Measurement of the Minority Carrier Diffusion Length in Thin Wafers of Semiconductor Crystals

A method for the measurement of the minority carrier diffusion length and the estimation of the surface recombination rate in thin silicon wafers is described. The method is based on the measurement of the photocurrent flowing through a wafer with identical shallow-lying p–n junctions occupying a sufficiently large area on both sides of the wafer (a phototransistor with a disrupted base). Measurements are performed at two polarities of the bias voltage and two diameters of the radiation beam. Practical recommendations concerning the implementation of this method are given.     

风电齿轮箱行星架多圆弧结构的优化设计研究

针对风电齿轮箱行星架阶梯轴处的应力集中现象,采用过渡多圆弧的改进措施.基于多圆弧曲线的通用几何关系,联合MATLAB和HyperWorks对多圆弧结构进行参数化建模.以多圆弧结构质量最小为优化目标,应力符合强度要求为约束条件建立优化问题,结合代理模型和粒子群算法对多圆弧结构进行优化设计,优化后的应力降低了9.8％,满足疲劳强度要求,优化了时间成本.     

薄壁缸套工作表面的储油结构

研究了薄壁缸套工作表面的储油结构及其对缸套耐磨性的影响 ,对比了松孔镀铬、平顶珩磨、自激振动加工、激光珩磨、冲击加工微坑方法的优缺点 ,提出了一种具有显著节油效果的高耐磨性薄壁缸套的观点     

面向催化剂载体应用的TiO2多孔陶瓷结构优化设计

周期性点阵结构的多孔陶瓷采用增材制造可有效解决传统粉末催化剂可回收性差和块状催化剂催化效率低的问题。由于结构特征参数与应用性能之间的复杂关系,周期性点阵结构的精确与快速设计仍是一个巨大的挑战。针对该挑战,构建了一套用于多孔陶瓷的仿真模型,采用3D打印技术成功制备了具有精细多孔结构的TiO2陶瓷样件,并通过实验实现了对仿真模型的验证和修正。在此基础上,采用单因素优化分析方法进一步探究了结构构成要素对性能的影响机制,选取角度a=153.4°、b=90°、c=45°作为最优参数设计了一种新型周期性点阵结构并进行了优化。对比结果显示,优化设计后的多孔结构的压降减小了57.2%,表面积增大了25.3%。该工作为扩展多孔陶瓷在催化剂载体领域的应用提供了一种新的结构设计方法。     

Control and Measurement of Carrier Gas Flow Rate for High-Precision Gas Chromatography

ABSTRACT

Two computer-compatible mass flow controllers and a mass flow transducer were evaluated by two methods. The first method employed a thermostatted bubble meter for volumetric measurements. The second involved a direct comparison performed either between two flow devices or between a flow device and a differential pressure transducer. The volumetric calibrations exhibited relative standard deviations of approximately 0.1%. However, direct comparison between electronic flow and pressure devices showed short-term resettabilities of better than 0.1% relative standard deviation. Larger day-to-day variations of 0.1 - 0.2% suggested that improved control of ambient conditions might be rewarding.     

响应面模型在结构疲劳优化设计中的应用

利用响应面模型和结构疲劳寿命可视化技术,给出了一种基于疲劳寿命的结构优化设计方法.通过某飞机起落架扭力臂疲劳寿命优化设计算例,验证了方法的有效性.该方法对工程中结构的疲劳优化设计具有重要的参考价值.     

表面结构对喷雾冷却临界热流密度的影响

在闭式循环喷雾冷却系统上,以蒸馏水为工质,研究了表面结构、喷雾流量对喷雾冷却临界热流密度的影响。结果表明,相较于光滑表面,微槽表面可提升临界热流密度;因具有适当的槽深(0.3mm)和较窄的槽宽(0.2mm),No.2槽面的临界热流密度最大,在流量为18.0m L/min时,临界热流密度为175.7W/cm2,比光滑表面提升了59.1%,对应的液体蒸发率达91.4%;增加喷雾流量能大幅提升临界热流密度,特别是对槽面而言更是如此;流量从13.0m L/min增至23.0m L/min时,No.6槽面的临界热流密度由130.7W/cm2增至212.4W/cm2,相对增加了62.5%,同样情况下,光滑表面临界热流密度仅增加了43.6%。表面开槽可有效阻止液滴滚离待冷面,延长液滴停留时间,这是微槽面临界热流密度更大的根本原因。     

Determination of the Orientation of Phospholipid Molecules in Planar Structures from Raman Spectra

A method is proposed for determining the orientation of phospholipid molecules in planar structures from spectra of non-polarized Raman scattering. The method is based on the sensitivity of the intensity of lines of Raman scattering from vibrations of CH2 groups to the orientation of phospholipid molecules. The validity of the method is illustrated on a planar sample of a saturated phospholipid prepared by drying from a solution. The principal component analysis is demonstrated to be a convenient tool for analyzing the spatial distribution of molecule orientations in the sample.     

氢化物发生-原子荧光光谱法测定地表水中微量砷

采用氢化物发生-原子荧光光谱法测定地表水中微量砷，在最佳反应条件和工作条件下，砷的检出限为O．0453ng／mL、精密度为0．3％、回收率分别为87．1％～103．6％之间、线性范围为1．0～100ng／mL。     

一、二阶释放模型在表面微机械中的应用

随着硅表面微机械技术的发展,使得许多微机械器件的制作成为可能.通过对一、二阶释放腐蚀模型进行深入研究,详细分析了一、二阶混合释放腐蚀模型在微机械中几种基本牺牲层腐蚀结构中的应用,并对分析结果进行仿真计算和分析.     

Multivariate Rational Response Surface Approximation of Nodal Displacements of Truss Structures

Polynomial-basis response surface method has some shortcomings for truss structures in structural optimization,concluding the low fitting accuracy and the great computational effort. Based on the theory of approximation, a response surface method based on Multivariate Rational Function basis(MRRSM) is proposed. In order to further reduce the computational workload of MRRSM, focusing on the law between the cross-sectional area and the nodal displacements of truss structure, a conjecture that the determinant of the stiffness matrix and the corresponding elements of adjoint matrix involved in displacement determination are polynomials with the same order as their respective matrices, each term of which is the product of cross-sectional areas, is proposed. The conjecture is proved theoretically for statically determinate truss structure, and is shown corrected by a large number of statically indeterminate truss structures. The theoretical analysis and a large number of numerical examples show that MRRSM has a high fitting accuracy and less computational effort. Efficiency of the structural optimization of truss structures would be enhanced.     

Determination of Zeeman Shifts of Spectral Structures in a Nonuniform Magnetic Field

The variation in the shift of spectral structures due to the Zeeman effect in a spatially nonuniform magnetic field has been studied. It has been found that this shift can be varied by changing the width and shape of spectral structures, their forms, and methods and conditions of recording. A method of accounting for magnetic-field nonuniformity for optically thin and thick media has been proposed.     

表面粗糙度对滑动电接触磨损率的影响

在电气化铁路弓网系统中,磨损率是衡量列车运行状态与接触导线使用状态的重要指标。为了充分模拟弓网系统中磨损率情况,利用自行搭建的滑动电接触摩擦磨损试验机对滑板和接触导线进行摩擦磨损试验,分析滑板表面粗糙度、法向压力、接触电流与运行速度对磨损率的影响。得出结论:滑板磨损率随滑板初始表面粗糙度、接触电流、法向压力、运行速度的增加而增加,而高载荷下粗糙度对于磨损率的影响降低;滑板摩擦从磨合期进入稳定摩擦期存在一个临界表面粗糙度,当滑板初始表面粗糙度值等于临界粗糙度值时,其磨损率最低;不同初始表面粗糙度的滑板在跑合期内磨损过程不同,在稳定摩擦期内磨损过程趋于一致,且摩擦试验后滑板表面粗糙度也接近。     

基于Kriging响应面法的盾构机行星架多目标优化

行星架作为土压平衡盾构主减速器关键零部件之一,为满足轻量化设计要求,考虑其动静态特性要求,建立以体积最小和转动惯量最小的多目标优化模型。为提高设计效率,对设计变量进行相关分析,剔除非敏感因素。通过增强型中心复合设计获得合适设计点,利用有限元方法对设计点进行仿真分析,根据仿真结果建立高精度的Kriging响应面模型。采用Shifted Hammersley技术抽取均匀分布的样本点并权衡优劣,获得了2个Pareto最优解,优化后体积和转动惯量均减小了10%以上,实现了行星架的体积和转动惯量最小的设计要求。     

两种工程结构用钢疲劳裂纹扩展速率的试验研究

对工程结构用钢20MnHR、A508-Ⅲ焊缝和热影响区的疲劳裂纹扩展速率进行了试验研究。试验采用CT试样，用七点递增多项式法求(da/dN)i与(△K)i，并分别将焊缝和热影响区同一组多个试样的(△K)i和(da/dN)i数据点合在一起进行整体回归分析。试验中得列了20MnHR疲劳裂纹扩展速率的斜率转折点，分别测出了平面应变区和平面应力区的Paris表达式。试验分析说明，以平面应变性质为基础的Paris表达式应用于实际工程结构较为安全。     

4号岩石铵梯油炸药爆速测定周期的探讨

本文列举和分析了4号岩石铵梯油炸药实际生产中爆速测定的影响因素,就是否减少4号岩石铵梯油炸药爆速测定的次数做一探讨。     

低载强化后汽车结构件疲劳裂纹扩展速度研究

为了从微观上揭示汽车结构件经过低载强化后疲劳强度和疲劳寿命提高的原因和机理,本文利用扫描电镜,对某汽车前轴低载强化前后试样断口的疲劳裂纹扩展速度进行了对比研究。研究结果表明,经过低载强化后的汽车结构件断口试样,其贝纹线的增长趋势减弱,疲劳辉度间距变小。这些微观变化有效地延缓了疲劳裂纹萌生,降低了疲劳裂纹扩展速率,使汽车结构件的疲劳强度和疲劳寿命都得到提高。     

表面粗糙度对金属平垫泄漏率的影响

为探究金属垫片表面形貌对泄漏率的影响,通过三维形貌仪对不同表面粗糙度的Cu、Al和316L金属垫片进行局部扫描,构建出真实法兰垫片的微观接触模型。在此基础上,进行静力学和计算流体力学分析,通过对流体域设置不同的边界条件,考察不同介质压力下,表面粗糙度和接触压力对泄漏率的影响。仿真结果表明：3种材质的垫片均呈现表面粗糙度越大,则泄漏率越大的趋势;其中,Al垫片的泄漏率对表面粗糙度最为敏感,316L垫片的泄漏率受表面粗糙度的影响最小;当表面粗糙度一定时,施加的接触压力越大,泄漏率越低,但当接触压力达到一定值后,增大接触压力对降低泄漏率的影响将越来越小。     

荧光光度法测定地表水叶绿素a的探讨

利用叶绿素a分子具有天然的荧光的性质,采用CaryEclipse荧光光度计以430nm为激发波长,663nm为发射波长,建立了对地表水叶绿素a含量测定的荧光光度分析方法。叶绿素a浓度在0—150．00μg／L范围内呈良好的线性关系。相关系数r=0．9999,检出限为0．066μg／L,回收率在98％～104％之间。该荧光光度法的灵敏度、准确度和精确度都较好,与传统分析采用的分光光度法进行了比对,结果显示二者并无显著性差异,而且该荧光光度法的操作相比更为简便而灵敏,可以满足并适用于常规地表水叶绿素a的监测。     

离子色谱法检测地表水中丁基黄原酸

目的研究了离子色谱检测地表水中的丁基黄原酸的分析方法。方法利用丁基黄原酸在碱性介质中的稳定性,调节水样pH为9．2,以IonPacAS20柱分离,50mmol／LNaOH为淋洗液,1．0mL／min流速,1mL进样,电导检测。结果丁基黄原酸在5～200p-g／L浓度范围呈良好的线性关系,方法检测限为2．0“g／L,水样平均加标回收率为93．1％,相对标准偏差为5．21％。结论该方法操作简便、灵敏度高、重现性好,适合于地表水的检测。