8,009 research outputs found
The evolution of the universe from noncompact Kaluza-Klein theory
We develope a 5D mechanism inspired in the Campbell's theorem, to explain the
(neutral scalar field governed) evolution of the universe from a initially
inflationary expansion that has a change of phase towards a decelerated
expansion and thereinafter evolves towards the present day observed celerated
(quintessential) expansion.Comment: version accepted in Eur. Phys. J.
Extra force and extra mass from noncompact Kaluza-Klein theory in a cosmological model
Using the Hamilton-Jacobi formalism, we study extra force and extra mass in a
recently introduced noncompact Kaluza-Klein cosmological model. We examine the
inertial 4D mass of the inflaton field on a 4D FRW bulk in two examples.
We find that has a geometrical origin and antigravitational effects on a
non inertial 4D bulk should be a consequence of the motion of the fifth
coordinate with respect to the 4D bulk.Comment: final version to be published in EPJ
The "UV-route" to search for Blue Straggler Stars in Globular Clusters: first results from the HST UV Legacy Survey
We used data from the HST UV Legacy Survey of Galactic Globular Clusters to
select the Blue Straggler Star (BSS) population in four intermediate/high
density systems (namely NGC 2808, NGC 6388, NGC 6541 and NGC 7078) through a
"UV-guided search". This procedure consists in using the F275W images in each
cluster to construct the master list of detected sources, and then force it to
the images acquired in the other filters. Such an approach optimizes the
detection of relatively hot stars and allows the detection of complete sample
of BSSs even in the central region of high-density clusters, because the light
from the bright cool giants, which dominates the optical emission in old
stellar systems, is sensibly reduced at UV wavelengths. Our UV-guided
selections of BSSs have been compared to the samples obtained in previous,
optical-driven surveys, clearly demonstrating the efficiency of the UV
approach. In each cluster we also measured the parameter A+, defined as the
area enclosed between the cumulative radial distribution of BSSs and that of a
reference population, which traces the level of BSS central segregation and the
level of dynamical evolution suffered by the system. The values measured for
the four clusters studied in this paper nicely fall along the dynamical
sequence recently presented for a sample of 25 clusters.Comment: 30 pages, 9 figures, 4 tables; accepted for publication in Ap
Performance Comparison Between Deep Learning-Based and Conventional Cryptographic Distinguishers
Blockchain-Based Distributed Trust and Reputation Management Systems: A Survey
Distributed Ledger Technologies (DLTs), like Blockchain, are characterized by features such as transparency, traceability, and security by design. These features make the adoption of Blockchain attractive to enhance information security, privacy, and trustworthiness in very different contexts. This paper provides a comprehensive survey and aims at analyzing and assessing the use of Blockchain in the context of Distributed Trust and Reputation Management Systems (DTRMS). The analysis includes academic research as well as initiatives undertaken in the business domain. The paper defines two taxonomies for both Blockchain and DTRMS and applies a Formal Concept Analysis. Such an approach allowed us to identify the most recurrent and stable features in the current scientific landscape and several important implications among the two taxonomies. The results of the analysis have revealed significant trends and emerging practices in the current implementations that have been distilled into recommendations to guide Blockchain's adoption in DTRMS systems
Origin of FRW cosmology in slow-roll inflation from noncompact Kaluza-Klein theory
Using a recently introduced formalism we discuss slow-roll inflaton from
Kaluza-Klein theory without the cylinder condition. In particular, some
examples corresponding to polynomic and hyperbolic -potentials are
studied. We find that the evolution of the fifth coordinate should be
determinant for both, the evolution of the early inflationary universe and the
quantum fluctuations.Comment: (final version) to be published in EPJ
Phantom cosmology with a decaying cosmological function induced from five-dimensional (5D) geometrical vacuum
Introducing a variable cosmological function in a geometrical
manner from a 5D Riemann-flat metric, we investigate the possibility of having
a geometrical criterion to choose a suitable cosmological function for every 4D dynamical hypersurface capable of generate phantom
cosmologies.Comment: final versio
Absolute proper motion of the Galactic open cluster M67
We derived the absolute proper motion (PM) of the old, solar-metallicity
Galactic open cluster M67 using observations collected with CFHT (1997) and
with LBT (2007). About 50 galaxies with relatively sharp nuclei allow us to
determine the absolute PM of the cluster. We find (mu_alpha
cos(delta),mu_delta)_J2000.0 = (-9.6+/-1.1,-3.7+/-0.8) mas/yr. By adopting a
line-of-sight velocity of 33.8+/-0.2 km/s, and assuming a distance of 815+/-50
pc, we explore the influence of the Galactic potential, with and without the
bar and/or spiral arms, on the galactic orbit of the cluster.Comment: 7 pages, 5 figures, and 3 tables. Published in Astronomy and
Astrophysics, Volume 513, id.A51
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