扩展重要抽样法及其在平尾转轴可靠性分析中的应用

提出了扩展重要抽样法，用以计算结构系统的多个失效模式中含有不全相同基本随机变量时的系统失效概率。通过构造扩展重要抽样法的抽样密度函数，给出该方法失效概率的估计值，以及其方差和变异系数的计算公式。并将此方法用于某型飞机平尾转轴的可靠性分析，算例结果表明其优越性。     

Measure concentration in optimization

We discuss some consequences of the measure concentration phenomenon for optimization and computational problems. Topics include average case analysis in optimization, efficient approximate counting, computation of mixed discriminants and permanents, and semidefinite relaxation in quadratic programming.     

Uncertainty evaluation from Monte-Carlo simulations by using Crystal-Ball software

The first Supplemental Guide to the current edition of the Guide to the expression of uncertainty measurement (GUM) deals with the propagation of distributions, and emphasizes the use of Monte-Carlo Simulation (MCS) for estimating the uncertainty of measurands. In order to carry out MCS we need computer programs for generating pseudo-random numbers and for solving numerically the integral equations arising when simulating the values of the specification variables with a given probability density function (PDF). Crystal-Ball commercial software is very suitable for performing MCS and to estimate the expanded uncertainty for the measurand. The use of Crystal-Ball is illustrated with two working examples dealing with specification models of non-linear features and with correlated variables (such as the slope and intercept of calibration straight lines), respectively.An erratum to this article can be found at     

Adsorption of small uremic toxin molecules on MFI type zeolites from aqueous solution

Adsorption properties of zeolites were investigated for the removal of p-cresol from aqueous solutions at 37 °C within the context of studying alternative methods to dialysis for removing uremic toxin from blood. MFI-framework type zeolites with different degrees of hydrophobicity and charge compensating cations were prepared: one pure silica MFI and four alumino-silicate MFIs (Si/Al = 30), with H⁺, Na⁺, K⁺ and Mg²⁺ as charge compensating cations. Adsorption isotherms and microcalorimetric measurements show a high affinity of p-cresol for all MFI type zeolites. The best capacity is obtained for the pure silica MFI, whereas the alumino-silicate samples show a higher affinity in the low concentration range. In the case of pure silica sample, the microscopic adsorption mechanism including the role of confined water is elucidated with the help of NMR, X-ray analysis (including Rietveld refinement) and Monte Carlo simulations. For all samples the high affinity is preserved in physiological serum solution, even in the presence of other toxin molecules such as urea. It is also shown that the compensating cation state of the samples is imposed by the physiological medium.     

Monte-carlo simulation of gas chromatographic separation for the prediction of retention times and peak half widths

Summary A new method for prediction of gas chromatographic retention times and peak half widths is based on the renewal theory. The only requirements are the heats of vaporization of the compounds to be separated and one calibration measurement. With this data, retention times and peak half widths can be predicted for isothermal as well as temperature-programmed gas chromatography. For the separation of non-polar substances on non-polar stationary phases the prediction error for retention times is approx. 1–2%. First simulations of polar molecules and polar stationary phases indicate that this method is also applicable in these cases but some extension will be required.     

圆形阵列法在能谱测量中的应用

在高能闪光照相技术中,高能X射线的能谱测量一直是一个难点。在以往研究方法的基础上,指出控制散射的影响程度是提高能谱测量精度的关键。提出采用圆形阵列法对X射线能谱进行测量,并针对一特定能谱的X射线设计了测量装置,蒙特卡罗模拟结果表明,可以将散射的影响控制在4%以内,这对提高能谱测量精度具有十分重要的意义。     

铝基碳化硼材料中子屏蔽性能的蒙特卡罗模拟

采用蒙特卡罗方法, 运用MCNP4C程序研究了碳化硼含量20%–40%、中子能量200 eV–15 keV、材料厚度0.3–2 cm对B₄C/Al复合材料中子屏蔽性能的影响. 结果表明: 碳化硼含量与中子透射系数呈一次线性下降关系; 同含量的碳化硼, B₄C/Al材料的中子屏蔽效果要大大优于聚乙烯碳化硼材料; 在等厚度条件下, 模拟试样B20等的中子屏蔽效果要优于水、铜、混凝土等常规屏蔽材料; 材料厚度与中子透射系数呈指数下降关系, 且单位厚度的增加对中子透射系数改变很大; 含硼量对热中子透射系数影响很大; 在热中子能区, 中子每单位能量的变化对中子透射系数改变较大; 在慢中子能区, 中子每单位能量的变化对中子透射系数改变很小. 关键词： 中子透射系数 蒙特卡罗 铝基复合材料 碳化硼     

乏燃料贮运用铝基碳化硼复合材料的屏蔽性能计算

采用蒙特卡罗方法, 利用MCNP程序计算了在中子能量为0.5–20 MeV, ²³⁵U核热中子裂变源条件下, 厚度为3–9 cm、碳化硼含量5%–15%的铝基碳化硼复合材料在空气、水、200–1400 ppm (1 ppm=10^-6) 硼酸溶液介质中的中子透射系数. 结果表明: B₄C/Al复合材料的透射系数随碳化硼含量和材料厚度的增加而减少, 随中子能量的升高而增大, 而硼酸浓度的改变对中子透射系数影响不大. B₄C/Al复合材料在水中比硼酸中更能发挥其屏蔽效果, 在空气中屏蔽特性显现出“反转”现象, 中子能量高于5 MeV时透射系数几乎没有变化. 在裂变源条件下的B₄C/Al复合材料中子透射系数均比稳定源20 MeV 低. 介质的中子屏蔽效果是硼酸溶液>水> 空气, 水介质的中子透射系数与介质厚度呈指数下降关系, 裂变源和稳定源条件下分别近似为e^-0.71x和e^-0.669x, x为厚度(cm). 关键词： 蒙特卡罗 乏燃料设备 中子吸收材料 4C/Al')" href="#">B₄C/Al     

飞秒电子衍射系统中调制传递函数的理论计算

主要介绍了飞秒电子衍射系统的组成及设计指标. 包括光电阴极、电子聚焦系统、电子偏转系统、双微通道板(MCP)电子探测器等，并给出了基本的设计思路、设计结果. 光电阴极是由位于蓝宝石晶体上面的银膜构成，为了获得足够小的电子束斑以及减小电子上靶时的角度，紧贴栅极后放置一个100μm的小孔，对电子束的形状和大小进行限制. 采用磁电子透镜进行聚焦，电子衍射图样由放置在样品后面的双MCP像增强器进行探测. 在设计计算时，用Monte Carlo方法对光电子的初能量、初角度以及初位置分布进行抽样，用有限元法计算磁透镜 关键词： 飞秒电子枪 有限元法 Monte Carlo模拟 调制传递函数     

蒙特卡罗模拟重建组织的自体荧光光谱

分别以一个双层的正常胃肠壁模型(包括正常粘膜层和粘膜下层)和一个双层的癌变胃肠壁模型(包括癌变粘膜层和粘膜下层)为研究对象，通过蒙特卡罗模拟计算出每层组织产生的荧光，从而重建出正常和癌变组织的自体荧光光谱，并和实验结果进行了比较。理论重建的光谱和实验测得的光谱在整体形状上的一致性表明，蒙特卡罗方法能够精确地模拟组织中荧光的产生和传输过程，明确解释癌变导致的组织生荧团信息的变化，从而确定组织是否发生病变。