1,942 research outputs found
Interacting spin 0 fields with torsion via Duffin-Kemmer-Petiau theory
Here we study the behaviour of spin 0 sector of the DKP field in spaces with
torsion. First we show that in a Riemann-Cartan manifold the DKP field presents
an interaction with torsion when minimal coupling is performed, contrary to the
behaviour of the KG field, a result that breaks the usual equivalence between
the DKP and the KG fields.
Next we analyse the case of Teleparallel Equivalent of General Relativity
Weitzenbock manifold, showing that in this case there is a perfect agreement
between KG and DKP fields. The origins of both results are also discussed.Comment: 10 pages, no figures, uses REVTEX. Changes in the presentation, minor
misprints and one equation corrected. References updated. To appear in
General Relativity and Gravitatio
Conformal invariance of massless Duffin-Kemmer-Petiau theory in Riemannian space-times
We investigate the conformal invariance of massless Duffin-Kemmer-Petiau
theory coupled to riemannian space-times. We show that, as usual, in the
minimal coupling procedure only the spin 1 sector of the theory -which
corresponds to the electromagnetic field- is conformally invariant. We show
also that the conformal invariance of the spin 0 sector can be naturally
achieved by introducing a compensating term in the lagrangian. Such a procedure
-besides not modifying the spin 1 sector- leads to the well-known conformal
coupling between the scalar curvature and the massless Klein-Gordon-Fock field.
Going beyond the riemannian spacetimes, we briefly discuss the effects of a
nonvanishing torsion in the scalar case.Comment: 8 pages, no figures. Major changes in contend and results. To appear
in Class.Quant.Gra
Spin 1 fields in Riemann-Cartan space-times "via" Duffin-Kemmer-Petiau theory
We consider massive spin 1 fields, in Riemann-Cartan space-times, described
by Duffin-Kemmer-Petiau theory. We show that this approach induces a coupling
between the spin 1 field and the space-time torsion which breaks the usual
equivalence with the Proca theory, but that such equivalence is preserved in
the context of the Teleparallel Equivalent of General Relativity.Comment: 8 pages, no figures, revtex. Dedicated to Professor Gerhard Wilhelm
Bund on the occasion of his 70th birthday. To appear in Gen. Rel. Grav.
Equations numbering corrected. References update
Relativistic Tunneling Through Two Successive Barriers
We study the relativistic quantum mechanical problem of a Dirac particle
tunneling through two successive electrostatic barriers. Our aim is to study
the emergence of the so-called \emph{Generalized Hartman Effect}, an effect
observed in the context of nonrelativistic tunneling as well as in its
electromagnetic counterparts, and which is often associated with the
possibility of superluminal velocities in the tunneling process. We discuss the
behavior of both the phase (or group) tunneling time and the dwell time, and
show that in the limit of opaque barriers the relativistic theory also allows
the emergence of the Generalized Hartman Effect. We compare our results with
the nonrelativistic ones and discuss their interpretation.Comment: 7 pages, 3 figures. Revised version, with a new appendix added.
Slightly changes in the styles and captions of Figures 1 and 2. To appear in
Physical Review
Bose-Einstein Condensation and Free DKP field
The thermodynamical partition function of the Duffin-Kemmer-Petiau theory is
evaluated using the imaginary-time formalism of quantum field theory at finite
temperature and path integral methods. The DKP partition function displays two
features: (i) full equivalence with the partition function for charged scalar
particles and charged massive spin 1 particles; and (ii) the zero mode sector
which is essential to reproduce the well-known relativistic Bose-Einstein
condensation for both theories.Comment: 12 pages, 2 eps figures. To be published in Physics Letter
Electromagnetic field at Finite Temperature: A first order approach
In this work we study the electromagnetic field at Finite Temperature via the
massless DKP formalism. The constraint analysis is performed and the partition
function for the theory is constructed and computed. When it is specialized to
the spin 1 sector we obtain the well-known result for the thermodynamic
equilibrium of the electromagnetic field.Comment: 6 pages, Latex2e, title changed and minimal modification
Incentivador respiratório em cirurgias de grande porte: uma revisão sistemática
OBJECTIVE: To conduct a systematic review to evaluate the evidence of the use of incentive spirometry (IS) for the prevention of postoperative pulmonary complications and for the recovery of pulmonary function in patients undergoing abdominal, cardiac and thoracic surgeries. METHODS: Searches were performed in the following databases: Medline, Embase, Web of Science, PEDro and Scopus to select randomized controlled trials which the IS was used in pre- and/or post-operative in order to prevent postoperative pulmonary complications and/or recover lung function after abdominal, cardiac and thoracic surgery. Two reviewers independently assessed all studies. In addition, the studies quality was assessed using the PEDro scale. RESULTS: Thirty studies were included (14 abdominal, 13 cardiac and 3 thoracic surgery; n=3,370 patients). In the analysis of the methodological quality, studies achieved a PEDro average score of 5.6, 4.7 and 4.8 points in abdominal, cardiac and thoracic surgeries, respectively. Five studies (3 abdominal, 1 cardiac and 1 thoracic surgery) compared the effect of the IS with control group (no intervention) and no difference was detected in the evaluated outcomes. CONCLUSION: There was no evidence to support the use of incentive spirometry in the management of surgical patients. Despite this, the use of incentive spirometry remains widely used without standardization in clinical practice.OBJETIVO: Realizar um levantamento da literatura para avaliar as evidências do uso do incentivador respiratório (IR) na prevenção de complicações pulmonares pós-operatórias (CPPs) e recuperação da função pulmonar em pacientes submetidos a cirurgias abdominal, cardÃaca e torácica. MÉTODOS: Esta revisão sistemática utilizou as bases de dados Medline, Embase, Web of Science, PEDro e Scopus para selecionar ensaios clÃnicos randomizados, nos quais o IR foi utilizado nos perÃodo pré e/ou pós-operatório, visando prevenir CPP e/ou recuperar função pulmonar após cirurgias abdominal, cardÃaca ou torácica. Dois revisores analisaram independentemente os estudos. Além disso, a qualidade dos estudos foi avaliada segundo a escala PEDro. RESULTADOS: Trinta estudos foram incluÃdos (14 de cirurgia abdominal, 13 de cardÃaca e três de torácica; n=3370 pacientes). Na análise de qualidade, os estudos obtiveram média de 5,6, 4,7 e 4,8 pontos nas cirurgias abdominais, cardÃacas e torácicas, respectivamente. Cinco estudos (três de cirurgia abdominal, um de cardÃaca e um de torácica) compararam o efeito do IR com grupo controle (sem intervenção) e não se verificou diferença nos desfechos estudados. CONCLUSÃO: Não se encontraram evidências que subsidiem o uso do IR no manejo de pacientes cirúrgicos. Apesar disso, o uso do IR continua não-padronizado e amplamente difundido na prática clÃnica.Conselho Nacional de Desenvolvimento CientÃfico e Tecnológico (CNPq
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