5,684 research outputs found
Energy in an Expanding Universe in the Teleparallel Geometry
The main purpose of this paper is to explicitly verify the consistency of the
energy-momentum and angular momentum tensor of the gravitational field
established in the Hamiltonian structure of the Teleparallel Equivalent of
General Relativity (TEGR). In order to reach these objectives, we obtained the
total energy and angular momentum (matter plus gravitational field) of the
closed universe of the Friedmann-Lemaitre-Robertson-Walker (FLRW). The result
is compared with those obtained from the pseudotensors of Einstein and
Landau-Lifshitz. We also applied the field equations (TEGR) in an expanding
FLRW universe. Considering the stress energy-momentum tensor for a perfect
fluid, we found a teleparallel equivalent of Friedmann equations of General
Relativity (GR).Comment: 19 pages, no figures. Revised in view of Referee's comments. Version
to appear in the Brazilian Journal of Physic
Space-time Torsion and Neutrino Oscillations in Vacuum
The objective of this study is to verify the consistency of the prescription
of alternative minimum coupling (connection) proposed by the Teleparallel
Equivalent to General Relativity (TEGR) for the Dirac equation. With this aim,
we studied the problem of neutrino oscillations in Weitzenbock space-time in
the Schwarzschild metric. In particular, we calculate the phase dynamics of
neutrinos. The relation of spin of the neutrino with the space-time torsion is
clarified through the determination of the phase differences between spin
eigenstates of the neutrinos.Comment: 07 pages, no figure
Angular Momentum of the BTZ Black Hole in the Teleparallel Geometry
We carry out the Hamiltonian formulation of the three- dimensional
gravitational teleparallelism without imposing the time gauge condition, by
rigorously performing the Legendre transform. Definition of the gravitational
angular momentum arises by suitably interpreting the integral form of the
constraint equation Gama^ik=0 as an angular momentum equation. The
gravitational angular momentum is evaluated for the gravitational field of a
rotating BTZ black hole.Comment: 17 pages, no figures, v2: some misprints corrected, Ref.s added, Eq.s
revised, submitted to General Relativity and Gravitatio
Dielectric mismatch and shallow donor impurities in GaN/HfO2 quantum wells
In this work we investigate electron-impurity binding energy in GaN/HfO
quantum wells. The calculation considers simultaneously all energy
contributions caused by the dielectric mismatch: (i) image self-energy (i.e.,
interaction between electron and its image charge), (ii) the direct Coulomb
interaction between the electron-impurity and (iii) the interactions among
electron and impurity image charges. The theoretical model account for the
solution of the time-dependent Schr\"odinger equation and the results shows how
the magnitude of the electron-impurity binding energy depends on the position
of impurity in the well-barrier system. The role of the large dielectric
constant in the barrier region is exposed with the comparison of the results
for GaN/HfO with those of a more typical GaN/AlN system, for two different
confinement regimes: narrow and wide quantum wells.Comment: 6 Pages, 7 figure
Rosacea with extensive extrafacial lesions
Rosacea is a very common skin disorder in the clinical practice that primarily affects the convex areas of the face. Extrafacial rosacea lesions have occasionally been described, but extensive involvement is exceptional. In the absence of its typical clinical or histological features, the diagnosis of extrafacial rosacea may be problematic. We describe an unusual case of rosacea with very exuberant extrafacial lesions, when compared with the limited involvement of the face
Obstrução Intestinal de Causa Rara e Ecografia Point-of-Care - Em que Ponto nos Encontramos?
Malignant neoplasms of the small bowel, especially from the jejunum, are among the rarest types of cancer. Given its location, a delayed diagnosis is frequent and sometimes only made in an emergency context. The authors present a case of intestinal obstruction, where ultrasonography was pivotal in establishing a diagnosis. Point-of-care ultrasonography seems to be particularly sensitive in assessing emergency patients with abdominal pain, allowing effective orientation and saving human and technical resources.info:eu-repo/semantics/publishedVersio
Effects of long term exposure to occupational noise on textile industry workers' lung function
Vibroacoustic disease is a pathology caused by long occupational exposure to large pressure amplitude and low frequency noise. It is a systemic disease, with evolvement of respiratory structures. The exposure workers to this noise of textile industry may favour alterations in lung function. We studied 28 women working more than ten years in cotton-mill rooms to evaluate their lung function, including Spirometry, forced oscillation technique (I.O.S.) and Diffusion capacity. These results were compared with those of 30 women of similar ages not exposed to similar noise and not presenting respiratory disease. Statistical significance (P<0.05) was found with FEV25, R5 and Delta Rs5-Rs20. There was a resistance frequency dependence in 36% of the population exposed to noise, not statistically confirmed. Neither restriction nor changes in diffusing capacity where detected. CONCLUSION: The analysis of global alterations of lung function parameters suggests small airways aggression by noise. However we cannot definitively exclude the influence of cotton dust inhalation in itself which effects could be increased by the loss of ciliated cells and impairment of airways clearance caused by noise
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