A population of binaries in the Asymptotic Giant Branch of 47 Tucanae?

We have used a set of archived Hubble Space Telescope/ACS images to probe the evolved populations of the globular cluster 47 Tucanae. We find an excess of Asymptotic Giant Branch (AGB) stars in the cluster core. We interpret this feature as the signature of an extra-population likely made by the progeny of massive stars originated by the evolution of binary systems. Indeed the comparison with theoretical tracks suggests that the AGB population of 47 Tuc can be significantly contaminated by more massive stars currently experiencing the first ascending Red Giant Branch.Comment: 14 pages, 4 figures, in press on ApJ Letter

Topology in SU(2) Yang-Mills theory

New results on the topology of the SU(2) Yang-Mills theory are presented. At zero temperature we obtain the value of the topological susceptibility by using the recently introduced smeared operators as well as a properly renormalized geometric definition. Both determinations are in agreement. At non-zero temperature we study the behaviour of the topological susceptibility across the confinement transition pointing out some qualitative differences with respect to the analogous result for the SU(3) gauge theory.Comment: 3 pages, 4 figures, contribution to Lattice-97. Latex file including espcrc2.st

Self-Commissioning of Inverter Nonlinear Effects in AC Drives

The paper presents a novel technique for an accurate identification of the inverter nonlinear effects, such as the dead-time and on-state voltage drops. The proposed technique is very simple and it is based only on a current control scheme. If the inverter load is an AC motor, the inverter effects can be identified at drive startup using as measured quantities the motor currents and the inverter DC link voltage. The identified inverter error is stored in a Look-Up Table (LUT) that can be subsequently used by the vector control algorithm. The proposed method has been tested on a 1 kVA inverter prototype and the obtained results demonstrate the feasibility of the proposed solutio

A complete census of HαH\alpha emitters in NGC 6397

We used a dataset of archival Hubble Space Telescope images obtained through the F555W, F814W and F656N filters, to perform a complete search for objects showing $H\alpha$ emission in the globular cluster NGC 6397. As photometric diagnostic, we used the $(V-H\alpha)_0$ color excess in the $(V-H\alpha)_0$-$(V-I)_0$ color-color diagram. In the analysed field of view, we identified 53 $H\alpha$ emitters. In particular, we confirmed the optical counterpart to 20 X-ray sources (7 cataclysmic variables, 2 millisecond pulsars and 11 active binaries) and identified 33 previously unknown sources, thus significantly enlarging the population of known active binaries in this cluster. We report the main characteristics for each class of objects. Photometric estimates of the equivalent width of the $H\alpha$ emission line, were derived from the $(V-H\alpha)_0$-excess and, for the first time, compared to the spectroscopic measurements obtained from the analysis of MUSE spectra. The very good agreement between the spectroscopic and photometric measures fully confirmed the reliability of the proposed approach to measure the $H\alpha$ emission. The search demonstrated the efficiency of this novel approach to pinpoint and measure $H\alpha$-emitters, thus offering a powerful tool to conduct complete census of objects whose formation and evolution can be strongly affected by dynamical interactions in star clusters.Comment: Accepted for publication by ApJ; 14 pages, 8 Figures, 1 Tabl

Clusters of Entrepreneurship

Employment growth is strongly predicted by smaller average establishment size, both across cities and across industries within cities, but there is little consensus on why this relationship exists. Traditional economic explanations emphasize factors that reduce entry costs or raise entrepreneurial returns, thereby increasing net returns and attracting entrepreneurs. A second class of theories hypothesizes that some places are endowed with a greater supply of entrepreneurship. Evidence on sales per worker does not support the higher returns for entrepreneurship rationale. Our evidence suggests that entrepreneurship is higher when fixed costs are lower and when there are more entrepreneurial people.Entrepreneurship, Industrial Organization, Chinitz, Agglomeration, Clusters, Cities.

About multi-resolution techniques for large eddy simulation of reactive multi-phase flows

A numerical technique for mesh refinement in the HeaRT (Heat Release and Transfer) numerical code is presented. In the CFD framework, Large Eddy Simulation (LES) approach is gaining in importance as a tool for simulating turbulent combustion pro- cesses, also if this approach has an high computational cost due to the complexity of the turbulent modeling and the high number of grid points necessary to obtain a good numerical solution. In particular, when a numerical simulation of a big domain is performed with a structured grid, the number of grid points can increase so much that the simulation becomes impossible: this problem can be overcomed with a mesh refinement technique. Mesh refinement technique developed for HeaRT numerical code (a staggered finite difference code) is based on an high order reconstruction of the variables at the grid interfaces by means of a least square quasi-eno interpolation: numerical code is written in modern Fortran (2003 standard of newer) and is parallelized using domain decomposition and message passing interface (MPI) standard

Imprinting a complete information about a quantum channel on its output state

We introduce a novel property of bipartite quantum states, which we call "faithfulness", and we say that a state is faithful when acting with a channel on one of the two quantum systems, the output state carries a complete information about the channel. The concept of faithfulness can also be extended to sets of states, when the output states patched together carry a complete imprinting of the channel.Comment: revtex4, 4 pages, submitted to PR

Deep multi-telescope photometry of NGC 5466. II. The radial behaviour of the mass function slope

We use a combination of data acquired with the Advanced Camera for Survey (ACS) on board the Hubble Space Telescope and the Large Binocular Camera (LBC-blue) mounted on the Large Binocular Telescope, to sample the main sequence stars of the globular cluster NGC~5466 in the mass range $0.3<M/M_\odot<0.8$. We derive the cluster's Luminosity Function in several radial regions, from the center of the cluster out to the tidal radius. After corrections for incompleteness and field-contamination, this has been compared to theoretical Luminosity Functions, obtained by multiplying a simple power law Mass Function in the form dN/dm$\propto m^{\alpha}$ by the derivative of the mass-luminosity relationship of the best-fit isochrone. We find that $\alpha$ varies from -0.6 in the core region to -1.9 in the outer region. This fact allows us to observationally prove that the stars in NGC 5466 have experienced the effects of mass segregation. We compare the radial variation of $\alpha$ from the center out to 5 core radii (r$_c$) in NGC 5466 and the globular cluster M10, finding that the gradient of $\alpha$ in the first 5r$_c$ is more than a factor of 2 shallower in NGC 5466 than in M10, in line with the differences in the clusters' relaxation timescales. NGC 5466 is dynamically younger than M10, with two-body relaxation processes only recently starting to shape the distribution of main sequence stars. This result fully agrees with the conclusion obtained in our previous works on the radial distribution of Blue Straggler Stars, further confirming that this can be used as an efficient clock to measure the dynamical age of stellar systems.Comment: Accepted for publications on Ap

Service composition in stochastic settings

With the growth of the Internet-of-Things and online Web services, more services with more capabilities are available to us. The ability to generate new, more useful services from existing ones has been the focus of much research for over a decade. The goal is, given a specification of the behavior of the target service, to build a controller, known as an orchestrator, that uses existing services to satisfy the requirements of the target service. The model of services and requirements used in most work is that of a finite state machine. This implies that the specification can either be satisfied or not, with no middle ground. This is a major drawback, since often an exact solution cannot be obtained. In this paper we study a simple stochastic model for service composition: we annotate the tar- get service with probabilities describing the likelihood of requesting each action in a state, and rewards for being able to execute actions. We show how to solve the resulting problem by solving a certain Markov Decision Process (MDP) derived from the service and requirement specifications. The solution to this MDP induces an orchestrator that coincides with the exact solution if a composition exists. Otherwise it provides an approximate solution that maximizes the expected sum of values of user requests that can be serviced. The model studied although simple shades light on composition in stochastic settings and indeed we discuss several possible extensions