Scala delle distanze in astrofisica

In astrofisica la determinazione delle distanze ha sempre assunto un ruolo molto importante, poiché essa consente una più accurata comprensione della struttura e dell’evoluzione dell’universo in cui ci troviamo. Ci sono molti metodi che possono essere seguiti, a seconda degli oggetti di studio e dello scopo della ricerca. I metodi diretti (geometrici), utilizzabili solo nei dintorni del Sistema Solare, permettono di calibrare quelli indiretti (indicatori primari e secondari), i quali sono utilizzabili a distanze molto maggiori. Ogni metodo consente di accurare il successivo, creando così un meccanismo di misura chiamato scala delle distanze cosmiche, la quale ha come fine ultimo la calibrazione della legge di Hubble, di fondamentale importanza in cosmologia

Jeans modeling of massive early-type galaxies with observed stellar kinematic profiles up to 2-3 effective radii

A recent integral-field spectroscopic (IFS) survey, the MASSIVE survey (Ma et al. 2014), observed the 116 most massive (MK 10^11.6 M⊙) early-type galaxies (ETGs) within 108 Mpc, out to radii as large as 40 kpc, that correspond to ∼ 2 − 3 effective radii (Re). One of the major findings of the MASSIVE survey is that the galaxy sample is split nearly equally among three groups showing three different velocity dispersion profiles σ(R) outer of a radius ∼ 5 kpc (falling, flat and rising with radius). The purpose of this thesis is to model the kinematic profiles of six ETGs included in the MASSIVE survey and representative of the three observed σ(R) shapes, with the aim of investigating their dynamical structure. Models for the chosen galaxies are built using the numerical code JASMINE (Posacki, Pellegrini, and Ciotti 2013). The code produces models of axisymmetric galaxies, based on the solution of the Jeans equations for a multicomponent gravitational potential (supermassive black hole, stars and dark matter halo). With the aim of having a good agreement between the kinematics obtained from the Jeans equations, and the observed σ and rotation velocity V of MASSIVE (Veale et al. 2016, 2018), I derived constraints on the dark matter distribution and orbital anisotropy. This work suggests a trend of the dark matter amount and distribution with the shape of the velocity dispersion profiles in the outer regions: the models of galaxies with flat or rising velocity dispersion profiles show higher dark matter fractions fDM both within 1 Re and 5 Re. Orbital anisotropy alone cannot account for the different observed trends of σ(R) and has a minor effect compared to variations of the mass profile. Galaxies with similar stellar mass M∗ that show different velocity dispersion profiles (from falling to rising) are successfully modelled with a variation of the halo mass Mh

Design and preliminary validation of a tool for the simulation of train braking performance

Train braking performance is important for the safety and reliability of railway systems. The availability of a tool that allows evaluating such performance on the basis of the main train features can be useful for train system designers to choose proper dimensions for and optimize train's subsystems. This paper presents a modular tool for the prediction of train braking performance, with a particular attention to the accurate prediction of stopping distances. The tool takes into account different loading and operating conditions, in order to verify the safety requirements prescribed by European technical specifications for interoperability of high-speed trains and the corresponding EN regulations. The numerical results given by the tool were verified and validated by comparison with experimental data, considering as benchmark case an Ansaldo EMU V250 train—a European high-speed train—currently developed for Belgium and Netherlands high-speed lines, on which technical information and experimental data directly recorded during the preliminary tests were available. An accurate identification of the influence of the braking pad friction factor on braking performances allowed obtaining reliable results

Localization algorithm for a fleet of three AUVs by INS, DVL and range measurements

The strong research efforts undergone in Marine Robotics during the last two decades open great possibilities for maritime operations. Autonomous Underwater Vehicles (AUVs) take the crew away from dangerous situations at depths of sea, with available and cost-affordable technology. MDM Lab, the Laboratory of Mechatronics and Dynamic Modelling of the University of Florence, is partner of the Thesaurus project, funded by Regione Toscana, with the aim of designing a moderate-cost AUV, called Tifone, to be used, in swarm, for research and monitoring of archaeological sites. In this paper we propose a Localization Algorithm for a fleet of three vehicles and a surface support ship which employs several sensors. Each AUV is equipped with low-cost sensors such as IMU, magnetometer and depth sensor; two of them have an high accuracy velocity sensor such as the Doppler Velocity Log. Acoustic modems, used for communication between AUVs, can provide the time of flight from an AUV to an another one. The positions estimated with a Range-Based algorithm fuse with the ones estimated by INS&DVL, avoiding unbounded error growth in the position estimate of the AUVs. © 2011 IEEE