429 research outputs found
Massive black hole and gas dynamics in galaxy nuclei mergers. I. Numerical implementation
Numerical effects are known to plague adaptive mesh refinement (AMR) codes
when treating massive particles, e.g. representing massive black holes (MBHs).
In an evolving background, they can experience strong, spurious perturbations
and then follow unphysical orbits. We study by means of numerical simulations
the dynamical evolution of a pair MBHs in the rapidly and violently evolving
gaseous and stellar background that follows a galaxy major merger. We confirm
that spurious numerical effects alter the MBH orbits in AMR simulations, and
show that numerical issues are ultimately due to a drop in the spatial
resolution during the simulation, drastically reducing the accuracy in the
gravitational force computation. We therefore propose a new refinement
criterion suited for massive particles, able to solve in a fast and precise way
for their orbits in highly dynamical backgrounds. The new refinement criterion
we designed enforces the region around each massive particle to remain at the
maximum resolution allowed, independently upon the local gas density. Such
maximally-resolved regions then follow the MBHs along their orbits, and
effectively avoids all spurious effects caused by resolution changes. Our suite
of high resolution, adaptive mesh-refinement hydrodynamic simulations,
including different prescriptions for the sub-grid gas physics, shows that the
new refinement implementation has the advantage of not altering the physical
evolution of the MBHs, accounting for all the non trivial physical processes
taking place in violent dynamical scenarios, such as the final stages of a
galaxy major merger.Comment: 11 pages, 11 figures, 1 table, it matches the published versio
Massive black hole and gas dynamics in mergers of galaxy nuclei - II. Black hole sinking in star-forming nuclear discs
Mergers of gas-rich galaxies are key events in the hierarchical built-up of
cosmic structures, and can lead to the formation of massive black hole
binaries. By means of high-resolution hydrodynamical simulations we consider
the late stages of a gas-rich major merger, detailing the dynamics of two
circumnuclear discs, and of the hosted massive black holes during their pairing
phase. During the merger gas clumps with masses of a fraction of the black hole
mass form because of fragmentation. Such high-density gas is very effective in
forming stars, and the most massive clumps can substantially perturb the black
hole orbits. After Myr from the start of the merger a gravitationally
bound black hole binary forms at a separation of a few parsecs, and soon after,
the separation falls below our resolution limit of pc. At the time of
binary formation the original discs are almost completely disrupted because of
SNa feedback, while on pc scales the residual gas settles in a circumbinary
disc with mass . We also test that binary dynamics is robust
against the details of the SNa feedback employed in the simulations, while gas
dynamics is not. We finally highlight the importance of the SNa time-scale on
our results.Comment: 10 pages, 11 figures, MNRAS in pres
Additive Manufacturing for Sustainability
This work stimulates on the need to include sustainability topics in the existing I4.0-related curricula via dedicated educational units and evaluate the impact of such themes from the students' and educators' perspectives. A specific focus on the process followed to add a new educational unit on sustainability for the AM course at the University of Pisa is offered. The adopted methodology in accordance with CA theory is detailed. A final survey was submitted to 20 students and 4 educators to validate the implemented topics and the perceived integration between sustainability topics and I4.0
On the connection between AGN radiative feedback and massive black hole spin
We present a novel implementation for active galactic nucleus (AGN) feedback
through ultra-fast winds in the code gizmo. Our feedback recipe accounts for
the angular dependence of radiative feedback upon black hole spin. We
self-consistently evolve in time i) the gas accretion process from resolved
scales to an unresolved AGN disc, ii) the evolution of the spin of the massive
black hole (MBH), iii) the injection of AGN-driven winds into the resolved
scales, and iv) the spin-induced anisotropy of the overall feedback process. We
test our implementation by following the propagation of the wind-driven outflow
into a homogeneous medium, and we compare the results against simple analytical
models. Then, we consider an isolated galaxy setup and there we study the
impact of the AGN feedback on the evolution of the MBH and the of the host
galaxy. We find that: i) AGN feedback limits the gas inflow that powers the
MBH, with a consequent weak impact on the host galaxy characterized by a star
formation (SF) suppression of about a factor of two in the nuclear region; ii)
the impact of AGN feedback on the host galaxy and on MBH growth is primarily
determined by the AGN luminosity, rather than by its angular pattern set by the
MBH spin; iii) the imprint of the angular pattern of the AGN radiation emission
manifest in a more clear way at high accretion rates. At such high rates the
more isotropic angular patterns, proper to higher spin values, sweep away gas
in the nuclear region more easily, hence causing a slower MBH mass and spin
growths and a higher quenching of the SF. We argue that the influence of
spin-dependent anisotropy of AGN feedback on MBH and galaxy evolution is likely
to be relevant in those scenarios characterized by high and prolonged MBH
accretion episodes and by high AGN wind-galaxy coupling. Such conditions are
more frequently met in galaxy mergers and/or high redshift galaxies
Laser powder bed additive manufacturing: A review on the four drivers for an online control
Online control of Additive Manufacturing (AM) processes appears to be the next challenge in the transition toward Industry 4.0 (I4.0). Although many efforts have been dedicated by industry and research in the last decades, there remains substantial room for improvement. Additionally, the existing scientific literature lacks a wide-ranging identification and classification of the primary drivers that enable online control of AM processes. This article focuses on online control of one of the most industrially widespread AM processes: metal Laser Powder Bed Fusion (L-PBF), with particular emphasis on two subcategories, namely Selective Laser Sintering (SLS) and Selective Laser Melting (SLM). Through a systematic literature review, this article initially identified over 200 manuscripts. The search was conducted utilizing a defined research query within the Scopus database, double checked on Scholar. The results were refined through multiple phases of inclusion/exclusion criteria, culminating in the selection of 95 pertinent papers. This article aims to provide a systematic and comprehensive review of four identified drivers i) Online controllable input parameters, ii) Online observable output signatures, iii) Online sensing techniques, iv) Online feedback strategies, adopted from the general Deming control loop Plan-Do-Check-Act (PDCA). Ultimately, this article delves into the challenges and prospects inherent in the online control of metal L-PBF
Static and dynamic weighing of rolling stocks by mean of a customized FBG-Sensorized-Patch
The structural health monitoring (SHM) of an infrastructure is of fundamental importance for the structure and people safety. Fiber Bragg Grating (FBG) sensors allow to design for each application, a tailored array of quasi-distributed sensors integrated to the infrastructure. To ensure the structural integrity of the railways is crucial to verify that the infrastructures comply with safety requirements to carry out their task. Railways rolling stock must comply with speed limits, the maximum number of wagons, maximum weight limit distributed on each axis of the wagons and the allowed number of trains on specific routes. The identification of the vertical load acting on each wheel is fundamental for the safety of a rolling-stock moving on a railway line. This paper presents the results of a test campaign on sensitive smart patches for static and dynamic weighing of trains. The system aims to generate a gripping system based on the magnetic force of a plastoferrite patch, taking advantage of the peculiarity that the rails are made of ferritic steel. This solution has the benefit of simplifying and speeding up the installation process and enabling a fast and easy removal or change in the configuration of the sensors array on the rail
The digital transformation of Engineering curricula: the categories that preserve Constructive Alignment
Scientific publications discussing online/distance learning have significantly increased throughout the last decade. The COVID-19 pandemic represented an unexpected condition that significantly changed people´s lifestyle along with the education domain boosting even further its digitalization, mostly at higher levels. In this work, we assume that Teaching Learning Activities (TLA) and Assessment Tasks (AT) should be adjusted to achieve the same Intended Learning Outcomes (ILO) set before distance learning. In view of the above, this paper assesses two courses selected from the Industrial Engineering study program offered in two prominent European higher education institutions. The Constructive Alignment (CA) approach is the baseline of this work and is used to analyse how the TLA and AT of the selected courses are adjusted to maintain alignment with the ILO defined before the digital transition. The main contribution is defining a set of categories to guide the digital transaction in engineering and beyond by maintaining the alignment on ILO-TLA-AT
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