How To Model Supernovae in Simulations of Star and Galaxy Formation

We study the implementation of mechanical feedback from supernovae (SNe) and stellar mass loss in galaxy simulations, within the Feedback In Realistic Environments (FIRE) project. We present the FIRE-2 algorithm for coupling mechanical feedback, which can be applied to any hydrodynamics method (e.g. fixed-grid, moving-mesh, and mesh-less methods), and black hole as well as stellar feedback. This algorithm ensures manifest conservation of mass, energy, and momentum, and avoids imprinting 'preferred directions' on the ejecta. We show that it is critical to incorporate both momentum and thermal energy of mechanical ejecta in a self-consistent manner, accounting for SNe cooling radii when they are not resolved. Using idealized simulations of single SN explosions, we show that the FIRE-2 algorithm, independent of resolution, reproduces converged solutions in both energy and momentum. In contrast, common 'fully-thermal' (energy-dump) or 'fully-kinetic' (particle-kicking) schemes in the literature depend strongly on resolution: when applied at mass resolution >100 solar masses, they diverge by orders-of-magnitude from the converged solution. In galaxy-formation simulations, this divergence leads to orders-of-magnitude differences in galaxy properties, unless those models are adjusted in a resolution-dependent way. We show that all models that individually time-resolve SNe converge to the FIRE-2 solution at sufficiently high resolution. However, in both idealized single-SN simulations and cosmological galaxy-formation simulations, the FIRE-2 algorithm converges much faster than other sub-grid models without re-tuning parameters.Comment: 18 pages, 9 figures (+8 pages, 6 figures in appendices). MNRAS (updated to match published version

The Difficulty of Getting High Escape Fractions of Ionizing Photons from High-redshift Galaxies: a View from the FIRE Cosmological Simulations

We present a series of high-resolution (20-2000 Msun, 0.1-4 pc) cosmological zoom-in simulations at z~6 from the Feedback In Realistic Environment (FIRE) project. These simulations cover halo masses 10^9-10^11 Msun and rest-frame ultraviolet magnitude Muv = -9 to -19. These simulations include explicit models of the multi-phase ISM, star formation, and stellar feedback, which produce reasonable galaxy properties at z = 0-6. We post-process the snapshots with a radiative transfer code to evaluate the escape fraction (fesc) of hydrogen ionizing photons. We find that the instantaneous fesc has large time variability (0.01%-20%), while the time-averaged fesc over long time-scales generally remains ~5%, considerably lower than the estimate in many reionization models. We find no strong dependence of fesc on galaxy mass or redshift. In our simulations, the intrinsic ionizing photon budgets are dominated by stellar populations younger than 3 Myr, which tend to be buried in dense birth clouds. The escaping photons mostly come from populations between 3-10 Myr, whose birth clouds have been largely cleared by stellar feedback. However, these populations only contribute a small fraction of intrinsic ionizing photon budgets according to standard stellar population models. We show that fesc can be boosted to high values, if stellar populations older than 3 Myr produce more ionizing photons than standard stellar population models (as motivated by, e.g., models including binaries). By contrast, runaway stars with velocities suggested by observations can enhance fesc by only a small fraction. We show that "sub-grid" star formation models, which do not explicitly resolve star formation in dense clouds with n >> 1 cm^-3, will dramatically over-predict fesc.Comment: 17 pages, 16 figures, MNRAS in pres

MusA: Using Indoor Positioning and Navigation to Enhance Cultural Experiences in a museum

In recent years there has been a growing interest into the use of multimedia mobile guides in museum environments. Mobile devices have the capabilities to detect the user context and to provide pieces of information suitable to help visitors discovering and following the logical and emotional connections that develop during the visit. In this scenario, location based services (LBS) currently represent an asset, and the choice of the technology to determine users' position, combined with the definition of methods that can effectively convey information, become key issues in the design process. In this work, we present MusA (Museum Assistant), a general framework for the development of multimedia interactive guides for mobile devices. Its main feature is a vision-based indoor positioning system that allows the provision of several LBS, from way-finding to the contextualized communication of cultural contents, aimed at providing a meaningful exploration of exhibits according to visitors' personal interest and curiosity. Starting from the thorough description of the system architecture, the article presents the implementation of two mobile guides, developed to respectively address adults and children, and discusses the evaluation of the user experience and the visitors' appreciation of these application

Training of Crisis Mappers and Map Production from Multi-sensor Data: Vernazza Case Study (Cinque Terre National Park, Italy)

This aim of paper is to presents the development of a multidisciplinary project carried out by the cooperation between Politecnico di Torino and ITHACA (Information Technology for Humanitarian Assistance, Cooperation and Action). The goal of the project was the training in geospatial data acquiring and processing for students attending Architecture and Engineering Courses, in order to start up a team of "volunteer mappers". Indeed, the project is aimed to document the environmental and built heritage subject to disaster; the purpose is to improve the capabilities of the actors involved in the activities connected in geospatial data collection, integration and sharing. The proposed area for testing the training activities is the Cinque Terre National Park, registered in the World Heritage List since 1997. The area was affected by flood on the 25th of October 2011. According to other international experiences, the group is expected to be active after emergencies in order to upgrade maps, using data acquired by typical geomatic methods and techniques such as terrestrial and aerial Lidar, close-range and aerial photogrammetry, topographic and GNSS instruments etc.; or by non conventional systems and instruments such us UAV, mobile mapping etc. The ultimate goal is to implement a WebGIS platform to share all the data collected with local authorities and the Civil Protectio

An information assistant system for the prevention of tunnel vision in crisis management

In the crisis management environment, tunnel vision is a set of bias in decision makers’ cognitive process which often leads to incorrect understanding of the real crisis situation, biased perception of information, and improper decisions. The tunnel vision phenomenon is a consequence of both the challenges in the task and the natural limitation in a human being’s cognitive process. An information assistant system is proposed with the purpose of preventing tunnel vision. The system serves as a platform for monitoring the on-going crisis event. All information goes through the system before arrives at the user. The system enhances the data quality, reduces the data quantity and presents the crisis information in a manner that prevents or repairs the user’s cognitive overload. While working with such a system, the users (crisis managers) are expected to be more likely to stay aware of the actual situation, stay open minded to possibilities, and make proper decisions

The hanging man: death, indeterminacy and the event

This article discusses approaches to the interpretation and analysis an event that is poised between reality and performance. It focuses upon a real event witnessed by the author while driving out of Los Angeles, USA. A body hanging on a rope from a bridge some 25/30 feet above the freeway held up the traffic. The status of the body was unclear. Was it the corpse of a dead human being or a stuffed dummy, a simulation of a death? Was it is tragic accident or suicide or was it a stunt, a protest or a performance? Whether a real body or not, it was an event: it drew an audience, it took place in a defined public space bound by time and it disrupted everyday normality and the familiar. The article debates how approaches to performance can engage with a shocking event, such as the Hanging Man, and the frameworks of interpretation that can be brought to bear on it. The analysis takes account of the function of memory in reconstructing the event, and the paradigms of cultural knowledge that offered themselves as parallels, comparators or distinctions against which the experience could be measured, such as the incidents of self-immolation related to demonstrations against the Vietnam War, the protest by the Irish Hunger Strikers and the visual impact of Anthony Gormley’s 2007 work, 'Event Horizon'. Theoretical frameworks deriving from analytical approaches to performance, media representation and ethical dilemmas are evaluated as means to assimilate an indeterminate and challenging event, and the notion of what an ‘event’ may be is itself addressed