20,474 research outputs found
The possibility of determining open-cluster parameters from BVRI photometry
In the last decades we witnessed an increase in studies of open clusters of
the Galaxy, especially because of the good determination for a wide range of
values of parameters such as age, distance, reddening, and proper motion. The
reliable determination of the parameters strongly depends on the photometry
available and especially on the U filter, which is used to obtain the color
excess E(B-V) through the color-color diagram (U-B) by (B-V) by fitting a zero
age main-sequence. Owing to the difficulty of performing photometry in the U
band, many authors have tried to obtain E(B-V) without the filter. But because
of the near linearity of the color-color diagrams that use the other bands,
combined with the fact that most fitting procedures are highly subjective (many
done "by eye") the reliability of those results has always been questioned. Our
group has recently developed, a tool that performs isochrone fitting in
open-cluster photometric data with a global optimization algorithm, which
removes the need to visually perform the fits and thus removes most of the
related subjectivity. Here we apply our method to a set of synthetic clusters
and two observed open clusters (Trumpler 1 and Melotte 105) using only
photometry for the BVRI bands. Our results show that, considering the cluster
structural variance caused only by photometric and Poisson sampling errors, our
method is able to recover the synthetic cluster parameters with errors of less
than 10% for a wide range of ages, distances, and reddening, which clearly
demonstrates its potential. The results obtained for Trumpler 1 and Melotte 105
also agree well with previous literature values.Comment: 5 pages, 5 figures, accepted for publication in
Astronomy&Astrophysic
Exact Renormalization of Massless QED2
We perform the exact renormalization of two-dimensional massless gauge
theories. Using these exact results we discuss the cluster property and
confinement in both the anomalous and chiral Schwinger models.Comment: 14 pages, no figures, introduction and conclusions modifie
Time dependent transformations in deformation quantization
We study the action of time dependent canonical and coordinate
transformations in phase space quantum mechanics. We extend the covariant
formulation of the theory by providing a formalism that is fully invariant
under both standard and time dependent coordinate transformations. This result
considerably enlarges the set of possible phase space representations of
quantum mechanics and makes it possible to construct a causal representation
for the distributional sector of Wigner quantum mechanics.Comment: 16 pages, to appear in the J. Math. Phy
On the Evaluation of the Mechanical Behaviour of Structural Glass Elements
Glass can be considered to be a high-technology engineering material with a
multifunctional potential for structural applications. However, the conventional approach to the use
of glass is often based only on its properties of transparency and isolation. It is thus highly
appropriate and necessary to study the mechanical behaviour of this material and to develop
adequate methods and models leading to its characterisation. It is evident that the great potential of
growth for structural glass applications is an important opportunity of development for the glass
industry and the building/construction sectors. The work presented in this paper is a reflection of
this conclusion. The authors shortly present the state-of-the-art on the application of glass as a
structural element in building and construction, and refer to other potential fields of application and
available glass materials. The experimental procedures and methods adopted in three-point bending
tests performed on 500 × 100 [mm2] float, laminated and tempered glass specimens with
thicknesses between 4 and 19 mm are thoroughly described. The authors evaluated the mechanical
strength and stiffness of glass for structural applications. This work contributes to a deeper
knowledge of the properties of this material
Paradeduction in Axiomatic Formal Systems
The concept of paradeduction is presented in order to justify that we can
overlook contradictory information taking into account only what is consistent.
Besides that, paradeduction is used to show that there is a way to transform
any logic, introduced as an axiomatic formal system, into a paraconsistent one
Anatomy of magnetic anisotropy induced by Rashba spin-orbit interactions
Magnetic anisotropy controls the orientational stability and switching
properties of magnetic states, and therefore plays a central role in
spintronics. First-principles density-functional-theory calculations are able,
in most cases, to provide a satisfactory description of bulk and interface
contributions to the magnetic anisotropy of particular film/substrate
combinations. In this paper we focus on achieving a simplified understanding of
some trends in interfacial magnetic anisotropy based on a simple tight-binding
model for quasiparticle states in a heavy-metal/ferromagnetic-metal bilayer
film. We explain how to calculate the magnetic anisotropy energy of this model
from the quasiparticle spin-susceptibility, compare with more conventional
approaches using either a perturbative treatment of spin-orbit interactions or
a direct calculation of the dependence of the energy on the orientation of the
magnetization, and show that the magnetic anisotropy can be interpreted as a
competition between a Fermi-sea term favoring perpendicular anisotropy and a
Fermi-surface term favoring in-plane anisotropy. Based on this finding, we
conclude that perpendicular magnetic anisotropy should be expected in an
itinerant electron thin film when the spin magnetization density is larger than
the product of the band exchange splitting and the Fermi level
density-of-states of the magnetic state
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