The uses of coherent structure (Dryden Lecture)

The concept of coherent structure in turbulent flow is a revolutionary idea which is being developed by evolutionary means. The main objective of this review is to list some solid achievements, showing what can be done by using the concept of coherent structure that cannot be done without it. The nature of structure is described in terms of some related concepts, including celerity, topology, and the phenomenon of coalescence and splitting of structure. The main emphasis is on the mixing layer, as the one flow whose structure is well enough understood so that technical applications are now being made in problems of mixing and chemistry. An attempt is made to identify some conceptual and experimental obstacles that stand in the way of progress in other technically important flows, particularly the turbulent boundary layer. A few comments are included about the role of structure in numerical simulations and in current work on manipulation and control of turbulent flow. Some recent developments are cited which suggest that the time is nearly right for corresponding advances to occur in turbulence modeling

Development and application of a new measure of employee engagement: the ISA engagement scale

We present a new measure for assessing employee engagement. We build on Kahn’s (1990) theory and develop a model of engagement that has three requirements: a work-role focus, activation and positive affect. This model was operationalized in a new measure: the Intellectual, Social, Affective Engagement Scale (ISA Engagement Scale) comprising three facets: intellectual, social and affective engagement. Data from two studies showed that the scale and its sub-scales have internal reliability. There were associations with task performance, OCB and turnover intentions. Implications are provided for academic enquiry into the engagement process, and for HRD practices that enhance the experience of wor