338 research outputs found
Automated Design of Elevator Systems: Experimenting with Constraint-Based Approaches
System configuration and design is a well-established topic
in AI. While many successful applications exists, there are still areas of
manufacturing where AI techniques find little or no application. We focus
on one such area, namely building and installation of elevator systems,
for which we are developing an automated design and configuration tool.
The questions that we address in this paper are: (i) What are the best
ways to encode some subtasks of elevator design into constraint-based
representations? (ii) What are the best tools available to solve the encodings? We contribute an empirical analysis to address these questions
in our domain of interest, as well as the complete set of benchmarks to
foster further researc
Property specification patterns at work: verification and inconsistency explanation
Property specification patterns (PSPs) have been proposed to ease the formalization of requirements, yet enable automated verification thereof. In particular, the internal consistency of specifications written with PSPs can be checked automatically with the use of, for example, linear temporal logic (LTL) satisfiability solvers. However, for most practical applications, the expressiveness of PSPs is too restricted to enable writing useful requirement specifications, and proving that a set of requirements is inconsistent can be worthless unless a minimal set of conflicting requirements is extracted to help designers to correct a wrong specification. In this paper, we extend PSPs by considering Boolean as well as atomic numerical assertions, we contribute an encoding from extended PSPs to LTL formulas, and we present an algorithm computing inconsistency explanations, i.e., irreducible inconsistent subsets of the original set of requirements. Our extension enables us to reason about the internal consistency of functional requirements which would not be captured by basic PSPs. Experimental results demonstrate that our approach can check and explain (in)consistencies in specifications with nearly two thousand requirements generated using a probabilistic model, and that it enables effective handling of real-world case studies
-M* Diagram: A Valuable Galaxy Evolution Diagnostic to Complement (s)SFR-M* Diagrams
The specific star formation rate (sSFR) is commonly used to describe the
level of galaxy star formation (SF) and to select quenched galaxies. However,
being a relative measure of the young-to-old population, an ambiguity in its
interpretation may arise because a small sSFR can be either because of a
substantial previous mass build up, or because SF is low. We show, using large
samples spanning 0 < z < 2, that the normalization of SFR by the physical
extent over which SF is taking place (i.e., SFR surface density,
) overcomes this ambiguity. has
a strong physical basis, being tied to the molecular gas density and the
effectiveness of stellar feedback, so we propose -M* as
an important galaxy evolution diagram to complement (s)SFR-M* diagrams. Using
the -M* diagram we confirm the Schiminovich et al.
(2007) result that the level of SF along the main sequence today is only weakly
mass dependent - high-mass galaxies, despite their redder colors, are as active
as blue, low-mass ones. At higher redshift, the slope of the
" main sequence" steepens, signaling the epoch of bulge
build-up in massive galaxies. We also find that based
on the optical isophotal radius more cleanly selects both the starbursting and
the spheroid-dominated (early-type) galaxies than sSFR. One implication of our
analysis is that the assessment of the inside-out vs. outside-in quenching
scenarios should consider both sSFR and radial
profiles, because ample SF may be present in bulges with low sSFR (red color).Comment: 16 pages. Accepted to ApJ. Comments on content or relevant missing
references welcom
Detecting and Characterizing Young Quasars. III. the Impact of Gravitational Lensing Magnification
We test the impact of gravitational lensing on the lifetime estimates of seven high-redshift quasars at redshift z 3 6. The targeted quasars are identified by their small observed proximity zone sizes, which indicate extremely short quasar lifetimes (t Q 2 105yr). However, these estimates of quasar lifetimes rely on the assumption that the observed luminosities of the quasars are intrinsic and not magnified by gravitational lensing, which would bias the lifetime estimates toward younger ages. In order to test the possible effects of gravitational lensing, we obtain high-resolution images of the seven quasars with the Hubble Space Telescope and look for signs of strong lensing. We do not find any evidence of strong lensing, i.e., all quasars are well described by point sources, and no foreground lensing galaxy is detected. We estimate that the strong-lensing probabilities for these quasars are extremely small ( 1/41.4 × 10-5) and show that weak lensing changes the estimated quasar lifetimes by only 20.2 dex. We thus confirm that the short lifetimes of these quasars are intrinsic. The existence of young quasars indicates a high obscured fraction, radiatively inefficient accretion, and/or flickering lightcurves for high-redshift quasars. We further discuss the impact of lensing magnification on measurements of black hole masses and Eddington ratios of quasars
The Zurich Environmental Study (ZENS) of galaxies in groups along the cosmic web. V. properties and frequency of merging satellites and centrals in different environments
We use the Zurich ENvironmental Study (ZENS) database to investigate the
environmental dependence of the merger fraction and merging galaxy
properties in a sample of ~1300 group galaxies with and
0.05<z<0.0585. In all galaxy mass bins investigated in our study, we find that
decreases by a factor of ~2-3 in groups with halo masses
relative to less massive systems, indicating a
suppression of merger activity in large potential wells. In the fiducial case
of relaxed groups only, we measure a variation dex, which is almost independent of galaxy mass
and merger stage. At galaxy masses , most mergers are dry
accretions of quenched satellites onto quenched centrals, leading to a strong
increase of with decreasing group-centric distance at these mass
scales.Both satellite and central galaxies in these high mass mergers do not
differ in color and structural properties from a control sample of nonmerging
galaxies of equal mass and rank. At galaxy masses , where
we mostly probe satellite-satellite pairs and mergers between star-forming
systems, close pairs (projected distance kpc) show instead
enhanced (specific) star formation rates and
larger sizes than similar mass, nonmerging satellites. The increase in both
size and SFR leads to similar surface star-formation densities in the merging
and control-sample satellite populations.Comment: Published in ApJ, 797, 12
A panchromatic spatially resolved analysis of nearby galaxies-II. The main sequence-gas relation at sub-kpc scale in grand-design spirals
In this work, we analyse the connection between gas availability and the position of a region with respect to the spatially resolved main-sequence (MS) relation. Following the procedure presented in Enia et al. (2020), for a sample of five face-on, grand design spiral galaxies located on the MS we obtain estimates of stellar mass and star formation rate surface densities (E∗ and ESFR) within cells of 500 pc size. Thanks to HI 21cm and 12CO(2-1) maps of comparable resolution, within the same cells we estimate the surface densities of the atomic (EHI) and molecular (EH2) gas and explore the correlations among all these quantities. E∗, ESFR, and EH2 define a 3D relation whose projections are the spatially resolved MS, the Kennicutt-Schmidt law and the molecular gas MS. We find that EH2 steadily increases along the MS relation and is almost constant perpendicular to it. EHI is nearly constant along the MS and increases in its upper envelope. As a result, ESFR can be expressed as a function of E∗ and E HI, following the relation log ESFR = 0.97log E∗ + 1.99log EH I-11.11. We show that the total gas fraction significantly increases towards the starburst regions, accompanied by a weak increase in star formation efficiency. Finally, we find that H2/HI varies strongly with the distance from the MS, dropping dramatically in regions of intense star formation, where the UV radiation from newly formed stars dissociates the H2 molecule, illustrating the self-regulating nature of the star formation process
CEERS Key Paper. III. The Diversity of Galaxy Structure and Morphology at z = 3–9 with JWST
We present a comprehensive analysis of the evolution of the morphological and structural properties of a large sample of galaxies at z = 3-9 using early James Webb Space Telescope (JWST) CEERS NIRCam observations. Our sample consists of 850 galaxies at z > 3 detected in both Hubble Space Telescope (HST)/WFC3 and CEERS JWST/NIRCam images, enabling a comparison of HST and JWST morphologies. We conduct a set of visual classifications, with each galaxy in the sample classified three times. We also measure quantitative morphologies across all NIRCam filters. We find that galaxies at z > 3 have a wide diversity of morphologies. Galaxies with disks make up 60% of galaxies at z = 3, and this fraction drops to ∼30% at z = 6-9, while galaxies with spheroids make up ∼30%-40% across the redshift range, and pure spheroids with no evidence for disks or irregular features make up ∼20%. The fraction of galaxies with irregular features is roughly constant at all redshifts (∼40%-50%), while those that are purely irregular increases from ∼12% to ∼20% at z > 4.5. We note that these are apparent fractions, as many observational effects impact the visibility of morphological features at high redshift. On average, Spheroid-only galaxies have a higher Sérsic index, smaller size, and higher axis ratio than disk or irregular galaxies. Across all redshifts, smaller spheroid and disk galaxies tend to be rounder. Overall, these trends suggest that galaxies with established disks and spheroids exist across the full redshift range of this study, and further work with large samples at higher redshift is needed to quantify when these features first formed.</p
CEERS Key Paper. III. The Diversity of Galaxy Structure and Morphology at z = 3–9 with JWST
We present a comprehensive analysis of the evolution of the morphological and structural properties of a large sample of galaxies at z = 3-9 using early James Webb Space Telescope (JWST) CEERS NIRCam observations. Our sample consists of 850 galaxies at z > 3 detected in both Hubble Space Telescope (HST)/WFC3 and CEERS JWST/NIRCam images, enabling a comparison of HST and JWST morphologies. We conduct a set of visual classifications, with each galaxy in the sample classified three times. We also measure quantitative morphologies across all NIRCam filters. We find that galaxies at z > 3 have a wide diversity of morphologies. Galaxies with disks make up 60% of galaxies at z = 3, and this fraction drops to ∼30% at z = 6-9, while galaxies with spheroids make up ∼30%-40% across the redshift range, and pure spheroids with no evidence for disks or irregular features make up ∼20%. The fraction of galaxies with irregular features is roughly constant at all redshifts (∼40%-50%), while those that are purely irregular increases from ∼12% to ∼20% at z > 4.5. We note that these are apparent fractions, as many observational effects impact the visibility of morphological features at high redshift. On average, Spheroid-only galaxies have a higher Sérsic index, smaller size, and higher axis ratio than disk or irregular galaxies. Across all redshifts, smaller spheroid and disk galaxies tend to be rounder. Overall, these trends suggest that galaxies with established disks and spheroids exist across the full redshift range of this study, and further work with large samples at higher redshift is needed to quantify when these features first formed.</p
The Diversity and Variability of Star Formation Histories in Models of Galaxy Evolution
Understanding the variability of galaxy star formation histories (SFHs)
across a range of timescales provides insight into the underlying physical
processes that regulate star formation within galaxies. We compile the SFHs of
galaxies at from an extensive set of models, ranging from cosmological
hydrodynamical simulations (Illustris, IllustrisTNG, Mufasa, Simba, EAGLE),
zoom simulations (FIRE-2, g14, and Marvel/Justice League), semi-analytic models
(Santa Cruz SAM) and empirical models (UniverseMachine), and quantify the
variability of these SFHs on different timescales using the power spectral
density (PSD) formalism. We find that the PSDs are well described by broken
power-laws, and variability on long timescales ( Gyr) accounts for
most of the power in galaxy SFHs. Most hydrodynamical models show increased
variability on shorter timescales ( Myr) with decreasing stellar
mass. Quenching can induce dex of additional power on timescales
Gyr. The dark matter accretion histories of galaxies have remarkably
self-similar PSDs and are coherent with the in-situ star formation on
timescales Gyr. There is considerable diversity among the different models
in their (i) power due to SFR variability at a given timescale, (ii) amount of
correlation with adjacent timescales (PSD slope), (iii) evolution of median
PSDs with stellar mass, and (iv) presence and locations of breaks in the PSDs.
The PSD framework is a useful space to study the SFHs of galaxies since model
predictions vary widely. Observational constraints in this space will help
constrain the relative strengths of the physical processes responsible for this
variability.Comment: 31 pages, 17 figures (+ appendix). Resubmitted to MNRAS after
responding to referee's comments. Comments are welcome
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