning (蔡宁), Zhai Jun-Yi (翟俊宜), Shi Zhan (施展), Lin Yuan-Hua (林元华), Nan Ce-Wen (南策文) Chinese Physics, 2004, 13 (8):  1348-1352.  DOI: 10.1088/1009-1963/13/8/030 Abstract ( 1138 )   PDF (4146KB) ( 575 )   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.

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Relationship between the magnetic field distribution and attractive force of single-domain YBCO bulk under different field cooling processes Yang Wan-Min (杨万民), Zhou Lian (周廉), Feng Yong (冯勇), Zhang Ping-Xiang (张平祥), R. Nicolsky Chinese Physics, 2004, 13 (8):  1353-1357.  DOI: 10.1088/1009-1963/13/8/031 Abstract ( 1102 )   PDF (227KB) ( 372 )   The levitation forces under different field cooling states were measured at 77K by changing the field cooling distance Zfc between a YBCO bulk and a permanent magnet. It is found that the relationship between the absolute maximum attractive force (Zmaf) and the corresponding gap distance (Zmaf) to Fmaf can be well described by exponential laws as a function of Zfc, which allow us to predict these values according to Zfc. It is also found that the distance between the Z0fa (gap distance corresponding to the zero force) and Zmaf 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 Zmaf-Z0fa is a constant value. These results are very interesting for fundamental research and helpful in practical designing and applications.

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Effect of magnetic field of light on refractive index Zhang Tao (张涛) Chinese Physics, 2004, 13 (8):  1358-1364.  DOI: 10.1088/1009-1963/13/8/032 Abstract ( 1599 )   PDF (238KB) ( 659 )   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.

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Structural evolution of a-Si:H/SiO2 multilayers upon step by step thermal annealing Mei Jia-Xin (梅嘉欣), Xu Jun (徐骏), Ma Zhong-Yuan (马忠元), Zhu-Da (朱达), Sui Yan-Ping (隋妍萍), Li Wei (李伟), Li Xin (李鑫), Rui Yun-Jun (芮云军), Huang Xin-Fan (黄信凡), Chen Kun-Ji (陈坤基) Chinese Physics, 2004, 13 (8):  1365-1369.  DOI: 10.1088/1009-1963/13/8/033 Abstract ( 1258 )   PDF (211KB) ( 473 )   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.

CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Fabrication of high growth rate solar-cell-quality μc-Si:H thin films by VHF-PECVD Zhang Xiao-Dan (张晓丹), Zhao Ying (赵颖), Zhu Feng (朱锋), Sun Jian (孙建), Wei Chang-Chun (魏长春), Hou Guo-Fu (侯国付), Geng Xin-Hua (耿新华), Xiong Shao-Zhen (熊绍珍) Chinese Physics, 2004, 13 (8):  1370-1374.  DOI: 10.1088/1009-1963/13/8/034 Abstract ( 958 )   PDF (226KB) ( 542 )   Several series of Si:H films were fabricated by the very high frequency plasma enhanced chemical vapour deposition (VHF-PECVD) at different substrate temperatures (Ts) and silane concentration (SC=[SiH$_4$]/[SiH$_4$+H$_2$]%). The results of Raman spectroscopy showed structural evolution of the Si:H films with the variation of Ts and SC. The results of x-ray diffraction (XRD) measurements indicated that Ts also influences the crystal orientation of the Si:H films. The modulation effect of Ts on crystalline volume fraction (Xc) is more evident for the high SC, which shows different trend compared to low SC. In addition, the growth rate of the films also showed a regular change with the variation of SC and Ts. Different samples in the series showed a similar increase in dark conductivity and a decrease in photosensitivity with increasing Ts and decreasing SC. Device-quality microcrystalline silicon materials were deposited at a high growth rate, characterized by relatively low dark conductivity and relatively high photosensitivity in a certain crystalline range. The microcrystalline silicon solar cell with a conversion efficiency of 4.55% has been prepared by VHF-PECVD.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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The variability of BL Lac 3C 66A Su Cheng-Yue (苏成悦) Chinese Physics, 2004, 13 (8):  1375-1376.  DOI: 10.1088/1009-1963/13/8/035 Abstract ( 1038 )   PDF (130KB) ( 431 )   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 ($2.5\times10^{7}$M⊙) may explain this period in 3C 66A.