表面裂纹蠕变分析的蠕变线弹簧模型方法

鉴于用通常的数值方法分析三维蠕变裂纹问题的困难,提出了一个三维表面裂纹蠕变断裂力学参量分析的蠕变线弹簧模型方法,并在非稳态蠕变条件下的位移、裂纹尖端J积分和C积分的工程估算公式及弹塑性线弹簧模型的基础上,建立了蠕变线弹簧模型方法的有关基本方程．具体分析计算了受均匀拉伸表面裂纹平板的J积分和C积分,并与三维有限元解进行了比较,其结果吻合良好．研究结果为进一步研究三维表面裂纹的蠕变扩展及寿命预报提供了基础．     

热声谐振管品质因数的实验研究

回热器中填充了玻璃丝绵,在声驱动的热声谐振管中发生共振,通过测量谐振频率,分析热声谐振管的频率特性,辨识谐振管的品质因数,其测量结果能与理论计算值较好的吻合。实验证实,品质因数是评价热声谐振管工作性能的重要参数。     

GaN光学微盘的显微荧光图像探讨

研制了不同厚度的直径为５－１５μｍ的ＧａＮ光学微盘,并 学微盘的显微荧光图像进行了细致观测和数据值采集。结果表明,在同一个ＧａＮ外延样品上由于厚度的差别,微盘呈现两种不同类型的荧光图像,     

美国肯塔基州的物理探究评价及其启示

美国于1996年出台<国家科学教育标准>之后,各州纷纷以此为基准开发各自的科学教育标准,这些标准的突出特征就是把科学探究作为重点课程目标,尽管科学探究的重要性已被普遍认同,但对科学探究能力的评价方式却有不同认识和做法,众所周知,由于评价的高利害性及人的趋利性,导致了评什么就教什么,怎么评就怎么教,这种做法在世界各国均不同程度存在.     

Optimization of molar content of amidoxime and acrylic acid in UHMWPE fibers for improvement of seawater uranium adsorption capacity

Ultra-high molecular weight polyethylene (UHMWPE) fibrous adsorbents with different molar content of amidoxime (M _AO) and acrylic acid (M _AA) were prepared by graft polymerization of acrylonitrile (AN) and acrylic acid (AA), followed by amidoximation. Uranium adsorption experiments in both artificial and natural seawater were carried out to investigate the effect of M _AO and M _AA on the uranium adsorption capacity of UHMWPE fibrous adsorbents. Adsorption results showed that the UHMWPE fibrous adsorbent with M _AO = 4.27 and M _AA = 4.64 mmol/g-ads exhibited better uranium adsorption capacity in both artificial (7.01 mg-U/g-ads) and natural (0.77 mg-U/g-ads) seawater.

     

热结构瞬态响应的耦合灵敏度分析方法与优化设计

研究结构瞬态热变形和热应力的灵敏度分析方法及其优化设计,灵敏度计算给出了直接法和伴随法两种算法.考虑了温度场的耦合作用,在直接法中需要计算温度场对设计变量的导数,在伴随法中需要计算热载荷对温度场的导数.数值算例验证了该方法的精度.伴随法在应用程序中的实现,为大型结构优化提供了高效率的灵敏度计算方法.     

基于虚拟激励法的结构随机振动声辐射分析

论文基于有限元法、边界元法和虚拟激励法,对随机激励下结构振动声辐射问题进行研究.提出了一种计算随机激励下结构振动声辐射问题的新方法,其中,有限元法用于计算结构谐振响应,边界元法用于计算结构振动声辐射,虚拟激励法结合有限元和边界元计算随机激励下结构振动声辐射问题.数值算例表明,论文方法在计算精度上与传统方法等价,且更具高效性.     

承压热冲击下反应堆压力容器的塑性失效分析

承压热冲击(PTS)使反应堆压力容器(RPV)的完整性面临极大的挑战,尤其是在喷嘴周围的环带区.考虑到瞬态温度处于零韧性参考温度之上,引入非线性材料性能来模拟一个真实RPV的混合温度场和应力场.应用扩展有限元法对喷嘴区中的裂纹扩展过程进行模拟,并得到了承压热冲击下的临界裂纹尺寸.结果显示,PTS初期的热应力效应显著,后期热-机械耦合作用产生的峰值应力很可能会引起结构失效.应用直接和间接耦合法得到的数值结果吻合,且后者的计算效率较高.在塑性极限承载状况下,裂纹尖端在靠近内壁的位置容易产生扩展.离内壁较远的裂纹尖端由于受热冲击影响较小,发生裂纹扩展的可能性相对较低.随着基体墙厚度的减小,容许的裂纹尺寸急剧缩小,接近临界承载状态时稳态裂纹扩展的程度明显降低.     

Doping effects in nanostructured cadmium tungstate scintillation films

This paper reports experimental study on the development of cadmium tungstate scintillator material in the form of nanocrystal films through controlled sol-gel processing and pre-designed doping. We chose cadmium tungstate as a base material for doping and nanostructure development due to its excellent inherent photoluminescence (PL) property, and chemical and thermal stability including non-hydroscopicity. Experimental results revealed that doping with Li⁺, B³⁺ and Bi³⁺ resulted in appreciably reduced grain size and increased density leading to enhanced optical transmittance. Further analyses indicated that PL output changed significantly with the introduction of dopants. The relationships between doping, microstructure, and PL were discussed.     

Tandem reactions of 1,3-diacid chlorides with 2-methylimidazoline and 2-methyl-1,4,5,6-tetrahydropyrimidine: one-pot synthesis of 1,8-naphthyridinetetraones

The reactions of 2-methylimidazoline and 2-methyl-1,4,5,6-tetrahydropyrimidine with 1,3-diacid chlorides, in the presence of Et3N in refluxing MeCN give highly functionalized potentially bioactive 1,8-naphthyridinetetraones. 2-Methylimidazoline and 2-methyl-1,4,5,6-tetrahydropyrimidine can be viewed as tridentate nucleophiles which give four consecutive tandem nucleophilic attacks on electrophiles.