197,727 research outputs found
Analisi della frequentazione di Grotta San Biagio (Ostuni, BR) attraverso le risorse vegetali tra Neolitico ed Eneolitico. Studio planimetrico e stratigrafico dei resti carpologici”
No full textStudio paleocarpologico di Grotta San Biagio, Ostuni (BR
Analisi della frequentazione di Grotta San Biagio (Ostuni, BR) attraverso le risorse vegetali tra Neolitico ed Eneolitico. Studio planimetrico e stratigrafico dei resti carpologici
No full textIl presente elaborato tratta della
ricerca carpologica e antracologica nel sito pugliese di Grotta San Biagio (BR); le analisi hanno permesso di individuare
numerosi reperti vegetali, per un totale di 3.857 resti, classificati secondo quattro principali tipologie: cereali, legumi,
frutti eduli e piante erbacee.
Attraverso un’indagine planimetrica e stratigrafica, si è ottenuta un’immagine fedele della vegetazione dell’area del sito
così da comprendere meglio quali specie vegetali venivano utilizzate dall’uomo e quale è stato l’utilizzo (frequente ma
non quotidiano) di questa cavità carsica nel periodo compreso tra Neolitico ed Eneolitico
Lyman break galaxies and the star formation rate of the Universe at z ~ 6
No full textWe determine the space density of UV-luminous starburst galaxies at z≈ 6 using deep HST ACS SDSS-i′ (F775W) and SDSS-z′ (F850LP) and VLT ISAAC J and Ks band imaging of the Chandra Deep Field South. We find eight galaxies and one star with (i′−z′) > 1.5 to a depth of z′AB= 25.6 (an 8σ detection in each of the 3 available ACS epochs). This corresponds to an unobscured star formation rate of ≈15 h−270 M⊙ yr−1 at z= 5.9, equivalent to L* for the Lyman-break population at z= 3–4 (ΩΛ= 0.7, ΩM= 0.3). We are sensitive to star-forming galaxies at 5.6 ≲z≲ 7.0 with an effective comoving volume of ≈1.8 × 105h−370 Mpc3 after accounting for incompleteness at the higher redshifts due to luminosity bias. This volume should encompass the primeval subgalactic-scale fragments of the progenitors of about a thousand L* galaxies at the current epoch. We determine a volume-averaged global star formation rate of (6.7 ± 2.7) × 10−4h70 M⊙ yr−1 Mpc−3 at z∼ 6 from rest-frame UV selected starbursts at the bright end of the luminosity function: this is a lower limit because of dust obscuration and galaxies below our sensitivity limit. This measurement shows that at z∼ 6 the star formation density at the bright end is a factor of ∼6 times less than that determined by Steidel et al. for a comparable sample of UV-selected galaxies at z= 3–4, and so extends our knowledge of the star formation history of the Universe to earlier times than previous work and into the epoch where reionization may have occurred
Revisiting the Oldest Stars as Cosmological Probes: New Constraints on the Hubble Constant
No full textDespite the tremendous advance of observational cosmology, the value of the Hubble constant (H (0)) is still controversial (the so-called "Hubble tension") because of the inconsistency between local/late-time measurements and those derived from the cosmic microwave background. As the age of the Universe is very sensitive to H (0), we explored whether the present-day oldest stars could place independent constraints on the Hubble constant. To this purpose, we selected from the literature the oldest objects (globular clusters, stars, white dwarfs, and ultrafaint and dwarf spheroidal galaxies) with accurate age estimates. Adopting a conservative prior on their formation redshifts (11 & LE; z (f) & LE; 30) and assuming & omega;( M ) = 0.3 & PLUSMN; 0.02, we developed a method based on Bayesian statistics to estimate the Hubble constant. We selected the oldest objects (>13.3 Gyr) and estimated H (0) both for each of them individually and for the average ages of homogeneous subsamples. Statistical and systematic uncertainties were properly taken into account. The constraints based on individual ages indicate that H (0) < 70.6 km s(-1) Mpc(-1) when selecting the most accurate estimates. If the ages are averaged and analyzed independently for each subsample, the most stringent constraints imply H (0) < 73.0 km s(-1) Mpc(-1) with a probability of 90.3% and errors around 2.5 km s(-1) Mpc(-1). We also constructed an "accuracy matrix" to assess how the constraints on H (0) become more stringent with further improvements in the accuracy of stellar ages and & omega;( M ). The results show the great potential of the oldest stars as independent and competitive cosmological probes not limited to just the Hubble constant
The local and distant Universe: stellar ages and H0
No full textThe ages of the oldest stellar objects in our galaxy provide an independent test of the current cosmological model as they give a lower limit to the age of the Universe. Recent accurate parallaxes by the Gaia space mission, accurate measurements of the metallicity of stars, via individual elemental abundances, and advances in the modelling of stellar evolution, provide new, higher-precision age estimates of the oldest stellar populations in the galaxy: globular clusters and very-low-metallicity stars. The constraints on the age of the Universe, t U , so obtained are determined from the local Universe and at late time. It is well known that local and early-Universe determinations of another cosmological parameter closely related to the age of the Universe, the Hubble constant H 0 , show a3 σ tension. In the standard cosmological model, ΛCDM, t U and H 0 are related by the matter density parameter Ω m,0 . We propose to combine local t U constraints with late-time Ω m,0 estimates in a ΛCDM framework, to obtain a low-redshift H 0 determination that does not rely on early Universe physics. A proof-of-principle of this approach with current data gives H 0 =71±2.8 (H 0 = 69.3 ± 2.7) km s -1 Mpc -1 from globular clusters (very-low-metallicity stars) with excellent prospects for improved constraints in the near future
Linguistic tools for embodied minds
No full textIn this paper, we outline the embodied perspective of language comprehension indicating some of its limitations. We claim that the notions of language as a tool (CLARK 2006a, 2006b), might be useful to overcome a view focused only on referential aspects of language. Words, in quality of tools, can: a. facilitate communication among speakers; b. influence categorization; c. have a different impact on concrete and abstract words; d. allow us to construct an inner speech. Finally, we discuss how thinking about language as tool can help inform future research on thought, language and bod
Automatic digitalization of railway interlocking systems engineering drawings based on hybrid machine learning methods
No full textEngineering drawings of the railway interlocking systems come often from a legacy since the railway networks were built several years ago. Most of these drawings remained archived on handwritten sheets and need to be digitalized to continue updating and safety checks. This digitalization task is challenging as it requires major manual labor, and standard machine learning methods may not perform satisfactorily because drawings can be noisy and have poor sharpness. Considering these challenges, this paper proposes to solve this problem with a hybrid method that combines machine learning models, clustering techniques, computer vision, and ruled-based methods. A fine-tuned deep learning model is applied to identify symbols, labels, specifiers, and electrical connections. The lines representing electrical connections are determined using a combination of probabilistic Hough transform and clustering techniques. The identified letters are joined to create the labels by applying rule-based methods, and electrical connections are attached to symbols in a graph structure. A readable output is created for a drawing interface using the edges from the graph structure and the position of the detected objects. The method proposed in this paper can support the digitization of other engineering drawings assisting in solving the challenge of digitizing engineering schemes
Formal reliability analysis of redundant architectures
No full textReliability is a fundamental property for critical systems. A thorough evaluation of the reliability is required
by the certification procedures in various application domains, and it is important to support the exploration of the
space of the design solutions.
In this paper we propose a new, fully automated approach to the reliability analysis of complex redundant architectures. Given an abstract description of the architecture, the approach automatically extracts a fault tree and a symbolic
reliability function, i.e. a program mapping the probability of fault of the basic components to the probability that the
overall architecture deviates from the expected behavior.
The proposed approach heavily relies on formal methods, by representing the architecture blocks as Uninterpreted
Functions, and using the so-called miter construction to model the deviation from the nominal behavior. The extraction
of all the deviation conditions is reduced to an AllSMT problem, and we extract the reliability function by traversing
the Binary Decision Diagram corresponding to the quantified formula. Predicate abstraction is used to partition and
speed up the computation.
The approach has been implemented leveraging formal tools for model checking and safety assessment. A thorough
experimental evaluation demonstrates its generality and effectiveness of the proposed techniques
Unveiling the oldest and most massive galaxies at very high redshift
No full textContext.
The identification and characterisation of massive galaxies over a wide
redshift range allow us to place stringent constraints on the cosmic
history of galaxy mass assembly and on current models of galaxy formation and evolution.
Aims.
This work explores the existence of high-redshift massive galaxies
unveiled with Spitzer+IRAC, but missed by conventional selection techniques
based on optical and near-infrared observations.
Methods.
To this end, we
used multi-wavelength imaging data available for the GOODS-South
field (130 arcmin2) and selected a flux-limited sample from the
IRAC 3.6 μm image to Jy (m(AB) < 23.26).
In order to identify the most extreme objects and to complement previously
published selections
in this field, we confined our study to the galaxies undetected by the
optical HST+ACS imaging and close to the detection limit of the
K-band image ( AB). Our selection unveiled 20 galaxies
on which we performed a detailed analysis.
For each galaxy, we built a spectral energy distribution (SED) based on
optical-to-8μm photometry. The SEDs were then used to estimate the
photometric redshifts and to derive the main galaxies' physical
properties.
Further constraints were also obtained from the available X-ray and 24 μm data.
Results.
The majority of the sample (14 out of 20) sources show degenerate/bimodal solutions for
the photometric redshifts. These can either be heavily dust-enshrouded
() starbursts at with bolometric luminosities
, or massive post-starburst
galaxies in the redshift interval with stellar masses of ~.
The remaining six galaxies present a less ambiguous
photometric redshift: with the exception of one low-z
dusty source, these latter objects favour a low-extinction solution, with
four of them showing best-fit photo-z solutions at . One galaxy, ID-6, the only
source in
our sample with both an X-ray and a 24 μm detection, might be an extremely
massive object at detected during a post-starburst phase with concomitant
QSO activity responsible for the 24 μm and X-ray emissions
(although a lower-z solution is not excluded).
Conclusions.
Our investigation of Spitzer-selected galaxies that have very red
SEDs and completely undetected in the optical reveals a potential
population of massive galaxies at , which appear to include significant
AGN emissions.
These sources may be the oldest stellar systems at , given that the estimated ages are close to the age of the Universe at that redshift.
We found that these, previously unrecognised, optically obscured objects
might provide an important contribution to the massive end
() of the high-z stellar mass function, and they
would almost double it.
Our evidence in these mature high-z galaxies of the
widespread presence of hidden AGNs may have important implications for
galaxy formation, due to their feedback effects on the surrounding ISM
- …
