共查询到18条相似文献,搜索用时 187 毫秒
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应用MonteCarlo模拟法研究了分层性物质的组合取样精度,探讨了组合样中组分含量的分布规律、组合取样方差的分布规律、组合取样方差估计值的精度与组合样本数目之间的关系等.考察了组分含量服从正态分布、均匀随机分布及多项分布的分层性总体.结果表明,当样本数目较多时,组合取样误差规律对于不同原始分布的总体是相似的. 相似文献
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应用ICP-AES技术测定了Sr、Ca、Mg、P、Fe、Cu、Mn和Zn等8种生命元素在海带中的分布,发现三种分布模式:(1)Fe、Cu、Mn、Zn在叶状体末端和边缘、固着器末端含量高.其余部位含量低;(2)Sr和Ca的分布规律与第一类相似,但固着器基部高于固着器末端;(3)Mg和P均匀分布.Sr和Ca分布上的相似性提示了它们生理功能上的相似性.这些数据为研究微量元素在海带中的生理功能提供了新资料。 相似文献
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应用ICP-AES技术测定了Sr,Ca,Mg,P,Fe,Cu,Mn和Zn等8种生命元素在海带中的分布,发现三种分布模式;(1)Fe,Cu,Mn,Zn在叶状体末端和边缘,固着器末端含量高,其余部位含量低;(2)Sr和Ca的分布规律与第一类相似,但固着器基部高于固着器末端;(3)Mg和P均匀分布。 相似文献
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应用溶剂化金属原子浸渍(SMAI)法和普通浸渍(CI)法制备了三种不同摩尔比的γ-Al2O3负载Ni-Ag双金属催化剂。XRD和磁测定结果表明SMAI催化剂中Ni和Ag的粒度均小于金属含量相同的CI催化剂,SMAI催化剂中Ni和Ag未形成合金,而CI催化剂中Ni和Ag形成了合金。SMAI和CI催化剂都具有超顺磁性。XPS测定结果表明SMAI催化剂中零价Ni和Ag的含量均高于CI催化剂。SMAI催化剂Ni在表面含量高于体相,Ni在表面富集,而CI催化剂Ni在表面和体相的含量相同 相似文献
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SMAI和CI法制备的Ni—Ag/SiO2催化剂的结构与催化性质研究 总被引:1,自引:0,他引:1
应用溶剂化金属原子浸渍(SMAI)法和普通浸渍(CI)法制备了金属含量相同的SiO2负载Ni-Ag双金属催化剂。XRD和磁测定结果表明SMAI催化剂中Ni和Ag的粒度均小于金属含量相同的CI催化剂,SMAI催化剂中Ni和Ag未形成合金,而CI催化剂中Ni和Ag形成了合金。SMAI和CI催化剂都具有超顺磁性。研究了这些催化剂在甲苯加氢反应的催化性质,结果表明与组成相同的普通浸渍法催化相比,SMAI催 相似文献
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制备了窄分布的含酞侧基聚芳醚砜(PES-C)级份样品,用光散射法测定样品的重均分子量,粘度法测定样品在DMF,CHCl3和1,2-C2H4Cl2中的特性粘数和Huggins参数k^’值,K^’值远大于0.5反映了体系中存在特殊的溶解行为,得到了PES-C在3种溶剂中的Mark-Houwink方程,(η)=2.79×10^-2M^0.615w,r=0.9998(DMF,25℃)(η)=3.96×10 相似文献
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Johan Bjerner Elvar Theodorsson Eivind Hovig Anders Kallner 《Accreditation and quality assurance》2009,14(4):185-192
This study aimed at validating common bootstrap algorithms for reference interval calculation.We simulated 1500 random sets
of 50–120 results originating from eight different statistical distributions. In total, 97.5 percentile reference limits were
estimated from bootstrapping 5000 replicates, with confidence limits obtained by: (a) normal, (b) from standard error, (c)
bootstrap percentile (as in RefVal) (d) BCa, (e) basic, or (f) student methods. Reference interval estimates obtained with
ordinary bootstrapping and confidence intervals by percentile method were accurate for distributions close to normality and
devoid of outliers, but not for log-normal distributions with outliers. Outlier removal and transformation to normality improved
reference interval estimation, and the basic method was superior in such cases. In conclusions, if the neighborhood of the
relevant percentile contains non-normally distributed results, bootstrapping fails. The distribution of bootstrap estimates
should be plotted, and a non-normal distribution should warrant transformation or outlier removal.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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The comparison of parametric and nonparametric bootstrap methods for reference interval computation in small sample size groups 总被引:1,自引:0,他引:1
Abdurrahman Coskun Elvan Ceyhan Tamer C. Inal Mustafa Serteser Ibrahim Unsal 《Accreditation and quality assurance》2013,18(1):51-60
According to the IFCC, to determine the population-based reference interval (RI) of a test, 120 reference individuals are required. However, for some age groups such as newborns and preterm babies, it is difficult to obtain enough reference individuals. In this study, we consider both parametric and nonparametric bootstrap methods for estimating RIs and the associated confidence intervals (CIs) in small sample size groups. We used data from four different tests [glucose, creatinine, blood urea nitrogen (BUN), and triglycerides], each in 120 individuals, to calculate the RIs and the associated CIs using nonparametric and parametric approaches. Also for each test, we selected small groups (m = 20, 30,…, 120) from among the 120 individuals and applied parametric and nonparametric bootstrap methods. The glucose and creatinine data were normally distributed, and the parametric bootstrap method provided more precise RIs (i.e., the associated CIs were narrower). In contrast, the BUN and triglyceride data were not normally distributed, and the nonparametric bootstrap method provided better results. With the bootstrap methods, the RIs and CIs of small groups were similar to those of the 120 subjects required for the nonparametric method, with a slight loss of precision. For original data with normal or close to normal distribution, the parametric bootstrap approach should be used, instead of nonparametric methods. For original data that deviate significantly from a normal distribution, the nonparametric bootstrap should be applied. Using the bootstrap methods, fewer samples are required for computing RIs, with only a slightly increased uncertainty around the end points. 相似文献
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Based on neural network calibration the confidence intervals of aromaticity determination from infrared reflectance spectra of raw brown coals were estimated by means of the bootstrap method, a simplified Monte Carlo Simulation. The standard deviations and the confidence intervals were estimated to characterise the analysis error.It is shown that confidence intervals of non-linear analysis methods like Back Propagation Neural Networks (BPNN) can be estimated by the bootstrap method. The estimated confidence intervals of the calibration confirm the analysis by BPNN. 相似文献
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Silicon-germanium thin films have been analyzed by EDS microanalysis in a field emission gun scanning transmission electron microscope (FEG-STEM) equipped with a high angular dark-field detector (STEM/HAADF). Several spectra have been acquired in the same homogeneous area of the cross-sectioned sample by drift-corrected linescan acquisitions. The Ge concentrations and the local film thickness have been obtained by using a previously described Monte Carlo based "two tilt angles" method. Although the concentrations are in excellent agreement with the known values, the resulting confidence intervals are not as good as expected from the precision in beam positioning and tilt angle position and readout offered by our state-of-the-art microscope. The Gaussian shape of the SiKalpha and GeKalpha X-ray intensities allows one to use the parametric bootstrap method of statistics, whereby it becomes possible to perform the same quantitative analysis in sample regions of different compositions and thicknesses, but by doing only one measurement at the two angles. 相似文献
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This paper extends past computer solutions for confidence intervals in paired counting. The net count is transformed to an
integer; the resultant probability distribution is identical with that for detection limits when the blank is counted an integer
number of times greater than the sample. Summation of the left tail of this distribution is used to determine left-hand and
right-hand confidence limits with specified confidence levels for a given observed net count and known expected blank count
in the sample count time. Poisson statistics are used throughout this paper and the Gaussian distribution is reserved for
approximate results. 相似文献
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Summary Two problems related to non-linear regression, the evaluation of the best set of fitting parameters and the reliability of
the methods used for the estimation of the standard errors of these parameters, are examined. It is shown that a non-linear
curve fitting routine, like the Microsoft Excel Solver, may give more than one solution for the same data set and a simple
Monte Carlo routine is described for the evaluation of the bestfit. For standard errors, the reliability of two procedures
based on the conventional curvature matrix method, four Jackknife techniques and the bootstrap method are examined by comparing
their results to those obtained from a Monte Carlo simulation of the experimental data. It is shown that a fitting parameter
may follow a nonnormal distribution when the equation to be fitted is complicated, even if the errors on the data are normally
distributed. In this case only Monte Carlo methods of data simulation can give accurate information about the standard errors
and the confidence intervals of these parameters. 相似文献
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基于多项分布理论,建立了组合取样方差与取样总体中各子区的大小及其组分含量之间的关系和计算公式,探讨了组合取样常数的物理意义.以颗粒物质为例,探讨了组合取样的逻辑质量单元的概念及其意义,为确定组合取样中的份样质量提供了理论依据.本文对于完善组合取样误差理论,保证组合取样的质量均具有重要意义. 相似文献