New insights into the biomechanics of Legg-Calvé-Perthes’ disease: The role of epiphyseal skeletal immaturity in vascular obstruction

ObjectivesLegg–Calvé–Perthes’ disease (LCP) is an idiopathic osteonecrosis of the femoral head that is most common in children between four and eight years old. The factors that lead to the onset of LCP are still unclear; however, it is believed that interruption of the blood supply to the developing epiphysis is an important factor in the development of the condition.MethodsFinite element analysis modelling of the blood supply to the juvenile epiphysis was investigated to understand under which circumstances the blood vessels supplying the femoral epiphysis could become obstructed. The identification of these conditions is likely to be important in understanding the biomechanics of LCP.ResultsThe results support the hypothesis that vascular obstruction to the epiphysis may arise when there is delayed ossification and when articular cartilage has reduced stiffness under compression.ConclusionThe findings support the theory of vascular occlusion as being important in the pathophysiology of Perthes disease

Vygotskian methods of teaching and learning in the English classroom: the case of grammar

This paper describes an alternative approachto the teaching of concepts related to theEnglish curriculum, namely literature, writing summaries and grammar. It combines ashift in the theory of school learning development by a combination with a psychologicaltheory of development. The research was conducted over the period of six months witha class of 20 Grade 10 girls at a private convent school. A method was designed whichincluded the concepts of “mediation”, “the zone of proximal development,” “the doublemove”, using the classical interpretations. In this paper, the research on grammar isdescribed; specifically, parts of speech. The result of this teaching experiment was a veryhigh level of English grammar learning in the classroom.Key words: Vygotsky, Hedegaard, Wells, Tharp and Gallimore, grammar, mediation,zone of proximal development, collaboration

Working in the Zone of Proximal Development (ZPD) in the English classroom: A Case Study on the Teaching of Literature

This paper details an innovative approach to the teaching of literature (fiction) in a Grade 10 convent classroom. This was embedded within a module on English teaching which took six months of the school year. It, however, took the teaching in a deeper way than envisaged in the curriculum, using as it does a theory of school learning within “The Cultural Historical Activity Theory”. The concepts used include “mediation”, “the zone of proximal development,” “the double move”, and “the social situation of development”. The outcome of this teaching experiment was a high level of learner competence in working with South African fiction.Keywords: Vygotsky, Hedegaard, Cultural Historical Activity Theory, Fiction, Mediation, Zone of Proximal Development, Group Wor

LINEAR AND NONLINEAR MIXED-EFFECTS MODELS

Recent developments in computational methods for maximum likelihood (ML) or restricted maximum likelihood (REML) estimation of parameters in general linear mixed-effects models have made the analysis of data in typical agricultural settings much easier. With software such as SAS PROC MIXED we are able to handle data from random-effects one-way classifications, from blocked designs including incomplete blocked designs, from hierarchical designs such as splitplot designs, and other types of data that may be described as repeated measures or longitudinal data or growth-curve data. It is especially helpful that the new computational methods do not depend on balance in the data so we are able to deal more easily with observational studies or with randomly missing data in a designed experiment . We describe some of the new computational approaches and how they are implemented in the nlme3.0 library for the S-PLUS language. One of the most powerful features of this language is the graphics capabilities, especially the trellis graphics facilities developed by Bill Cleveland and his coworkers at Bell Labs. Although most participants in this conference may be more familiar with SAS, and most of the models described here can be fit with PROC MIXED or the NLiNMIX macro or new PROC NLM IXED in SAS version 7, some exposure to the combination of graphical display and model-fitting approaches from S-PLUS may be informative . We show how data exploration with trellis graphics, followed by fitting and comparing mixedeffects models, followed by graphical assessment of the fitted model can be used in a variety of situations. On some occasions, such as modeling growth curves, a linear trend or polynomial trend or other types of linear statistical models for the within-subject time dependence are just not going to do an adequate job of representing the data. In those cases, a nonlinear model is more appropriate. We show how the concept of a random coefficient model can be extended to nonlinear models so as to fit nonlinear mixed-effects models