The detonation wave from solid explosives

It has been shown that the detonation wave from a solid explosive changes in velocity after leaving the explosive. In the case of some low-velocity explosives, e.g., about 2400 metres per second, the velocity of the detonation wave increases by approximately 100–200 metres per second. With other high-velocity explosives, 5000–6000 m./sec., the velocity may decrease to around 4400 metres in some cases.Careful measurements have shown that a zone of uniform velocity exists beyond the surface of the explosive, the dimensions of the zone depending on the diameter of the sphere of the explosive or the diameter of the cartridge detonated. In the case of a $\text{1}\text{1}\text{4}$-inch dynamite cartridge, the zone of uniform velocity extended for about ten inches, while, with a sphere of explosive four inches in diameter, the zone extended for about 25 inches.An explanation of the reason for the high velocity of the detonation wave in the gaseous medium is suggested, linking it up with either the velocity of sound at the temperatures prevailing or the kinetic velocity of the gaseous particles themselves, the latter explanation appearing to be more in accordance with the determined facts. Such an explanation implies the assumption of extremely high momentary temperatures at the wave front, in some cases of over 40,000° C. These extremely high temperatures are due partly to the heat of combustion of the explosive ingredients but more to the heating effect resulting from the enormous pressures developed at the moment of explosion, as previously applied by Berthelot and Dixon in the study of gaseous explosions. Adiabatic conditions are assumed in such calculations. With such an explanation, reasonable agreement between theory and fact is obtained for a number of explosives, and the discrepancies that exist are in cases where discrepancies might be expected.     

Working Memory and Children’s Mathematical Skills: Implications for mathematical development and mathematics curricula

This study examined the contributions of the different components of the working memory (WM) model to a range of mathematical skills in children, using measures of WM function that did not involve numerical stimuli. A sample of 148 children (78 Year 3, mean age 8 years and 1 month, and 70 Year 5 pupils, mean age 9 years and 10 months) completed WM measures and age‐appropriate mathematics tests designed to assess four mathematical skills defined by the National Curriculum for England. Visuo‐spatial sketchpad and central executive, but not phonological loop, scores predicted unique variance in children’s curriculum‐based mathematical attainment but the relative contributions of each component did not vary much across the different skills. Subsequently, the mathematics data were re‐analysed using cluster analysis and new performance‐related mathematics factors were derived. All three components of WM predicted unique variance in these performance‐related skills, but revealed a markedly distinct pattern of associations across the two age groups. In particular, the data indicated a stronger role for the visuo‐spatial sketchpad in the younger children’s mathematics performance. We discuss our findings in terms of the importance of WM in the development of early mathematical ability.     

Urban teachers’ perceptions of inclusion of migrant children in the Chinese educational institution: a comparative study

Recently China has been undergoing an unprecedented urbanisation process which has resulted in millions of rural families living in urban areas. As part of a study of Chinese migrant children's educational experiences, surveys and interviews were conducted with primary school teachers in a metropolitan city in East China. The objectives of this study were to describe teachers’ perceptions of migrant children's education in both migrant schools and in public schools, and to investigate differences in their beliefs between school types. Results found that urban teachers’ perceptions of educational inclusion of migrant students were slightly negative in general. However, teachers in public schools showed significantly more positive attitudes to inclusion of migrant students than migrant school teachers. In the light of these findings, the paper concludes with implications for practice and policy for education of migrant children in China.     

Children born at risk: What's happening in kindergarten?

Many studies examine the development of infants born at risk for medical and developmental problems during the early years of life, but far fewer follow these children into their school years. This project compared high-risk vs. low-risk children in their performance on the WPPSI at pre- and postkindergarten levels. In general, both groups of children demonstrated increases in performance; however, their patterns of performance were different. The high-risk children showed increases predominantly in the Performance areas of the test, whereas the low-risk children demonstrated increases predominantly in the Verbal areas.     

Informal learning: Student achievement and motivation in science through museum-based learning

This study examined changes in student motivation and achievement in science during a visit to a university children’s science museum. The study was based on the pretest–posttest control comparison group design with four treatment groups: control, exhibit, lesson and exhibit/lesson. The sample consisted of 228 sixth-grade students from a Louisiana public school who were randomly assigned to one of the four experimental groups. Pretest, posttest and delayed posttest measures of intrinsic motivation and achievement in science were obtained using the Children’s Academic Intrinsic Motivation Inventory and an achievement test written to measure areas of science incorporated in the museum exhibits. The data were analysed using a one-way ANOVA, dependent t tests and Pearson r. Significant differences were found within groups for (1) the lesson group in motivation and (2) the exhibit group in achievement from pretest to posttest and from posttest to delayed posttest. A significant relationship between level of motivation and science achievement was revealed for the exhibit group on the delayed posttest. There were no other significant findings to support that the treatment led to any long-term effects on motivation or achievement within any of the four experimental groups.