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.     

Teachers' Perceptions of Their Pupils' Views on Rewards and Punishments

Although sabbatical leave for teachers was suggested in the James Report more than 25 years ago, it remains as much of an unattainable ideal as ever—a sad fact in the light of the message of this paper. What Les Summers tells us clearly illustrates the potential value that sabbaticals might have for teachers: how they might return to school both refreshed and with new and innovatory ideas. The chance to study some schools in Australia enabled Summers to do just this, and he was able to see issues of disaffection here from a new perspective as a result of his experiences. He then went on to develop the idea of a programme which responds to the needs of young school leavers.     

Using game‐based learning to support struggling readers at home

Significant numbers of children (6% of 11‐year‐olds) have difficulties learning to read. Meanwhile, children who receive appropriate support from their parents do better in literacy than those who do not. This study uses a case study approach to investigate how digital games designed to support struggling readers in school were used at home, by the parents of six children to support their children’s literacy. Mostly, the children enjoyed playing the games and believe that it helped improve their reading. The parents all valued the opportunity to participate in their child’s learning and believe that the games’ approach to learning is effective. The study considers key influences on the successful use of games to support struggling readers (repetition, feedback, motivation, self‐efficacy, parental beliefs) and raises questions, further consideration of which might usefully inform the future development of effective game‐based learning.     

Relationship Reciprocation Modulates Resource Allocation in Adolescent Social Networks: Developmental Effects

Adolescence is characterized as a period of social reorientation toward peer relationships, entailing the emergence of sophisticated social abilities. Two studies (Study 1: N = 42, ages 13–17; Study 2: N = 81, ages 13–16) investigated age group differences in the impact of relationship reciprocation within school‐based social networks on an experimental measure of cooperation behavior. Results suggest development between mid‐ and late adolescence in the extent to which reciprocation of social ties predicted resource allocation. With increasing age group, investment decisions increasingly reflected the degree to which peers reciprocated feelings of friendship. This result may reflect social‐cognitive development, which could facilitate the ability to navigate an increasingly complex social world in adolescence and promote positive and enduring relationships into adulthood.