Production and changeover control policies of a class of failure prone buffered flow-shops

This article deals with a stochastic optimal control problem for a class of buffered multi-parts flow-shops manufacturing system. The involved machines are subject to random breakdowns and repairs. The flow-shop under consideration is not completely flexible and hence requires setup time and cost in order to switch the production from a part type to another, this changeover is carried on the whole line. Our objective is to find the production plan and the sequence of setups that minimise the cost function, which penalises inventories/backlogs and setups. A continuous dynamic programming formulation of the problem is presented. Then, a numerical scheme is adopted to solve the obtained optimality conditions equations for a two buffered serial machines two parts case. A complete heuristic policy, based on the numerical observations which describe the optimal policies in system states, is developed. It will be shown that the obtained policy is a combination of a KANBAN/CONWIP and a modified hedging corridor policy. Moreover, based on our observations and existent research studies extension to cover more complex flow-shops is henceforth possible. The robustness of such a policy is illustrated through sensitivity analysis.     

On smoothness of Tukey depth contours

The smoothness of Tukey depth contours is a regularity condition often encountered in asymptotic theory, among others. This condition ensures that the Tukey depth fully characterizes the underlying multivariate probability distribution. In this paper we demonstrate that this regularity condition is rarely satisfied. It is shown that even well-behaved probability distributions with symmetrical, smooth and (strictly) quasi-concave densities may have non-smooth Tukey depth contours, and that the smoothness behaviour of depth contours is fairly unpredictable.     

Self-Reported Personal Well-Being of Youth Accessing Intensive Mental Health Treatment

Normative samples have been shown to rate their personal wellbeing (PWB) as positively high and high PWB is associated with many enduring benefits. Cummins (J Happiness Stud 10(6):1–17, 2009) has suggested that PWB has an equilibrium that is set at a rather high positive state and maintained through psychological mechanisms he termed homeostatic protected mood (HPM). Investigators who have explored PWB and mental health disorders have often focused on schizophrenia in adult populations, with varied results, and scant attention has been paid to clinical samples of youth with emotional and/or behavioral disorders. The purpose for this report was to explore the level of PWB reported by a subsample of youth who accessed residential treatment (n = 30) and intensive home based treatment (n = 33) at 12–18 months post-discharge, and explore whether clinical variables could predict PWB. Many youth reported high PWB despite experiencing continued challenges in symptoms and psychosocial functioning. Demographic and clinical characteristics did not predict participants’ PWB scores, lending support for the HPM theory with this sample of youth with emotional and behavioral disorder.     

Are plant communities mainly determined by anthropogenic land cover along urban riparian corridors?

Often used as a mitigation tool to landscape fragmentation, urban riparian corridors also suffered from the effects of the urban expansion. This study explored the relationships between plant riparian communities and two major environmental variables (land cover, soil characteristics) and analyzed the floristic change along an urbanization gradient. Fifteen sites were surveyed on both riverbanks of two riparian corridors characterized by contrasting water regimes in Strasbourg, North Eastern France. Data of spontaneous species abundance was collected from 180 quadrats using (i) all plant species, (ii) herbaceous stratum and (iii) ligneous stratum (bush and tree). The diversity and compositional patterns of riparian plant species were analyzed within each corridor according to three levels of urbanization (urban, suburban, peri-urban). Relationships between riparian communities, land cover and soil chemical properties (pH, nitrogen and carbon content, moisture) were established by between-class co-inertia analyses. Land cover emerged as the main factor explaining changes in riparian communities along the rural–urban gradient while soil chemical properties discriminate water stress and fluvial dynamics of the two corridors. Similar compositional patterns were found within the most urbanized sites with the establishment of ubiquitous species. The herbaceous stratum is best linked to the level of urbanization, whereas the tree stratum is primarily correlated with corridor attributes (hydrological regime, soil properties). Although riparian species and communities are mainly determined by land cover, urban riparian corridors maintain native biodiversity up to the urban center.     

Influence of competition level on referees’ decision-making in handball

The influence of competition level on referees’ decision-making was investigated. Referees’ decisions in 90 handball games (30 games X 3 competition levels) were observed in different situations related to the advantage rule, and 100 referees from two different levels of expertise were subsequently asked to offer explanations for the competition-level effects from the first part of the study. Results revealed that at the highest level of competition referees intervened less frequently with sporting sanctions, but more frequently with disciplinary sanctions. These effects were apparent mainly in immediate intervention situations and unsuccessful advantage situations, but not in successful situations. Referees explained these effects of competition level in terms of a player competence stereotype, in addition to referees’ different expertise across competition level. The implications of the findings for understanding how status-related stereotypes impact on intervention behavior are discussed.     

The effects of teenage childbearing on long-term health in the US: a twin-fixed-effects approach

This paper explores the effect of teenage childbearing on long-term health outcomes and behaviors of mothers using the Midlife Development in the US dataset. Within-family estimations, using samples of siblings, and twin pairs, are employed to overcome the bias generated by unobserved family background and genetic traits. The results suggest no significant effects on health outcomes, and modest effects on health behaviors, including exercise and preventive care. However, accounting for life-cycle effects demonstrates that teenage childbearing has significant effects on both health outcomes and behaviors early in life, but very few significant effects later in life. Moreover, teenage childbearing has a particularly acute effect among minorities. Finally, this paper provides evidence that the effects operate through reduced income and labor force participation, and matching with a lower “quality” spouse.     

Early Retirement: The Case of The Netherlands

ABSTRACT This article takes a closer look at the scope of actual early retirements, reasons for choosing early retirement, the popularity of different types of flexible retirement schemes, and the status of elderly employees within their own organization. It appears that positive reasons for choosing early retirement are more often mentioned by persons in higher professional groups, by those with a higher level of education, and by those who work in the civil service or the service sector. Neutral and negative reasons are mentioned more often by persons in lower professional groups, by those with a lower level of education, and by those working in the industrial sector. Although the motives for opting for early retirement differ, there do not appear to be great differences between categories of respondents if they have been able to choose their age at retirement personally, within specified age limits. Approximately a quarter of the respondents indicated they would leave work at the age of 60, even if this meant a 30% drop in net income.     

Subset sum problems with digraph constraints

We introduce and study optimization problems which are related to the well-known Subset Sum problem. In each new problem, a node-weighted digraph is given and one has to select a subset of vertices whose total weight does not exceed a given budget. Some additional constraints called digraph constraints and maximality need to be satisfied. The digraph constraint imposes that a node must belong to the solution if at least one of its predecessors is in the solution. An alternative of this constraint says that a node must belong to the solution if all its predecessors are in the solution. The maximality constraint ensures that no superset of a feasible solution is also feasible. The combination of these constraints provides four problems. We study their complexity and present some approximation results according to the type of input digraph, such as directed acyclic graphs and oriented trees.