简单随机抽样中几个问题的探讨

介绍了与简单随机抽样有关的一些概念和这种抽样方式的若干特点,指出了统计教材中对简单随机抽样论述的欠缺,接着对简单随机抽样中的若干难点如每个单位的入样概率是相等的、抽样中的随机原则和如何用随机数字表进行简单随机抽样等进行了探讨.     

挥发酚测定影响因素的控制

为了保证挥发酚成果质量的可靠性和准确性,在挥发酚监测过程中,针对产生误差的因素提出了相应的控制措施。     

基于LabVIEW的抽样定理仿真研究

与连续时间信号相比,离散时间信号的处理更加灵活、方便,应用更加广泛。在实际应用中,通常先将连续时间信号转换成离散时间信号,前提是抽样过程必须满足抽样定理。抽样定理在连续时间信号与离散时间信号之间架起了一座桥梁。本文利用LabVIEW对抽样过程进行仿真,并对抽样定理的条件与结论进行验证和讨论,通过研究可以得到符合实际应用的结论,同时加深对抽样定理的理解和把握。     

压缩采样中基于离散时间马尔科夫链的动态控制机制

针对信号稀疏度在大多数情况下时变且未知的问题,提出了一种实时信号稀疏度预测及最优采样速率确定机制.利用离散时间马尔科夫链对信号稀疏度进行建模,分析信号稀疏度各状态之间变化的规律,根据当前状态预测下一个采样周期内信号的稀疏度状态及概率.此外,基于预测结果,综合考虑采样过程中的能量消耗和信号重构的精确度,以最大化预期收益为...     

基于马尔可夫随机场的图像分割方法研究

在计算机视觉和图像处理等相关领域的Markov(Markov Random Field,即马尔可夫随机场)引入概率这个概念后可以很好地描述图像中各像素间由于处于不同位置而形成的一些特性.主要研究了基于MRF的一种模型——条件随机场CRFs(Conditional Random Fields)模型及其在图像分割中的应用.     

Expectancy-value appraisals and achievement emotions in an online learning environment: Within- and between-person relationships

Motivation and emotion are of critical importance for students' academic learning and achievement. Drawing on Eccles and Wigfield's situated expectancy-value theory and Pekrun's control-value theory, we examined to what extent specific expectancy-value appraisals related to studentsʼ achievement emotions. We collected intensive state data of N = 95 university students over one semester in an online learning environment. Students' appraisals were analyzed on different aggregation levels in a hierarchical design, which accounts for variability within learning situations and between students. Our results corroborated theoretical assumptions that expectancy-value appraisals are positively associated with positive emotions and negatively with negative emotions. However, we found that students experienced positive emotions in learning situations of high intrinsic and utility value, but not in situations of high attainment value. Examining appraisal combinations and discrete emotions, we found that particularly studentsʼ perceived costs moderated the relationship between expectancy and frustration and boredom on the situation level.     

The differences and similarities between curiosity and interest: Meta-analysis and network analyses

Three studies on the relationship between curiosity and interest are reported. The first study was a meta-analysis that examined the Pearson correlations between scales assessing curiosity and interest. Based on 24 studies (31 effect sizes), we found that the curiosity scales correlated with the interest scales at a moderate level (r = 0.53), but they had extremely high heterogeneity. The second and third studies applied network analyses (i.e., co-occurrence analysis and correlation-based analysis) to data that was collected using experience sampling method. Across the studies, we found that while the feelings of curiosity reflected feelings of inquisitiveness, the feelings of interest were aligned with positive affect such as enjoyment and happiness. Importantly, an asymmetrical pattern also was found in curiosity-interest co-occurrences: when feelings of curiosity occurred, the co-occurrence of feelings of interest was highly likely, but not so vice versa. Overall, our findings suggest that feelings of curiosity are special cases of feelings of interest that pertain to knowledge acquisition. Theoretical and practical implications of these findings are discussed.     

Uncovering everyday dynamics in students’ perceptions of instructional quality with experience sampling

Within-student dynamics in perceptions of instructional quality have been neglected, although student states constitute a major share of these perceptions. The present study examined the structure and correlates of student state perceptions of the three basic dimensions, teacher support, cognitive activation, and classroom management. We conducted a three-week experience sampling study using state measures in four subjects (observations: n_mathematics = 2,681, n_physics = 1,555, n_German = 2,026, n_English = 1,835) and analyzed data from 372 German secondary school students (M_age = 15.3 years), conducting two-level confirmatory factor analyses. Against more parsimonious solutions, the postulated three-factor structure was confirmed within- and between-students across subjects, entailing 51% within-student variance on average. Similar to trait-like perceptions, state perceptions were positively related to grades and academic interest. Our results support the factorial and convergent validity of state student perceptions of instructional quality, expanding upon between-person-based literature and uncovering opportunities to enhance teaching effectiveness.     

Childhood sexual experiences with an older partner among men who have sex with men in Buenos Aires,Argentina

This study sought to describe childhood sexual experiences with older partners (CSEOP) among men who have sex with men (MSM) in Buenos Aires, Argentina. MSM were recruited through respondent driven sampling. They responded to a computer administered self-interview with questions on CSEOP, operationalized as manual, oral, genital, or anal contact prior to age 13 with a partner at least 4 years older. Of the 500 respondents, only 25% identified as gay. Eighteen percent of the respondents reported CSEOP, the majority of whom did not feel they were hurt by the experience and did not consider it to be childhood sexual abuse (CSA). Over two-thirds of MSM who reported CSEOP said that their older partner was a female. Only 4% of those with a female partner felt their experience was CSA compared to 44% of those who had a male partner. Among all men reporting CSEOP, those who felt sexually abused were more likely to have been physically forced or threatened, physically hurt, and emotionally hurt than those who did not feel sexually abused. Having CSEOP, being hurt by the experiences, and perceiving the experiences as sexual abuse were not associated with current HIV sexual risk or substance use behavior. In this sample of MSM in Argentina, a substantial minority reported CSEOP. Those who felt they had been sexually abused were much more likely to have had an older male partner than an older female partner, and were more likely to report having been physically forced and threatened by their older partner.