Stochastic modelling of the invasion process of nematodes in fly larvae

Stochastic models based on Markov birth processes are constructed to describe the process of invasion of a fly larva by entomopathogenic nematodes. Various forms for the birth (invasion) rates are proposed. These models are then fitted to data sets describing the observed numbers of nematodes that have invaded a fly larval after a fixed period of time. Non-linear birthrates are required to achieve good fits to these data, with their precise form leading to different patterns of invasion being identified for three populations of nematodes considered. One of these (Nemasys) showed the greatest propensity for invasion. This form of modelling may be useful more generally for analysing data that show variation which is different from that expected from a binomial distribution.

Voices of lay principals: Promoting a Catholic character and culture in schools in an era of change

This paper reports a qualitative study of the practice of leadership in Catholic schools to ascertain the perceptions of lay principals, who as positional leaders play a critical role in embracing and creatively rebuilding the Catholic vision of life within the reality that the Catholic school principalship is now a ministry of the laity. The methodology included semi-structured interviews, field notes, reflexive journals, direct observation, and document nalysis. The study examined both individual human behaviour and the structure of the social order in Catholic schools. The findings point towards successful leadership in Catholic schools being highly influenced by the cultural and spiritual capital that a principal brings to a school signifying a fundamental importance of appointing principals who are not only professionally competent but spiritually as well. In an era of unprecedented social, educational and ecclesial change, and with an ever widening role description, lay principals are challenged to redefine and re-articulate their Catholic character and identity, and will need to look for new ways to make this explicit. Embracing a new leadership paradigm of shared leadership, the preparation and on-going formation of lay principals were identified as critical for the continuance of the Catholic school’s distinctive mission in the future.

Pockets of flexibility in workflow specification

Workflow technology is currently being deployed in quite diverse domains. However, the element of change is present in some degree and form in almost all domains. A workflow implementation that does not support the process of change will not benefit the organization in the long run. Change can be manifested in different forms in workflow processes. In this paper, we first present a categorization of workflow change characteristics and divide workflow processes into dynamic, adaptive and flexible processes. We define flexibility as the ability of the workflow process to execute on the basis of a loosely, or partially specified model, where the full specification of the model is made at runtime, and may be unique to each instance. To provide a modeling framework that offers true flexibility, we need to consider the factors, which influence the paths of (unique) instances together with the process definition. We advocate an approach that aims at making the process of change part of the workflow process itself. We introduce the notion of an open instance that consists of a core process and several pockets of flexibility, and present a framework based on this notion, which makes use of special build activities that provide the functionality to integrate the process of defining a change, into the open workflow instance.