8,355 research outputs found
Rotating 5D-Kaluza-Klein Space-Times from Invariant Transformations
Using invariant transformations of the five-dimensional Kaluza-Klein (KK)
field equations, we find a series of formulae to derive axial symmetric
stationary exact solutions of the KK theory starting from static ones. The
procedure presented in this work allows to derive new exact solutions up to
very simple integrations. Among other results, we find exact rotating solutions
containing magnetic monopoles, dipoles, quadripoles, etc., coupled to scalar
and to gravitational multipole fields.Comment: 24 pages, latex, no figures. To appear in Gen. Rel. Grav., 32,
(2000), in pres
Dynamics of a Self-interacting Scalar Field Trapped in the Braneworld for a Wide Variety of Self-interaction Potentials
We apply the dynamical systems tools to study the linear dynamics of a
self-interacting scalar field trapped in the braneworld, for a wide variety of
self-interaction potentials. We focus on Randall-Sundrum (RS) and on
Dvali-Gabadadze-Porrati (DGP) braneworld models exclusively. These models are
complementary to each other: while the RS brane produces ultra-violet (UV)
corrections to general relativity, the DGP braneworld modifies Einstein's
theory at large scales, i. e., produces infra-red (IR) modifications of general
relativity. This study of the asymptotic properties of both braneworld models,
shows -- in the phase space -- the way the dynamics of a scalar field trapped
in the brane departs from standard general relativity behaviour.Comment: 12 pages, 5 figures and 5 table
On the Space Time of a Galaxy
We present an exact solution of the averaged Einstein's field equations in
the presence of two real scalar fields and a component of dust with spherical
symmetry. We suggest that the space-time found provides the characteristics
required by a galactic model that could explain the supermassive central object
and the dark matter halo at once, since one of the fields constitutes a central
oscillaton surrounded by the dust and the other scalar field distributes far
from the coordinate center and can be interpreted as a halo. We show the
behavior of the rotation curves all along the background. Thus, the solution
could be a first approximation of a ``long exposition photograph'' of a galaxy.Comment: 8 pages REVTeX, 11 eps figure
Axisymmetric Stationary Solutions as Harmonic Maps
We present a method for generating exact solutions of Einstein equations in
vacuum using harmonic maps, when the spacetime possesses two commutating
Killing vectors. This method consists in writing the axisymmetric stationry
Einstein equations in vacuum as a harmonic map which belongs to the group
SL(2,R), and decomposing it in its harmonic "submaps". This method provides a
natural classification of the solutions in classes (Weil's class, Lewis' class
etc).Comment: 17 TeX pages, one table,( CINVESTAV- preprint 12/93
Nonequilibrium charge dynamics of light-driven rings threaded by a magnetic flux
We study theoretically the charge polarization and the charge current
dynamics of a mesoscopic ring driven by short asymmetric electromagnetic pulses
and threaded by an external static magnetic flux. It is shown that the
pulse-induced charge polarization and the associated light-emission is
controllable by tuning the external magnetic flux. Applying two mutually
perpendicular pulses triggers a charge current in the ring. The interplay
between this nonequilibrium and the persistent currents is investigated and the
conditions under which the pulses stop the persistent current are identified.Comment: 6 pages, 2 figures; submitted to EP
Solutions in Self-Dual Gravity Constructed Via Chiral Equations
The chiral model for self-dual gravity given by Husain in the context of the
chiral equations approach is discussed. A Lie algebra corresponding to a finite
dimensional subgroup of the group of symplectic diffeomorphisms is found, and
then use for expanding the Lie algebra valued connections associated with the
chiral model. The self-dual metric can be explicitly given in terms of harmonic
maps and in terms of a basis of this subalgebra.Comment: Plain Latex, 13 Pages, major revisions of style in the above proof,
several Comments added. Version to appear in Physical Review
Using text mining to analyse digital transformation impact on people
Digital transformation is changing people's lives in many ways, creating competition between people and machines. All aspects of people’s lives are being influenced with global impacts for society. In this context, many problems have emerged for which there is still no clear ideas of their effects on people's lives. To study these problems, new tools and methodologies are needed in order to compare large volumes of data. The analysis of texts, using Text Mining, has been gaining prominence, among researchers, as one of the most relevant methodologies. However, methodologies using Text Mining are not robust enough to allow researchers to compare data from different sources, such as report data and text data. The main objective of this paper is to propose an innovative Text Mining methodology that allows to compare different texts. This study is exploratory, and it is supported by quantitative methodologies. Using Text Mining to explore ECIAIR 2019 proceedings and other European reputed reports about digital transformation, and comparing the opinions expressed by researchers with those manifested by other people, it is intended to understand if there are coincidences in the language used by researchers and on the reports in what concerns what people feel about the impacts of digital transformation on their lives. This paper belongs to an ongoing research aiming to develop text mining tools that consider corpora as variables with specific values, treating those variables as statistic variables, contributing to the enrichment of the statistical methodologies used to study digital transformation impacts. The results show that there is a gap between the language of the investigators and the one used on the reports. At the same time, there are also overlaps in some topics analysed in the documents. These results indicate that there are topics that concern both the scientific community and the international organisations responsible for the preparation of public policy guiding reports.info:eu-repo/semantics/acceptedVersio
Quintessence and Scalar Dark Matter in the Universe
Continuing with previous works, we present a cosmological model in which dark
matter and dark energy are modeled by scalar fields and ,
respectively, endowed with the scalar potentials and . This model contains 95% of
scalar field. We obtain that the scalar dark matter mass is The solution obtained allows us to recover the success of the
standard CDM. The implications on the formation of structure are reviewed. We
obtain that the minimal cutoff radio for this model is Comment: 4 pages REVTeX, 3 eps color figures. Minor changes and references
updated. To appear in Classical and Quantum Gravity as a Letter to the
Editor. More information at http://www.fis.cinvestav.mx/~siddh/PHI
Two Distinct, Geographically Overlapping Lineages of the Corallimorpharian Ricordea Florida (Cnidaria: Hexacorallia: Ricordeidae)
We examined the genetic variation of the corallimorpharian Ricordea florida; it is distributed throughout the Caribbean region and is heavily harvested for the marine aquarium trade. Eighty-four distinct individuals of R. florida were sequenced from four geographically distant Caribbean locations (Curaçao, Florida, Guadeloupe, and Puerto Rico). Analysis of the ribosomal nuclear region (ITS1, 5.8S, ITS2) uncovered two geographically partially overlapping genetic lineages in R. florida, probably representing two cryptic species. Lineage 1 was found in Florida and Puerto Rico, and Lineage 2 was found in Florida, Puerto Rico, Guadeloupe, and Curaçao. Because of the multi-allelic nature of the ITS region, four individuals from Lineage 1 and six from Lineage 2 were cloned to evaluate the levels of hidden intra-individual variability. Pairwise genetic comparisons indicated that the levels of intra-individual and intra-lineage variability (\u3c1%) were approximately an order of magnitude lower than the divergence (~9%) observed between the two lineages. The fishery regulations of the aquarium trade regard R. florida as one species. More refined regulations should take into account the presence of two genetic lineages, and they should be managed separately in order to preserve the long-term evolutionary potential of this corallimorpharian. The discovery of two distinct lineages in R. florida illustrates the importance of evaluating genetic variability in harvested species prior to the implementation of management policies
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