激光粒度仪在分析样品分散方法的比较

激光粒度仪测试粉体粒度中分散方法的选择尤为重要,对测量结果的影响很大。在湿法测试粉体粒度中,同一种粉体在不同的分散剂和分散媒中,因为不同的分散效果在实际的测量中粒度分布并不相同。选用了多组粉体样品分别用水、无水乙醇、汽油3种分散剂进行了测试比较分析。结果表明,在不影响实验结果的前提下,水为首选分散剂;其次为无水乙醇;最后为汽油。     

激光粒度分析仪测试条件对粒径分析的影响

合适的激光粒度分析仪测试条件对于粒径分布数据的准确性至关重要。对比不同粒径粉末在欧美克LS-909激光粒度分析仪、SCF-105B湿法进样器中的测试结果并进行分析。结果表明,对于小于1μm的粉末样品,建议超声60 min以上,遮光率选择5%～8%,泵速选择2 000～3 000 r/min;对于几十μm的粉末样品,可不超声,遮光率选择10%～15%,泵速选择1 500～2 500 r/min;对于几百μm的样品,建议不超声,遮光率选择10%～20%,泵速选择2 500～3 500 r/min。在以上条件下测得的数据可靠且重复性高。     

激光技术在泥沙颗粒分析中的应用

介绍了泥沙颗粒分析的发展及现状 ,简述了激光技术应用于颗粒分析的基本原理及操作流程 ,通过实测资料的对比分析 ,论证了使用激光技术进行河流泥沙颗粒分析的可行性 ,并对保障分析成果质量提出了一些有益的建议     

The Model Size Effect in SEM: Inflated Goodness-of-Fit Statistics Are Due to the Size of the Covariance Matrix

The size of a model has been shown to critically affect the goodness of approximation of the model fit statistic T to the asymptotic chi-square distribution in finite samples. It is not clear, however, whether this “model size effect” is a function of the number of manifest variables, the number of free parameters, or both. It is demonstrated by means of 2 Monte Carlo computer simulation studies that neither the number of free parameters to be estimated nor the model degrees of freedom systematically affect the T statistic when the number of manifest variables is held constant. Increasing the number of manifest variables, however, is associated with a severe bias. These results imply that model fit drastically depends on the size of the covariance matrix and that future studies involving goodness-of-fit statistics should always consider the number of manifest variables, but can safely neglect the influence of particular model specifications.     

消除测量深孔尺寸误差和形状误差的方法

在精度要求较高而且较深的内孔尺寸测量中,往往存在尺寸上的误差,通过采用百分表轴向方向尺寸测量和径向方向尺寸测量重合法,可有效消除测量时的深孔尺寸误差和形状误差,保证工件加工质量。