Impact and extinction signatures in complete Cretaceous-Tertiary (K-T) boundary sections

The Zumaya, Caravaca and Agost sections in Spain, the El Kef section in Tunisia and the Negev (Nahal Avdat) sections in Israel are among the most continuous, expanded and complete K-T boundary sections. The distribution patterns of the planktic faunas were quantitatively analyzed in closely spaced samples across the K-T boundary in these sections, in conjuction with the geochemistry, stable isotopes, mineralogy and magnetostratigraphy. Three hundred foraminiferal specimens were randomly selected and determined. Reliable estimates for the foraminiferal productivity changes across the K-T boundary and for the 1 to 2 Ma interval preceding the K-T boundary were made from the numbers of individuals/gram of sediment corrected for the sedimentation rates (calculated from magnetic reversals and lithology). No gradual or stepwise extinction is seen below the K-T boundary nor any productivity decrease. Stable isotope analyses show a warming just after deposition of the ejecta layer, not cooling as predicted by nuclear winter scenarios, although the duration of such cooling may be too short to be observed even in these complete sections. Low REE values and cpx spherules with quench textures idential to quench-textures in diagenetically altered spherules, strongly indicate an oceanic site of (one of) the impactor(s)

On the Evolution of Product Portfolio Coherence of Cooperatives versus Corporations: An Agent-Based Analysis of the Single Origin Constraint

Agent-based methodology is adopted to analyze the relationship between governance structure and the evolution of product portfolio. A corporation and a cooperative are distinguished by the single origin constraint. The single origin constraint entails that the product requiring the inputs of the members of a cooperative will never be divested. It is es-tablished that a concentric diversification strategy results in randomly distributed clusters of related products of the product portfolio of corporations, while the single origin constraint of a cooperative is responsible for pulling all prod-ucts together in one cluster. More general, the centripetal effect of one product with infinite lifetime on portfolio com-position dominates the centrifugal effect of products with finite lifetime, regardless the number of products with finite lifetime.cooperatives;Concentric diversification;agent-based analysis;product lifetime

Sexual hormones in Achyla. V. Properties of hormone A of Achyla bisexualis

1. The hormonal coordinating mechanism of the sexual process in Achlya is briefly reviewed. 2. A technique is described for culturing the female plant of Achlya bisexualis in sufficient quantity to furnish material for the chemical study of hormone A. 3. A modification of the biological assay for hormone A is described. 4. Many of the properties of hormone A have been determined: (a) solubilities in common organic solvents, (b) adsorption, (c) stability, (d) inactivation, and (e) reactions with certain reagents. 5. A procedure is described whereby enormous enrichment of the active principle has been achieved

Involved fathering: Expanding conceptualisations of men’s paternal caring

Fatherhood has received increased attention during the past few decades in both scholarly writings and public forums, yet the conceptualisation of involved fathering has remained largely limited to the idea that men are merely childcare assistants. In this article the generativity perspective on fathering is considered as a possible theoretical expansion of what paternal involvement may entail. Taking the concept of generativity, as defined by Erik Erikson in his psychosocial development theory, as point of departure, generative fathering refers to paternal conduct that responds to the physical, emotional and cognitive needs of a child. This kind of involved fathering implies that a father is focused on lovingly nurturing his child and improving the wellbeing of his offspring, instead of merely conforming to what is stipulated by society and cultural norms with regard to paternal role obligations

The secret life of woody species : a study on woody species establishment, interactions with herbivores and vegetation succession

Woody species are generally known to be among the most successful plant strategist in the world. They play a prominent role in vegetation dynamics because of their size, longevity and ability to survive under stressful conditions. Nevertheless, the establishment stage, involving seed dispersal, germination and seedling survival is very critical. The main objective of this study is to investigate the biotic and abiotic factors that limit woody species establishment. Furthermore, I investigated the role of woody species in plant-animal interactions, i.e. the direct and indirect interactions between woody species and herbivores.Since woody species do not form seed banks, they strongly depend on the production and dispersal of seeds. During research on secondary succession on abandoned fields, after 30-45 years, woody species became dominant depending on habitat productivity. On rich soils, the colonisation rate of woody species was slower than on poor soils. This difference can be explained by the higher abundance of perennial herbs and grasses on the rich soil type, which inhibited woody species establishment through competition for light, water and nutrients. Establishment chances for late successional 'forest' woody species were found to be higher in early successional communities than in intermediate or late successional communities due to a lower granivory pressure. In early successional communities, abiotic stress was the key factor in woody species establishment of both pioneer as well as mature forest species. During the intermediate and late successional stages, seed predation by small rodents had a negative effect on the establishment of woody species. In the late successional stage, forest species establishment is reduced due to a severe parent tree effect through seedling defoliation by host-specific insects. Grazing exclusion of large herbivores in former, heavily grazed pine woodland resulted in a fast recovery of graze-tolerant shrub species, while grazing introduction in pine forest and oak-beech forest did not have significant effects on the shrub layer. While graze-tolerant woody species were able to recover rapidly following release of grazing, this was not the case for graze-sensitive species like deciduous tree species. Small rodent densities and seed predation intensities were higher in vegetation communities excluded from grazing than in those introduced to grazing. Grazing by large herbivores caused a decrease in small rodent densities. Small rodents depend on vegetation cover for shelter and food. Differences between the effects of introduction and exclusion of grazing by large herbivores on small rodent communities can be explained by differences in vegetation structure development. The recovery of heavily browsed understory vegetation following release of grazing by large herbivores proceeded faster than the understory degradation due to grazing introduction. Introduction of red deer ( Cervus elaphus L.) in former roe deer ( Capreolus capreolus L . ) habitats triggered a significant decrease in roe deer performance in these areas. Shifts in habitat use as well as a lower reproduction success of the latter species pointed to competition for woody forage (browse) between red deer, as superior competitor and roe deer as inferior one. Within the context of vegetation dynamics, woody species play a prominent role in important plant-animal interactions. The establishment stage of woody species can be considered as a significant bottleneck in vegetation succession

Work-family spillover revisited: Is there hope for marital happiness in the dual-earner family?

In the past few decades social scientists have increasingly become aware of the dynamic qualities of gender and marital roles in the family. The changes taking place in terms of both the role contents and role behaviour of especially dual-earner couples have been identified as aspects affecting family life to a large extent. The increasing interface between the work and family spheres, based on the so-called work-family spillover model, has led to the conventional thesis that the non-traditional role behaviour of dualearner spouses and marital dissolution are causally related. The strenuous lifestyle associated with the dual-earner family may therefore have a detrimental effect on marital and familial relationships. This article gives, in the first place, an overview of the dilemmas the dualearner family may be confronted with. In the second place, possible intervening or mediating variables that may come into play in the process of facilitating a work-family fit in the dual-earner family are discussed. Recent research suggests that these intervening variables may not only help dualearner families to cope successfully with strenuous dilemmas, but may even contribute to the experience of higher levels of marital integration and happiness