Robin D. Morris

Monte Carlo simulations have been performed, aimed at finding a critical fractional volume (CFV) associated with the onset of percolation for randomly oriented nanotubes (or, indeed, any conductive particles with large aspect ratios) that are randomly dispersed in a low thermo- or electroconductive medium. The nanotubes were treated as capped interpenetrating conductive cylinders (``sticks'') with high (up to 2000) aspect ratio $a$. It has been found that for these aspect ratios the CFV is inversely proportional to $a$ resulting in surprisingly low filler volume loadings, of the order of 0.01%, required to achieve percolation in such systems. By studying fluctuations of the CFV and the density of the percolation clusters, various critical indices of the percolation theory have been calculated including the critical index of conductivity, $t$. For three-dimensional systems it has been found that $t$ decreases substantially with an increase in the aspect ratio. The calculated thermal and electrical conductivity of the nanotube suspensions and composites as functions of the nanotube loading is in good agreement with recent experimental data.

Eight measures of cognitive and language functions in 232 children were subjected to multiple methods of cluster analysis in an effort to identify subtypes of reading disability. Clustering yielded 9 reliable subtypes representing 90% of the sample, including 2 nondisabled subtypes, and 7 reading-disabled subtypes. Of the reading-disabled subtypes, 2 were globally deficient in language skills, whereas 4 of the 5 specific reading-disabled subtypes displayed a relative weakness in phonological awareness and variations in rapid serial naming and verbal short-term memory. The remaining disabled subtype was impaired on verbal and nonverbal measures associated with rate of processing, including rate and accuracy of oral reading. Studies showed evidence for discriminative validity among the 7 reading-disabled subtypes. Results support the view that children with reading disability usually display impairments on phonological awareness measures, with discriminative variability on other measures involving phonological processing, language, and cognitive skills.

In this longitudinal investigation, the development of word-retrieval speed and its relationship to reading was studied in 72 average and 11 severely impaired readers in the kindergarten to grade 2 period (5-8 years). Subjects received a battery of 3 reading measures and 4 continuous naming tests with varied stimulus requirements. Results indicated that the relationship of retrieval speed to reading is a function of development and the correspondence between higher- and lower-level processes in the specific retrieval and reading measures. As automaticity in retrieval developed in average readers, naming-speed/reading relationships moved from strong, general predictions to highly differentiated ones. The strongest correlations were between naming speed for graphological stimuli and lower-level reading tasks. Impaired readers performed slower than average readers on all naming measures across all years, particularly on graphological symbols. 3 dyslexic subgroups emerged: the largest was globally impaired across all naming rate and reading tasks; 2 smaller subgroups had early specific, retrieval-rate deficits and dissociated reading deficits.

The past two decades have witnessed an explosion in our understanding of dyslexia (or specific reading disability), the most common and most carefully studied of the learning disabilities. We first review the core concepts of dyslexia: its definition, prevalence, and developmental course. Next we examine the cognitive model of dyslexia, especially the phonological theory, and review empiric data suggesting genetic and neurobiological influences on the development of dyslexia. With the scientific underpinnings of dyslexia serving as a foundation, we turn our attention to evidence-based approaches to diagnosis and treatment, including interventions and accommodations. Teaching reading represents a major focus. We first review those reading interventions effective in early grades, and then review interventions for older students. To date the preponderance of intervention studies have focused on word-level reading; newer studies are beginning to examine reading interventions that have gone beyond word reading to affect reading fluency and reading comprehension. The article concludes with a discussion of the critical role of accommodations for dyslexic students and the recent neurobiological evidence supporting the need for such accommodations.

This study investigated issues related to commonly used socioeconomic status (SES) measures in 140 participants from three cities (Atlanta, Boston, and Toronto) in two countries (United States and Canada). Measures of SES were two from the United States (four-factor Hollingshead scale, Nakao and Treas scale) and one from Canada (Blishen, Carroll, and Moore scale). Reliability was examined both within (interrater agreement) and across (intermeasure agreement) measures. Interrater reliability and classification agreement was high for the total sample (ranger = .86 to .91), as were intermeasure correlations and classification agreement (range r = .81 to .88). The weakest agreement across measures was found when families had one wage earner who was female. Validity data for these SES measures with academic and intellectual measures also were obtained. Some support for a simplified approach to measuring SES was found. Implications of these findings for the use of SES in social and behavioral science research are discussed.