FH4-060型高分辨堆积拒绝门

本文介绍一种用于快闪烁探测器能谱测量系统的堆积拒绝门,其分辨时间好于10ns。线路采用更新计时器,定时电容的更新时间包含在门宽度之内,原则上电路无死时间,输入计数率无上限,特别适用于高计数率的场合。电路内附反符合控制输入和门信号放大器,可实现对多道分析器的堆积拒绝和反符合控制。     

Behavior of strain at a thin Ge pile-up layer formed by dry oxidation of a Si0.7Ge0.3 film

The change of strain in Si_0.7Ge_0.3 films was investigated with medium energy ion scattering (MEIS). Si was removed in the films by selective oxidation at 800 °C, resulting in the formation of a Ge pile-up layer on the surface. The relaxation and the thickness of the pile-up layer were closely related to the oxidation time. MEIS data demonstrated that relaxation of the Ge layer in the depth direction occurred partially, and that the rates of relaxation decreased with depth. In addition, the rate of relaxation increased with the oxidation time. Lastly, the relaxation of the Ge layer affected the strain of the remaining Si_0.7Ge_0.3 substrate.     

High Count Rate Electron Probe Microanalysis

Reducing the measurement uncertainty of quantitative analyses made using electron probe microanalyzers (EPMA) requires a careful study of the individual uncertainties from each definable step of the measurement. Those steps include measuring the incident electron beam current and voltage, knowing the angle between the electron beam and the sample (takeoff angle), collecting the emitted x rays from the sample, comparing the emitted x-ray flux to known standards (to determine the k-ratio) and transformation of the k-ratio to concentration using algorithms which includes, as a minimum, the atomic number, absorption, and fluorescence corrections.This paper discusses the collection and counting of the emitted x rays, which are diffracted into the gas flow or sealed proportional x-ray detectors. The representation of the uncertainty in the number of collected x rays collected reduces as the number of counts increase. The uncertainty of the collected signal is fully described by Poisson statistics. Increasing the number of x rays collected involves either counting longer or at a higher counting rate. Counting longer means the analysis time increases and may become excessive to get to the desired uncertainty. Instrument drift also becomes an issue. Counting at higher rates has its limitations, which are a function of the detector physics and the detecting electronics.Since the beginning of EPMA analysis, analog electronics have been used to amplify and discriminate the x-ray induced ionizations within the proportional counter. This paper will discuss the use of digital electronics for this purpose. These electronics are similar to that used for energy dispersive analysis of x rays with either Si(Li) or Ge(Li) detectors except that the shaping time constants are much smaller.     

重荷载大跨度叠合式预应力板梁合一结构在铁路旅客天桥中的设计与应用

本文通过某铁路旅客站人行天桥工程实例的设计,在大跨度天桥中应用叠合式预应力板梁合—结构,对其各阶段应力状态进行分析,并对其节点构造等若干问题进行探讨。     

赤泥的综合利用和安全堆存

随着铝工业的发展,赤泥的环境保护问题显得尤为迫切.本文简要评述了赤泥在综合利用和安全堆存方面的研究进展,并从"以废治废"的角度,对赤泥堆场绿化和赤泥用于燃煤脱硫的可行性进行了分析,以期为赤泥的处理找到一条新途径.     

铸铁类模具刃口堆焊工艺技术

介绍了在以普通灰口铸铁为基体的汽车模具刃口上堆焊的工艺过程,以及在焊后对模具刃口修理、焊接质量的检验等方面的注意事项,为汽车模具的制造、修理提供可借鉴的经验。     

基于化学计量学分析堆青时间对白茶香气的影响

堆青是一种有利于茶叶香气转化的手段,本文研究了堆青时间对白茶香气的影响,并分析了感官香气与化合物变化间的联系。感官审评结果表明,堆青使白茶甜香增强而鲜度下降。通过顶空固相微萃取和气相色谱-串联质谱联仪从样品中表征出55种化合物,它们的组成受堆青影响甚微,但含量变化显著。基于化学计量学方法筛选并分析37种差异化合物;主成分分析和层次聚类分析均可区分不同堆青处理的样品,其中堆青前后样品间差异明显。苯乙醇、苯甲醛和苯乙醛等随堆青的总体上升,以及β-环柠檬醛、反-2-辛烯醛和α-紫罗兰酮在堆青后含量的普遍增加,可能是引起甜香增强的原因。而正己醇、反,反-2,4-己二烯醛和辛醛在堆青后含量的普遍减少,则可能与鲜度下降相关。32 h的堆青较有利于白茶香气的发展。化学计量学方法的引入使得样品间差异信息的获取更有效率。     

纳观界面应力集中对复合晶粒断裂应力的影响

为了准确分析纤维增强复合陶瓷内复合晶粒力学性能,提出了一种考虑纳观界面应力集中效应的复合晶粒强度预测方法.基于纤维增强复合陶瓷的显微结构特征,考虑纳米纤维间的相互作用,应用有效自洽法确定纳观界面模型的有效应力场;假设纳观界面处基体和纤维间的应力和位移均连续,利用叠加法将单向拉伸应力状态分解为双向均匀拉伸状态和纯剪切应力状态的组合,根据纤维增强复合陶瓷承受横向载荷的位移函数得到纳观界面附近基体和纤维的位移场和应力场,并计算了纳观界面产生的应力集中因子,综合考虑了复合晶粒内纳观界面和位错塞积相互作用导致的应力集中效应,建立了纤维增强复合陶瓷中复合晶粒的断裂应力预报模型.分析了增强纤维半径和体积分数对复合晶粒断裂应力的影响,结果表明:增强纤维半径越小,断裂应力越大,复合晶粒强度越高,且增强纤维半径大于50 nm后,半径大小对复合晶粒断裂应力影响较小;纤维体积分数越大,断裂应力越小,复合晶粒越易发生破坏.     

残余应力影响压痕尺寸和隆起量的研究

残余应力的存在直接影响材料的力学性能,在压痕法中影响其压痕形状大小、压入载荷-位移曲线和隆起量,因此通过比较压痕形状大小、压入载荷-位移曲线和隆起量的大小,可以推断出构件内部残余应力,再通过有限元研究不同程度的残余应力对压痕形状、压入载荷-位移曲线和隆起量的影响.研究结果表明, 残余压应力使压痕尺寸变小,残余拉应力使压痕尺寸变大,不同性质和大小分布的残余应力使压痕形状为椭圆形,压入载荷-位移曲线斜率和隆起量高度随着残余压应力的增加而增加,随着拉应力的减小而减小,当构件内部存在一定程度的残余拉应力时,随着压入载荷的继续增加出现负隆起量(沉降量),沉降量的大小与压入载荷的大小和残余拉应力的程度有关.     

高效率快裂变室设计方案

介绍了一支用于瞬发中子衰减常数测量的高效率快裂变室的设计方案.裂变室采用21层平板型电极结构设计,镀层235U质量350mg,对快中子的探测效率达到1‰.采用极板窄间距设计和5路信号输出方式实现裂变室的快时间响应,其通过142型电荷灵敏前置放大器输出的信号上升时间约16ns.