Comments on the shortcomings of predicting the precision of Cavalieri volume estimates based upon assumed measurement functions

It is well known that the estimation of an object's volume by means of serial cross-sections, the so-called Cavalieri method, yields an unbiased estimate. But by itself it provides no means by which to estimate how precise this estimate is unless the shape of the volume is fully known beforehand. This knowledge can only be partially determined from the serial section information that is collected. Methods have been developed that claim to surmount this difficulty by using the serial section data to create a mathematical model of the volume's shape properties. The model then is used to estimate (predict) the precision of the volume estimate (its CE) from the single set of data available. Unfortunately, the theory underlying the model is flawed and so the model itself amounts to no more than an unsubstantiated guess about the shape of the volume. Therefore, the precision of the volume estimates that one obtains from the method is only as good as the model and this cannot be ascertained from the single set of acquired data. In this letter I explain the inadequacies of the modelling method. I suggest that it be used only with caution, if at all. Instead I suggest two alternative ways to predict the CE, one that is based upon a rule-of-thumb approach to the object's shape, and another that is based upon spectral analysis of the measurement function and that is easy to implement with available computer software.     

并行程序设计环境MPICH的应用机理分析

阐述了在PC集群中运用消息传递接口MPICH（Message Passing Interface and Chameleon）进行并行程序设计的基本方法，并以计算圆周率π值的并行算法程序为例，介绍了MPICH中基本例程的功能和调用方法，并行程序设计的关键技术是如何处理好各个进程之间的通信问题，MPICH采用紧迫协议和约定协议来协调各个进程之间的通信，同时也提供了一些阻塞处理函数和非阻塞处理函数，它们能够使进程充分利用系统资源，大大增加用户编程的灵活性。     

测量输入光窗台阶指标的指示表的选择

阐述了对近贴聚焦型微通道板像增强管中输入光窗台阶高度和平整度指标进行测量时，所用指示仪表的选择依据，并详细分析了指示表在检定过程中的误差来源，进一步计算出其合成标准不确定度和扩展不确定度，从而选定可用于测试的指标表。     

调谐质量阻尼器参数设计中的两个问题

本文以单自由度系统安装一个调谐质量阻尼器（简称TMD）为例，对抗风和抗震两类不同激励工况下TMD的参数设计问题进行了理论研究与对比分析。通过给出相对误差系数的概念，定量评价了不同的参数方法对TMD减振性能的影响程度。本文的研究为TMD的参数设计提供了理论指导。     

提高曲面近似展开精度的方法与实现

通过对不可展曲面近似展开精度的研究，提出了根据曲面曲率的大小对曲面自动进行网格划分，通过对综合展开误差数据场进行数据拟合来选取最优展开基点，基于空间曲面与其展开图间近似的等距变换关系进行展开样形的误差矫正等3种方法，这几种方法的实现在不同程度上有效地减小了曲面的近似展开误差，提高了曲面的近似展开精度。     

城市环境的影响与作用

揭示了城市环境的基本性质的基本特征，研究了城市环境对人的心理影响和生理影响。指出城市环境建设不公要满足人的物质需要，还要满足人的精神需要。     

一种适用于有限长度混合相位未知脉冲的最小平方反褶积新方法

普通的最小平方反褶积只有在子波为最小相位脉冲和反射序列为白噪声的假设下才是成立的,而对于混合相位未知脉冲来说,这种最小平方反褶积就不再适用了。本文提出一种适合于有限长度混合相位未知脉冲的最小平方反褶积方法。运用此法只需预先估计一个混合相位子波的长度。合成数据的试验结果表明,该方法有较好的效果,且对预先估计出的子波长度不敏感。文中还证明混合相位未知脉冲最小平方反褶积等效于一种有间隙的平滑误差滤波器的作用,而这种有间隙的平滑误差滤波又可分解为一个前向多步预测误差滤波与一个后向多步预测误差滤波之和。可以预计这种新的反滤积方法将在地震数据处理中得到有效的应用。     

预防HIV传播的药物

药物预防HIV传播是人类战胜HIV的重要手段。现将预防HIV感染药的研发现状，抗HIV药在预防母婴传播，暴露前后预防的研发和应用动态作一综述。     

静态电子轨道衡组成部分解析及其合理选择

阐述静态电子轨道衡诸多优点;工作原理、允许误差及误差分配;轨道衡的结构组成部分、解析各部分的工作特性及技术指标要求;合理选配及推荐实例.     

How Meta-Analysis Increases Statistical Power.

One of the most frequently cited reasons for conducting a meta-analysis is the increase in statistical power that it affords a reviewer. This article demonstrates that fixed-effects meta-analysis increases statistical power by reducing the standard error of the weighted average effect size (T?.) and, in so doing, shrinks the confidence interval around T?.. Small confidence intervals make it more likely for reviewers to detect nonzero population effects, thereby increasing statistical power. Smaller confidence intervals also represent increased precision of the estimated population effect size. Computational examples are provided for 3 effect-size indices: d (standardized mean difference), Pearson's r, and odds ratios. Random-effects meta-analyses also may show increased statistical power and a smaller standard error of the weighted average effect size. However, the authors demonstrate that increasing the number of studies in a random-effects meta-analysis does not always increase statistical power. (PsycINFO Database Record (c) 2010 APA, all rights reserved)