Produtividade do algodoeiro em rotação com soja no sistema plantio direto.

bitstream/item/65691/1/Cot-34-2001.pd

O algodoeiro em rotação com a soja no sistema plantio direto.

bitstream/item/40080/1/PA-1-1999.pd

Maize yield and rainfall on different spatial and temporal scales in Southern Brazil

This study aimed to establish relationships between maize yield and rainfall on different temporal and spatial scales, in order to provide a basis for crop monitoring and modelling. A 16-year series of maize yield and daily rainfall from 11 municipalities and micro-regions of Rio Grande do Sul State was used. Correlation and regression analyses were used to determine associations between crop yield and rainfall for the entire crop cycle, from tasseling to 30 days after, and from 5 days before tasseling to 40 days after. Close relationships between maize yield and rainfall were found, particularly during the reproductive period (45-day period comprising the flowering and grain filling). Relationships were closer on a regional scale than at smaller scales. Implications of the crop-rainfall relationships for crop modelling are discussed.Título em português: Rendimento de milho e chuva em diferentes escalas espaço-temporais no Sul do Brasil

High Temperature Matter and Gamma Ray Spectra from Microscopic Black Holes

The relativistic viscous fluid equations describing the outflow of high temperature matter created via Hawking radiation from microscopic black holes are solved numerically for a realistic equation of state. We focus on black holes with initial temperatures greater than 100 GeV and lifetimes less than 6 days. The spectra of direct photons and photons from $\pi^0$ decay are calculated for energies greater than 1 GeV. We calculate the diffuse gamma ray spectrum from black holes distributed in our galactic halo. However, the most promising route for their observation is to search for point sources emitting gamma rays of ever-increasing energy.Comment: 33 pages, 13 figures, to be submitted to PR

Calculation of the emergent spectrum and observation of primordial black holes

We calculate the emergent spectrum of microscopic black holes, which emit copious amounts of thermal ``Hawking'' radiation, taking into account the proposition that (contrary to previous models) emitted quarks and gluons do not directly fragment into hadrons, but rather interact and form a photosphere and decrease in energy before fragmenting. The resulting spectrum emits copious amount of photons at energies around 100MeV. We find that the limit on the average universal density of black holes is not significantly affected by the photosphere. However we also find that gamma ray satellites such as EGRET and GLAST are well suited to look for nearby black holes out to a distance on the order of 0.3 parsecs, and conclude that if black holes are clustered locally as much as luminous matter, they may be directly detectable.Comment: 10 pages, Latex, submitted to PR

Numerical Study of Hawking Radiation Photosphere Formation around Microscopic Black Holes

Heckler has recently argued that the Hawking radiation emitted from microscopic black holes has sufficiently strong interactions above a certain critical temperature that it forms a photosphere, analogous to that of the sun. In this case, the visible radiation is much cooler than the central temperature at the Schwarzschild radius, in contrast to the naive expectation for the observable spectrum. We investigate these ideas more quantitatively by solving the Boltzmann equation using the test particle method. We confirm that at least two kinds of photospheres may form: a quark-gluon plasma for black holes of mass M_{BH} < 5 times 10^{14} g and an electron-positron-photon plasma for M_{BH} < 2 times 10^{12} g. The QCD photosphere extends from the black hole horizon to a distance of 0.2--4.0 fm for 10^9 g < M_{BH} < 5 10^{14} g, at which point quarks and gluons with average energy of order \Lambda_{QCD} hadronize. The QED photosphere starts at a distance of approximately 700 black hole radii and dissipates at about 400 fm, where the average energy of the emitted electrons, positrons and photons is inversely proportional to the black hole temperature, and significantly higher than was found by Heckler. The consequences of these photospheres for the cosmic diffuse gamma ray and antiproton backgrounds are discussed: bounds on the black hole contribution to the density of the universe are slightly weakened.Comment: 25 pages, Latex, 33 figures ; some incorrect references fixe

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Relativistic Viscous Fluid Description of Microscopic Black Hole Wind

Microscopic black holes explode with their temperature varying inversely as their mass. Such explosions would lead to the highest temperatures in the present universe, all the way to the Planck energy. Whether or not a quasi-stationary shell of matter undergoing radial hydrodynamic expansion surrounds such black holes is been controversial. In this paper relativistic viscous fluid equations are applied to the problem. It is shown that a self-consistent picture emerges of a fluid just marginally kept in local thermal equilibrium; viscosity is a crucial element of the dynamics.Comment: 11 pages, revte

Bubble Wall Velocity at the Electroweak Phase Transition

We calculate the velocity and thickness of a bubble wall at the electroweak phase transition in the Minimal Standard Model. We model the wall with semiclassical equations of motion and show that friction arises from the deviation of massive particle populations from thermal equilibrium. We treat these with Boltzmann equations in a fluid approximation in the background of the wall. Our analysis improves on the previous work by using the two loop effective potential, accounting for particle transport, and determining the wall thickness dynamically. We find that the wall is significantly thicker than at phase equilibrium, and that the velocity is fairly high, $v_w \simeq 0.7c$, and quite weakly dependent on the Higgs mass.Comment: 8 pages, plain LaTe