Application of wavelet transform in-ray spectra analysis

The frequency distribution of different ingredients in-ray spectra,e.g.,photo-peak,fluctuations of counts and Compton region,is separately analyzed.After wavelet transform of-ray spectra,the wavelet coefficients of a photo-peak increase with transforming scales and these coefficients show direct proportion with intensity of peak at determinate scale.A novel algorithm based on wavelet transform is proposed and studied.The results indicate that most of the photo-peaks in multi-spectra can be determined accurately,the-rays energy and intensity of the peak can also be determined.This method has the prospect of being applied in on-line multi-spectra analysis in such fields as radioprotection and nuclear safety monitoring.     

Optical bistability based on surface plasmon coupled between two noble metal films involving Kerr materials

We successfully investigate an optical bistability phenomenon in a layered structure consisting of Kretschmann configuration involving the Kerr-type nonlinear and the silver film. Pure theoretical approaches are employed to investigate that the surface plasmon could easily be coupled and both the reflection and transmission curves versus the incident intensity forms optical bistability. The transmission curves are greatly influenced by the thickness of the second silver film. These results may be useful for designing novel surface plasmon-based optical devices and will be essential for future classical and quantum information processes.     

THERMODYNAMIC ANALYSIS AND FORMATION ENTHALPY CALCULATION OF OXYGEN VACANCY DEFECT IN DOPED LITHIUM NIOBATE CRYSTALS

Based on the thermodynamic analysis of oxygen vacancy defects in lithium niobate (LiNbO₃ (LN)) and the data of thermogravimetric experiment, the formation enthalpies of congruent and several rare-earth (RE) doped LN crystals have been calculated. It was found that the formation enthalpy of oxygen vacancies can be decreased evidently by doping with valence-changeable RE ions. The experimental results were discussed and a new reduction process for photorefractive LN crystals at a relatively low temperature was proposed, and the reduction-treated crystals showed good effect in practical use.     

宏观放电参数对快原子态氮(N+,Nf)的影响

采用氮直流辉光放电等离子体中快电子和重粒子(N₂⁺,N⁺,N_f)混合的蒙特卡罗方法,模拟研究了快原子态粒子(N⁺,N_f)的产生率及轰击阴极的能量分布随宏观放电参数(P,V)的变化规律.结果表明,存在一最佳放电条件,使阴极壁处粒子(N⁺,N_f)的粒子数密度大且能量高;当电压大于800V时,轰击阴极的活性粒子(N⁺,N_f),主要由N₂⁺-N₂离解过程产生,电压小于300V时,主要由e^--N₂离解过程产生,模拟结果与实验结果相符合.     

GEOMETRIC AND ELECTRONIC STRUCTURES OF Ti8C12 CLUSTER

The electronic structure of Ti₈C₁₂ clusters with three possible geometric structures suggested in the literature is studied using the discrete-variational local-density-functional method. The results show that the ground states of the clusters are all degenerate, which means further Jahn-Teller distortions for the geometric structures of clusters. The results also indicate that the distorted dodecahedral Ti₈C₁₂ cluster, which is proposed by Guo et al. and optimized by the first principle calculations, is the most stable one among the clusters we considered and its electronic structure can explain the experimental observations. In this cluster, there is a strong pd bonding between Ti and C atoms, and the density of states at the Fermi energy is high.     

A DOUBLE-TEMPERATURE-GRADIENT TECHNIQUE FOR THE GROWTH OF PURE C60 SINGLE CRYSTALS FROM THE VAPOR PHASE

Pure C₆₀ single crystals were grown by a sublimation-condensation method in an evacuated dosed quartz tube situated in a double-temperature-gradient furnace. Large C₆₀ single crystals, up to a size of 0.6 mm×1.0 mm×2.0 mm with quite smooth and shiny faces, were obtained. X-ray diffraction, electron diffraction and X-ray morphology were carried out and showed that the quality of large C₆₀ single crystals grown by the double-temperature-gradient technique is excellent. In this paper the experimental results of the growth of large C₆₀ single crystals are reported and the morphological and structural characterizations are discussed in detail.     

PROPERTIES OF TEMPERATURE DEPENDENCE OF THRESHOLD IN PURE AND IMPUHITY-DOPED BLUE BRONZES

Temperature dependence of the threshold of pure and impurity-doped blue bronzes has been studied. It is found that for pare blue bronzes the threshold field near 100K has an anomalous peak, but for impurity-doped samples no anomaly is observed in the range of liquid nitrogen temperature, and the value of the threshold field gradu-ally increases with the decrease of temperature. The results show that in the high-quality pure blue bronzes, there may exist an incommensurate to quasi-commensurate transition near 100K. But for the impurity-doped or "dirty" pure samples, such an incommensurate to quasi-commensurate transition near 100K can be extensively re-strained by impurities or defects, which leads to a pure incommensurate CDW in a wide temperature range.     

SYSTEMATIC STUDY OF POLARIZATION OF TWO-PHOTON ABSORPTION IN SYMMETRY ASSIGNMENTS

In this paper, we have systematically analyzed the degenerate and nondegenerate two-photon polarization ratios of various point groups. We present the maximum of symmetry assignments of two-photon transition with the combination of degenerate and nondegenerate two-photon absorption. These results provide the theoretical basis for the experimental assignments.     

“PPAS” X-RAY ABSORPTION SPECTROSCOPY IN LASER-PRODUCED ALUMINUM PLASMA

We have developed and successfully demonstrated the "point projection absorption spectroscopy (hereafter abbreviated to PPAS)" technique to record keV X-ray absorption spectra in the coronal region of laser produced aluminum plasma which provides spatial information in the corona. Absorption spectrum of the Al Ⅻ 1s²-1s2p resonant line for time delays up to 250, 500 and 750 ps after the peak of the incident laser pulse have been observed. Analysis of an absorption spectrum should allow a high spatial resolution (< 25μm) history of the absorbing ion population density to be determined. The 1-D hydro-code JB19 has been used to simulate the experiment and the predictions are compared to the observations. Such comparison can be useful in validating parts of the codes used for gain prediction on recombination X-ray laser transitions.     

无规分形衬底上银膜逾渗系统的交流特性

通过对沉积在具有无规自相似结构的α-Al₂O₃断裂面上的银薄膜逾渗系统交流特性的测量,证明了在逾渗阈值p_c附近这一系统的交流电导率和介电常数满足指数临界规律和普适标度关系。还给出了这种逾渗系统的电容与直流电阻的关系,并对其意义作了讨论。 关键词：