16,600 research outputs found
Efeito da extrusão sobre a densidade absoluta, aparente e índice de expansão volumétrica em produtos extrudados à base de grits de milho e gergelim em grão.
Influência do preparo do solo nas perdas de água de chuva na cultura do milho.
Os diferentes sistemas de preparo dos solos utilizados pelos agricultores no Semi-Árido brasileiro apresentam situações diversas quanto ao aproveitamento da água para as culturas exploradas em condições dependentes de chuva. Neste trabalho, objetivou-se avaliar as perdas de água escoada de uma área submetida a diferentes sistemas de preparo do solo, cultivada com milho (Zea mays L.), correspondendo a T1 (Guimarães Duque); T2 (Aração profunda); T3 (Aração parcial); T4 (Sulcos barrados) e T5 (Sistema tradicional), que corresponde ao plantio no plano. A análise dos resultados referentes aos tratamentos apresenta que o T1 proporcionou maior volume de água escoado no ciclo da cultura (6.696 L), superando a testemunha (T5) que foi de 5.163,3 L. Por outro lado, o menor volume escoado ocorreu no tratamento com sulcos barrados (T4) que correspondeu a 1.066 L no mesmo período. Neste tratamento (T4) também foram obtidas as maiores produtividades de grão da cultura do milho (606 kg ha-1)
Caracterização química, morfológica e reológica dos extrudados (pellets) elaborados com grits de milho e gergelim em grão.
Scattering and self-adjoint extensions of the Aharonov-Bohm hamiltonian
We consider the hamiltonian operator associated with planar sec- tions of
infinitely long cylindrical solenoids and with a homogeneous magnetic field in
their interior. First, in the Sobolev space , we characterize all
generalized boundary conditions on the solenoid bor- der compatible with
quantum mechanics, i.e., the boundary conditions so that the corresponding
hamiltonian operators are self-adjoint. Then we study and compare the
scattering of the most usual boundary con- ditions, that is, Dirichlet, Neumann
and Robin.Comment: 40 pages, 5 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
Gravitational Lorentz Force and the Description of the Gravitational Interaction
In the context of a gauge theory for the translation group, we have obtained,
for a spinless particle, a gravitational analog of the Lorentz force. Then, we
have shown that this force equation can be rewritten in terms of magnitudes
related to either the teleparallel or the riemannian structures induced in
spacetime by the presence of the gravitational field. In the first case, it
gives a force equation, with torsion playing the role of force. In the second,
it gives the usual geodesic equation of General Relativity. The main conclusion
is that scalar matter is able to feel anyone of the above spacetime geometries,
the teleparallel and the metric ones. Furthermore, both descriptions are found
to be completely equivalent in the sense that they give the same physical
trajectory for a spinless particle in a gravitational field.Comment: Equations (44)-(47) correcte
Teleparallel Spin Connection
A new expression for the spin connection of teleparallel gravity is proposed,
given by minus the contorsion tensor plus a zero connection. The corresponding
minimal coupling is covariant under local Lorentz transformation, and
equivalent to the minimal coupling prescription of general relativity. With
this coupling prescription, therefore, teleparallel gravity turns out to be
fully equivalent to general relativity, even in the presence of spinor fields.Comment: 2 pages, RevTeX, to appear in Phys. Rev D (Brief Report
A New Spin Foam Model for 4d Gravity
Starting from Plebanski formulation of gravity as a constrained BF theory we
propose a new spin foam model for 4d Riemannian quantum gravity that
generalises the well-known Barrett-Crane model and resolves the inherent to it
ultra-locality problem. The BF formulation of 4d gravity possesses two sectors:
gravitational and topological ones. The model presented here is shown to give a
quantization of the gravitational sector, and is dual to the recently proposed
spin foam model of Engle et al. which, we show, corresponds to the topological
sector. Our methods allow us to introduce the Immirzi parameter into the
framework of spin foam quantisation. We generalize some of our considerations
to the Lorentzian setting and obtain a new spin foam model in that context as
well.Comment: 40 pages; (v2) published versio
Estimativas de parâmetros genéticos para escores visuais de conformação, precocidade e musculatura e suas relações com peso à desmama em bovinos da raça Nelore.
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