650 research outputs found
Durabilidade pós-colheita de bananas é estudada.
bitstream/item/75707/1/art-038.pdfPublicado também em: Mundo Rural, 26 out. 2010
Auxiliary fields in the geometrical relativistic particle dynamics
We describe how to construct the dynamics of relativistic particles
following, either timelike or null curves, by means of an auxiliary variables
method instead of the standard theory of deformations for curves. There are
interesting physical particle models governed by actions that involve higher
order derivatives of the embedding functions of the worldline. We point out
that the mechanical content of such models can be extracted wisely from a lower
order action, which can be performed by implementing in the action a finite
number of constraints that involve the geometrical relationship structures
inherent to a curve and by using a covariant formalism. We emphasize our
approach for null curves. For such systems, the natural time parameter is a
pseudo-arclength whose properties resemble those of the standard proper time.
We illustrate the formalism by applying it to some models for relativistic
particles.Comment: 13 pages, no figure
Avaliacao de NPK na cultura do milho cultivado em um podzolico vermelho-escuro degradado submetido a diferentes fontes de nutrientes, no Municipio de Prados, MG.
bitstream/item/62887/1/CNPS-PESQ.-AND.-7-98.pd
Diagnostico do estado nutricional de seringais implantados na regiao da zona da mata de Minas Gerais.
bitstream/item/62881/1/CNPS-PESQ.-AND.-5-98.pd
Frenet-Serret dynamics
We consider the motion of a particle described by an action that is a
functional of the Frenet-Serret [FS] curvatures associated with the embedding
of its worldline in Minkowski space. We develop a theory of deformations
tailored to the FS frame. Both the Euler-Lagrange equations and the physical
invariants of the motion associated with the Poincar\'e symmetry of Minkowski
space, the mass and the spin of the particle, are expressed in a simple way in
terms of these curvatures. The simplest non-trivial model of this form, with
the lagrangian depending on the first FS (or geodesic) curvature, is
integrable. We show how this integrability can be deduced from the Poincar\'e
invariants of the motion. We go on to explore the structure of these invariants
in higher-order models. In particular, the integrability of the model described
by a lagrangian that is a function of the second FS curvature (or torsion) is
established in a three dimensional ambient spacetime.Comment: 20 pages, no figures - replaced with version to appear in Class.
Quant. Grav. - minor changes, added Conclusions sectio
Anti-de Sitter curvature radius constrained by quasars in brane-world scenarios
This paper is intended to investigate the luminosity due to accretion of gas
in supermassive black holes (SMBHs) in the center of quasars, using a
brane-world scenario naturally endowed with extra dimensions, whereon theories
formulated introduce corrections in the field equations at high energies. SMBHs
possess the necessary highly energetic environment for the introduction of
these corrections, which are shown to produce small deviations in all SMBH
properties and, consequentely, corrections in the accretion theory that
supports quasars radiative processes. The radiative flux observed from quasars
indicates these deviations, from which the magnitude of the AdS bulk
curvature radius, and consequently the extra dimension compactification radius
is estimated.Comment: 11 pages, RevTeX, Eq.(2) and (3) expanded, and comments thereon
update
Geometric dynamical observables in rare gas crystals
We present a detailed description of how a differential geometric approach to
Hamiltonian dynamics can be used for determining the existence of a crossover
between different dynamical regimes in a realistic system, a model of a rare
gas solid. Such a geometric approach allows to locate the energy threshold
between weakly and strongly chaotic regimes, and to estimate the largest
Lyapunov exponent. We show how standard mehods of classical statistical
mechanics, i.e. Monte Carlo simulations, can be used for our computational
purposes. Finally we consider a Lennard Jones crystal modeling solid Xenon. The
value of the energy threshold turns out to be in excellent agreement with the
numerical estimate based on the crossover between slow and fast relaxation to
equilibrium obtained in a previous work by molecular dynamics simulations.Comment: RevTeX, 19 pages, 6 PostScript figures, submitted to Phys. Rev.
Legacy effects override soil properties for CO 2 and N 2 O but not CH 4 emissions following digestate application to soil
The application of organic materials to soil can recycle nutrients and increase organic matter in agricultural lands. Digestate can be used as a nutrient source for crop production but it has also been shown to stimulate greenhouse gas (GHG) emissions from amended soils. While edaphic factors, such as soil texture and pH, have been shown to be strong determinants of soil GHG fluxes, the impact of the legacy of previous management practices is less well understood. Here we aim to investigate the impact of such legacy effects and to contrast them against soil properties to identify the key determinants of soil GHG fluxes following digestate application. Soil from an already established field experiment was used to set up a pot experiment, to evaluate N2O, CH4 and CO2 fluxes from cattle‐slurry‐digestate amended soils. The soil had been treated with farmyard manure, green manure or synthetic N‐fertilizer, 18 months before the pot experiment was set up. Following homogenization and a preincubation stage, digestate was added at a concentration of 250 kg total N/ha eq. Soil GHG fluxes were then sampled over a 64 day period. The digestate stimulated emissions of the three GHGs compared to controls. The legacy of previous soil management was found to be a key determinant of CO2 and N2O flux while edaphic variables did not have a significant effect across the range of variables included in this experiment. Conversely, edaphic variables, in particular texture, were the main determinant of CH4 flux from soil following digestate application. Results demonstrate that edaphic factors and current soil management regime alone are not effective predictors of soil GHG flux response following digestate application. Knowledge of the site management in terms of organic amendments is required to make robust predictions of the likely soil GHG flux response following digestate application to soil
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