Market ecology of active and passive investors

We study the role of active and passive investors in an investment market with uncertainties. Active investors concentrate on a single or a few stocks with a given probability of determining the quality of them. Passive investors spread their investment uniformly, resembling buying the market index. In this toy market stocks are introduced as good and bad. If a stock receives sufficient investment it will survive, otherwise die. Active players exert a selective pressure since they can determine to an extent the investment quality. We show that the active players provide the driving force whereas the passive ones act as free riders. While their gains do not differ too much, we show that the active players enjoy an edge. Their presence also provides better gains to the passive players and stocks themselves.Comment: 16 pages, 4 figure

Taxonomy and clustering in collaborative systems: the case of the on-line encyclopedia Wikipedia

In this paper we investigate the nature and structure of the relation between imposed classifications and real clustering in a particular case of a scale-free network given by the on-line encyclopedia Wikipedia. We find a statistical similarity in the distributions of community sizes both by using the top-down approach of the categories division present in the archive and in the bottom-up procedure of community detection given by an algorithm based on the spectral properties of the graph. Regardless the statistically similar behaviour the two methods provide a rather different division of the articles, thereby signaling that the nature and presence of power laws is a general feature for these systems and cannot be used as a benchmark to evaluate the suitability of a clustering method.Comment: 5 pages, 3 figures, epl2 styl

«A Chain is gonna come». Building a penicillin production plant in post-war Italy

In 1947, Ernst Chain moved from Oxford to Rome, hired as head of a new biochemistry department and of a penicillin production pilot plant in the Istituto Superiore di Sanità (Higher Health Institute). Here, he managed to make Rome one of the most important centres in the international network of antibiotic science. However, the development of the state-operated centre was not easy. Political and economic pressures, exerted both from home and abroad, posed many obstacles to the plan devised by Domenico Marotta, the general director of the Institute. The paper reconstructs Chain’s venture in Rome, which lasted until 1964, while framing the history of the penicillin production plant in the context of diplomatic negotiations, national politics, and science policies

«A Chain is gonna come». Building a penicillin production plant in post-war Italy

In 1947, Ernst Chain moved from Oxford to Rome, hired as head of a new biochemistry department and of a penicillin production pilot plant in the Istituto Superiore di Sanità (Higher Health Institute). Here, he managed to make Rome one of the most important centres in the international network of antibiotic science. However, the development of the state-operated centre was not easy. Political and economic pressures, exerted both from home and abroad, posed many obstacles to the plan devised by Domenico Marotta, the general director of the Institute. The paper reconstructs Chain's venture in Rome, which lasted until 1964, while framing the history of the penicillin production plant in the context of diplomatic negotiations, national politics, and science policies

Beauty and Distance in the Stable Marriage Problem

The stable marriage problem has been introduced in order to describe a complex system where individuals attempt to optimise their own satisfaction, subject to mutually conflicting constraints. Due to the potential large applicability of such model to describe all the situation where different objects has to be matched pairwise, the statistical properties of this model have been extensively studied. In this paper we present a generalization of this model, introduced in order to take into account the presence of correlations in the lists and the effects of distance when the player are supposed to be represented by a position in space.Comment: 8 pages, 3 figures, submitted to ep

Introduction

Drugs are at the centre of a complexly entangled web of science, politics, economics and culture. They are the product of scientific in- novation, and are usually brought to the bedside by private com- panies, following regulations issued by national and international authorities. These regulations are in turn the product of health poli- cies usually reflecting local cultures and ideologies