Optimal preventive maintenance of leased equipment with corrective minimal repairs

For leased equipment, the lessor carries out the maintenance of the equipment. Usually, the contract of lease specifies the penalty for equipment failures and for repairs not being carried out within specified time limits. This implies that optimal preventive maintenance policies must take these penalty costs into account and properly traded against the cost of preventive maintenance actions. The costs associated with failures are high as unplanned corrective maintenance actions are costly and the resulting penalties due to lease contract terms being violated. The paper develops a model to determine the optimal parameters of a preventive maintenance policy that takes into account all these costs to minimize the total expected cost to the lessor for new item lease. The parameters of the policy are (i) the number of preventive maintenance actions to be carried out over the lease period, (ii) the time instants for such actions, and (iii) the level of action. (c) 2005 Elsevier B.V. All rights reserved.

Get the picture? The effects of iconicity on toddlers' reenactment from picture books

What do toddlers learn from everyday picture-book reading interactions? To date, there has been scant research exploring this question. In this study, the authors adapted a standard imitation procedure to examine 18- to 30-month-olds' ability to learn how to reenact a novel action sequence from a picture book. The results provide evidence that toddlers can imitate specific target actions on novel real-world objects on the basis of a picture-book interaction. Children's imitative performance after the reading interaction varied both as a function of age and the level of iconicity of the pictures in the book. These findings are discussed in terms of children's emerging symbolic capacity and the flexibility of the cognitive representation.

Changes in social identity when joining a new group: The role of individual-level and group-level adaptation processes

While classic intergroup theories have specified the processes explaining situational shifts in social identification, the processes whereby social identities change more profoundly and become integrated within the self have to be proposed. To this aim, the present studies investigate the processes by which group members integrate a new social identity as they are joining a new group. Combining a social identity approach and stress and coping models, this research tests if social factors (i.e., needs satisfied by fellow group members, social support), have an impact on the adaptation strategies group members use to deal with the novelty of the situation and to fit into their new group (seeking information & adopting group norms vs. disengaging). These strategies, in turn, should predict changes in level of identification with the new social group over time, as well as enhanced psychological adjustment. These associations are tested among university students over the course of their first academic year (Study 1), and among online gamers joining a newly established online community (Study 2). Path analyses provide support for the hypothesised associations. The results are discussed in light of recent theoretical developments pertaining to intraindividual changes in social identities and their integration in the self.