22,437 research outputs found
Issues on 3D Noncommutative Electromagnetic Duality
We extend the ordinary 3D electromagnetic duality to the noncommutative (NC)
space-time through a Seiberg-Witten map to second order in the noncommutativity
parameter (theta), defining a new scalar field model. There are similarities
with the 4D NC duality, these are exploited to clarify properties of both
cases. Up to second order in theta, we find that duality interchanges the
2-form theta with its 1-form Hodge dual *theta times the gauge coupling
constant, i.e., theta --> *theta g^2 (similar to the 4D NC electromagnetic
duality). We directly prove that this property is false in the third order
expansion in both 3D and 4D space-times, unless the slowly varying fields limit
is imposed. Outside this limit, starting from the third order expansion, theta
cannot be rescaled to attain an S-duality. In addition to possible applications
on effective models, the 3D space-time is useful for studying general
properties of NC theories. In particular, in this dimension, we deduce an
expression that significantly simplifies the Seiberg-Witten mapped Lagrangian
to all orders in theta.Comment: 15 pages, revtex4. v.2: We added a proof that the terms in (4.9) are
not surface terms, a new paragraph in our conclusion and new references. v.3:
improvements in our introduction and conclusions. v.4: Published version
(PRD): additional comments and reference
Inspection and diagnosis tests for structural safety evaluation: A case study
Diagnosis and assessment of existing structures is a developing area due to the appearance of a high number of building defects, structural and non-structural deterioration and precocious loss of quality, and, consequently, lower expected durability. With the aim of verifying the viability of rehabilitation or the need to demolish an existing fifteen year old parking building, several inspections and diagnostic non-destructive and destructive testing, visual inspection, were carried out to evaluate the structural safety conditions
A Representation of the Virasoro Algebra via Wigner-Heisenberg Algebraic Technique to Bosonic Systems
Using the Wigner-Heisenberg algebra for bosonic systems in connection with
oscillators we find a new representation for the Virasoro algebra.Comment: Revised version. Revtex, 7 pages, no figures. This work was presented
in the XXII Brazilian National Meeting on Particles and Fields
(October/2001), to appear in Braz. J. of Phys., 33, 1 (2003
Correlating the interstellar magnetic field with protostellar jets and its sources
This article combines new CCD polarimetric data with previous information
about protostellar objects in a search for correlations involving the
interstellar magnetic field. Specifically, we carried out an optical
polarimetric study of a sample of 28 fields of 10 X 10 arcmin^2 located in the
neighborhood of protostellar jets and randomly spread over the Galaxy. The
polarimetry of a large number of field stars is used to estimate both the
average and dispersion of the interstellar magnetic field (ISMF) direction in
each region. The results of the applied statistical tests are as follows.
Concerning the alignment between the jet direction and the interstellar
magnetic field, the whole sample does not show alignment. There is, however, a
statistically significant alignment for objects of Classes 0 and I. Regarding
the interstellar magnetic field dispersion, our sample presents values slightly
larger for regions containing T Tauri objects than for those harboring younger
protostars. Moreover the ISMF dispersion in regions containing high-mass
objects tends to be larger than in those including only low-mass protostars. In
our sample, the mean interstellar polarization as a function of the average
interstellar extinction in a region reaches a maximum value around 3% for A(V)
= 5, after which it decreases. Our data also show a clear correlation of the
mean value of the interstellar polarization with the dispersion of the
interstellar magnetic field: the larger the dispersion, the smaller the
polarization. Based on a comparison of our and previous results, we suggest
that the dispersion in regions forming stars is larger than in quiescent
regions.Comment: ApJ accepte
Seismic performance and strengthening of traditional masonry buildings in the city centre of Coimbra
The increasing concern and consequent appraisal on durability, conservation state
and changeable use and function of old buildings in urban centres relies a great deal on the
structural safety evaluation of vertical load capacity but also the capable resistance to
horizontal forces. The need to assess seismic vulnerability, particularly of the traditional
masonry buildings is a key issue. Particular attention has been put upon the building stock of
the old city centre of Coimbra, mainly constituted by old masonry load-bearing buildings of
significant architectural value.
The evaluation of the seismic vulnerability of old buildings is essential in the definition of the
strengthening needs and minimization of possible damages due to seismic actions, in
safeguarding of built heritage or in the identification of critical buildings. This paper intends
to contribute for the assessment of old buildings considering the local seismic risk.
A three dimensional model was developed for an aggregate of four buildings. The finite
element modelling of these buildings has intended to identify structural fragilities, help
understand the damages detected in the existing structures (crack opening) and evaluate the
global structural safety of this type of buildings.
It will be presented the main results obtained in this study, interpreted the structural damage,
stress distribution and verified the global stability and its consequences. The dynamic
response of such constructions to seismic actions has allowed studying the structural
vulnerability. Different strengthening techniques to improve the global behaviour of these
buildings were modelled and analysed. Efficiency comparison of the strengthening strategies
is also discussed
Estudo da vulnerabilidade e soluções de reforço de edifícios em alvenaria: Centro Histórico de Coimbra
O presente trabalho propõe contribuir para a promoção de métodos simplificados de avaliação
da segurança das construções antigas, nomeadamente face a acções sísmicas contribuindo com
informação referente à caracterizaçãomecânica e física das alvenarias antigas e do seu comportamento
face às diversas solicitações: peso próprio, sobrecargas regulamentares e acções sísmicas. Para a
análise estrutural foram utilizadas ferramentas numéricas de elementos finitos, com a elaboração de
um modelo numérico tridimensional, caracterizando com omáximo rigor, o comportamento estrutural
dos edifícios antigos.
É estudado o comportamento de um aglomerado de 4 edifícios da Baixa de Coimbra. É aferido o
comportamento dinâmico deste conjunto de edifícios, é avaliada a influência das ligações entre paredes
de alvenaria e da deformabilidade dos pavimentos na vulnerabilidade estrutural, para vários níveis de
intensidade sísmica.
Neste artigo são apresentados os resultados obtidos, são interpretados os danos estruturais
observados, é verificada a estabilidade global, e são propostas algumas soluções de reforço a adoptar
na recuperação e reforço estrutural deste tipo de edifícios
How was the Hubble sequence 6 Gyrs ago?
The way galaxies assemble their mass to form the well-defined Hubble sequence
is amongst the most debated topic in modern cosmology. One difficulty is to
link distant galaxies to those at present epoch. We aim at establishing how
were the galaxies of the Hubble sequence, 6 Gyrs ago. We intend to derive a
past Hubble sequence that can be causally linked to the present-day one. We
selected samples of nearby galaxies from the SDSS and of distant galaxies from
the GOODS survey. We verified that each sample is representative of galaxies.
We further showed that the observational conditions necessary to retrieve their
morphological classification are similar in an unbiased way. Morphological
analysis has been done in an identical way for all galaxies in the two samples.
We found an absence of number evolution for elliptical and lenticular galaxies,
which strikingly contrasts with the strong evolution of spiral and peculiar
galaxies. Spiral galaxies were 2.3 times less abundant in the past, that is
exactly compensated by the strong decrease by a factor 5 of peculiar galaxies.
It strongly suggests that more than half of the present-day spirals had
peculiar morphologies, 6 Gyrs ago, and this has to be accounted by any scenario
of galactic disk evolution and formation. The past Hubble sequence can be used
to test these scenarios as well as to test evolution of fundamental planes for
spirals and bulges.Comment: Version accepted by Astronomy and Astrophysics, October 21 2009.
Including low resolution images. 11 pages, 8 figure
The Evolution of the Baryonic Tully-Fisher Relation over the past 6 Gyr
Scaling relations are salient ingredients of galaxy evolution and formation
models. I summarize results from the IMAGES survey, which combines
spatially-resolved kinematics from FLAMES/GIRAFFE with imaging from HST/ACS and
other facilities. Specifically, I will focus on the evolution of the stellar
mass and baryonic Tully-Fisher Relations (TFR) from z=0.6 down to z=0. We found
a significant evolution in zero point and scatter of the stellar mass TFR
compared to the local Universe. Combined with gas fractions derived by
inverting the Schmidt-Kennicutt relation, we derived for the first time a
baryonic TFR at high redshift. Conversely to the stellar mass TFR, the baryonic
relation does not appear to evolve in zero point, which suggests that most of
the reservoir of gas converted into stars over the past 6 Gyr was already
gravitationally bound to galaxies at z=0.6.Comment: To be published in the proceedings of the IAU Symposium 277 "Tracing
the Ancestry of Galaxies"; 4 pages, 1 figur
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