Vitamin D. a dynamic molecule. how relevant might the dynamism for a vitamin be

Cholecalciferol, the precursor of Vitamin D3, is a very old, highly conserved, molecule. Its presence is evident in non-mineralized 750 million-year-old living species, such as plankton. The more active metabolites, a receptor and a D binding protein, appear later, along with the increasing complexity of animal species living in the sea. In the sea, however, the biological function of vitamin D is unlikely to be linked with mineral metabolism, and we can hypothesize a relationship with an immune response. It is in terrestrial animals exhibiting cellular bone that the complexity of vitamin D increases. At this stage of evolution, we see the appearance of bone cells that are capable of producing hormones that regulate and are regulated by vitamin D. This interaction starts a sophisticated metabolic system that modulates both mineral and energy metabolism for the requirements of the musculoskeletal system. Among the so-called pleiotropic effects of vitamin D, those resulting from the inhibitory effect on the renin-angiotensin system are of particular interest for nephrologists. Intriguingly, however, more than for anti-hypertensive effects, this interaction could be relevant for anti-inflammatory actions, possibly representative of a residual ancestral role of vitamin D. In addition, this evolutionary dynamism of the vitamin D system should not be separated from the chemical dynamism that characterizes the ligand molecule and its specific receptor. Both are capable of significant tridimensional modifications that contribute to an increase in the variability and the partial predictability of their final biological effect. A dynamic overview of this system that takes into account its evolutionary and adaptive aspects may be helpful to understand its biological complexity and to envisage why using vitamin D metabolites for therapeutic purposes is still a matter of debate

How to get what you want when you do not know what you want. A model of incentives, organizational structure and learning

In this paper we present a model of the interplay between learning, incentives and the allocation of decision rights in the context of a generalized agency problem. Within this context, not only actors face conflicting interests but diverging cognitive ?visions? of the right course of action as well. We show that a principal may obtain the implementation of desired organizational policies by means of appropriate incentives or by means of appropriate design of the allocation of decisions, when the latter is cheaper but more complex. We also show that when the principal is uncertain about which course of action is more appropriate and wants to learn it from the environment, organizational structure and incentives interact in non-trivial ways and must be carefully tuned. When learning is not at stake, incentives and organizational structure are substitutes. When instead learning is at stake, organizational structure and incentives may complement each other and have to be fine tuned according to the complexity of the learning process and the competitive pressure which is put on fast or slow learning.Incentives, Organizational Structure, Learning

A computational voting model

Social choice models usually assume that choice is among exogenously given and non decomposable alternatives. Often, on the contrary, choice is among objects that are constructed by individuals or institutions as complex bundles made of many interdependent components. In this paper we present a model of object construction in majority voting and show that, in general, by appropriate changes of such bundles, different social outcomes may be obtained, depending upon initial conditions and agenda, intransitive cycles and median voter dominance may be made appear or disappear, and that, finally, decidability may be ensured by increasing manipulability or viceversa.Social choice; object construction power; agenda power; intransitive cycles; median voter theorem.