Risk-sharing and probabilistic network structure

This paper studies the impact of a probabilistic risk-sharing network structure on the optimal portfolio composition. We show that, even assuming identical agents, we are able to differentiate their optimal risk-choice once we assume the link-structure defining their relationship probabilistic. In particular, the final agent's portfolio composition is function of his location in the network. If we assume positive asset-correlation coefficients, the relative location of a player in the graph influences his risk-behaviour as much as those of his direct and indirect partners in a not-straightforward way. We analyse also two potential "centrality measures" able to select the key-player in the risk-sharing network. The findings may help to select the "central" agent in a risk-sharing community and to forecast the risk-exposure of the players. Finally, this paper may explain natural differences between identical rational agents' choices emerging in a probabilistic network setup

Abnormal electrocardiographic findings in athletes: Correlation with intensity of sport and level of competition.

INTRODUCTION: Athletes can exhibit abnormal electrocardiogram (ECG) phenotypes that require further evaluation prior to competition. These are apparently more prevalent in high-intensity endurance sports. The purpose of this study was to assess the association between ECG findings in athletes and intensity of sport and level of competition. METHODS: A cohort of 3423 competitive athletes had their ECGs assessed according to the Seattle criteria (SC). The presence of abnormal ECGs was correlated with: (1) intensity of sport (low/moderate vs. at least one high static or dynamic component); (2) competitive level (regional vs. national/international); (3) training volume (≤20 vs. >20 hours/week); (4) type of sport (high dynamic vs. high static component). The same endpoints were studied according to the 'Refined Criteria' (RC). RESULTS: Abnormal ECGs according to the SC were present in 225 (6.6%) athletes, more frequently in those involved in high-intensity sports (8.0% vs. 5.4%; p=0.002), particularly in dynamic sports, and competing at national/international level (7.1% vs. 4.9%; p=0.028). Training volume was not significantly associated with abnormal ECGs. By multivariate analysis, high-intensity sport (OR 1.55, 1.18-2.03; p=0.002) and national/international level (OR 1.50, 95% CI 1.04-2.14; p=0.027) were independent predictors of abnormal ECGs, and these variables, when combined, doubled the prevalence of this finding. According to the RC, abnormal ECGs decreased to 103 (3.0%), but were also more frequent in high-intensity sports (4.2% vs. 2.0%; p<0.001). CONCLUSIONS: There is a positive correlation between higher intensity of sports and increased prevalence of ECG abnormalities. This relationship persists with the use of more restrictive criteria for ECG interpretation, although the number of abnormal ECGs is lower

A two-step method for retrieving the longitudinal profile of an electron bunch from its coherent radiation

The coherent radiation emitted by an electron bunch provides a diagnostic signal that can be used to estimate its longitudinal distribution. Commonly only the amplitude of the intensity spectrum can be measured and the associated phase must be calculated to obtain the bunch profile. Very recently an iterative method was proposed to retrieve this phase. However ambiguities associated with non-uniqueness of the solution are always present in the phase retrieval procedure. Here we present a method to overcome the ambiguity problem by first performing multiple independent runs of the phase retrieval procedure and then second, sorting the good solutions by mean of cross-correlation analysis. Results obtained with simulated bunches of various shapes and experimental measured spectra are presented, discussed and compared with the established Kramers-Kronig method. It is shown that even when the effect of the ambiguities is strong, as is the case for a double peak in the profile, the cross-correlation post-processing is able to filter out unwanted solutions. We show that, unlike the Kramers-Kronig method, the combined approach presented is able to faithfully reconstruct complicated bunch profiles.Comment: 22 pages, 5 figure

Phase-and-amplitude recovery from a single phase contrast image using partially spatially coherent X-ray radiation

A simple method of phase-and-amplitude extraction is derived that corrects for image blurring induced by partially spatially coherent incident illumination using only a single intensity image as input. The method is based on Fresnel diffraction theory for the case of high Fresnel number, merged with the space-frequency description formalism used to quantify partially coherent fields and assumes the object under study is composed of a single material. A priori knowledge of the object's complex refractive index and information obtained by characterizing the spatial coherence of the source is required. The algorithm was applied to propagation-based phase contrast data measured with a laboratory-based micro-focus X-ray source. The blurring due to the finite spatial extent of the source is embedded within the algorithm as a simple correction term to the so-called Paganin algorithm and is also numerically stable in the presence of noise

Statistical Image Reconstruction for High-Throughput Thermal Neutron Computed Tomography

Neutron Computed Tomography (CT) is an increasingly utilised non-destructive analysis tool in material science, palaeontology, and cultural heritage. With the development of new neutron imaging facilities (such as DINGO, ANSTO, Australia) new opportunities arise to maximise their performance through the implementation of statistically driven image reconstruction methods which have yet to see wide scale application in neutron transmission tomography. This work outlines the implementation of a convex algorithm statistical image reconstruction framework applicable to the geometry of most neutron tomography instruments with the aim of obtaining similar imaging quality to conventional ramp filtered back-projection via the inverse Radon transform, but using a lower number of measured projections to increase object throughput. Through comparison of the output of these two frameworks using a tomographic scan of a known 3 material cylindrical phantom obtain with the DINGO neutron radiography instrument (ANSTO, Australia), this work illustrates the advantages of statistical image reconstruction techniques over conventional filter back-projection. It was found that the statistical image reconstruction framework was capable of obtaining image estimates of similar quality with respect to filtered back-projection using only 12.5% the number of projections, potentially increasing object throughput at neutron imaging facilities such as DINGO eight-fold

Bargaining in global communication networks

Abstract We study a Rubinstein-Stahl two-player non-cooperative bargaining game played by n players connected in a communication network. We allow the players to communicate with any peer in the same component via the existing paths connecting the peers in a given communication network (global interaction). The unique stationary subgame perfect equilibrium profile characterizes the players’ expected payoff as function of their betweenness centrality score. Secondly, we study a dynamic link-formation game which allows the players to activate new linkages or sever existing ones in order to increase their bargaining power for a given marginal cost per link. We identify the conditions under which the pairwise stable network structures which arise belong to the family of the nested split graphs. These are graphs where the neighbourhood of each node is contained in the neighbourhoods of nodes with higher degrees

Quando eravamo badanti. Storie di donne della Polonia

Attraverso l’utilizzo dell’approccio biografico, sono state ricostruire le traiettorie di vita delle migranti polacche altamente qualificate presenti sul territorio della provincia romana. Si è indagato sulle modalità e sulle motivazioni dei progetti migratori all’interno di una prospettiva transnazionale, mettendo in risalto il ruolo attivo del social network polacco che giustifica l’elevata presenza polacca nella città di Roma da non ricondurre, in maniera riduttiva, a ragioni puramente economiche. Infine, largo spazio è stato dato all’analisi del percorso formativo e professionale per indagare su possibili problematiche legate al corretto utilizzo delle competenze professionali e al riconoscimento del titolo di studio alla luce del fenomeno del sottoinquadramento o del cosiddetto brain waste (spreco dei cervelli)