Strengths of Sapphire Crystals
THE strength of single crystals of entirely brittle materials should depend on the presence of stress raising flaws. Internally these could be formed by static dislocation arrays, voids or inclusions of foreign material. On the surface the flaws could be formed by mechanical damage or by surface steps as suggested by Marsh1.
The Bakerian Lecture, 1963. Fracture
Under a large tensile stress the atoms in a solid may slide past one another or they may pull apart. The great contrast between ductile solids such as gold and brittle ones such as diamond has led to a widely held belief that yielding and fracture are independent processes, each occurring at its own characteristic stress, and that a solid is ductile when its yield stress lies below its fracture stress and is brittle conversely. Recent work has shown, however, that they are usually closely interlinked processes, even in the most unlikely solids. One of my aims in this lecture is to show how various types of fracture all depend in some way or other on plastic yielding.
Teaching self-care to delinquent adolescents.
Adolescent delinquency is an ever-increasing societal concern. Certain health problems are concentrated in the delinquent population. Families of delinquent youths often fail to reinforce self-care. Therefore health care providers need to focus on ways to teach delinquent adolescents to care for themselves. This article reviews delinquency and characteristics of juvenile delinquents and their families. A model is presented to guide health care providers to assess delinquent adolescents' abilities to care for themselves and to teach them strategies for self-care.