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81.
Within the collective coordinate approach to chiral soliton models we suggest that breaking of SU(3) flavor symmetry mainly resides in the baryon wave-functions while the charge operators maintain a symmetric structure. Sizable symmetry breaking in the wave-functions is required to reproduce the observed spacing in the spectrum of the
baryons. The matrix elements of the flavor symmetric charge operators nevertheless yield gA/gV ratios for hyperon beta-decay which agree with the empirical data approximately as well as the successful F&D parameterization of the Cabibbo scheme. Demanding the strangeness component in the nucleon to vanish in the two flavor limit of the model, determines the structure of the singlet axial charge operator and yields the various quark flavor components of the axial charge of the Λ-hyperon. The suggested picture gains support from calculations in a realistic model using pion and vector meson degrees of freedom to build up the soliton. 相似文献
82.
Rodrigo Santos Rui M. Almeida Lothar Wondraczek 《Journal of solid state chemistry》2010,183(1):128-2701
Niobium germanosilicate glasses are potential candidates for the fabrication of transparent glass ceramics with interesting non-linear optical properties. A series of glasses in the (Ge,Si)O2-Nb2O5-K2O system were prepared by melting and casting and their characteristic temperatures were determined by differential thermal analysis. Progressive replacement of GeO2 by SiO2 improved the thermal stability of the glasses. Depending on the composition and the crystallization heat-treatment, different nanocrystalline phases—KNbSi2O7, K3Nb3Si2O13 and K3.8Nb5Ge3O20.4 could be obtained. The identification and characterization of these phases were performed by X-ray diffraction and Raman spectroscopy.The 40 GeO2-10 SiO2-25 Nb2O5-25 K2O (mol%) composition presented the higher ability for volume crystallization and its nucleation temperature was determined by the Marotta's method. An activation energy for crystal growth of ∼529 kJ/mol and a nucleation rate of 9.7×1018 m−3 s−1 was obtained, for this composition. Transparent glass ceramics with a crystalline volume fraction of ∼57% were obtained after a 2 h heat-treatment at the nucleation temperature, with crystallite sizes of ∼20 nm as determined by transmission electron microscopy. 相似文献
83.
In this paper, high-luminance yellow-emitting Y3Al5O12:Ce3+ phosphor (YAG:Ce) microparticles were prepared in a solid flame using a 1.425Y2O3+2.5Al2O3+0.15CeO2+k(KClO3+urea)+mNH4F precursor mixture (here k is the number of moles of the KClO3+urea red-ox mixture, and m is the number of moles of NH4F). The self-sustaining combustion process for the entire reaction sample was provided by the heat generated from the KClO3+urea mixture. Parametric studies demonstrated that the maximum temperature in the combustion wave varied from 885 to 1200 °C for k=2.0-3.0 mole and m=0-1.5 mole. X-ray analysis results showed that the product obtained in the solid flame consisted of Y3Al5O12:Ce3+ and KCl phases. Therefore, after dissolving potassium chloride in distillated water, pure-phase YAG:Ce phosphor powder was obtained. The as-prepared YAG:Ce phosphor particles had diameters of 10-25 μm and good dispersity and exhibited luminescence properties comparable to those of YAG:Ce phosphor powders prepared by conventional high-temperature processing. 相似文献
84.
Thermoluminescence properties of lanthanum aluminum oxide (LaAlO3) crystals doped with optically active rare earth ions have been investigated for ultraviolet dosimetry purposes. Single crystals co-doped with 5.0 at.% of Ce3+ and 1.0 at.% of Dy3+ ions have two thermoluminescent (TL) peaks at 151 °C and 213 °C which can be sensitized after 1 h of UV exposure. The material shows very high TL output and linear response for UV spectral irradiance ranging from 0.04 to 1.20 mJ cm−2, that corresponds to 10 times the TL response of the Al2O3:C oxides. From 0.62 to 148.0 mJ cm−2 the dependence is linear with the logarithm of the spectral irradiance. The investigation demonstrates that LaAlO3:Ce,Dy crystals are very attractive to be investigated as UV dosimeters. 相似文献
85.
文章用提拉法生长出Li6Gd(BO3)3:Ce晶体,并对其光谱性能与发光过程进行了探索. 借助于真空紫外-紫外透过光谱测试,发现晶体的透过光谱中存在Ce3+离子和Gd3+的特征吸收峰,同时还存在与Ce4+离子相关的电荷迁移带. 对晶体的真空紫外-紫外激发发射光谱进行研究发现,在晶体存在着Ce3+离子的5d→4f辐射跃迁发光与Gd3+离子的4f→4f辐射跃迁发光,而且存在着Gd3+→Ce3+之间的能量传递. 对Li6Gd(BO3)3:Ce晶体的X射线与γ射线激发发射光谱研究可知,晶体在高能射线激发下的闪烁光主要是Ce3+离子的发光.
关键词:
6Gd(BO3)3:Ce晶体')" href="#">Li6Gd(BO3)3:Ce晶体
真空紫外-紫外透过光谱
真空紫外-紫外激发发射光谱
能量传递 相似文献
86.
SHI Wensheng CHEN Zhenghao LIU Ningning L Huibin ZHOU Yueliang CUI Dafu YANG Guozhen 《中国科学A辑(英文版)》2000,43(5)
Pulsed laser ablation epitaxial Strancky-Krastanow growth of self-organized complex oxide Ce:BaTiO3 quantum dots on MgO(100) substrates is demonstrated.Atomic force microscopy and X-ray diffraction are used to observe the structure and the growth process of the self-organized complex oxide quantum dots.The average dimension,height,and the density of self-organized complex oxide Ce:BaTiO3 quantum dots are given.The nonlinear refractive indexes of the wetting layer and the self-organized ordered quantum dots are determined by the single beam Z-scan method.The mechanisms of the nonlinear effect enhancement for these low-dimensional structure are discussed. 相似文献
87.
Here we comment on the thermodynamic inconsistency problem and the reformulation of statistical mechanics of widely studied quasiparticle models of quark–gluon plasma. Their starting relation, the expression for pressure itself is a wrong choice and lead to thermodynamic inconsistency and the requirements of the reformulation of statistical mechanics. We propose a new approach to the problem using the standard statistical mechanics and is thermodynamically consistent. We also show that the other quasiparticle models may be obtained from our general formalism as a special case under certain restrictive condition. Further, as an example, we have applied our model to explain the nonideal behaviour of gluon plasma and obtained a remarkable good fit to the lattice results by adjusting just a single parameter. 相似文献
88.
以NH4Cl作助溶剂,碳还原硫酸钙的方法合成了CaS:Ce。在紫外光激发下,CaS:Ce中存在着Ce^3+的^2D-^2F5/2(500nm)和^2D-^2F7/2(550nm)跃迁发射,但在蓝色光激发下,只有波峰为532nm半宽度为92nm的宽带发射。当Ce^3+的浓度为0.075mol%时,^2D-^2F5/2跃迁发射强度与^2D-^2F7/2跃迁发射强度相等,而532nm发射猝灭。 相似文献
89.
90.
Hongtao Sun Zhongchao Duan Gang Zhou Junjie Zhang Zhonghong Jiang 《Solid State Communications》2005,135(3):174-178
Tm3+-doped oxide-chloride germanate and tellurite glasses have been synthesized by conventional melting method. Intense up-conversion luminescence emissions were simultaneously observed at room temperature in these glasses. The possible up-conversion mechanisms are discussed and estimated. However, in these Tm3+-doped glasses, tellurite glass showed weaker up-conversion emissions than germanate glass, which is inconsistent with the prediction from the difference of maximum phonon energy between tellurite and germanate glasses. In this paper, Raman spectroscopy was employed to investigate the origin of the difference in up-conversion luminescence in the two glasses. Our results confirm that, besides the maximum phonon energy, the phonon density of host glasses is also an important factor in determining the up-conversion efficiency. 相似文献