Table of Content

20 June 2005, Volume 13 Issue 11 Previous Issue    Next Issue

GENERAL

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Variable separation solutions and new solitary wave structures to the (1+1)-dimensional equations of long-wave－short-wave resonant interaction Xu Chang-Zhi, He Bao-Gang, Zhang Jie-Fang 2004, 13 (11):  1777-1783.  doi: 10.1088/1009-1963/13/11/001 Abstract ( 0 )   PDF (212KB) ([an error occurred while processing this directive])   A variable separation approach is proposed and extended to the (1+1)-dimensional physical system. The variable separation solutions of (1+1)-dimensional equations of long-wave－short-wave resonant interaction are obtained. Some special type of solutions such as soliton solution, non-propagating solitary wave solution, propagating solitary wave solution, oscillating solitary wave solution are found by selecting the arbitrary function appropriately.

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Non-Noether symmetries and conserved quantities of the Lagrange mechano-electrical systems Fu Jing-Li, Chen Li-Qun, Liu Rong-Wan 2004, 13 (11):  1784-1789.  doi: 10.1088/1009-1963/13/11/002 Abstract ( 0 )   PDF (179KB) ([an error occurred while processing this directive])   This paper focuses on studying non-Noether symmetries and conserved quantities of Lagrange mechano-electrical dynamical systems. Based on the relationships between the motion and Lagrangian, we present conservation laws on non-Noether symmetries for Lagrange mechano-electrical dynamical systems. A criterion is obtained on which non-Noether symmetry leads to Noether symmetry of the systems. The work also gives connections between the non-Noether symmetries and Lie point symmetries, and further obtains Lie invariants to form a complete set of non-Noether conserved quantity. Finally, an example is discussed to illustrate these results.

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Non-Noether symmetrical conserved quantity for nonholonomic Vacco dynamical systems with variable mass Qian Yong-Fen, Li Ren-Jie, Zhao Shu-Hong 2004, 13 (11):  1790-1795.  doi: 10.1088/1009-1963/13/11/003 Abstract ( 0 )   PDF (173KB) ([an error occurred while processing this directive])   Using a form invariance under special infinitesimal transformations in which time is not variable, the non-Noether conserved quantity of the nonholonomic Vacco dynamical system with variable mass is studied. The differential equations of motion of the systems are established. The definition and criterion of the form invariance of the system under special infinitesimal transformations are studied. The necessary and sufficient condition under which the form invariance is a Lie symmetry is given. The Hojman theorem is established. Finally an example is given to illustrate the application of the result.

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A series of new double periodic solutions to a (2+1)-dimensional asymmetric Nizhnik－Novikov－Veselov equation Chen Yong, Wang Qi 2004, 13 (11):  1796-1800.  doi: 10.1088/1009-1963/13/11/004 Abstract ( 0 )   PDF (176KB) ([an error occurred while processing this directive])   By means of a new general ans?tz and with the aid of symbolic computation, a new algebraic method named Jacobi elliptic function rational expansion is devised to uniformly construct a series of new double periodic solutions to (2+1)-dimensional asymmetric Nizhnik－Novikov－Veselov (ANNV) equation in terms of rational Jacobi elliptic function.

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Teleportation of N-particle entangled W state via entanglement swapping Zhan You-Bang 2004, 13 (11):  1801-1805.  doi: 10.1088/1009-1963/13/11/005 Abstract ( 0 )   PDF (150KB) ([an error occurred while processing this directive])   A scheme for teleporting an unknown N-particle entangled W state is proposed via entanglement swapping. In this scheme, N maximally entangled particle pairs are used as quantum channel. As a special case, the teleportation of an unknown four-particle entangled W state is studied.

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Two-dimensional hydrogen negative ion in a magnetic field Xie Wen-Fang 2004, 13 (11):  1806-1810.  doi: 10.1088/1009-1963/13/11/006 Abstract ( 0 )   PDF (165KB) ([an error occurred while processing this directive])   Making use of the adiabatic hyperspherical approach, we report a calculation for the energy spectrum of the ground and low-excited states of a two-dimensional hydrogen negative ion H^{-} in a magnetic field. The results show that the ground and low-excited states of H^{-} in low-dimensional space are more stable than those in three-dimensional space and there may exist more bound states.

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Stochastic resonance of bias signal-modulated noise in a single-mode laser Wang Jun, Cao Li, Wu Da-Jin 2004, 13 (11):  1811-1814.  doi: 10.1088/1009-1963/13/11/007 Abstract ( 0 )   PDF (178KB) ([an error occurred while processing this directive])   Stochastic resonance (SR) for bias signal modulation is studied in a single-mode laser system. By investigating a gain-noise model driven by correlated pump noise and quantum noise, we find that, whether the correlation coefficient between both the noises is positive or negative, SR always appears in the dependence of signal-to-noise ratio (SNR) upon the noise correlation time and the frequency of the modulation signal. However, only when the correlation coefficient between both noises is negative can SR occur in the dependence of SNR upon the quantum noise intensity and pump noise intensity, while when the correlation coefficient between both noises is positive, it shows monotonically.

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Influence of structural parameters on the immunity of short-channel effects in grooved-gate nMOSFET Tong Jian-Nong, Zou Xue-Cheng, Shen Xu-Bang 2004, 13 (11):  1815-1819.  doi: 10.1088/1009-1963/13/11/008 Abstract ( 0 )   PDF (212KB) ([an error occurred while processing this directive])   This paper presents the influences of structural parameters on the immunity of short-channel effects in grooved-gate n-channel metal－oxide－semiconductor field effect transistor (nMOSFET) using the simulator PISCES-II. The zero or negative groove-junction depth is beneficial to the improvement of the threshold characters, but there exists a limited range. The doping concentration of both substrate and channel has a significant influence on the threshold characters as well as on the device transconductance. Thus, the variation in these adjustable parameters may help to optimize the device design.

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A normalized data-reusing least-mean-square algorithm of noise cancellation for magnetocardiography Kong Xiang-Yan, Wang Hui-Wu, Tian Ye, Huang Xu-Guang, Zhang Li-Hua, Ren Yu-Feng, Chen Geng-Hua, Yang Qian-Sheng 2004, 13 (11):  1820-1825.  doi: 10.1088/1009-1963/13/11/009 Abstract ( 0 )   PDF (317KB) ([an error occurred while processing this directive])   An adaptive filter based on Data-Reusing Least-Mean-Square algorithm has been proposed and applied in magnetocardiography (MCG) to suppress ambient noise. Numerical simulation studies indicate that the adaptive filter is a powerful noise suppresser for correlated interferences, especially for those with amplitude changing and time delay. Also the filter has a wide frequency bandwidth. With this filter, the signal-to-noise ratio of an MCG is improved to the intrinsic noise level. The periodic average method for further improvement of the noise level in MCG is also discussed.

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Spectral focusing characteristics of a grazing-incidence flat-field grating spectrometer Xie Xin-Hua, Liu Ya-Qing, Fan Pin-Zhong, Li Ru-Xin 2004, 13 (11):  1826-1829.  doi: 10.1088/1009-1963/13/11/010 Abstract ( 0 )   PDF (154KB) ([an error occurred while processing this directive])   The spectral focusing characteristics of a grazing-incidence flat-field spectrometer with a spherical variable-line-spacing grating in the 5－40nm spectral range are presented. The spectrometer can be used for any object at a distance in the 50mm－infinity range from the grating apex with a diffracted spectrum sharply focused on an almost flat focal plane at a constant distance from the grating apex.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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A new energy source originating from extra dimensions Tao Bi-Xiu, Ji Shi-Yin, Li Fang-Qiong 2004, 13 (11):  1830-1834.  doi: 10.1088/1009-1963/13/11/011 Abstract ( 0 )   PDF (171KB) ([an error occurred while processing this directive])   In this work the Einstein gravitational field equations and the Lichnerowicz boundary formalism in the extra dimensions are used to build up our black hole model from 6-dimensional space－time. From the internal stress－energy tensor the solutions with energy levels and semiclassical space-quantization are obtained, which combines with only one metric condition outside the defect. We show a new type of energy source, which originates from extra dimensions. A part of the energy source of quasi-stellar object (QSO) maybe come from extra dimensions in that way. The theoretical arithmetic upper limit is identical to that of the output energy of QSO.

NUCLEAR PHYSICS

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Triaxial interaction effect in the structure of 148-158Sm Zhang Jing-Juan, Falih H. Al-Khudair, Li Yan-Song, Long Gui-Lu 2004, 13 (11):  1835-1842.  doi: 10.1088/1009-1963/13/11/012 Abstract ( 0 )   PDF (288KB) ([an error occurred while processing this directive])   The structures of {}^{148-158}Sm are studied in the frame of the interacting boson model. Attention is given to the triaxial interaction, and it is found that the triaxial interaction plays an important role in the detailed structure of this isotopic chain. The potential surfaces of these nuclei are also studied and the shapes of them are analysed. And it is found that though the triaxial interaction plays an important role in these nuclei, there are no stable triaxial shapes in the low-lying structures of these nuclei.

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Description of nucleus 44Ti in new symmetry limit in IBM-3 Zhang Jin-Fu, Bai Hong-Bo 2004, 13 (11):  1843-1847.  doi: 10.1088/1009-1963/13/11/013 Abstract ( 0 )   PDF (195KB) ([an error occurred while processing this directive])   Analysis of the spectra and E2 transition rates shows that the empirical scheme of {}^{44}Ti is in good agreement with the predictions of the [U_d (5) \otimes U_{T_d} (3)]⊕U_{T_s} (3) symmetry limit.

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Effect of three-body interaction on hot asymmetric nuclear matter Li Zeng-Hua, Zuo Wei, Lu Guang-Cheng 2004, 13 (11):  1848-1853.  doi: 10.1088/1009-1963/13/11/014 Abstract ( 0 )   PDF (202KB) ([an error occurred while processing this directive])   The properties of hot asymmetric nuclear matter are studied in the framework of the finite temperature Brueckner－Hartree－Fock theory that is extended to include the contribution of microscopic three-body forces. We give the variation of the critical temperature with the asymmetry parameter and show the effect brought by this three-body repulsive potential on the value of the critical asymmetry of the phase transition for asymmetric nuclear matter. Owing to the additional repulsion provided by three-body forces, this value decreases. In addition, the domain of mechanical instability for hot nuclear matter is also indicated, which gradually shrinks with increasing asymmetry and temperature.

ATOMIC AND MOLECULAR PHYSICS

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Enhanced Raman scattering from nano-SnO2 grains Ding Shuo, Liu Jin-Quan, Liu Yu-Long 2004, 13 (11):  1854-1856.  doi: 10.1088/1009-1963/13/11/015 Abstract ( 0 )   PDF (150KB) ([an error occurred while processing this directive])   We present the Raman spectra of nano-SnO_{2} grains with sizes from 4nm to 80nm excited by 532nm and 1.06μm lines. The enhanced Raman scattering of the nanograins is observed for both exciting lines when the grain size is less than 8nm. The less the grain size is, the more intensely the Raman scattering is enhanced. According to our results, the enhancements of the Raman intensity are a few tenfolds and different for different exciting lines when the grain size is 4nm. It can be attributed to enhanced Raman scattering by electron－hole pair excitations in the nanograins that originate from sub-microscopic (10nm) size and other defect- and surface-related features. A critical size that divides respective predominance of bulk properties and the defect-, surface-, and size-related features can be determined to be about 8nm.

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Theoretical calculation of triple differential cross sections of 3s orbital of argon in coplanar symmetric (e, 2e) reaction Wu Xing-Ju, Chen Xiang-Jun, Shan Xu, Chen Li-Qing, Xu Ke-Zun 2004, 13 (11):  1857-1861.  doi: 10.1088/1009-1963/13/11/016 Abstract ( 0 )   PDF (191KB) ([an error occurred while processing this directive])   The triple differential cross section for the low-energy electron impact ionization of inner-valence 3s orbital of argon has been calculated using the modified distorted wave Born approximation in coplanar symmetric energy-sharing geometry. Satisfactory agreement between theory and experiment is achieved when the polarization and post-collisional interaction (PCI) are included in the calculations. It is shown that the polarization and PCI effects play a very important role in the case of argon at low incident energies.

CLASSICAL AREAS OF PHENOMENOLOGY

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Preparation of nonclassical states and measurement of the Wigner function for the collective motion of N trapped ions Zheng Shi-Biao 2004, 13 (11):  1862-1865.  doi: 10.1088/1009-1963/13/11/017 Abstract ( 0 )   PDF (145KB) ([an error occurred while processing this directive])   We propose a scheme for generating nonclassical states for the centre-of-mass vibrational mode of N trapped ions, including superpositions of several coherent states on a circle and Fock states. In the scheme N trapped ions are driven by a laser beam tuned to the carrier. The scheme also provides a new prospect for laser cooling. The scheme can be used to measure the Wigner function of the collective vibrational mode.

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Second harmonic generation of propagating collective excitations in Bose－Einstein condensates Huang Guo-Xiang 2004, 13 (11):  1866-1876.  doi: 10.1088/1009-1963/13/11/018 Abstract ( 0 )   PDF (270KB) ([an error occurred while processing this directive])   We consider a possible second harmonic generation (SHG) of propagating collective excitations in a two-component Bose－Einstein condensate (BEC) with repulsive atom－atom interactions. We show that the phase-matching condition for the SHG can be fulfilled if the wave vectors and frequencies of the excitations are chosen adequately from different dispersion branches. We solve the nonlinear amplitude equations for the SHG derived using a method of multiple-scales and provide SHG solutions similar to those obtained for a SHG in nonlinear optical media. A possible experimental realization of the SHG for the propagating collective modes in a cigar-shaped two-component BEC is also discussed.

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26W near diffraction limited Q-switched green laser based on a diode-end-pumped master oscillator power amplifier Zhang Ying, Hou Wei, Yao Ai-Yun, Yang Xiao-Dong, Li Rui-Ning, Cui Da-Fu, Xu Zu-Yan 2004, 13 (11):  1877-1880.  doi: 10.1088/1009-1963/13/11/019 Abstract ( 0 )   PDF (229KB) ([an error occurred while processing this directive])   An efficient acousto-optically Q-switched extracavity frequency-doubled 532nm laser based on a diode-end-pumped master oscillator power amplifier (MOPA) is demonstrated. With a type I non-critically phase-matched LBO, 26W of average power at 532nm in a near diffraction limited mode at a repetition rate of 30kHz was generated under 43W pump power of 1064nm Nd:YVO_{4} laser, which correspond to a frequency-doubling conversion efficiency of 60%.

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Entanglement and disentanglement from cascade beam-splitter for squeezed vacuum state inputs Zhou Qing-Ping, Fang Mao-Fa, Liu Xiao-Juan, Chen Xiao-Mei, Wu Qin, Xu Hong-Zhi 2004, 13 (11):  1881-1886.  doi: 10.1088/1009-1963/13/11/020 Abstract ( 0 )   PDF (302KB) ([an error occurred while processing this directive])   Properties of the entanglement at the outputs of a cascade beam-splitter are investigated for two single-mode squeezed vacuum state inputs. It is shown that the entanglement depends on the squeezing amplitudes of the input states and the reflection coefficients of the cascade beam-splitter, and the composite phase shift Δ between the cascade beam-splitter and the input fields has a great effect on the entanglement. In particular, the properties of the entanglement of a cascade beam-splitter differ from those of only one beam-splitter. A further method for manipulating entanglement by adjusting the parameters of the cascade beam-splitter and the input fields is proposed.

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Study of refractive index and thickness of TiO2/ormosil planar waveguide Wang Bao-Ling, Hu Li-Li 2004, 13 (11):  1887-1891.  doi: 10.1088/1009-1963/13/11/021 Abstract ( 0 )   PDF (185KB) ([an error occurred while processing this directive])   Hybrid titania/ormosil waveguide films have been prepared by sol-gel method at low thermal treatment temperature of 150℃. The influence of processing parameters including the molar ratios of Ti(OBu)_{4}/glycidoxypropyltrimethoxysilane (GLYMO) and H_{2}O/Ti(OBu)_{4} (expressed as R), especially aging of sol, on the refractive index and thickness of film was investigated. The optical properties of films were measured with Scanning Electron Microscope and m-line spectroscopy. The results indicate that the film thickness increases with the aging time of sol, but the variation of refractive index as a function of aging time of sol depends on the relative ratio of GLYMO to Ti-alkoxide. The relation between film thickness and corresponding sol viscosity is linear as the volume of GLYMO is 80% within the range of measured data.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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One-step alternating direction implicit FDTD algorithm Liu Shao-Bin, Liu San-Qiu 2004, 13 (11):  1892-1895.  doi: 10.1088/1009-1963/13/11/022 Abstract ( 0 )   PDF (186KB) ([an error occurred while processing this directive])   In this paper, a novel unconditionally stable alternating direction implicit finite-different time-domain method (ADI-FDTD) called the one-step ADI-FDTD method is presented, where the calculation for one discrete time step is performed using only one procedure, but not the original two sub-updating procedures. Consequently, the proposed one-step ADI-FDTD methods have consumed less computer memory and computation resources and have been faster than the conventional ADI-FDTD methods. We analytically and numerically verified that the new algorithm is unconditionally stable and free from the Courant condition.

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Influence of gas pressure on the pattern evolutions of dust clusters and fractals in a dusty plasma system Huang Feng, Ye Mao-Fu, Wang Long, Jiang Nan 2004, 13 (11):  1896-1901.  doi: 10.1088/1009-1963/13/11/023 Abstract ( 0 )   PDF (9527KB) ([an error occurred while processing this directive])   Dusty plasma has been produced through chemical reaction in a capacitively coupled radio frequency (rf) discharge system. Dust clusters with a few particles and dust fractals are observed. As gas pressure is increased, the suspended height of dust particles descends and the average interparticle distance decreases accordingly. The influence of gas pressure on the pattern evolutions is investigated. Dust clusters or fractals not only can evolve regularly on a horizontal plane, but also can evolve from a horizontal plane to a vertical line array. Under appropriate conditions, the evolutions are reversible. When the evolution is from a symmetrical pattern with a centre particle to another pattern, the centre particle will first show its unsteadiness.

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Radiation loss in a compound plasma system with high and low temperature regions Cheng Fa-Yin, Tomonori Takizuka, Nobuhiko Hayashi, Shi Bing-Ren 2004, 13 (11):  1902-1906.  doi: 10.1088/1009-1963/13/11/024 Abstract ( 0 )   PDF (194KB) ([an error occurred while processing this directive])   A code has been developed for calculating the non-coronal radiation of impurity in a compound plasma system which consists of high and low temperature regions. The radiation loss of impurity carbon in this system is calculated and analysed. The cooling rate in this system is smaller than that in a homogeneous plasma system due to the particle exchange between the two regions of the system. The volumetric radiation is much bigger in the low temperature region than in the high temperature region because of the relatively low temperature and high electron density, despite the much smaller volume.

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Discharge characteristics in plasma display cell at high frequency Ouyang Ji-Ting, Cao Jing, Callegari Thierry, Boeuf Jean-Pierre 2004, 13 (11):  1907-1912.  doi: 10.1088/1009-1963/13/11/025 Abstract ( 0 )   PDF (6117KB) ([an error occurred while processing this directive])   We present the experimental and simulation studies of the glow discharge plasma in a macroscopic AC plasma display panel cell operating at a high frequency. We find that at high frequencies the plasma from the previous pulse has a significant influence on the discharge properties. The xenon excitation efficiency is larger than that at low frequencies. The discharge mode and efficiency at high frequencies have been discussed in this paper.

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Controlling chaos by a delayed continuous feedback in a gas discharge plasma Huang Wei, Yu Chang-Xuan, Zheng Jian, Xie Jin-Lin, Liu Wan-Dong, Feng Dong-Lai, Ding Wei-Xing 2004, 13 (11):  1913-1917.  doi: 10.1088/1009-1963/13/11/026 Abstract ( 0 )   PDF (227KB) ([an error occurred while processing this directive])   Control of chaos by a delayed continuous feedback is studied experimentally in a gas discharge plasma. The power spectrum, the maximum of Lyapunov exponents and the time series of the signals all indicate that the period-1 unstable periodic orbit is controlled successfully. The dependence of the control on the delay time and the feedback gain as well as the strength of white noise is also investigated in detail. The experimental results show that the scaling index of the control versus the strength of white noise is 1.995, which is very close to that obtained from the simple logistic map.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Electrical conductivity of individual polypyrrole microtube Long Yun-Ze, Xiao Hong-Mei, Chen Zhao-Jia, Wan Mei-Xiang, Jin Ai-Zi, Gu Chang-Zhi 2004, 13 (11):  1918-1921.  doi: 10.1088/1009-1963/13/11/027 Abstract ( 0 )   PDF (10179KB) ([an error occurred while processing this directive])   Conducting microtubes (0.4－0.5μm in outer diameter) made of polypyrrole (PPy) doped with p-toluene sulfonic acid (PTSA) were synthesized by a self-assembly method. We report the electrical conductivity of an individual PPy microtube, on which a pair of platinum micro-leads was fabricated by focused ion beam deposition. The measured room-temperature conductivity of the individual PPy microtube was 0.29S/cm, which is comparable to that of template-synthesized PPy micro/nanotubes. The temperature dependence of conductivity of the individual microtube follows the three-dimensional variable-range hopping (3D VRH) model.

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Nanoscale carbon tubules deposited in anodic aluminium oxide template: a study of soft x-ray transmission Liu Li-Feng, Zhou Wei-Ya, Zhu Pei-Ping, Cui Ming-Qi, Zheng Lei, Zhu Jie, Zhao Yi-Dong, Song Li, Yan Xiao-Qin, Zhou Zhen-Ping, Yuan Hua-Jun, Ci Li-Jie, Liu Dong-Fang, Gao Yan, Wang Jian-Xiong, Wang Gang 2004, 13 (11):  1922-1926.  doi: 10.1088/1009-1963/13/11/028 Abstract ( 0 )   PDF (8054KB) ([an error occurred while processing this directive])   Well-aligned, catalyst-free nanoscale carbon tubules array was prepared by organic compound vapour deposition method using anodic aluminium oxide (AAO) as a template. The experiment of soft x-ray channelling in such carbon tubules array deposited in AAO template was performed at Beijing Synchrotron Radiation Facility. The transmission of x-rays in carbon tubules array with AAO template support was found even higher than that in bare AAO template at high-energy part of energy spectrum though the porous area of the former was smaller than that of the latter. A qualitative explanation is presented to interpret our results.

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Improved liquid－solid－gas interface deposition of nanoparticle thin films Diao Jia-Jie, Chen Guang-De, Qiu Fu-Sheng, Yan Guo-Jun 2004, 13 (11):  1927-1930.  doi: 10.1088/1009-1963/13/11/029 Abstract ( 0 )   PDF (10931KB) ([an error occurred while processing this directive])   A liquid－solid－gas interface deposition method to prepare nanoparticle thin films is presented in this paper. The nanoparticles in the part of suspension located close to the solid－liquid－gas interface grow on the substrate under the influence of interface force when the partially immersed substrate moves relatively to the suspension. By using statistical theory of the Brownian motion, growth equations for mono-component and multi-component nanoparticle thin films are obtained and some parameters for deposition process are discussed.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Study on defects associated with interstitial oxygen in PbWO4 crystal Liu Feng-Song, Gu Mu, Zhang Rui 2004, 13 (11):  1931-1935.  doi: 10.1088/1009-1963/13/11/030 Abstract ( 0 )   PDF (227KB) ([an error occurred while processing this directive])   The defects associated with interstitial oxygen in lead tungstate crystals (PbWO_{4}) are investigated by the relativistic self-consistent discrete variational embedded cluster method. The research work is focused on the density of states of interstitial oxygen defects and relational Frankel defects. The transition state method is used to calculate excitation energy of different electron orbits. Simulation results show that the existence of defects related to interstitial oxygen can diminish the bandwidth of the WO_{4}^{2-} group, and it might produce the green luminescence. Frankel defects associated with interstitial oxygen could result in the absorption at 420nm.

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Effects of barium on the nonlinear electrical characteristics and dielectric properties of SnO2-based varistors Wang Chun-Ming, Wang Jin-Feng, Wang Chun-Lei, Chen Hong-Cun, Su Wen-Bin, Zang Guo-Zhong, Qi Peng, Zhao Ming-Lei, Ming Bao-Quan 2004, 13 (11):  1936-1940.  doi: 10.1088/1009-1963/13/11/031 Abstract ( 0 )   PDF (202KB) ([an error occurred while processing this directive])   The effects of barium on electrical and dielectric properties of the SnO_2·Co_2O_3·Ta_2O_5 varistor system sintered at 1250℃ for 60min were investigated. It is found that barium significantly improves the nonlinear properties. The breakdown electrical field increases from 378.0 to 2834.5V/mm, relative dielectric constant (at 1kHz) falls from 1206 to 161 and the resistivity (at 1kHz) rises from 60.3 to 1146.5kΩ·cm with an increase of BaCO_3 concentration from 0mol% to 1.00mol%. The sample with 1.00mol% barium has the best nonlinear electrical property and the highest nonlinear coefficient (α=29.2). A modified defect barrier model is introduced to illustrate the grain-boundary barrier formation of barium-doped SnO_{2}-based varistors.

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Electronic structure of Yb/H－Si (111) interface Li Hong-Nian, Wang Xiao-Xiong, He Shao-Long, Zhang Han-Jie, Li Hai-Yang, Bao Shi-Ning 2004, 13 (11):  1941-1946.  doi: 10.1088/1009-1963/13/11/032 Abstract ( 0 )   PDF (244KB) ([an error occurred while processing this directive])   Photoemission spectra are measured for Yb covered surface of wet-chemically-etched H－Si (111). The results reveal that the lattice structure of the H－Si (111) surface is stable against the deposition of Yb atoms. X-ray photoemission spectra indicate the formation of a polarized (dipole) surface layer, with the silicon negatively charged. Ultraviolet photoemission spectra exhibit the semiconducting property of the interface below one monolayer coverage. Work function variation during the formation of the Yb/H－Si (111) interface is measured by the secondary-electron cutoff in the ultraviolet photoemission spectral line. The largest decrease of work function is ～1.65eV. The contributions of the dipole surface layer and the band bending to the work function change are determined to be ～1.15eV and ～0.5eV, respectively. The work function of metal Yb is determined to be ～2.80±0.05eV.

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Raman spectra and XPS studies of phase changes in Ge2Sb2Te5 films Liu Bo, Song Zhi-Tang, Zhang Ting, Feng Song-Lin, Chen Bomy 2004, 13 (11):  1947-1950.  doi: 10.1088/1009-1963/13/11/033 Abstract ( 0 )   PDF (175KB) ([an error occurred while processing this directive])   Ge_2Sb_2Te_5 film was deposited by RF magnetron sputtering on Si (100) substrate. The structure of amorphous and crystalline Ge_2Sb_2Te_5 thin films was investigated using XRD, Raman spectra and XPS. XRD measurements revealed the existence of two different crystalline phases, which has a FCC structure and a hexagonal structure, respectively. The broad peak in the Raman spectra of amorphous Ge_2Sb_2Te_5 film is due to the amorphous －Te－-Te－ stretching. As the annealing temperature increases, the broad peak separates into two peaks, which indicates that the heteropolar bond in GeTe_4 and the Sb－Sb bond are connected with four Te atoms, and other units such as (TeSb) Sb－Sb (Te_2) and (Sb_2) Sb－Sb (Te_2), where some of the four Te atoms in the above formula are replaced by Sb atoms, remain in crystalline Ge_2Sb_2Te_5 thin film. And from the results of Raman spectra and XPS, higher the annealing temperature, more Te atoms bond to Ge atoms and more Sb atoms substitute Te in (Te_2) Sb－Sb (Te_2).

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Green's function formalism in semi-infinite composites: an investigation of local field distribution Li Chen, Gu Ying, Dai Bing, Gong Qi-Huang 2004, 13 (11):  1951-1956.  doi: 10.1088/1009-1963/13/11/034 Abstract ( 0 )   PDF (843KB) ([an error occurred while processing this directive])   In the resonant composites, the formerly developed Green's function formalism (GFF) can be used to compute the local field distribution near resonance. In this paper, we extend the GFF in the infinite network to the semi-infinite networks by the method of image. Using the formalism, we investigate the local field distribution near resonance for the impurity clusters with admittance ε_0 embedded in one semi-infinite network with ε_1. With varying the admittance ε_2 of another semi-infinite network, we find that the local fields in the boundary experience great changes, especially at ε_2=-ε_1. The existence of the boundary enhances the localization of the fields within and around the metallic clusters. Therefore, the intensity of local field is influenced by the arrangement of impurity metallic bonds and its distance from the boundary.

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Resistivity－temperature characteristics of sol gel YBa2Cu3Oy samples synthesized in flowing oxygen atmosphere Zhou Zeng-Jun, Zhou Zuo-Wei, Zhou Liang-Yu, Lin Li, Li Xing-Guo, Feng Qing-Rong 2004, 13 (11):  1957-1961.  doi: 10.1088/1009-1963/13/11/035 Abstract ( 0 )   PDF (228KB) ([an error occurred while processing this directive])   The relationship of resistivity versus synthesizing temperature of sol gel YBa_2Cu_3O_y samples was studied when prepared under flowing oxygen conditions. A set of high-temperature ρ－T curves was obtained for the whole process. After the sample finished the test measuring, its resistivity was ρ_{300}=9.83×10^{-3 }Ω·cm at room temperature. The ρ－T curve also showed that the orthorhombic－tetragonal phase transformation of sol-gel YBa_2Cu_3O_y sample occurred at 581℃ for the sample in the rising temperature process, but at 613℃ in the cooling process, lower than that of the samples made by using the conventional powder metallurgy methods.

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Thermally-assisted tunnelling of magnetization in (Mn0.96Cr0.04)12-ac He Lun-Hua, Cao Hui-Bo, Wang Fang-Wei 2004, 13 (11):  1962-1964.  doi: 10.1088/1009-1963/13/11/036 Abstract ( 0 )   PDF (1303KB) ([an error occurred while processing this directive])   The thermally assisted resonant tunnelling in a single crystal (Mn_{0.96}Cr_{0.04})12-ac is studied in this paper. The obtained hysteresis loops at seven different temperatures between 1.8 and 3K show obvious dependence on temperature. The magnetization steps occur at specific field values of nH_R with H_R≈0.46T, which are approximately independent of the temperature. As the temperature decreases, the area enclosed in the hysteresis loops and the actual number n of the resonances increase, which provides clear evidence of thermally assisted resonant tunnelling in (Mn_{0.96}Cr_{0.04})12-ac.

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The anisotropy of Gd－Fe exchange interaction for Gd2Fe17 and Gd2Fe17H3 Yan Yu, Xu Shu-Wei, Jin Han-Min, Du Xiao-Bo, Su Feng 2004, 13 (11):  1965-1968.  doi: 10.1088/1009-1963/13/11/037 Abstract ( 0 )   PDF (159KB) ([an error occurred while processing this directive])   The magnetization curves along the crystal axes for Gd_2Fe_{17} and Gd_2Fe_{17}H_3 were analysed based on the single-ion model. If the Gd－Fe exchange interaction has been taken as isotropic as usual, the fitted values of magneto-crystalline anisotropy of the Fe sublattices in Gd_2Fe_{17} and Gd_2Fe_{17}H_3 would become unreasonably different from those of the corresponding Y or Lu compounds. It was shown that the large difference is caused by the neglect of the anisotropy of the Gd－Fe exchange interaction.

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Effects of underlayer materials and substrate temperatures on the structural and magnetic properties of Nd2Fe14B films Ma Yun-Gui, Yang Zheng, M. Matsumoto, A. Morisako, S. Takei 2004, 13 (11):  1969-1974.  doi: 10.1088/1009-1963/13/11/038 Abstract ( 0 )   PDF (5242KB) ([an error occurred while processing this directive])   Thin films of Nd_2Fe_{14}B were fabricated on heated glass substrates by dc magnetron sputtering. Different material underlayers (Ta, Mo, or W) were used to examine the underlayer influence on the structural and magnetic properties of the NdFeB films. Deposited on a Ta buffer layer at 420℃, the 300 nm thick NdFeB films were shown to be isotropic. But when the substrate temperature T_s was elevated to 520℃, the Nd_2Fe_{14}B crystallites of (00l) plane were epitaxially grown on Ta (110) underlayer. In contrast, Mo (110) buffer layer could not induce any preferential orientation in NdFeB film irrespective of the substrate temperature or film thickness. The W buffer layer was found to be most effective for the nucleation of Nd_2Fe_{14}B crystallites with c-axis alignment perpendicular to the film plane when T_s<490℃. But at T_s=490℃ the magnetic layer became isotropic. The maximum coercivity obtained was about 995 kA/m for the 100nm film deposited on W underlayer at 490℃. These variations were tentatively explained in terms of the lattice misfit between the underlayer and the magnetic layer, combined with the considerations of underlayer morphologies.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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A simple capacitor model for radio emission associated with earthquakes Ares de Parga Gonzalo, Ramírez-Rojas Alejandro 2004, 13 (11):  1975-1976.  doi: 10.1088/1009-1963/13/11/039 Abstract ( 0 )   PDF (132KB) ([an error occurred while processing this directive])   In this brief report we propose a simple model based on the properties of an electric capacitor under short-circuit conditions as a possible mechanism of radio emissions associated with earthquakes. This model can be considered as complementary to other models concerning the same problem.