31 research outputs found
Canonical Formulation of Gravitational Teleparallelism in 2+1 Dimensions in Schwinger's Time Gauge
We consider the most general class of teleparallel gravitational {}{}theories
quadratic in the torsion tensor, in three space-time dimensions, and carry out
a detailed investigation of its Hamiltonian formulation in Schwinger's time
gauge. This general class is given by a family of three-parameter theories. A
consistent implementation of the Legendre transform reduces the original theory
to a one-parameter family of theories. By calculating Poisson brackets we show
explicitly that the constraints of the theory constitute a first-class set.
Therefore the resulting theory is well defined with regard to time evolution.
The structure of the Hamiltonian theory rules out the existence of the
Newtonian limit.Comment: 17 pages, Latex file, no figures; a numerical coefficient has been
corrected and a different result is achieve
Black Holes in 2+1 Teleparallel Theories of Gravity
We apply the Hamiltonian formulation of teleparallel theories of gravity in
2+1 dimensions to a circularly symmetric geometry. We find a family of
one-parameter black hole solutions. The BTZ solution fixes the unique free
parameter of the theory. The resulting field equations coincide with the
teleparallel equivalent of Einstein's three-dimensional equations. We calculate
the gravitational energy of the black holes by means of the simple expression
that arises in the Hamiltonian formulation and conclude that the resulting
value is identical to that calculated by means of the Brown-York method.Comment: 20 pages, Latex file, no figure
Diallel analysis and estimation of genetic parameters of hot pepper (Capsicum chinense Jacq.).
The degree of heterosis in the genus Capsicum spp. is considered high; however, most of the studies refer to the species Capsicum annuum L. In spite of the potential use of F1 hybrids in pungent peppers of the species Capsicum chinense, few studies are available which assess the magnitude of heterosis in this species . This study was carried out to assess heterosis and its components in F1 hybrids from a diallel cross between hot pepper lines (Capsicum chinense) and to obtain data on the allelic interaction between the parents involved in the crosses. Trials were made in Rio Branco-Acre, Brazil, from March through October 1997. A randomized complete block design with fifteen treatments and three replications was used. The treatments were five C. chinense accessions (from the Vegetable Germplasm Bank of the Universidade Federal de Viçosa ? BGH/UFV) and 10 F1 hybrids derived from single crosses between them (reciprocals excluded). Diallel analyses were performed for total yield, fruit length/diameter ratio, fruit dry matter per plant, Xanthomonas campestris pv. vesicatoria incidence, capsaicin yield per plant and number of seeds per fruit. Non-additive genetic effects were larger than additive effects for all the traits assessed. Epistasis was detected for fruit dry matter per plant, capsaicin yield per plant and number of seeds per fruit. In these cases, epistasis seemed to be largely responsible for heterosis expression. Dominant gene action, ranging from incomplete dominance to probable overdominance, was responsible for heterosis in those traits where no epistatic genetic action was detected
Produtividade e qualidade de frutos de cultivares de polinização aberta e híbridos F1 de beringela (Solanum melongena L.).
Este trabalho foi conduzido no período de fevereiro a outubro de 1992, no campus da UFLA em Lavras-MG (21º14'S920m). Foram utilizadas sete cultivares de polinização aberta (Embu = E, Santa Genebra = SG, Viserba = V, Aubergine de Barbentane = AB, Flórida Market = FM, Black Beauty = BB e Melitino = M), duas linhagens (B-14-07 = B1 e B-31-06 = B2), dezoito híbridos experimentais F1 (E x FM x E x BB x E x M, E x B1, E x B2, SG x FM, SG x BB, SG x M, SG x B1, SG x B2, V x FM, V x B1, V x B2, AB x FM, AB x M, AB x B1, AB x B2 e M x FM) e dois híbridos comerciais (F-100 e F-1000). O delineamento experimental utilizado foi de blocos causalizados completos com três repetições de dez plantas por parcela espaçadas em 0,5 e 1,2m. Foram feitas adubações de plantio (100g/cova 4-14-8, 3L/cova de cama de aviário) e de cobertura (100g/cova de Sulfato de Amônio em 5 aplicações). Todos os tratos culturais, normalmente utilizados em plantios comerciais, foram realizados e a irrigação foi por aspersão. Foram realizadas quatroze colheitas, escalonadas de sete em sete dias. Levando-se em conta tanto a produção total, a produção de frutos de primeira, quanto as características de formato do fruto, cor de fruto e de cálice, destacaram-se os híbridos F1 (Embu x Melitino), F1 (Embu x B-31-06) e F1 (Santa Genebra x Flórida Market 10), que além de superarem seus respectivos progenitores, podem ser considerados comercialmente competitivos com o híbrido padrão F-100
Graviton resonances on two-field thick branes
This work presents new results about the graviton massive spectrum in
two-field thick branes. Analyzing the massive spectra with a relative
probability method we have firstly showed the presence of resonance structures
and obtained a connection between the thickness of the defect and the lifetimes
of such resonances. We obtain another interesting results considering the
degenerate Bloch brane solutions. In these thick brane models, we have the
emergence of a splitting effect controlled by a degeneracy parameter. When the
degeneracy constant tends to a critical value, we have found massive resonances
to the gravitational field indicating the existence of modes highly coupled to
the brane. We also discussed the influence of the brane splitting effect over
the resonance lifetimes.Comment: 15 pages, 8 figure
Energy of general 4-dimensional stationary axisymmetric spacetime in the teleparallel geometry
The field equation with the cosmological constant term is derived and the
energy of the general 4-dimensional stationary axisymmetric spacetime is
studied in the context of the hamiltonian formulation of the teleparallel
equivalent of general relativity (TEGR). We find that, by means of the integral
form of the constraints equations of the formalism naturally without any
restriction on the metric parameters, the energy for the asymptotically flat/de
Sitter/Anti-de Sitter stationary spacetimes in the Boyer-Lindquist coordinate
can be expressed as . It is surprised to learn that the
energy expression is relevant to the metric components ,
and only. As examples, by using this formula
we calculate the energies of the Kerr-Newman (KN), Kerr-Newman Anti-de Sitter
(KN-AdS), Kaluza-Klein, and Cveti\v{c}-Youm spacetimes.Comment: 12 page
Energy and Angular Momentum Densities in a Godel-Type Universe in the Teleparallel Geometry
The main scope of this research consists in evaluating the energy-momentum
(gravitational field plus matter) and gravitational angular momentum densities
in the universe with global rotation, considering the Godel-Obukhov metric. For
this, we use the Hamiltonian formalism of the Teleparallel Equivalent of
General Relativity (TEGR), which is justified for presenting covariant
expressions for the considered quantities. We found that the total energy
density calculated by the TEGR method is in agreement with the results reported
by other authors in the literature using pseudotensors. The result found for
the angular momentum density depends on the rotational parameter as expected.
We also show explicitly the equivalence among the field equations of the TEGR
and Einstein equations (RG), considering a perfect fluid and Godel-Obukhov
metric.Comment: 20 pages, no figures. Revised in view of Referee's comments. Version
to appear in the Gravitation and Cosmolog
Charged Dilaton, Energy, Momentum and Angular-Momentum in Teleparallel Theory Equivalent to General Relativity
We apply the energy-momentum tensor to calculate energy, momentum and
angular-momentum of two different tetrad fields. This tensor is coordinate
independent of the gravitational field established in the Hamiltonian structure
of the teleparallel equivalent of general relativity (TEGR). The spacetime of
these tetrad fields is the charged dilaton. Our results show that the energy
associated with one of these tetrad fields is consistent, while the other one
does not show this consistency. Therefore, we use the regularized expression of
the gravitational energy-momentum tensor of the TEGR. We investigate the energy
within the external event horizon using the definition of the gravitational
energy-momentum.Comment: 22 Pages Late