Treatment of realistic tidal field in Monte Carlo simulations of star clusters

We present a new implementation of the Monte Carlo method to simulate the evolution of star clusters. The major improvement with respect to the previously developed codes is the treatment of the external tidal field taking into account for both the loss of stars from the cluster boundary and the disk/bulge shocks. We provide recipes to handle with eccentric orbits in complex galactic potentials. The first calculations for stellar systems containing 21000 and 42000 equal-mass particles show good agreement with direct N-body simulations in terms of the evolution of both the enclosed mass and the Lagrangian radii provided that the mass-loss rate does not exceed a critical value.Comment: 17 pages, 13 figures, accepted for publication by MNRA

Mitigation technologies for counteracting the UHI effects and for improving outdoor thermal comfort in mediterranean urban open spaces: a study of vegetation and cool materials effects on pedestrian comfort in Rome

The present study investigates the influence of building materials, traditional as well as innovative, and vegetated urban surfaces on the urban microclimate and on pedestrian outdoor thermal comfort in a typical Mediterranean city: Rome. It focuses the attention on selected mitigation technologies aiming to increase the albedo of cities: high reflective materials called cool colored materials, and the use of vegetative surfaces: green roofs, green walls and trees, with the main purpose to test, verify and quantify the overall microclimate mitigation and thermal performance of the aforementioned strategies, The study proposes and analyses, through CFD calculations (ENVImet v.4.0), five renovations scenarios: applying cool materials and vegetation on roofs, walls and pavements of the selected square. In order to support planning authorities and researches by going beyond the traditional way of urban heat island studies, the present study aims to highlight the multiple effects of cool colored materials on human comfort and to investigates which could be the best combination materials in terms of mitigation of ambient temperatures and pedestrian thermal stress. Therefore, air temperature as well as the physiologically equivalent temperature (PET) were applied to take into account the effect of the variations of urban materials on human comfort, the studies focuses the attention and draw its conclusions through the comparison of the Envimet thermal maps and the values of the different scenarios in terms of deltas variations. The results show the negative effect of cool colored materials on human thermal comfort when applied isolated to surfaces in direct contact with pedestrians, such as pavements and urban façades, nevertheless it underlines the benefit associated with a mixed combination of cool materials and trees, setting the path for further research in this direction

Characterizing Dust Attenuation in Local Star-Forming Galaxies: Near-Infrared Reddening and Normalization

We characterize the near-infrared (NIR) dust attenuation for a sample of ~5500 local (z<0.1) star-forming galaxies and obtain an estimate of their average total-to-selective attenuation $k(\lambda)$. We utilize data from the United Kingdom Infrared Telescope (UKIRT) and the Two Micron All-Sky Survey (2MASS), which is combined with previously measured UV-optical data for these galaxies. The average attenuation curve is slightly lower in the far-UV than local starburst galaxies, by roughly 15%, but appears similar at longer wavelengths with a total-to-selective normalization at V-band of $R_V=3.67\substack{+0.44 \\ -0.35}$. Under the assumption of energy balance, the total attenuated energy inferred from this curve is found to be broadly consistent with the observed infrared dust emission ($L_{\rm{TIR}}$) in a small sample of local galaxies for which far-IR measurements are available. However, the significant scatter in this quantity among the sample may reflect large variations in the attenuation properties of individual galaxies. We also derive the attenuation curve for sub-populations of the main sample, separated according to mean stellar population age (via $D_n4000$), specific star formation rate, stellar mass, and metallicity, and find that they show only tentative trends with low significance, at least over the range which is probed by our sample. These results indicate that a single curve is reasonable for applications seeking to broadly characterize large samples of galaxies in the local Universe, while applications to individual galaxies would yield large uncertainties and is not recommended.Comment: 14 pages, 10 figures, 1 table. Accepted for publication in Ap

Percolation threshold of carbon nanotubes filled unsaturated polyesters

This paper reports on the development of electrically conductive nanocomposites containing multi-walled carbon nanotubes in an unsaturated polyester matrix. The resistivity of the liquid suspension during processing is used to evaluate the quality of the filler dispersion, which is also studied using optical microscopy. The electrical properties of the cured composites are analysed by AC impedance spectroscopy and DC conductivity measurements. The conductivity of the cured nanocomposite follows a statistical percolation model, with percolation threshold at 0.026 wt.% loading of nanotubes. The results obtained show that unsaturated polyesters are a matrix suitable for the preparation of electrically conductive thermosetting nanocomposites at low nanotube concentrations. The effect of carbon nanotubes reaggregation on the electrical properties of the spatial structure generated is discussed

MiBACT: le Linee guida per l’efficienza energetica dei beni culturali

Le “Linee guida di indirizzo per il miglioramento dell’efficienza energetica nel patrimonio culturale dell’Architettura e dei Centri e nuclei storici e urbani”, elaborate nel 2015 da un apposito tavolo di lavoro del MiBACT, costituiscono per l’Italia un fondamentale strumento per orientare gli interventi di efficientamento energetico del patrimonio culturale costruito, stimolare il dialogo tra gli stakeholder settoriali e promuovere la ricerca scientifica. Le Linee guida MiBACT, pur non codificando prescrizioni metodologiche a carattere vincolante, ma fornendo informazioni operative a progettisti e tecnici attivi nel settore, offrono indicazioni di base per il miglioramento energetico del patrimonio tutelato nell’ottica di una stategia di contenimento dei consumi sinergica con le strategie istituzionali di gestione, valorizzazione e conservazione. MiBACT: energy efficiency Guidelines in historic buildings The “Guidelines for Energy Performance in Cultural Heritage and Historical Buildings”, devised in 2015 by a special MiBACT working table, constitute a fundamental tool for Italy to guide energy efficiency improvements of its cultural heritage buildings, stimulating dialogue between sector-specific stakeholders and promoting scientific research. The MiBACT Guidelines, whilst not methodological requirements of a binding nature, instead provide operational information to designers and technicians working in this sector, with general guidelines for improving energy efficiency of protected heritage sites and with a view to an energy-saving strategy in combination with Institutional management, development and conservation strategies

Probing the formation history of the nuclear star cluster at the Galactic Centre with millisecond pulsars

The origin of the Nuclear Star Cluster in the centre of our Galaxy is still unknown. One possibility is that it formed after the disruption of stellar clusters that spiralled into the Galactic Centre due to dynamical friction. We trace the formation of the Nuclear Star Cluster around the central black hole, using state-of-the-art N-body simulations, and follow the dynamics of the neutron stars born in the clusters. We then estimate the number of Millisecond Pulsars (MSPs) that are released in the Nuclear Star Cluster, during its formation. The assembly and tidal dismemberment of globular clusters lead to a population of MSPs distributed over a radius of about 20 pc, with a peak near 3 pc. No clustering is found on the sub-parsec scale. We simulate the detectability of this population with future radio telescopes like the MeerKAT radio telescope and SKA1, and find that about of order ten MSPs can be observed over this large volume, with a paucity of MSPs within the central parsec. This helps discriminating this scenario from the in-situ formation model for the Nuclear Star Cluster that would predict an over abundance of MSPs closer to the black hole. We then discuss the potential contribution of our MSP population to the gamma-ray excess at the Galactic Centre.Comment: 11 pages, 8 figures, accepted for publication in MNRA

Scalar Field Theory on Non-commutative Snyder Space-Time

We construct a scalar field theory on the Snyder non-commutative space-time. The symmetry underlying the Snyder geometry is deformed at the co-algebraic level only, while its Poincar\'e algebra is undeformed. The Lorentz sector is undeformed at both algebraic and co-algebraic level, but the co-product for momenta (defining the star-product) is non-co-associative. The Snyder-deformed Poincar\'e group is described by a non-co-associative Hopf algebra. The definition of the interacting theory in terms of a non-associative star-product is thus questionable. We avoid the non-associativity by the use of a space-time picture based on the concept of realization of a non-commutative geometry. The two main results we obtain are: (i) the generic (namely for any realization) construction of the co-algebraic sector underlying the Snyder geometry and (ii) the definition of a non-ambiguous self interacting scalar field theory on this space-time. The first order correction terms of the corresponding Lagrangian are explicitly computed. The possibility to derive Noether charges for the Snyder space-time is also discussed.Comment: 10 pages; v2: introduction rewritten, co-algebraic analysis improved, references added; to appear in PR

High performance astrophysics computing

The application of high end computing to astrophysical problems, mainly in the galactic environment, is under development since many years at the Dep. of Physics of Sapienza Univ. of Roma. The main scientific topic is the physics of self gravitating systems, whose specific subtopics are: i) celestial mechanics and interplanetary probe transfers in the solar system; ii) dynamics of globular clusters and of globular cluster systems in their parent galaxies; iii) nuclear clusters formation and evolution; iv) massive black hole formation and evolution; v) young star cluster early evolution. In this poster we describe the software and hardware computational resources available in our group and how we are developing both software and hardware to reach the scientific aims above itemized.Comment: 2 pages paper presented at the Conference "Advances in Computational Astrophysics: methods, tools and outcomes", to be published in the ASP Conference Series, 2012, vol. 453, R. Capuzzo-Dolcetta, M. Limongi and A. Tornambe' ed