White LED based on nano-YAG:Ce3+/YAG:Ce3+,Gd3+ hybrid phosphors

Nano-YAG:Ce³⁺ and YAG:Ce³⁺,Gd³⁺ phosphors were synthesized by glycothermal method. The X-ray diffraction (XRD) measurements showed that the samples can be well-crystallized at 600 °C. The transition electron microscope (TEM) showed that the particles have sizes mostly in the range between 35 and 100 nm. The YAG:Ce nano-phosphor had a wide emission band ranging from blue to yellow peaking at 532 nm, due to the transition from the lowest 5d band to ²F_7/2, ²F_5/2 states of the Ce³⁺ ion. Red-shift of emission peak wavelength from 532 nm to 568 nm has been achieved as doping Gd³⁺ ions into the YAG:Ce³⁺ to substitute some Y³⁺ ions. White LEDs were fabricated by combining GaN (460 nm) chip with the YAG:Ce³⁺ and YAG:Ce³⁺,Gd³⁺. Color rendering index of the white LED as a function of the ratios of theses two kinds of phosphors was studied. As the ratio of YAG:Ce³⁺,Gd³⁺ phosphor increased, the color rendering index of the LED improved significantly under the forward bias of 20 mA. As the ratio of YAG:Ce³⁺ and YAG:Ce³⁺,Gd³⁺ was 11:9, the white LED had a color rendering index, CIE chromaticity coordinates and color temperature T_c of 85, (0.3116, 0.3202) and 6564 K, respectively.     

基于ISC-SVR方法预测Th细胞表位

外源性抗原蛋白被抗原提呈细胞(APC)摄取送入溶酶体中被降解为长度不一的肽段. 在HLA-DM分子辅助下, MHC II类分子相关恒定链多肽(class II-associated invariant chain peptide, CLIP)从MHC II类分子的肽结合槽解离, 使得外源性抗原降解的肽段进入MHC II类分子空的肽结合槽中, 形成稳定的抗原肽-MHC II类分子复合物. 之后再被提呈到APC细胞表面供CD4⁺Th细胞的TCR识别, 激活Th细胞分泌细胞因子, 促进CTL细胞特异性杀伤靶细胞或辅助B细胞产生抗体. Th细胞的活化对机体的细胞免疫和体液免疫功能都有重要的辅助作用. 本工作基于迭代自洽策略与支持向量回归机(ISC-SVR)方法建立了MHC II类分子与外源性抗原肽结合亲合力预测模型, 采用13mer扩展核心结合序列可以提高预测模型的性能, 分别按照均值法、最大值法、结合法、加权平均值法4种方法计算MHC II类分子与抗原肽的结合亲合力值. 对17种MHC II类分子配型进行了回归分析, 与其他预测模型相比较, 本工作模型都得到了最佳AUC值. 最后, 以HLA DRB1*0101分子为例, 分析讨论了MHC II类分子与抗原肽的结合特异性.     

聚乳酸/聚氧化乙烯共混体系的热行为和力学性能及流变行为

采用熔融共混方法制备了聚乳酸与聚氧化乙烯的共混物.细致研究了重均分子量分别为2 kDa、10kDa1、00 kDa和600 kDa的聚氧化乙烯对聚乳酸的改性效果,并使用DSC、DMA及旋转流变仪等分析了共混物的相容性、热行为、力学性能和流变行为.结果表明,在聚氧化乙烯的组分含量不超过20 wt%的前提下,共混体系保持为完全相容体系,当聚氧化乙烯的分子量超过10 kDa时,其对聚乳酸的增塑效果,不随分子量增加而降低;增加聚氧化乙烯的分子量,可以提高材料的弹性模量和熔体强度.     

Preparation and properties of chitosan nanocomposites with nanofillers of different dimensions

In this work, the chitosan ternary nanocomposites with two-dimensional (2D) clay platelets and one-dimensional (1D) CNTs have been successfully prepared by a simple solution-intercalation/mixing method in acid media. It was found that the thermal degradation temperature of chitosan (at 50% weight loss) could be only improved in about 20-30 °C by adding 3 wt% either clay or CNTs, however, almost 80 °C increase of degradation temperature could be achieved by adding 2 wt% clay and 1 wt% CNTs together. Dynamic mechanical measurement demonstrated an obviously improved storage modulus for chitosan/clay-CNTs than that for the corresponding binary chitosan/clay or chitosan/CNT nanocomposites with the same total filler content (3 wt%). For the solvent vapor permeation properties, a largely improved benzene vapor barrier property was observed only in chitosan/clay-CNT ternary nanocomposites and depended on the ratio of clay to CNTs. XRD, SEM and TEM results showed that both clay and CNTs could be well dispersed in the ternary nanocomposites with the nanotubes located around the clay platelets. FTIR showed an improved interaction between the fillers and chitosan by using both clay and CNTs. A much enhanced solid-like behavior was observed in the ternary nanocomposites, compared with the corresponding binary nanocomposites with the same total filler content, as indicated by rheological measurement. The unique synergistic effect of two-dimensional (2D) clay platelets and one-dimensional (1D) CNTs on the property enhancement could be tentatively understood as due to a formation of much jammed filler network with 1D CNTs and 2D clay platelets combined together. Our work demonstrates a good example for the preparation of high performance polymer nanocomposites by using nanofillers with different dimensions together.     

正交各向异性圆柱壳与平板连接处边缘应力分析

根据各向异性薄壳理论对承压圆柱壳与平板连接结构进行了力学分析,获得了圆柱壳连接处的剪力、弯矩、应力解,计算了各向异性弹性模量比对结构连接处的剪力、弯矩以及沿筒体纵向应力分布的影响,并与各向同性的结果进行了对比。结果表明:剪力和弯矩均随着各项异性弹性模量比的增大而增大;各项异性弹性模量与各项同性的情况相比对结构部位的应力影响显著;合理利用材料各向异性性能,可以降低承压结构连接部位的应力水平。研究结果为带有平板封头正交各向异性承压圆柱壳设计提供了参考。     

利用分频带空间谱和波束域的输出直流跳变与起伏比值融合检测未知线谱目标

目标辐射噪声中高强度稳定线谱可以用来提高常规宽带能量积分的检测性能。理论分析了已知线谱检测优于宽带能量积分检测的谱级比条件。给出了线谱频带可检测条件下,线谱谱级与最小可检测信噪比关系。分析分频带空间谱和波束域的输出直流跳变与起伏比值特征。在此基础上提出了一种构造频率、方位滤波矩阵的方法。该矩阵作用类似频带方位滤波器,通过对线谱频带目标方位的信号放大,与其他频带判决结果融合,来提高常规宽带能量积分的性能。最后给出该算法适用条件和性能分析。数据仿真和海试数据处理结果可知,该算法在多干扰源存在下对弱线谱目标提取能力强,且不需多帧统计,在检测效果上更接近于理想的窄带线谱检测方法。      

White light-emitting diodes using blue and yellow-orange-emitting phosphors

A blue-emitting phosphor, BaMgAl₁₀O₁₇:Eu²⁺ (BAM) and a yellow-orange phosphor, Ba²⁺-codoped Sr₃SiO₅:Eu²⁺ were prepared by the solid-state reaction. Excitation and emission spectra results showed that BAM and Ba²⁺-codoped Sr₃SiO₅:Eu²⁺ can be efficiently excited by near-ultraviolet (n-UV)-visible light from 250 to 440 nm. The effects of the doped-Eu²⁺ concentration in BAM and Ba²⁺-codoped Sr₃SiO₅:Eu²⁺ on the photoluminescence were investigated in detail. White light-emitting diodes (LED) was obtained by combining n-UV LED chip (GaN-based 380 nm emitting) with BaMgAl₁₀O₁₇:0.09Eu²⁺ and 0.1Ba²⁺-codoped Sr₃SiO₅: 0.2Eu²⁺ phosphors with the characteristic of color-rendering index of 86, CIE chromaticity coordinates (x,y) of (0.3216,0.3096), and color temperature T_c of 5700 K. As the current increases, the relative intensity simultaneously increases. The CIE chromaticity coordinates (x,y) of the white LED tends to decrease. The correlated color temperature T_c increases from 4100 to 7500 K and the color-rendering index R_a increases from 82 to 87 simultaneously.     

Unification Theory of Different Causal Algebras and Its Applications to Theoretical Physics

This paper gives a generalization of group theory, i.e. a unification theory of different causal algebras, and its applications to theoretical physics. We propose left and right causal algebras, left and right causal decomposition algebras, causal algebra and causal decomposition algebras in terms of quantitative causal principle. The causal algebraic system of containing left (or right) identity I _jL (or I _jR ) is called as the left (or right) causal algebra, and associative law is deduced. Furthermore the applications of the new algebraic systems are given in theoretical physics, specially in the reactions of containing supersymmetric particles, we generally obtain the invariance of supersymmetric parity of multiplying property. In the reactions of particles of high energy, there may be no identity, but there are special inverse elements, which make that the relative algebra be not group, however, the causal algebra given in this paper is just a tool of severely and directly describing the real reactions of particle physics. And it is deduced that the causal decomposition algebra is equivalent to group.     

基于Kriging模型的非概率可靠度计算

Kriging模型可以适应各种极限状态函数,HL-RF修正算法可以有效地计算非线性问题。对于难以获得极限状态函数的结构,提出了用Kriging模型进行回归拟合极限状态方程,同时使用HL-RF修正算法计算结构的非概率可靠度指标的计算方法。数值算例以及球形压力容器可靠性分析表明,本文提出的计算方法具有求解精度好、适应能力强的特点。     

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针对我校光弹性实验教学中存在的问题,采取了一些改进措施：开发了 用作随堂教具和实验演示装置的微型机电光弹仪, 可以将实验结果实时显示在教室的大屏幕上;开发了数值光弹实验的多媒体课件,可以将光 弹原理以及光弹实验中的一些现象再现,供学生课后学习;又开发了具有航空航天特色的实 验项目,培养了学生的理论联系实际的能力. 一年的教学实践结果表明：这些教改措施改善 了教学效果,提高了学生们的学习热情和主观能动性.