双程前向近高斯型掺铒超荧光光纤光源的实验研究

研究了输出谱型为近高斯型的掺铒超荧光光纤光源,分析了高斯型光谱的自相干函数和影响平均波长稳定性的因素.采用双程前向光源结构,通过选择铒纤长度获得高斯型光谱输出,同时调节泵浦功率来优化铒纤的本征温度系数对光源的影响,得到铒纤长度10.05 m,泵浦功率为172 mW时,整体光路(除半导体泵浦激光器及其驱动电源)在全温-4...     

Symmetry role on the preedge X—ray absorption fine structure at the metal K edge

The preedge features in a system with “even”symmetry,apart from quadrupolar transition contribution,are mainly dipolar in character,associated with the existence of unoccupied states made up of mixed cation-4p with higher-neighboring cation-3d orbitals,and reflect the density of states due to the medium-range order of the system.In “odd“symmetry materials these preedge features ate the result of a transition from the ls to a final density of states of p symmetry due to an unsymmetrical mixing of the ligand wave functions with the central cation 3d orbitals,similar to atetrahedral configuration.These results are validated for Fe as a photoabsorber by comparing XAS spectra of Fe2SiO4(fayalite) to ab initio full multiple scattering calculations at the fe K edge,but pertain to all systems containing sixfold-coordinated cations.     

Lebesgue-Bochner函数空间Lp(μ,X)中的drop性质

主要给出了如下结论:设(Ω,Σ,μ)为有限测度空间,1相似文献   

广义相对论的珍宝

 从前人们的生活很简单,科学不发达,要跟上物理发展的步伐并不难。今天要做到这一点,对我们大多数人来说,把全部精力和时间都投进去也是不够的。总之,我抓住这条理由,来辩解为什么没有对广义相对论在它从一种鉴赏品发展到一门硬科学的过程中给予关注。     

Optical and Electronic Properties of InGaN／GaN Multi—Quantum—Wells Near—Ultraviolet Lighting—Emitting—Diodes Grown by Low—Pressure Metalorganic Vapour Phase Epitaxy

The near-ultraviolet lighting-emitting-diodes (UV-LEDs) with the InGaN/GaN multi-quantum-well (MQW) structure were grown by low-pressure metalorganic vapour phase epitaxy. The double crystal x-ray diffraction revealed a distinct second-order satellite peak. The near-ultraviolet InGaN/GaN MQW LEDs have been successfully fabricated to emit at 401.2nm with narrow FWHM of 14.3nm and the forward voltage of 3.6 V at 20 mA injection current at room temperature. With increasing forward current from l 0 mA to 50 mA, the redshift of the peak wavelength was observed due to the band-gap narrowing caused by heat generation.     

L—fuzzy拓扑空间中近良紧集的刻画

本文在Ｌ－ｆｕｚｚｙ拓扑空间中，针对Ｌ－ｆｕｚｚｙ子集定义子Ｍｒ－复盖及具有有限Ｍｒ交性质的闭集族等概念，并以此刻画了近良紧集的一组特性，证明了近良紧的对正则闭集遗传以及是“Ｌ－ｇｏｏｄ ｅｘｔｅｎｓｉｏｎ”等结论。     

高中数学向量知识的内容定位与教学建议

1 数学课程改革当中的向量背景和前景分析 1．1 向量的双重身份 向量是近代数学最重要和最基本的概念之一．向量是既有大小又有方向的量，要用两个实数、三个实数甚至更多的实数才能确切地表达．所以它既具有图形的直观性，又有代数推理的严密性．从而向量是一个具有几何和代数双重身份的概念．     

一个关于球面和环面上嵌入图的近-三角剖分嵌入的内插定理(I)

一个近-三角剖分嵌入是指一个曲面上的嵌入图使得几乎所有的面都是三角形,至多只有一个可能的例外.文中作者证明了如下结论:如果一个图G 在球面S₀(或环面S₁)上有近-三角剖分嵌入,那么G在每一个可定向曲面S_k有近-三角剖分嵌入,其中k=h,h+1,\cdots ,\lfloor\frac{\beta(G)}{2}\rfloor$, 而h=0(或1)并且β(G)是图G的Betti数.特别地,G是上可嵌入的.     

Asymptotic Analysis of a Modified Lorenz System

We investigate the dynamical behaviour of a modified Lorenz system.Some basic dynamical properties,such as bifurcations,routes to chaos,periodic windows,and some Poincare mappings of this system are studied,either analytically or numerically.Also,the compound structure of the butterfly-shaped attractor is explored.     

管柱型近周期声子晶体点缺陷结构的大尺寸压电超声换能器

大尺寸压电超声换能器的耦合振动会导致其辐射面纵向位移振幅的平均值较小,振幅分布不均匀,严重影响系统的性能和可靠性.为了改善大尺寸超声振动系统性能,可利用二维孔/槽型近周期声子晶体结构对横向振动进行抑制,但在对横向振动抑制的同时,该结构会对换能器机械强度和工作带宽等性能参数造成不利的影响.针对这一问题,本文提出利用管柱型近周期声子晶体点缺陷结构对大尺寸夹心式纵振压电陶瓷换能器进行优化的新思路.该方法不仅可以利用构造的固/气二维近周期声子晶体结构的点缺陷模式,获得极低的能量损耗,有效提高系统辐射面的纵向位移振幅和振幅分布均匀度;也可以利用管柱结构中的双环形孔增强声波的多重散射,使得换能器在管柱柱高较低的条件下产生禁带,在有效抑制横向振动的同时,大幅拓宽换能器系统的工作带宽,增强系统的稳定性和机械强度,降低加工成本.仿真结果证明了优化的有效性.