15,002 research outputs found
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
Implicit solutions with consistent additive and multiplicative components
Use of multiple-point-constraint
Fitting isochrones to open cluster photometric data III. Estimating metallicities from UBV photometry
The metallicity is a critical parameter that affects the correct
determination fundamental characteristics stellar cluster and has important
implications in Galactic and Stellar evolution research. Fewer than 10 % of the
2174 currently catalog open clusters have their metallicity determined in the
literature. In this work we present a method for estimating the metallicity of
open clusters via non-subjective isochrone fitting using the cross-entropy
global optimization algorithm applied to UBV photometric data. The free
parameters distance, reddening, age, and metallicity simultaneously determined
by the fitting method. The fitting procedure uses weights for the observational
data based on the estimation of membership likelihood for each star, which
considers the observational magnitude limit, the density profile of stars as a
function of radius from the center of the cluster, and the density of stars in
multi-dimensional magnitude space. We present results of [Fe/H] for nine
well-studied open clusters based on 15 distinct UBV data sets. The [Fe/H]
values obtained in the ten cases for which spectroscopic determinations were
available in the literature agree, indicating that our method provides a good
alternative to determining [Fe/H] by using an objective isochrone fitting. Our
results show that the typical precision is about 0.1 dex
Generalized Weyl-Wigner map and Vey quantum mechanics
The Weyl-Wigner map yields the entire structure of Moyal quantum mechanics
directly from the standard operator formulation. The covariant generalization
of Moyal theory, also known as Vey quantum mechanics, was presented in the
literature many years ago. However, a derivation of the formalism directly from
standard operator quantum mechanics, clarifying the relation between the two
formulations is still missing. In this paper we present a covariant
generalization of the Weyl order prescription and of the Weyl-Wigner map and
use them to derive Vey quantum mechanics directly from the standard operator
formulation. The procedure displays some interesting features: it yields all
the key ingredients and provides a more straightforward interpretation of the
Vey theory including a direct implementation of unitary operator
transformations as phase space coordinate transformations in the Vey idiom.
These features are illustrated through a simple example.Comment: 15 pages, LaTe
Improving the Knowledge on Seismogenic Sources in the Lower Tagus Valley for Seismic Hazard Purposes
The Lower Tagus Valley, that includes the metropolitan area of Lisbon, has been struck by several earthquakes which produced significant material damage and loss of lives. Their exact location remains unknown. Our goal is to shed some light into the seismogenic sources in the area using seismic reflection and geological data. In areas with no seismic coverage, potential-field data interpretation was carried out. Seismicity was overlaid to the potential seismogenic structures and high-resolution data was acquired in order to confirm which structures have been active into the Quaternary. Three major fault-zones affecting the Neogene were identified: V. F. Xira, Samora-Alcochete and Pinhal Novo. For the first fault, strong evidences suggest it is active. The other two fault-zones and other structures previously unknown can be correlated with several epicentres. Empirical relationships between maximum moment magnitude and fault area indicate that MW > 6.5 earthquakes can be expected for the larger structures
Primeiro relato de Braga patagonica Schödte & Meinert, 1884 (Crustacea: Isopoda) parasitando peixes cultivados no Brasil.
Resumo simples
On the Renormalizability of Theories with Gauge Anomalies
We consider the detailed renormalization of two (1+1)-dimensional gauge
theories which are quantized without preserving gauge invariance: the chiral
and the "anomalous" Schwinger models. By regularizing the non-perturbative
divergences that appear in fermionic Green's functions of both models, we show
that the "tree level" photon propagator is ill-defined, thus forcing one to use
the complete photon propagator in the loop expansion of these functions. We
perform the renormalization of these divergences in both models to one loop
level, defining it in a consistent and semi-perturbative sense that we propose
in this paper.Comment: Final version, new title and abstract, introduction and conclusion
rewritten, detailed semiperturbative discussion included, references added;
to appear in International Journal of Modern Physics
Pair creation of higher dimensional black holes on a de Sitter background
We study in detail the quantum process in which a pair of black holes is
created in a higher D-dimensional de Sitter (dS) background. The energy to
materialize and accelerate the pair comes from the positive cosmological
constant. The instantons that describe the process are obtained from the
Tangherlini black hole solutions. Our pair creation rates reduce to the pair
creation rate for Reissner-Nordstrom-dS solutions when D=4. Pair creation of
black holes in the dS background becomes less suppressed when the dimension of
the spacetime increases. The dS space is the only background in which we can
discuss analytically the pair creation process of higher dimensional black
holes, since the C-metric and the Ernst solutions, that describe respectively a
pair accelerated by a string and by an electromagnetic field, are not know yet
in a higher dimensional spacetime.Comment: 10 pages; 1 figure included; RexTeX4. v2: References added. Published
version. v3: Typo in equation (46) fixe
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