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271.
The behaviour of vacancies during isothermal ageing following quenching of an Al-1.7at.% Mg-1.1at.% Cu alloy has been studied by positron annihilation lifetime spectroscopy. The positron lifetime parameters vary in parallel with the Vickers hardness of the alloy, suggesting simultaneous migration of vacancies and changes in the size and concentration of vacancies containing clusters and dislocation loops. The results also explain the long hardness plateau observed previously in ageing experiments carried out between 100 and 240°C in terms of a continuous growth of Mg-Cu-vacancy clusters during ageing. The vacancy concentration of the clusters increases gradually until the setting in of the cluster Guinier-Preston-Bagaryatsky zone transformation. 相似文献
272.
A.S. Schneider C.P. Frick E. Arzt W.J. Clegg S. Korte 《Philosophical Magazine Letters》2013,93(6):331-338
Previous research has shown that body-centred cubic (bcc) metals exhibit a smaller size dependence of strength than what is commonly observed in face-centred cubic (fcc) metals. This work investigates compression testing of focused ion beam-manufactured molybdenum pillars ranging in size from 300?nm to 5?μm, both above and below its critical temperature at 300 and 500?K. At 500?K the size effect is found to be consistent with what is observed in fcc metals, owing to the increased mobility of screw dislocations. 相似文献
273.
Joshua M. Englehart 《Social Psychology of Education》2006,9(3):245-272
In an attempt to describe class size effects on student behavior that might be predictable from one setting to the next, the author proposes a social psychology framework. He hypothesizes that social loafing, deindividuation, and social facilitation can explain patterns of student participation, off-task behavior, and in-class performance, respectively, as a function of the size of the class. Data from interviews with eight middle-school teachers suggest that these concepts are marginally applicable to the behaviors in question. At the same time, other class size effects on student behavior are described which may be inherent in class size and thus be reasonably predictable. Josh Englehart is a recent PhD receipient from Cleveland State University. He is currently a public school Physical Education teacher in Painesville, Ohio. His research to date has included class size effects on various outcome variables, teacher perceptions of student intelligence, and student motivation. 相似文献
274.
Single-case designs are a class of repeated measures experiments used to evaluate the effects of interventions for small or specialized populations, such as individuals with low-incidence disabilities. There has been growing interest in systematic reviews and syntheses of evidence from single-case designs, but there remains a need to further develop appropriate statistical models and effect sizes for data from the designs. We propose a novel model for single-case data that exhibit nonlinear time trends created by an intervention that produces gradual effects, which build up and dissipate over time. The model expresses a structural relationship between a pattern of treatment assignment and an outcome variable, making it appropriate for both treatment reversal and multiple baseline designs. It is formulated as a generalized linear model so that it can be applied to outcomes measured as frequency counts or proportions, both of which are commonly used in single-case research, while providing readily interpretable effect size estimates such as log response ratios or log odds ratios. We demonstrate the gradual effects model by applying it to data from a single-case study and examine the performance of proposed estimation methods in a Monte Carlo simulation of frequency count data. 相似文献
275.
Andrew Brand M. T. Bradley Lisa A. Best George Stoica 《The Journal of general psychology》2013,140(4):281-291
The reporting of exaggerated effect size estimates may occur either through researchers accepting statistically significant results when power is inadequate and/or from repeated measures approaches aggregating, averaging multiple items, or multiple trials. Monte-Carlo simulations with input of a small, medium, or large effect size were conducted on multiple items or trials that were either averaged or aggregated to create a single dependent measure. Alpha was set at the .05 level, and the trials were assessed over item or trial correlations ranging from 0 to 1. Simulations showed a large increase in observed effect size averages and the power to accept these estimates as statistically significant increased over numbers of trials or items. Overestimation effects were mitigated as correlations between trials increased but still remained substantial in some cases. The implications of these findings for meta-analyses and different research scenarios are discussed. 相似文献
276.
Jana Holtmann Tobias Koch Katharina Lochner Michael Eid 《Multivariate behavioral research》2016,51(5):661-680
Multilevel structural equation models are increasingly applied in psychological research. With increasing model complexity, estimation becomes computationally demanding, and small sample sizes pose further challenges on estimation methods relying on asymptotic theory. Recent developments of Bayesian estimation techniques may help to overcome the shortcomings of classical estimation techniques. The use of potentially inaccurate prior information may, however, have detrimental effects, especially in small samples. The present Monte Carlo simulation study compares the statistical performance of classical estimation techniques with Bayesian estimation using different prior specifications for a two-level SEM with either continuous or ordinal indicators. Using two software programs (Mplus and Stan), differential effects of between- and within-level sample sizes on estimation accuracy were investigated. Moreover, it was tested to which extent inaccurate priors may have detrimental effects on parameter estimates in categorical indicator models. For continuous indicators, Bayesian estimation did not show performance advantages over ML. For categorical indicators, Bayesian estimation outperformed WLSMV solely in case of strongly informative accurate priors. Weakly informative inaccurate priors did not deteriorate performance of the Bayesian approach, while strong informative inaccurate priors led to severely biased estimates even with large sample sizes. With diffuse priors, Stan yielded better results than Mplus in terms of parameter estimates. 相似文献
277.
Tim Rakow Rebecca J. Wright David J. Spiegelhalter Catherine Bull 《British journal of psychology (London, England : 1953)》2015,106(2):327-348
Funnel plots, which simultaneously display a sample statistic and the corresponding sample size for multiple cases, have a range of applications. In medicine, they are used to display treatment outcome rates and caseload volume by institution, which can inform strategic decisions about health care delivery. We investigated lay people's understanding of such plots and explored their suitability as an aid to individual treatment decisions. In two studies, 172 participants answered objective questions about funnel plots representing the surgical outcomes (survival or mortality rates) of institutions varying in caseload, and indicated their preferred institutions. Accuracy for extracting objective information was high, unless question phrasing was inconsistent with the plot's survival/mortality framing, or participants had low numeracy levels. Participants integrated caseload‐volume and outcome‐rate data when forming preferences, but were influenced by reference lines on the plot to make inappropriate discriminations between institutions with similar outcome rates. With careful choice of accompanying language, funnel plots can be readily understood and are therefore a useful tool for communicating risk. However, they are less effective as a decision aid for individual patient's treatment decisions, and we recommend refinements to the standard presentation of the plots if they are to be used for that purpose. 相似文献
278.
279.
采用词汇判断任务和ERP技术, 操纵义符和声符的家族大小, 考察形声字识别中义符和声符的家族效应。结果发现：(1)当义符为大家族时, 大家族声符字比小家族声符字诱发了更小的P200波幅; 当义符为小家族时, 大家族声符字和小家族声符字诱发的P200波幅差异不显著。(2)大家族声符字比小家族声符字诱发了更大的N400波幅, 但当义符为大家族时, 大、小家族声符字之间的差异比义符为小家族时更加显著。这说明, 义符和声符的家族大小共同影响形声字的识别, 声符的家族效应受义符的家族大小调节。研究表明, 在词汇识别的不同阶段, 义符和声符对资源的获取处于变化状态, 这取决于两者的呈现率差异。整个研究表明, 在形声字的识别中, 义符与声符的作用存在着博弈, 二者作用的此消彼长与加工阶段和家族大小有关。 相似文献
280.
本研究采用3个实验考察编码强度对字体大小效应的影响,探讨由于知觉特征而引发的元认知错觉的内在产生机制(实验1)与有效的矫正措施(实验2和实验3)。结果发现:(1)大字体词语的知觉流畅性显著优于小字体,并且贝叶斯多层中介分析结果表明,知觉流畅性对字体大小效应起部分中介作用(实验1);(2)随着编码强度的增加,由字体大小引起的学习判断错觉逐渐消失(实验2和实验3)。以上结果表明,刺激的知觉特征(字体大小)对个体学习判断的影响,随编码强度激活线索的增加而逐渐减弱。这一结果为真实教学情境中提高学习者的编码强度,进而削弱学习判断对知觉特征线索的依赖,并准确地监测自身的学习进程提供了科学依据。 相似文献