Study of electronic structures and absorption bands of BaMgF4 crystal with F colour centre

The electronic structures of BaMgF 4 crystals containing an F colour centre are studied within the framework of the fully relativistic self-consistent Direc-Slater theory,using a numerically discrete variational (DV-Xα) method. It is concluded from the calculated results that the energy levels of the F colour centre are located in the forbidden band. The optical transition energy from the ground state to the excited state for the F colour centre is about 5.12 eV,which corresponds to the 242-nm absorption band. These calculated results can explain the origin of the absorption bands.     

Grain size reduction of copper subjected to repetitive uniaxial compression combined with accumulative fold

This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicronto nanocrystalline copper starting with a coarse grained counterpart. Grain size reduction and microstrain variations of the high purity copper samples after different passes of compression and fold are investigated by scanning electron microscope and x-ray diffraction (XRD), respectively. Our results show that the average grain size of samples decreases from about 830 nm to 127 nm as the number of compression passes increases to 30. Microstrain in the compressed sample is found to increase for the first 20 passes, but to decrease at the last 10 passes. The variations of compressive yield strength and the shift of XRD peaks to larger diffraction angles are observed in the squeezed sample. Our experimental results demonstrate that the repetitive uniaxial compression combined with accumulative fold is an effective method to prepare bulk nanocrystalline metallic materials, in particular for soft metals such as Cu, Al and Pb.     

boldmath Study of electronic structures and absorption bands of BaMgF4 crystal with F colour centre

The electronic structures of BaMgF₄ crystals containing an F colour centre are studied within the framework of the fully relativistic self-consistent Direc-Slater theory, using a numerically discrete variational (DV-Xα) method. It is concluded from the calculated results that the energy levels of the F colour centre are located in the forbidden band. The optical transition energy from the ground state to the excited state for the F colour centre is about 5.12 eV, which corresponds to the 242-nm absorption band. These calculated results can explain the origin of the absorption bands.     

Optical Interference Effects by Metal Cathode in Organic Light-Emitting Diodes

The dependence of light intensities of organic light-emitting diodes (OLEDs) on the distance of emission zone to metal cathode is investigated numerically. The investigation is based on the half-space optical model that accounts for optical interference effects of metal cathode. We find that light intensities of OLEDs are functions of the distance of emission zone from the metal cathode because of the effect of interference of the metal cathode.This interference leads to an optimal location of emission zone in OLEDs for the maximum of light intensities.Optimal locations of emission zone are numerically shown in various emitting colour OLEDs with different metalcathodes and these results are expected to give insight into the preparation of high efficiency full colour or white light OLEDs.     

Seasonal variability of cloud optical depth over northwestern China derived from CERES/MODIS satellite measurements

The seasonal variability of cloud optical depth over northwestern China derived from Clouds and the Earth's Radiant Energy System(CERES)Single Scanner Footprint(SSF)Aqua Moderate Resolution Imaging Spectroradiometer(MODIS)Edition 1B data from July 2002 to June 2004 is presented.The regions of interest are those with Asia monsoon influence,the Tianshan and Qilian Mountains,and the Taklimakan Desert.The results show that the instantaneous measurements presented here are much higher than the previous results derived from International Satellite Cloud Climatology Project(ISCCP) D2 monthly mean data.Generally the measurements of cloud optical depth are the highest in summer and the lowest in winter,however,Taklimakan Desert has the lowest measurements in autumn.The regional variation is quite significant over northwestern China.     

Linear and nonlinear optical properties of Au/SiO2 nanocomposite prepared by P123

Mesoporous silica thin films loaded with gold nanoparticles are synthesized in the presence of EO20PO70EO20（P123）.Transmission electron microscope images show that the matrix of the nanocomposite is an ordered porous structure with a two-dimensional hexagonal phase.The wide-angle X-ray diffraction pattern implies that the nanocomposite contains gold crystals.These metallic nanoparticleembedded solid thin films show some linear and nonlinear optical properties due to their special structure and composition.Gold nanoparticles bring about surface plasmon resonance,and an absorption peak stemming from this effect has been observed.The linear absorption property is analyzed by a quantum mechanism,and the results show that it is influenced by the size and volume fraction of gold nanoparticles. Furthermore,it shows an obviously clear nonlinear optical property measured by the z-scan technique.The magnitude of the nonlinear refractive index of the nanocomposite is estimated to be about 10？ 10 cm 2 /W.     

Seasonal variability of cloud optical depth over northwestern China derived from CERES/MODIS satellite measurements

The seasonal variability of cloud optical depth over northwestern China derived from Clouds and the Earth＇s Radiant Energy System （CERES） Single Scanner Footprint （SSF） Aqua Moderate Resolution Imaging Spectroradiometer （MODIS） Edition IB data from July 2002 to June 2004 is presented. The regions of interest are those with Asia monsoon influence, the Tianshan and Qilian Mountains, and the Taklimakan Desert. The results show that the instantaneous measurements presented here are much higher than the previous results derived from International Satellite Cloud Climatology Project （ISCCP） D2 monthly mean data. Generally the measurements of cloud optical depth are the highest in summer and the lowest in winter, however, Taklimakan Desert has the lowest measurements in autumn. The regional variation is quite significant over northwestern China.     

Time-resolved energy spectrum measurement of a linear induction accelerator with the magnetic analyzer

We recently set up a time-resolved optical beam diagnostic system. Using this system, we measured the high current electron beam energy in the accelerator under construction. This paper introduces the principle of the diagnostic system, describes the setup, and shows the results. A bending beam line was designed using an existing magnetic analyzer with a 300 mm-bending radius and a 60° bending angle at hard-edge approximation. Calculations show that the magnitude of the beam energy is about 18 MeV, and the energy spread is within 2%. Our results agree well with the initial estimates deduced from the diode voltage approach.     

Influence of Strain-Reducing Layer on Strain Distribution of Self-Organized InAs/GaAs Quantum Dot and Redshift of Photoluminescence Wavelength

A systematic investigation about the strain distributions around the InAs/GaAs quantum dots using the finite element method is presented. A special attention is paid to influence of an Ino.2 Gao.sAs strain reducing layer. The numerical results show that the horizontal- and vertical-strain components and the biaz~ial strain are reinforced in the InAs quantum dot due to the strain-reducing layer. However, the hydrostatic strain in the quantum dot is reduced. In the framework of eight-band k · p theory, we study the band edge modifications due to the presence of a strain reducing layer. The results demonstrate that the strain reducing layer yields the decreasing band gap, i.e., the redshift phenomenon is observed in experiments. Our calculated results show that degree of the redshift will increase with the increasing thickness of the strain-reducing layer. The calculated results can explain the experimental results in the literature, and further confirm that the long wavelength emission used for optical fibre communication is realizable by adjusting the dependent parameters. However, based on the calculated electronic and heavy-hole wave function distributions, we find that the intensity of photoluminescence will exhibits some variations with the increasing thickness of the strain-reducing layer.     

Determination of bulk viscosity of liquid water via pulse duration measurements in stimulated Brillouin scattering

We present a method by which to determine the bulk viscosity of water from pulse duration measurements of stimulated Brillouin scattering （SBS）. Beginning from a common model of Brillouin scattering, the bulk viscosity is shown to play an important role in Brillouin linewidth determination. Pulse durations of SBS back-reflected optical pulses are measured over the temperature range of 5-40℃. SBS linewidths are de- termined via Fourier transformation of the time-domain results, and the bulk viscosity of water is measured and derived from the obtained values. Our results show that the proposed method for measurement of pulse durations is an effective approach for determining bulk viscosity. The method can be easily extended to determine bulk viscosities of other Newtonian liquids.     

H0323+022天体的光变特性和黑洞质量研究

从大量文献资料中，收集了BL Lac天体H0323+022光学V波段的大量观测数据，获得了H0323+ 022从1982年至2003年的长期光变曲线.给出了从2000年至2003年，使用云南天文台1米望远 镜和上海天文台的156米望远镜，对H0323+022进行光学波段近4年的监测数据，观测发现 了H0323+022在光学R波段有7min的短时标光变.色指数B—V与V波段的星等值有较强的相关性 ，对H0323+022 CCD测光的结果与Bai（1998）观测的结果ΔR=063 ΔI=081是 一致的.由观测所发现的短时标光变，推算出了BL Lac天体H0323+022的中心黑洞质量和辐射 区域. 关键词： BL Lac天体 光变曲线 短时标光变 辐射区域 中心黑洞质量     

Observation of active galactic nuclei on the GT-48 CrAO γ-ray telescope in 2004

The results of observations of active galactic nuclei on the γ-ray telescope GT-48 (Crimean Astrophysical Observatory) in 2004 are reported. Fluxes of very-high-energy γ rays (E ≥ 10¹² eV) from the 3C 66A, Mkn 421, Mkn 501, and 1H 1426 objects have been recorded at a level exceeding 4σ. The upper values of γ-ray fluxes for the active nuclei of the 1ES 1959 and BL Lac galactics are presented. Analysis of the data on the 3C66A object confirmed the existence of γ-ray fluxes from this source. This object was previously discovered in Crimea.     

Coordinated observation of the massive system 4U1700+24=HD154791

Summary We report results from multifrequency observations of the X-ray source 4U1700+24/HD154791. This source was observed simultaneously with the EXOSAT and IUE satellites on March 25, 1985, and it is continuously monitored in the optical band at the Bologna Astronomical Observatory since July 1984. Our observations show source features which are different from those measured during previous observations. The X-ray spectrum is significantly softer than in previous measurements, and much more absorbed; high excitation lines in UV spectra (C IV and N V) have disappeared; the optical spectrum, despite a fairly good photometric stability of the M giant HD154791 in V and B bands also shows differences with respect to previous observations. We discuss our results in the framework of both a binary model and a coronal model. We point out that our observations strengthen the hypothesis that the X-ray emission is due to mass accretion onto a compact object orbiting around the M giant star HD154791. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Very high energy γ rays from close active galactic nuclei Mkn 421, Mkn 501, and NGC 1275

The results of observations of two types of metagalactic sources, BLLacs Mkn 421 (z = 0.031) and Mkn 501 (z = 0.034) and the Seyfert galaxy NGC 1275 (z = 0.017) are reported. These observations have been carried out with the SHALON mirror telescope (Lebedev Institute of Physics, Russian Academy of Sciences). The γ-ray fluxes (with energies E > 0.8 TeV) from Mkn 421 and Mkn 501, averaged over the entire observation period, were estimated to be (0.63 ± 0.14) × 10^?12 and (0.86 ± 0.13) × 10^?12 cm^?2 s^?1, respectively. The flux from the source NGC 1275 was (0.78 ± 0.13) × 10^?12 cm^?2 s^?1. The energy spectra of γ rays and images of the sources are reported.     

Mkn 501 X射线和TeV射线准周期震荡的可能机制

我们提出了对流占主导的吸积流（ADAF）盘的辐射线是Mkn 501中从X射线到Tevγ射线的源光子；而且此盘的不稳定性可以解释Mkn 501中在X射线和Tevγ射线光变曲线23天的准周期光变。在这个模型中,光学到X射线辐射进入喷流，后由于喷流内相对论电子的作用而转化成高能光子。在这个过程中，发生在ADAF盘中的不稳定性导致源光子的准周期变化，从而导致了X射线和γ射线的变化。     

Hole-interface optical phonon relaxation rates with valence band-mixing effects

We theoretically investigate the hole-interface optical phonon scattering rates for a InGaAs-AlGaAs quantum well structure, taking into account the valence-band mixing. The dispersion relation and the electrostatic potentials for interface optical phonon modes are obtained based on the macroscopic dielectric continuum model. For the hole dispersion relation, the Luttinger-Kohn Hamiltonian is used. The hole-interface optical phonon interaction is evaluated by the Fermi's golden rule taking into account the Bloch overlap factor.Our results show that the hole-interface phonon scattering rates within the parabolic band approximation are different from those including valence band mixing effects. Especially, in the low energy region, the hole-interface phonon scattering rates within the parabolic band approximation are overestimated very significantly.     

Tachyonic cascade spectra of supernova remnants and TeV blazars

The superluminal spectral densities of relativistic electrons in uniform motion are derived, semiclassically and in second quantization. The effect of electron spin on the tachyonic radiation field, a Proca field with negative mass-square, is studied. There is a longitudinally polarized spectral component due to the negative mass-square of the tachyonic quanta. The radiation densities are averaged with electron distributions, and high- and low-temperature expansions are obtained. Spectral fits to the γ-ray spectra of the Crab Nebula, the supernova remnant RX J1713.7–3946, and the BL Lacertae objects H1426+428, 1ES 1959+650, Mkn 501, and Mkn 421 are performed. In contrast to TeV photons, the extragalactic tachyon flux is not attenuated by interaction with the background light; there is no absorption of tachyonic γ-rays, as tachyons do not interact with infrared photons. The curvature of the TeV spectra in double-logarithmic plots is caused by the Boltzmann factor of the electron densities generating the tachyon flux. The extended spectral plateau in the GeV band, visible in the spectral maps of the two Galactic supernova remnants as well as in the flare spectra of the BL Lacertae objects, is reproduced by the tachyonic radiation densities. Estimates of the electron populations in the supernova remnants and active galactic nuclei are inferred from the spectral fits, such as power-law indices, electron temperatures, and source counts. Upper bounds on the Lorentz factors in the source populations are derived and compared to the breaks in the high-energy cosmic-ray spectrum. PACS  95.30.Gv; 11.10.Lm; 98.70.Sa; 03.50.Kk     

基于聚合经验模态分解方法的OJ 287 射电流量变化周期分析

BL Lac 天体OJ 287 是一个重要的Blazar天体, 光变具有准周期特点. 本文从密歇根大学射电天文台数据库收集了OJ 287射电波段4.8, 8.0和 14.5 GHz超过30年时间的观测数据. 由于天文观测资料的复杂性, 一些传统寻找周期的方法不是太理想. 近几年迅速发展起来的聚合经验模态分解(EEMD) 特别适合于具有非线性和非平稳动态变化特性的Blazar天体光变规律的研究. 运用EEMD方法对OJ 287 的3个射电波段流量分别进行多时间尺度分解, 各获得6个代表不同时间尺度局部特征信息的本征模态函数分量和一个趋势项. 研究结果表明: 4.8 GHz射电流量变化的主要周期是18.9, 11.9, 5.7 和2.4年; 8.0 GHz 的主要周期是12.2, 5.2和2.4 年; 14.5 GHz的主要周期是21.8, 12.0, 4.3和 2.4 年. 尽管3个波段流量变化主要周期大小有一定的差别, 但是存在着近似相同的变化周期12.0 和2.4年, 说明这3个波段可能来源于相同的辐射机制, 也证实了OJ 287 射电波段和光学波段具有相同的长光变周期12.0 年. 这些结论表明: EEMD 作为一种全新的非线性、非平稳信号处理方法, 可以更精确地提取Blazar天体中不同光变周期的分量. 关键词： OJ 287 光变周期 聚合经验模态分解     

A defect model for the optical and EPR activity of the T-center in yttrium-stabilized zirconia

Abstract

Direct quantitative correlations have been recently observed between the T-centre EPR signal and an optical absorption band at 370 nm, in X-irradiated YSZ, suggesting that the colour centre and the paramagnetic centre might be the same entity. In order to confirm this hypothesis, theoretical modeling was undertaken, where by appropriate refinement the known electronic structure of the T-centre is shown to be compatible with an optical transition, having an oscillator strength of the correct magnitude.