395 research outputs found
On scale symmetry breaking and confinement in D=3 models
Within the framework of the gauge-invariant, but path-dependent, variables
formalism, we study the connection between scale symmetry breaking and
confinement in three-dimensional gluodynamics. We explicitly show that the
static potential profile contains a linear potential, leading to the
confinement of static charges. Also, we establish a new type of equivalence
among different three-dimensional effective theories.Comment: 6 pages, references adde
On the stability of general relativistic geometric thin disks
The stability of general relativistic thin disks is investigated under a
general first order perturbation of the energy momentum tensor. In particular,
we consider temporal, radial and azimuthal "test matter" perturbations of the
quantities involved on the plane . We study the thin disks generated by
applying the "displace, cut and reflect" method, usually known as the image
method, to the Schwarzschild metric in isotropic coordinates and to the
Chazy-Curzon metric and the Zipoy-Voorhees metric (-metric) in Weyl
coordinates. In the case of the isotropic Schwarzschild thin disk, where a
radial pressure is present to support the gravitational attraction, the disk is
stable and the perturbation favors the formation of rings. Also, we found the
expected result that the thin disk models generated by the Chazy-Curzon and
Zipoy-Voorhees metric with only azimuthal pressure are not stable under a
general first order perturbationComment: 11 pages, RevTex. Phys Rev D (in press
Composição botânica da dieta consumida por bovinos em pastagens de quicuio-da-amazônia (Brachiaria humidicola) e braquiarão (Brachiaria brizantha), consorciada com leguminosas, com e sem queima (segunda fase experimental).
On the gravitational field of static and stationary axial symmetric bodies with multi-polar structure
We give a physical interpretation to the multi-polar Erez-Rozen-Quevedo
solution of the Einstein Equations in terms of bars. We find that each
multi-pole correspond to the Newtonian potential of a bar with linear density
proportional to a Legendre Polynomial. We use this fact to find an integral
representation of the function. These integral representations are
used in the context of the inverse scattering method to find solutions
associated to one or more rotating bodies each one with their own multi-polar
structure.Comment: To be published in Classical and Quantum Gravit
Avaliação da solarização do solo para o controle de Ralstonia solanacearum.
O presente trabalho avaliou o emprego da solarização como uma alternativa para o controle da murcha bacteriana, causada por Ralstonia solanacearum, em amostras de solo infestado com o patógeno, dispostas em bolsas de náilon e enterradas em parcelas solarizadas ou não. Dois experimentos foram instalados, um em Campinas (SP), de fevereiro a abril de 2001, e o outro em Piracicaba (SP), de dezembro de 2001 a janeiro de 2002. Os ensaios foram efetuados em delineamento inteiramente casualizado, esquema fatorial, com quatro repetições, tendo cada parcela 4 x 4 m. Os fatores avaliados foram a solarização (com ou sem), efetuada com filme plástico transparente de 100 µm de espessura, o período de tratamento (30 e 60 dias e 37 e 60 dias para o primeiro e o segundo experimentos, respectivamente) e a profundidade de colocação das amostras (10 e 20 cm), fator verificado apenas no segundo ensaio. Após os períodos estipulados de solarização, o solo de cada bolsa foi colocado em vasos, para os quais foram transplantadas mudas de tomateiro (Lycopersicon esculentum). No solo não solarizado, em ambos os experimentos, 43 a 100% dos tomateiros murcharam. No segundo experimento, 6 a 22% dos tomateiros murcharam no solo solarizado por 37 dias. Entretanto não foram detectadas plantas murchas nas parcelas solarizadas do primeiro experimento e no segundo ensaio nenhum tomateiro murchou solo solarizado por 60 dias, nas duas profundidades estudadas. Os resultados indicam que a solarização é uma técnica promissora para o controle de R. solanacearum
Brazilian coffee free-air carbon dioxide enrichment (face) facility: predicting the impact of climate change.
Relativistic and Newtonian core-shell models: analytical and numerical results
We make a detailed analysis of Newtonian as well as relativistic core-shell
models recently proposed to describe a black hole or neutron star surrounded by
shells of matter, and in a seminal sense also galaxies, supernovae and star
remnants since there are massive shell-like structures surrounding many of them
and also evidences for many galactic nuclei hiding black holes. We discuss the
unicity of the models in relation to their analyticity at the black hole
horizon and also to the full elimination of conical singularities. Secondly, we
study the role played by the presence/lack of discrete reflection symmetries
about equatorial planes in the chaotic behavior of the orbits, which is to be
contrasted with the almost universal acceptance of reflection symmetries as
default assumptions in galactic modeling. We also compare the related effects
if we change a true central black hole by a Newtonian central mass. The
numerical findings are: 1- The breakdown of the reflection symmetry about the
equatorial plane in both Newtonian and relativistic core-shell models does i)
enhance in a significant way the chaoticity of orbits in reflection symmetric
oblate shell models and ii) inhibit significantly also the occurrence of chaos
in reflection symmetric prolate shell models. In particular, in the prolate
case the lack of the reflection symmetry provides the phase space with a robust
family of regular orbits that is otherwise not found at higher energies. 2- The
relative extents of the chaotic regions in the relativistic cases (i. e. with a
true central black hole) are significantly larger than in the corresponding
Newtonian ones (which have just a central potential).Comment: AASTEX, 22 pages plus 28 postscript figures, to appear in Ap.
Brazilian coffee free-air carbon dioxide enrichment (face) facility: predicting the impact of climate change.
Remarks on Screening in a Gauge-Invariant Formalism
In this paper we display a direct and physically attractive derivation of the
screening contribution to the interaction potential in the Chiral Schwinger
model and generalized Maxwell-Chern-Simons gauge theory. It is shown that these
results emerge naturally when a correct separation between gauge-invariant and
gauge degrees of freedom is made. Explicit expressions for gauge-invariant
fields are found.Comment: 13 pages, 1 figure, to appear in PR
Exact General Relativistic Thick Disks
A method to construct exact general relativistic thick disks that is a simple
generalization of the ``displace, cut and reflect'' method commonly used in
Newtonian, as well as, in Einstein theory of gravitation is presented. This
generalization consists in the addition of a new step in the above mentioned
method. The new method can be pictured as a ``displace, cut, {\it fill} and
reflect'' method. In the Newtonian case, the method is illustrated in some
detail with the Kuzmin-Toomre disk. We obtain a thick disk with acceptable
physical properties. In the relativistic case two solutions of the Weyl
equations, the Weyl gamma metric (also known as Zipoy-Voorhees metric) and the
Chazy-Curzon metric are used to construct thick disks. Also the Schwarzschild
metric in isotropic coordinates is employed to construct another family of
thick disks. In all the considered cases we have non trivial ranges of the
involved parameter that yield thick disks in which all the energy conditions
are satisfied.Comment: 11 pages, RevTex, 9 eps figs. Accepted for publication in PR
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