Study of crystal structure and phase transition studies in perovskite-type oxides using powder-diffraction techniques and symmetry-mode analysis.

251 p.

铒离子浓度对掺Er^3＋碲酸盐玻璃的Judd-Ofelt理论参数的影响

制备了四种不同铒离子掺杂浓度的碲酸盐玻璃，通过测定吸收光谱计算了吸收谱线的振子强度，根据Judd-Ofelt理论计算了不同浓度下Er^3＋离子发光光谱的强度参数Ω（i=2，4，6），计算了自发辐射电偶和磁偶跃迁概率、辐射寿命、荧光分支比等参数，讨论了Er^3＋离子浓度变化对以上这些参数的影响。测试了Er^3＋：^4I13／2→^4I15／2跃迁对应的荧光光谱和Er^3＋：^4I13／2能级荧光寿命。最后应用McCumber理论计算了玻璃中Er^3＋：^4I13／2→^4I15／2跃迁对应的受激发射截面大小

掺铒碲酸盐玻璃的热力学稳定性和光谱性质的研究

分析了掺Er^3+碲酸盐玻璃的热力学稳定性能，研究了掺Er^3+碲酸盐玻璃的吸收和荧光光谱性质；应用Judd-Ofelt理论计算了碲酸盐玻璃中Er^3+离子的强度参数Ω(Ω2=4．79×10^-20cm^2,Ω4=1．52×10^-20cm^2，Ω6=0．66×10^-20cm^2)，计算了离子的自发跃迁几率，荧光分支比；应用McCumber理论计算了Er^3+的受激发射截面(σe=10．40×10^-21cm^2)、Er^3+离子^4I13／2→^4I15／2发射谱的荧光半高宽(FWHM=65．5nm)

一种新型掺铒碲酸盐玻璃的光谱性质研究

研究了一种新型掺Er^3+碲酸盐玻璃的光谱性质；应用Judd-Ofelt理论计算了碲酸盐玻璃中Er^3+离子的强度参数Ω(Ω2=4．79×10^-20cm^2，Ω4=1．52×10^-20cm^2，Ω6=0．66×10^-20cm^2)，计算了离子的自发跃迁概率，荧光分支比；应用McCumber理论计算了Er^3+的受激发射截面(σe=10．40×10^-21cm^2)，Er^3+离子^4I13/2→^4I15/2发射谱的荧光半高宽(FWHM=65．5nm)及各能级的荧光寿命(^4I13/2能级为τrad

Stability against crystallization and spectroscopic properties of Tm3+ doped fluorophosphate glasses

Fluorophosphate glasses with various content of Al(PO3)(3) were prepared. With the increment of Al(PO3)(3) content, density decreases while refractive index increases, and transition temperature, crystallization peak temperature and melt temperature increase which were suggested by differential scanning calorimetry. These glasses exhibit the best stability against crystallization with 7-9 mol'Yo Al(PO3)(3) content. Normalized Raman spectra were used to analyze structure and phonon state. The increment of Al(PO3)(3) content does not affect phonon energy but results in the augment of phonon density. Absorption spectra were measured. H-3(6) -> F-3(4) transition exhibits absorption at L band of the third communication window. Compared with the energy of Tm3+ excited states in other glass system, F-3(4) energy of Tm3+ in these glasses is considerable higher and H-3(4) energy is considerable lower, and it can be predicted that emission band of H-3(4) -> F-3(4) transition is close to the amplified band of gain-shift Tm3+ doped fiber amplifier. Analyses of Judd-Ofelt theory suggest when Al(PO3)(3) content is no more than 7 mol%, Judd-Ofelt parameters Omega(t) and the lifetime of H-3(4) energy level of TM3+ vary little with the increment of Al(PO3)(3) content, and when Al(PO3)(3) content is more than 7 mol%, Omega(2) and Omega(6) increase and radiative lifetime of H-3(4) energy level of Tm3+ drops sharply with the increment of Al(PO3)(3) content. (c) 2006 Elsevier B.V. All rights reserved.

Investigation on nonradiative decay of the (Er3+I13/2)-I-4 -> I-4(15/2) transition in different tellurite glass matrix

Three kinds of Er3+-doped tellurite glasses with different hydroxyl groups are prepared by the conventional melt-quenching method. Infrared spectra are measured to estimate the exact content of OH- groups in samples. The maximum phonon energy in glasses are obtained by measuring the Raman scattering spectra. The strength parameters Omega(t) (t = 2, 4, 6) for all the samples are calculated and compared. The nonradiative decay rate of the Er3+ I-4(13/2) -> I-4(15/2) transition are calculated for the glass samples with different phonon energy and OH- group contents. Finally, the effect of OH- groups on fluorescence decay rate of Er3+ is analysed, the constant KOH-Er Of TWN, TZPL and TZL glasses are calculated to be 9.2 x 10(-19) cm(4)s(-1), 5.9 x 10(-19) cm(4)s(-1), and 3.5 x 10(-19) cm(4)s(-1), respectively.

European Newspapers’ Digital Transition: New Products and New Audiences

The adaptation of traditional newspapers to new digital media and its interface, far from being a mere technical transformation, has contributed to a gradual change in the media themselves and their audiences. With a sample including the top general information pay newspaper in each of the 28 countries of the European Union, this research has carried out an analysis using 17 indicators divided in 4 categories. The aim is to identify the transformations that the implementation of digital media have brought to the top European newspapers. In general terms, the results show that most dailies have managed to keep their leadership also in online environment. Moreover, an emerging group of global media is growing up, based in preexisting national media. Digital and mobile media have contributed to the appearance of new consumption habits as well, where users read more superficially and sporadically. The audience uses several formats at a time, and digital devices already bring the biggest amount of users to many media. The Internet-created new information windows –search engines, social networks, etc. –are also contributing to the change in professional work routines.

Polarized spectral analysis of Ho3+ ions in biaxial YAlO3 crystal for 2 mu m lasers

An Ho3+-doped YAlO3 (Ho : YAP) single crystal has been grown by the Czochralski technique. The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curve of the crystal are measured at room temperature. The spectroscopic parameters are calculated based on Judd-Ofelt theory, and the effective phenomenological intensity parameters Omega(2,eff), Omega(4,eff) and Omega(6,eff) are obtained to be 2.89 x 10(-20), 2.92 x 10(-20) and 1.32 x 10(-20) cm(2), respectively. The room-temperature fluorescence lifetime of the Ho3+ 5I(7) -> I-5(8) transition is measured to be 8.1 ms. Values of the absorption and emission cross-sections with different polarizations are presented for the I-5(7) manifold, and the polarized gain cross-section curves are also provided and discussed.

Ichthyoplankton community structure and comparative trophodynamics in an estuarine transition zone

Surveys were conducted to evaluate and compare assemblage structure and trophodynamics of ichthyoplankton, and their variability, in an estuarine transition zone. Environmental gradients in the saltfront region of the Patuxent River subestuary, Chesapeake Bay, were hypothesized to define spatiotemporal distributions and assemblages of ichthyoplankton. Larval fishes, zooplankton, and hydrographic data were collected during spring through early summer 2000 and 2001. Larvae of 28 fish species were collected and species richness was similar each year. Total larval abundance was highest in the oligohaline region down-estuary of the salt front in 2000, but highest at the salt front in 2001. Larvae of anadromous fishes were most abundant at or up-estuary of the salt front in both years. Two ichthyoplankton assemblages were distinguished: 1) riverine—characterized predominantly by anadromous species (Moronidae and Alosinae); and 2) estuarine—characterized predominantly by naked goby (Gobiosoma bosc) (Gobiidae). Temperature, dissolved oxygen, salinity-associated variables (e.g., salt-front location), and concentrations of larval prey, specifically the calanoid copepod Eurytemora affinis and the cladoceran Bosmina longirostris, were important indicators of larval fish abundance. In the tidal freshwater region up-estuary of the salt front, there was substantial diet overlap between congeneric striped bass (Morone saxatilis) and white perch (M. americana) larvae, and also larvae of alewife (Alosa pseudoharengus) (overlap= 0.71–0.93). Larval abundance, taxonomic diversity, and dietary overlap were highest within and up-estuary of the salt front, which serves to both structure the ichthyoplankton community and control trophic relationships in the estuarine transition zone.

Parameterizing probabilities for estimating age-composition distributions for mixture models

When estimating parameters that constitute a discrete probability distribution {pj}, it is difficult to determine how constraints should be made to guarantee that the estimated parameters { pˆj} constitute a probability distribution (i.e., pˆj>0, Σ pˆj =1). For age distributions estimated from mixtures of length-at-age distributions, the EM (expectationmaximization) algorithm (Hasselblad, 1966; Hoenig and Heisey, 1987; Kimura and Chikuni, 1987), restricted least squares (Clark, 1981), and weak quasisolutions (Troynikov, 2004) have all been used. Each of these methods appears to guarantee that the estimated distribution will be a true probability distribution with all categories greater than or equal to zero and with individual probabilities that sum to one. In addition, all these methods appear to provide a theoretical basis for solutions that will be either maximum-likelihood estimates or at least convergent to a probability distribut