Discrete-time synchronization strategy for input time-delay mobile robots

This paper considers a synchronization strategy for a group of differentially driven mobile robots subject to input time-delayed control signals. The continuous time model of the vehicles is exactly discretized in order to obtain a larger dimension representation free of delays. The control strategy is based on the concept of synchronization, under two main assumptions: a specific formation for the group of robots and the tracking of a particular desired trajectory. The control strategy proposed in this work allows the consideration of causal feedback laws avoiding the use of an additional prediction strategy that counteracts the undesired input time-delay effects. The performance of the synchronization strategy is evaluated by real-time experiments with the help of a group of three mobile robots and an indoor absolute localization system based on artificial vision.     

Evolutionary learning of document categories

This paper deals with a supervised learning method devoted to producing categorization models of text documents. The goal of the method is to use a suitable numerical measurement of example similarity to find centroids describing different categories of examples. The centroids are not abstract or statistical models, but rather consist of bits of examples. The centroid-learning method is based on a Genetic Algorithm for Texts (GAT). The categorization system using this genetic algorithm infers a model by applying the genetic algorithm to each set of preclassified documents belonging to a category. The models thus obtained are the category centroids that are used to predict the category of a test document. The experimental results validate the utility of this approach for classifying incoming documents.     

Influence of surface roughness on the color of dental-resin composites

This study deals with the influence of surface roughness on the color of resin composites. Ten resin composites (microfilled, hybrid, and microhybrid) were each polished with 500-grit, 1 200-grit, 2 000-grit, and 4 000-grit SiC papers. The roughness parameter (R _a) was measured using a Plμ confocal microscope, and field-emission scanning electron microscope (Fe-SEM) images were used to investigate filler morphology. Color was measured using a spectroradiometer and a D65 standard illuminant (geometry diffuse/0° specular component excluded (SCE) mode). Surface roughness decreased with grit number and was not influenced by filler size or size distribution. A significant influence of R _a on lightness (L*) was found. Lightness increased with decreases in roughness, except for specimens that underwent polishing procedure 4 (PP4; 500-grit, 1 200-grit, 2 000-grit, and 4 000-grit SiC papers consecutively). Generally, it was found that surface roughness influenced the color of resin composites. The composites that underwent PP1 (500-grit SiC paper) exhibited significant differences in chroma (C*), hue (h°), and lightness (L*) compared to composites that underwent PP3 (500-grit, 1 200-grit, and 2 000-grit SiC papers consecutively) and PP4. Color difference (ΔE*) between the polishing procedures was within acceptability thresholds in dentistry.     

Constructing Explanations in Science: Informal Formative Assessment Practices Among Science Teachers of English Learners

Research in Science Education - Informal formative assessments (IFAs) are classroom interactions teachers use to gather information about their students’ learning, interpret it, and act on...     

Reading achievement in relation to phonological coding and awareness in deaf readers: a meta-analysis

The relation between reading ability and phonological coding and awareness (PCA) skills in individuals who are severely and profoundly deaf was investigated with a meta-analysis. From an initial set of 230 relevant publications, 57 studies were analyzed that experimentally tested PCA skills in 2,078 deaf participants. Half of the studies found statistically significant evidence for PCA skills and half did not. A subset of 25 studies also tested reading proficiency and showed a wide range of effect sizes. Overall PCA skills predicted 11% of the variance in reading proficiency in the deaf participants. Other possible modulating factors, such as task type and reading grade level, did not explain the remaining variance. In 7 studies where it was measured, language ability predicted 35% of the variance in reading proficiency. These meta-analytic results indicate that PCA skills are a low to moderate predictor of reading achievement in deaf individuals and that other factors, most notably language ability, have a greater influence on reading development, as has been found to be the case in the hearing population.     

A cross-cultural study of possible iatrogenic effects of gifted education programs: tenth graders’ perceptions of academically high performing classmates

Previous empirical studies have yielded inconclusive results about peer perceptions of academically high performing students. The purpose of this study was to investigate students’ perceptions of the intellectual ability, positive social qualities, and popularity of a hypothetical new high performing classmate. Participants were 1060 Vietnamese, South Korean, British, Australian, Peruvian, and Spanish boys and girls in 10th grade. The results revealed that the perceptions of academically high performing classmates differed by country group. Positive perceptions of intellectual ability and social qualities were commonly found in all countries except the two Asian countries (Vietnam and South Korea), where the students reported more neutral views of high performers. In conclusion, it is argued that there is no evidence for possible iatrogenic effects of gifted education programs aiming at high achievements     

大学与中小学伙伴协作:美国教师教育中的实践

美国职前教师教育专业计划是与教师准备任教的学生年龄段及科目相对应的,其中特别强调师范生获取大量的教育现场经验。美国在职教师教育的特点主要有,安排经验丰富的教师指导新教师;在职教师必须进行持续的学习。为改进教师教育的质量,美国普遍推行建立大学与中小学之间的伙伴协作关系,其采取的主要形式是建立专业发展学校。专业发展学校的使命有:为教师候选人提供专业准备、促进指导教师的专业发展、开展旨在改进教学实践的探究、提高学生的学业成绩。在美国,大学与中小学之间的伙伴协作既取得了明显的成效,也面临着多方面的挑战。