Stochastic approximations of hybrid systems

This paper introduces a method for approximating the dynamics of deterministic hybrid systems. Within this setting, we shall consider jump conditions that are characterized by spatial guards. After defining proper penalty functions along these deterministic guards, corresponding probabilistic intensities are introduced and the deterministic dynamics are approximated by the stochastic evolution of a continuous-time Markov process. We would illustrate how the definition of the stochastic barriers can avoid ill-posed events such as "grazing", and show how the probabilistic guards can be helpful in addressing the problem of event detection. Furthermore, this method represents a very general technique for handling Zeno phenomena; it provides a universal way to regularize a hybrid system. Simulations would show that the stochastic approximation of a hybrid system is accurate, while being able to handle ''pathological cases". Finally, further generalizations of this approach are motivated and discussed

Baryonic acoustic oscillations simulations for the Large Synoptic Survey Telescope (LSST)

The baryonic acoustic oscillations are features in the spatial distribution of the galaxies which, if observed at different epochs, probe the nature of the dark energy. In order to be able to measure the parameters of the dark energy equation of state to high precision, a huge sample of galaxies has to be used. The Large Synoptic Survey Telescope will survey the optical sky with 6 filters from 300nm and 1100nm, such that a catalog of galaxies with photometric redshifts will be available for dark energy studies. In this article, we will give a rough estimate of the impact of the photometric redshift uncertainties on the computation of the dark energy parameter through the reconstruction of the BAO scale from a simulated photometric catalog.Comment: 4 pages, 2 figures, 10th Rencontres de Blois proceedin

VANTAGGI DELL’UTILIZZO DEL SISTEMA DOSIMETRICO OSL IN CASO DI EMERGENZA

VANTAGGI DELL’UTILIZZO DEL SISTEMA DOSIMETRICO OSL IN CASO DI EMERGENZA S. Abate, F. Campi, L. Garlati, O. Tambussi Politecnico di Milano, Dipartimento di Energia, via La Masa 34, 20156 Milano [email protected] Il sistema dosimetrico per corpo intero OSL (Optically Stimulated Luminescence) è un tipo di dosimetria che si sta sempre più diffondendo in vari paesi. In Europa molti centri di ricerca si sono dotati di un proprio sistema dosimetrico, mentre commercialmente Landauer rappresenta il maggior fornitore di tale servizio dosimetrico, ma anche del sistema stesso (dosimetri e apparecchio di lettura). Il vantaggio di questo tipo di dosimetro consiste nella semplicità e velocità di lettura e azzeramento, anche se risulta meno affidabile dei film-badge. Inoltre, rispetto ai dosimetri a TL, risultano essere più stabili nel tempo, non dovendo subire cicli termici che ne alterano la struttura cristallina e di conseguenza le loro performance. Questo permette di utilizzare, leggere e azzerare anche il singolo dosimetro e non l’intero lotto di appartenenza. Questa caratteristica permette di utilizzare il dosimetro a OSL come un dosimetro passivo, ma col vantaggio della lettura indiretta al termine delle operazioni, proprio come per un dosimetro elettronico viene effettuata la lettura diretta su display. In questo lavoro si vogliono paragonare i vantaggi e gli svantaggi dei sistemi dosimetrici tradizionali (film-badge e TLD) con il sistema OSL. Si presentano i risultati sperimentali delle performance (dipendenza energetica, dosimetrica e angolare) del sistema dosimetrico OSL Inlight con sistema di lettura MicroStar. Infine si presentano i risultati degli irraggiamenti condotti in parallelo presso un centro LAT tra il sistema OSL e i dosimetri elettronici DMC 2000 (Mirion Technologies). Le caratteristiche di questo dosimetro permettono di concludere che questo tipo di sistema dosimetrico ha degli aspetti positivi per il suo utilizzo in caso di emergenza radiologica senza i costi di una dosimetria con strumentazione attiva

Modelling the observed properties of carbon-enhanced metal-poor stars using binary population synthesis

The stellar population in the Galactic halo is characterised by a large fraction of CEMP stars. Most CEMP stars are enriched in $s$-elements (CEMP-$s$ stars), and some of these are also enriched in $r$-elements (CEMP-$s/r$ stars). One formation scenario proposed for CEMP stars invokes wind mass transfer in the past from a TP-AGB primary star to a less massive companion star which is presently observed. We generate low-metallicity populations of binary stars to reproduce the observed CEMP-star fraction. In addition, we aim to constrain our wind mass-transfer model and investigate under which conditions our synthetic populations reproduce observed abundance distributions. We compare the CEMP fractions and the abundance distributions determined from our synthetic populations with observations. Several physical parameters of the binary stellar population of the halo are uncertain, e.g. the initial mass function, the mass-ratio and orbital-period distributions, and the binary fraction. We vary the assumptions in our model about these parameters, as well as the wind mass-transfer process, and study the consequent variations of our synthetic CEMP population. The CEMP fractions calculated in our synthetic populations vary between 7% and 17%, a range consistent with the CEMP fractions among very metal-poor stars recently derived from the SDSS/SEGUE data sample. The results of our comparison between the modelled and observed abundance distributions are different for CEMP-$s/r$ stars and for CEMP-$s$ stars. For the latter, our simulations qualitatively reproduce the observed distributions of C, Na, Sr, Ba, Eu, and Pb. Contrarily, for CEMP-$s/r$ stars our model cannot reproduce the large abundances of neutron-rich elements such as Ba, Eu, and Pb. This result is consistent with previous studies, and suggests that CEMP-$s/r$ stars experienced a different nucleosynthesis history to CEMP-$s$ stars.Comment: 17 pages, 11 figures, accepted for publication on Astronomy and Astrophysic

Preparation, performances and reaction mechanism for the synthesis of H2O2 from H2 and O2 based on palladium membranes

Taking a critically informed approach, this innovative text examines emerging approaches to social procurement within the context of New Public Government (NPG), and examines the practices of social procurement across Europe, North America and Australia. Considering both the possibilities and limitations of social procurement, and the types of value it can generate, this book also provides empirically driven insights into the practicalities of 'triple bottom line' procurement, the related challenges of measuring social value and the management of both the strategic and operational dimensions of procurement processes. As such it will be invaluable reading for all those interest in social services, public governance and social enterprise