328 research outputs found
Tailoring temporal description logics for reasoning over temporal conceptual models
Temporal data models have been used to describe how data can evolve in the context of temporal databases. Both the Extended Entity-Relationship (EER) model and the Unified Modelling Language (UML) have been temporally extended to design temporal databases. To automatically check quality properties of conceptual schemas various encoding to Description Logics (DLs) have been proposed in the literature. On the other hand, reasoning on temporally extended DLs turn out to be too complex for effective reasoning ranging from 2ExpTime up to undecidable languages. We propose here to temporalize the ‘light-weight’ DL-Lite logics obtaining nice computational results while still being able to represent various constraints of temporal conceptual models. In particular, we consider temporal extensions of DL-Lite^N_bool, which was shown to be adequate for capturing non-temporal conceptual models without relationship inclusion, and its fragment DL-Lite^N_core with most primitive concept inclusions, which are nevertheless enough to represent almost all types of atemporal constraints (apart from
covering)
Stellar feedback from HMXBs in cosmological hydrodynamical simulations
We explored the role of X-ray binaries composed by a black hole and a massive
stellar companion (BHXs) as sources of kinetic feedback by using hydrodynamical
cosmological simulations. Following previous results, our BHX model selects low
metal-poor stars () as possible progenitors. The model that
better reproduces observations assumes that a fraction of
low-metallicity black holes are in binary systems which produce BHXs. These
sources are estimated to deposit erg of kinetic energy per
event. With these parameters and in the simulated volume, we find that the
energy injected by BHXs represents of the total energy released by
SNII and BHX events at redshift and then decreases rapidly as baryons
get chemically enriched. Haloes with virial masses smaller than (or K) are the most directly affected
ones by BHX feedback. These haloes host galaxies with stellar masses in the
range M. Our results show that BHX feedback is able to
keep the interstellar medium warm, without removing a significant gas fraction,
in agreement with previous analytical calculations. Consequently, the
stellar-to-dark matter mass ratio is better reproduced at high redshift. Our
model also predicts a stronger evolution of the number of galaxies as a
function of the stellar mass with redshift when BHX feedback is considered.
These findings support previous claims that the BHXs could be an effective
source of feedback in early stages of galaxy evolution.Comment: 11 pages, 8 figures, accepted for publication in MNRA
The High Mass X-ray Binaries in star-forming galaxies
The high mass X-ray binaries (HMXBs) provide an exciting framework to
investigate the evolution of massive stars and the processes behind binary
evolution. HMXBs have shown to be good tracers of recent star formation in
galaxies and might be important feedback sources at early stages of the
Universe. Furthermore, HMXBs are likely the progenitors of gravitational wave
sources (BH--BH or BH--NS binaries that may merge producing gravitational
waves). In this work, we investigate the nature and properties of HMXB
population in star-forming galaxies. We combine the results from the population
synthesis model MOBSE (Giacobbo et al. 2018) together with galaxy catalogs from
EAGLE simulation (Schaye et al. 2015). Therefore, this method describes the
HMXBs within their host galaxies in a self-consistent way. We compute the X-ray
luminosity function (XLF) of HMXBs in star-forming galaxies, showing that this
methodology matches the main features of the observed XLF.Comment: 4 pages, 2 figures. To appear in Proc. IAUS 346: High-mass X-ray
binaries: illuminating the passage from massive binaries to merging compact
object
Alignment of the central galaxies with the environment
In this work, we combine ellipticity and major axis position angle
measurements from the Sloan Digital Sky Server Data Release 16 (SDSS DR16) with
the group finder algorithm of Rodriguez \& Merch\'an to determine the alignment
of the central galaxies with the surrounding structures and satellite galaxies
lying in their group. We use two independent methods: A modified version of the
two-point cross-correlation function and the angle between the central galaxy
orientation and the satellite galaxies relative position. The first method
allows us to study the inner and outer regions of the cluster, while the second
method provides information within the halos. Our results show that central
galaxies present anysotropy in the correlation function up to , which becomes 10\% stronger for the brightest ones
(). When we split the galaxy sample by colour, we find that
red central galaxies are the main contributors to this anisotropy. We also show
that this behaviour does not depend on the group mass or central galaxy
ellipticity. Finally, our results are in agreement with previous findings,
showing that the two-point cross-correlation function is a best tracer of the
galaxy alignments using all galaxies and not only those of the group to which
it belongs. In addition, this feature allows us to explore the behaviour of the
alignment on larger scales.Comment: 10 pages, 9 figures, sent to MNRA
The complexity of clausal fragments of LTL
We introduce and investigate a number of fragments of propositional temporal logic LTL over the flow of time (ℤ, <). The fragments are defined in terms of the available temporal operators and the structure of the clausal normal form of the temporal formulas. We determine the computational complexity of the satisfiability problem for each of the fragments, which ranges from NLogSpace to PTime, NP and PSpace
Computing FO-Rewritings in EL in Practice: from Atomic to Conjunctive Queries
A prominent approach to implementing ontology-mediated queries (OMQs) is to
rewrite into a first-order query, which is then executed using a conventional
SQL database system. We consider the case where the ontology is formulated in
the description logic EL and the actual query is a conjunctive query and show
that rewritings of such OMQs can be efficiently computed in practice, in a
sound and complete way. Our approach combines a reduction with a decomposed
backwards chaining algorithm for OMQs that are based on the simpler atomic
queries, also illuminating the relationship between first-order rewritings of
OMQs based on conjunctive and on atomic queries. Experiments with real-world
ontologies show promising results
Anisotropic correlation functions as tracers of central galaxy alignments in simulations
Motivated by observational results, we use IllustrisTNG hydrodynamical
numerical simulations to study the alignment of the central galaxies in groups
with the surrounding structures. This approach allows us to analyse galaxy and
group properties not available in observations. To perform this analysis, we
use a modified version of the two-point cross-correlation function and a
measure of the angle between the semi-major axes of the central galaxies and
the larger structures. Overall, our results reproduce observational ones, as we
find large-scale anisotropy, which is dominated by the red central galaxies. In
addition, the latter is noticeably more aligned with their group than the blue
ones. In contrast to the observations, we find a strong dependence of the
anisotropy on the central galaxy with mass, probably associated with the
inability of observational methods to determine them. This result allows us to
link the alignment to the process of halo assembly and the well-known
dependence of halo anisotropy on mass. When we include the dark matter
distribution in our analysis, we conclude that the galaxy alignment found in
simulations (and observations) can be explained by a combination of physical
processes at different scales: the central galaxy aligns with the dark matter
halo it inhabits, and this, in turn, aligns with the surrounding structures at
large scales.Comment: 9 pages, 11 figures, Accepted by MNRA
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