The application and a substitution defect model for Eu3+ -> Eu2+ reduction in non-reducing atmospheres in borates containing BO4 anion groups

The variations of emission intensities of SrB4O7:Eu2+ and Sr2B5O9Cl:Eu2+ prepared in different atmospheres are discussed in view of the structure of host compounds. A model of substitution defects is proposed to explain the abnormal reduction of Eu3+ --> Eu2+ in non-reducing atmospheres of N-2, air and O-2. Experiment results show that SrB4O7:Eu2+ phosphor sample prepared in N-2 atmosphere has an emission intensity of 94% as high as that of the sample prepared in H-2 gas. This implies that the reduction of Eu2+ --> Eu2+ in non-reducing atmospheres could be potentially used in preparing phosphors, such as SrB4O7:Eu2+. (C) 1999 Elsevier Science Ltd. All rights reserved.

Restructuring and redispersion of silver on SiO2 under oxidizing/reducing atmospheres and its activity toward CO oxidation

The effects of oxygen-hydrogen pretreatments of nanosilver catalysts in cycle mode on the structure and particle size of silver particles, and subsequently the activity of the catalyst toward CO oxidation (or CO selective oxidation in the presence of H-2) are reported in this paper. Ag/SiO2 catalyst with silver particle sizes of ca. 6 similar to 8 nm shows relatively high activity in the present reaction system. The adopting of a cycle of oxidation/reduction pretreatment has a marked influence on the activity of the catalyst. Oxygen pretreatment at 500 degrees C results in the formation of subsurface oxygen and activates the catalyst. As evidenced by in-situ XRD and TEM, the following H-2 treatment at low temperatures (100 similar to 300 degrees C) causes surface faceting and redispersing of the silver particles without destroying the subsurface oxygen species. The subsequent in-situ FTIR and catalytic reaction results show that CO oxidation occurs at -75 degrees C and complete CO conversion can be obtained at 40 degrees C over such a nanosilver catalyst pretreated with oxygen at 500 degrees C followed by H-2 at 100 degrees C. However, prolonged hydrogen treatment at high temperatures (> 300 degrees C) after oxygen pretreatment at 500 degrees C induces the aggregation of silver particles and also depletes so much subsurface oxygen species that the pathway of CO oxidation by the subsurface oxygen species is inhibited. Meanwhile, the ability of the catalyst to adsorb reactants is greatly depressed, resulting in a 20 similar to 30% decrease in the activity toward CO oxidation. However, the activity of the catalyst pretreated with oxygen at 500 degrees C followed by hydrogen treatment at high temperatures (> 300 degrees C) is still higher than that directly pretreated with H,. This kind of catalytic behavior of silver catalyst is associated with physical changes in the silver crystallites because of surface restructuring and crystallite redispersion during the course of oxygen-hydrogen pretreatment steps.

Rossby Vortex Simulation on a Paraboloidal Coordinate System Using the Lattice Boltzmann Method

In this paper, we apply our compressible lattice Boltzmann model to a rotating parabolic coordinate system to simulate Rossby vortices emerging in a layer of shallow water flowing zonally in a rotating paraboloidal vessel. By introducing a scaling factor, nonuniform curvilinear mesh can be mapped to a flat uniform mesh and then normal lattice Boltzmann method works. Since the mass per unit area on the two-dimensional (2D) surface varies with the thickness of the water layer, the 2D flow seems to be "compressible" and our compressible model is applied. Simulation solutions meet with the experimental observations qualitatively. Based on this research, quantitative solutions and many natural phenomena simulations in planetary atmospheres, oceans, and magnetized plasma, such as the famous Jovian Giant Red Spot, the Galactic Spiral-vortex, the Gulf Stream, and the Kuroshio Current, etc,, can be expected.

Growth of liquid bridge in AFM

Capillary forces are dominant in adhesive forces measured with an atomic force microscope (AFM) in ambient air, which are thought to be dependent on water film thickness, relative humidity and the free energy of the water film. In this paper, besides these factors, we study the nature of the 'pull-off' force on a variety of atmospheres as a function of the contact time. It is found that capillary forces strongly depend on the contact time. In lower relative humidity atmosphere, the adhesion force is almost independent of the contact time. However, in higher relative humidity, the adhesion force increases with the contact time. Based on the experiment and a model that we present in this paper, the growth of the liquid bridge can be seen as undergoing two processes: one is water vapour condensation; the other is the motion of the thin liquid film that is absorbed on the substrate. The experiment and the growth model presented in this paper have direct relevance to the working mechanism of AFM in ambient air.

Asymmetric structure of an isolated flux arch

This paper extends two-dimensional model of symmetric magnetostatic flux arches confined in stratified atmospheres (Zhang and Hu, 1992, 1993) to asymmetric models. Numerical results show that the flux structure is influenced greatly by the boundary condition of magnetic field, the force-free factor, the atmospheric pressure distribution and the position of footpoints (especially the width ratio of outlet to entrance, which differs from symmetric case).

The effect of variable currents on internal solitary waves

The effect of variable currents on internal solitary waves is described within the context of a variable coefficient Korteweg-de Vries (KdV) equation, and the approximate slowly varying, solitary-wave solution of this equation. The general theory which leads to the variable coefficient KdV equation is described; a derivation for the special case when the solitary wave and the current are aligned in the same direction is given in the Appendix. Using further simplifications and approximations, a number of analytical expressions are obtained for the variation in the solitary wave amplitude resulting from variable shear in the basic current or from when the basic current is a depth-independent flow which is a simple representation of a geostrophic current, tidal flow or inertial wave.

A model of an isolated magnetic-flux tube in a stratified atmosphere

A two-dimensional model of a magnetic flux tube confined in a gravitational stratified atmosphere is discussed. The magnetic field in the flux tube is assumed to be force-free. By using the approximation of large scale height, the problem of a free boundary with nonlinear conditions may be reduced to one involving a fixed boundary. The two-dimensional features are obtained by applying the perturbation method and adopting the Luest-Schlueter model as the basic state. The results show that the configuration of a flux tube confined in a gravitational stratified atmosphere is divergent, and the more twisted the magnetic field, the more divergent is the flux tube.

高硅氧发光玻璃的制备及其荧光性能

abstract {Silica glass is an attractive host matrix for the emission ions of rare earth and transition metal ions because it has small thermal expansion coefficient, strong thermal resistance, large fracture strength and good chemical durability and so on. However, a major obstacle to using it as the host matrix is a phenomenon of concentration quenching. In this paper, we introduces a novel method to restrain the concentration quenching by using a porous glass with SiO₂ content > 95% (in mass) and prepare intense fluorescence high-SiO₂ glasses and high-SiO₂ laser glass. The porous glass with high-SiO₂ content was impregnated with rare-earth and transition metal ions, and consequently sintered into a compact non-porous glass in reduction or oxidization atmospheres. Various intense fluorescence glasses with high emission yields, a vacuum ultraviolet-excited intensely luminescent glass, high silica glass containing high concentration of Er³⁺ ion, ultrabroad infrared luminescent Bi-doped high silica glass and Nd³⁺-doped silica microchip laser glass were obtained by this method. The porous glass is also favorable for co-impregnating multi-active-ions. It can bring effective energy transferring between various active ions in the glass and increases luminescent intensity and extend range of excitation spectrum. The luminescent active ions-doped high-SiO₂ glasses are potential host materials for high power solid-state lasers and new transparent fluorescence materials.}

Fluorescence properties and laser demonstrations of Nd-doped high silica glasses prepared by sintering nanoporous glass

Porous glass with high-SiO2 content was impregnated with Nd ions, and subsequently sintered at 1100 degrees C into a compact non-porous glass in air or reducing atmosphere. Sintering in a reducing atmosphere produced an intense violet-blue fluorescence at 394 nm. However, the sintering atmospheres almost did not affect the fluorescence properties in the infrared range. A good performance Nd3+-doped silica microchip laser operating at 1064 nm was demonstrated. The Nd-doped sintering glasses with high-SiO2 content are potential host materials for high power solid-state lasers and new transparent fluorescence materials. (c) 2007 Elsevier B.V. All rights reserved.

不同退火气氛下γ-LiAlO2形貌和结构研究

研究了温度梯度法生长的γ-LiAlO2晶体在1100℃下富Li气氛和空气中退火处理后的表面形貌、表面结构以及吸收光谱。发现γ-LiAlO2晶体的抛光面在1100℃空气中退火后变为粗糙面，X射线衍射(XRD)分析表明此粗糙面为单相的LiAl5O8。而γ-LiAlO2晶体的抛光面在1100℃富Li气氛中处理后几乎没有变化。同时对不同气氛下热处理的γ-LiAlO2晶体进行了光谱分析，确认了晶片中196nm的吸收峰是由Li空位引起的。