241Am-Be中子参考辐射的蒙特卡罗模拟研究

研究用于校准场所中子剂量监测仪表的241Am-Be中子参考辐射场计量特性。采用蒙特卡罗方法模拟了空气自由中子参考辐射(FRNR),GB/T 14055规定的最小尺寸中子参考辐射(SRNR)和实际中子参考辐射(ARNR)中不同检验点处中子周围剂量当量率、散射中子占比和能谱分布特征。研究结果表明,空气对FRNR中的剂量率和能谱分布影响小,近似为理想中子参考辐射;采用5%含硼聚乙烯作屏蔽的最小尺寸SRNR可减少热中子,降低散射中子占比,影锥法不适用于小尺寸中子参考辐射中对散射中子的修正;ARNR中的散射中子更少、占比更低,影锥法所得散射中子占比与理论值基本一致。     

Overview of finite elements simulation of temperature profile to estimate properties of materials 3D-printed by laser powder-bed fusion

Laser powder bed fusion(LPBF),like many other additive manufacturing techniques,offers flexibility in design expected to become a disruption to the manufacturing industry.The current cost of LPBF process does not favor a try-anderror way of research,which makes modelling and simulation a field of superior importance in that area of engineering.In this work,various methods used to overcome challenges in modeling at different levels of approximation of LPBF process are reviewed.Recent efforts made towards a reliable and computationally effective model to simulate LPBF process using finite element(FE)codes are presented.A combination of ray-tracing technique,the solution of the radiation transfer equation and absorption measurements has been used to establish an analytical equation,which gives a more accurate approximation of laser energy deposition in powder-substrate configuration.When this new analytical energy deposition model is used in in FE simulation,with other physics carefully set,it enables us to get reliable cooling curves and melt track morphology that agree well with experimental observations.The use of more computationally effective approximation,without explicit topological changes,allows to simulate wider geometries and longer scanning time leading to many applications in real engineering world.Different applications are herein presented including:prediction of printing quality through the simulated overlapping of consecutive melt tracks,simulation of LPBF of a mixture of materials and estimation of martensite inclusion in printed steel.     

一种测试小分子迁移的新方法

针对高聚物材料中小分子的迁移现象,结合数字图像处理技术,提出了一种基于钠光和斐索等厚原理的光学干涉法.介绍了系统测试原理,针对光学系统的设计作了详细的分析与计算;通过实验测试,设计的光学系统能够采集到清晰的干涉条纹,且满足测试精度要求,由条纹间距随时间的变化测出了丙酮和乙醇小分子迁移时高聚物折射率的变化规律为:丙酮小分...     

邻溴苯基—2—恶唑啉的合成研究

改进了邻溴苯基－２－恶唑的合成方法，使得Ｎ－（β羟乙基）－２－溴苯甲酰胺在氯化亚砚作用了缩合成恶唑啉的收率从４０％左右提高到８４％，并避免了使用ＮａＨ试剂，为芳基－２－恶唑啉的合成提供一条方便，经济的路线。     

Oscillatory and Asymptotic Behavior for Second Order Quasilinear Difference Equations

1 IntroductionConsider the second order quasilinear difference equationA(g(Ay.--l)) + f(n,y.) = 0, for n E N(no), (l'l)where A is defined by Ay. = Vn+1--yn, n E N(no) = {no, no + 1,'' }, nO E N = {l, 2,'. }.The following hold throughout the paPer:(H0) (i) g: R-R is a continuous increasing fUnction with propertiessgng(y) = sgny) g(R) = R;(il) f: N(no) x R--+ R is continuous as a function of y E R;(iii) yf(n,y) > 0 for n E N and y / 0.By a solution of the equation (1.l) we mean a non…     

第七届全国分析化学年会暨第七届全国原子光谱分析学术报告会紧急通知

考虑诸多因素 ,第七届全国分析化学年会暨第七届全国原子光谱分析学术报告会商定 ,两会合并、联合召开 ,统一组织、统一领导。会期 :2 0 0 0年 1 0月　　地址 :重庆市西南师范大学收稿截止日期 :2 0 0 0年 3月 3 1日 (以邮戳为准 )论文处理 :会议筹备组将组织专家对应征论文进行评审 ,决定取舍。录用的论文将安排在会上口头报告或报展 ,并在会前出论文集。请自留底稿 ,恕不退还。收稿地址 :两个收稿地址等效。1　重庆市西南师范大学化学化工学院周光明、黄玉明同志收 ,邮编 :4 0 0 71 52　北京海淀区学院南路 76号光谱与分析期刊社孟广政同…     

离子束辅助沉积对类金刚石膜结构影响的计算机模拟

采用分子动力学(MD)模拟研究了离子束辅助沉积(1BAD)生长类金刚石(DLC)膜的物理过程.分 别选C₂分子和Ar离子作为沉积源和辅助沉积粒子.改变Ar的入射能量和到达比(A r／C)，研 究了它对DLC膜结构的影响.重点讨论了Ar辅助沉积引起表面原子的瞬间活性变化对薄膜结构 产生的影响.分析表明，由于Ar离子的轰击引起的能量和动量的传递，大大地增强了C原子在 表面的反冲动能及迁移概率，增加了合成薄膜的SP³键含量.研究结果和实验 观察一致，并从合成机理上给出了一些定量解释. 关键词： 类金刚石膜 离子束辅助沉积 分子动力学模拟     

直流高压加速管轴向绝缘的优化设计

 为了降低500 mA直流高压加速管高梯度区的电位梯度，对加速管轴向绝缘结构进行优化设计。首先分析了沿面闪络的机理和该加速管轴向绝缘体结构。根据SEEA理论并通过数值模拟，发现阴极、真空和绝缘体三结合点处电场畸变是产生高场强的原因，并分别对4种绝缘体结构进行模拟分析，最终确定出比较理想的结构：绝缘体沿面与阴极电极夹角为+45°，绝缘体两端开槽并均匀嵌入金属电极环，绝缘体均匀嵌入阳极电极片内。