Y2O2S∶Er3+，Yb3+的制备及Er3+离子在晶场中的能级分裂

采用沉淀法制备前驱体,通过不同温度合成了上转换发光材料Y2O2S∶Er3+,Yb3+,运用XRD,SEM和上转换发射光谱对其进行表征。结果表明,所合成的Y2O2S∶Er3+Yb3+属于六方晶系晶体,随着合成温度的升高,产物的粒径不断增大,上转换发射光强度逐渐增加。研究Y2O2S∶Er3+Yb3+的上转换发光过程,红光发射和绿光发射分别源于Er3+离子的4F9/2→4I15/2以及2H11/2→4I15/2,4S3/2→4I15/2能级跃迁。利用群论计算了晶场中Er3+离子的能级分裂数目。     

一类含测度的非强制拟线性椭圆方程解的存在性和不存在性

本文主要研究如下含非线性梯度项的非强制拟线性椭圆方程\begin{equation*}\left \{\begin{array}{rl}-\text{div}(\frac{|\nabla u|^{p-2}\nabla u}{(1+|u|)^{\theta(p-1)}})+\frac{|u|^{p-2}u|\nabla u|^{p}}{(1+|u|)^{\theta p}}=\mu,~&x\in\Omega,\\ u=0,~&x\in\partial\Omega,\end{array}\right.\end{equation*} 弱解的存在性和不存在性, 其中$\Omega\subseteq\mathbb{R}^N(N\geq3)$ 是有界光滑区域, $1相似文献   

Neutron diffraction and computer simulation study of liquid CS2 and CSe2

The structure factor of liquid CS₂ has been measured at ambient temperature by the 7C2 diffractometer at the Laboratoire Leon Brillouin?, Saclay, France. The result has been modelled by the reverse Monte Carlo (RMC) method. The only reported neutron diffraction measurement on liquid CSe₂ has also been investigated in detail. In both cases initial configurations for the RMC runs have been obtained by molecular dynamics simulation using a simple soft sphere potential. It has been found that the main features of experimental results have been reproduced even by this choice suggesting that the structure of these systems is almost entirely described by the excluded volume. Examination of model size dependence of results has also been carried out revealing the importance of using large simulation boxes.     

带多个形状参数的Bézier曲线

基于Bézier曲线升阶的思想,构造了带多个形状参数的Bézier曲线,它具有与Bézier曲线相同的性质.在控制顶点不变的情况下,可通过改变多个形状参数的取值调整曲线的形状.n次Bézier曲线是n次带多个形状参数的Bézier曲线的一个特例,多个形状参数可使曲线变化更灵活.     

乙酸铵离心交换法和乙酸钙离心交换法测定土壤阳离子交换量

土壤阳离子交换量(CEC)的测定在农业中有重要的意义,对农业行业标准NY/T295—1995和NY/T1121.5—2006中的离心交换法测定土壤中CEC值的方法进行了优化,讨论了不同pH值的土壤样品对两种方法的选择依据,分析了CEC值测定重现性较差的原因。结果表明,pH值的范围是方法选择的重要依据,pH7.0的样品适合用乙酸铵离心交换法,pH≥7.0的样品则适用乙酸钙离心交换法。优化后方法的准确度和精密度有了较大的改善,实验中对各步骤的优化缩短了约40%的操作时间,减少工作量,适合于批量样品的准确测定。     

纳氏试剂测定水中氨氮影响因素的探讨

对国家生活饮用水标准检验方法"GB/T5750—2006"中涉及到的水中氨氮的检测条件进行了探讨,讨论了样品的采集与保存,影响显色、空白值的各项因素,并提出相应的解决办法。对国家标准物质以及实际样品的验证表明,方法的相对误差为0.03%~1.5%,相对标准偏差RSD为0.55%~5.3%,准确度也能满足分析要求,对国家标准方法进行了补充与细化,在实际工作中有参考价值。     

Triblock copolymer Pluronic®F127 sustains insulin release and reduces initial burst of microspheres—in vitro and in vivo study

In many cases, initial release of drugs from microparticles is undesirable. In the present study, Pluronic^®F127, which shows thermosensitive characteristic, was used for controlling both the initial release and the sustained release of insulin from microspheres. Calcium-alginate insulin microspheres were prepared by emulsion technology and dispersed in a thermosensitive semisolid gel, the PF127. In vitro study demonstrated that PF127 could protect the activity of insulin in some extent and control the initial release and sustained release of insulin well. The results of in vivo hypoglycemic experiment carried out on diabetic rats also displayed a well correlation with in vitro release patterns. The results suggested that PF127 could sustain insulin release through a subcutaneous injection, and this material was available to deliver insulin aiming for prolonged and smooth hypoglycemic function.     

Carbon stable isotopes reveal complex trophic interactions in lake plankton

The lower trophic linkages in lake plankton food webs are generally described as relatively simple, even accounting for the additional complexity of potential 'microbial looping'. Crustacean zooplankton are frequently amalgamated into one trophic functional group as grazers of autotrophic production. The carbon stable isotope ratios for separated zooplankton species, particulate organic matter (POM) and phytoplankton from a number of lakes in Finland and the UK were analysed. These revealed greater complexity in trophic interactions than would otherwise be observed if the zooplankton had been represented by a mixed sample. Grazing zooplankton were usually depleted in (13)C relative to the bulk POM on which they might feed, with (13)C deviating by up to 17 per thousand There were no consistent differences between (13)C values for copepods and cladocerans. Predatory cladocerans were generally enriched by greater than 1 per thousand compared to their putative prey. We suggest that care in separating the zooplankton species for stable isotope analysis may expose otherwise undetected sources of carbon and facilitate unravelling trophic links further up the food web. Copyright 1999 John Wiley & Sons, Ltd.     

Boundedness of Commutators of θ-Type Calderόn-Zygmund Operators on Non-homogeneous Metric Measure Spaces

Let(X, d, μ) be a metric measure space satisfying both the upper doubling and the geometrically doubling conditions in the sense of Hyt?nen. In this paper, the authors obtain the boundedness of the commutators of θ-type Calderón-Zygmund operators with RBMO functions from L~∞(μ) into RBMO(μ) and from H_(at)~(1,∞)(μ) into L~1(μ), respectively.As a consequence of these results, they establish the L~p(μ) boundedness of the commutators on the non-homogeneous metric spaces.     

液相混合铋系超导前驱粉体工艺研究

本研究采用溶胶凝胶颗粒包覆技术，将钙铜离子均匀包覆在2212颗粒表面，通过适当的热处理，使包覆层转变为Ca2CuO3 CuO相，同时确保2212相结构稳定，从而获得了均匀混合的装管前驱粉体．详细研究了钙铜溶胶体系的胶凝工艺，2212悬浮体系的稳定性以及Ca2CuO3成相温区等工艺参数，并利用XRD，SEM等分析手段，研究了粉体的粒度分布，形貌，相组成及其均匀性．