前近贴脉冲电压对三代微光像增强器halo效应的影响

为了探讨三代微光像增强器的合适工作电压,研究了前近贴脉冲电压对微光像增强器halo效应的影响.将脉冲电压信号加在光电阴极上,分别改变脉冲信号的高低电平电压幅值和占空比,利用高分辨率CCD采集了微光像增强器的halo图像,对比分析了halo图像中心线上各像素点对应的灰度值分布和光子计数.研究结果表明,随着高电平电压幅值和占空比的提高,灰度值为255的像素点数目变多,halo图像中背景和信号的边界越来越清晰.当前近贴电压增加到200 V以上和占空比大于60％左右时,其对三代微光像增强器halo图像中心线上各像素点的灰度值分布影响不大.当低电平电压增加到2V以上时,光电子在低电平阶段无法克服阻滞场到达微通道板.此研究有利于探讨微光像增强器的最佳工作电压和光电子从阴极面出射时的能量分布,为提高三代微光像增强器的性能提供了实验支撑.     

钢筋混凝土烟囱爆破拆除的下坐及早期断裂预测

为分析钢筋混凝土烟囱在爆破拆除时发生下坐与空中断裂现象的机制并对其进行预测,对一高180 m烟囱的下坐和空中断裂过程进行了观测和分析。基于混凝土的压缩全应力-应变曲线特征,分析了烟囱支撑区的破坏过程,构建了烟囱失稳下坐的判别模型。通过建立烟囱下坐冲击作用下爆破切口以上烟囱的动力响应模型,分析了下坐冲击附加动应变波在烟囱中的传播特征。研究结果表明,考虑混凝土全应力-应变曲线特征和支撑区横截面应力和应变分布特征时,倾覆力矩与抵抗力矩的比值f可作为失稳下坐的判别条件之一;烟囱发生下坐的必要条件是支撑区最小残余承载力小于烟囱的重量。烟囱在下坐结束阶段,获得一定初速度的烟囱冲击基础时将产生冲击荷载,并在烟囱中部引起大于底端应变的应变,即产生动应变高程放大效应,该效应是导致烟囱发生早期断裂的主要原因。烟囱越高,下坐冲击历时越短,动应变高程放大效应越显著,发生断裂的风险也越大。随着烟囱高度的增加,烟囱最危险截面的位置也越高:由烟囱中下部移至烟囱中上部。     

First principle study of the influence of vacancy defects on optical properties of GaN

We employ plane-wave with ultrasoft pseudopotential method to calculate and compare the total density of states and partial density of states of bulk-phase GaN,Ga0.9375 N,and GaN0.9375 systems based on the first-principle density-functional theory(DFT).For Ga and N vacancies,the electronic structures of their neighbor and next-neighbor atoms change partially.The Ga0.9375 N system has n-type semiconductor conductive properties,whereas the GaN0.9375 system has p-type semiconductor conductive properties.By studying the optical properties,the influence of Ga and N vacancy defects on the optical properties of GaN has been shown as mainly in the low-energy area and very weak in high-energy area.The dielectric peak influenced by vacancy defects expands to the visible light area,which greatly increases the electronic transition in visible light area.