Avaliacao de gramineas forrageiras para equinos.

bitstream/item/137594/1/PESQ-EM-ANDAMENTO-45.pdfCNPGC

Coulomb and nuclear breakup of 8^8B

The cross sections for the ($^8$B,$^7$Be-$p$) breakup reaction on $^{58}$Ni and $^{208}$Pb targets at the beam energies of 25.8 MeV and 415 MeV have been calculated within a one-step prior-form distorted-wave Born approximation. The relative contributions of Coulomb and nuclear breakup of dipole and quadrupole multipolarities as well as their interference have been determined. The nuclear breakup contributions are found to be substantial in the angular distributions of the $^7$Be fragment for angles in the range of 30$^\circ$ - 80$^\circ$ at 25.8 MeV beam energy. The Coulomb-nuclear interference terms make the dipole cross section larger than that of quadrupole even at this low beam energy. However, at the incident energy of 415 MeV, these effects are almost negligible in the angular distributions of the ($^7$Be-p) coincidence cross sections at angles below 4$^\circ$.Comment: Revised version, accepted for publication in Phys. Rev.

Phase lag in epidemics on a network of cities

We study the synchronisation and phase-lag of fluctuations in the number of infected individuals in a network of cities between which individuals commute. The frequency and amplitude of these oscillations is known to be very well captured by the van Kampen system-size expansion, and we use this approximation to compute the complex coherence function that describes their correlation. We find that, if the infection rate differs from city to city and the coupling between them is not too strong, these oscillations are synchronised with a well defined phase lag between cities. The analytic description of the effect is shown to be in good agreement with the results of stochastic simulations for realistic population sizes.Comment: 10 pages, 6 figure

Stability of antiphase line defects in nanometer-sized boron-nitride cones

We investigate the stability of boron nitride conical sheets of nanometer size, using first-principles calculations. Our results indicate that cones with an antiphase boundary (a line defect that contains either B-B or N-N bonds) can be more stable than those without one. We also find that doping the antiphase boundaries with carbon can enhance their stability, leading also to the appearance of localized states in the bandgap. Among the structures we considered, the one with the smallest formation energy is a cone with a carbon-modified antiphase boundary that presents a spin splitting of about 0.5 eV at the Fermi level.Comment: 5 two-column pages with 2 figures Accepted for publication in Physical Review B (vol 70, 15 Nov.

Cluster approximations for infection dynamics on random networks

In this paper, we consider a simple stochastic epidemic model on large regular random graphs and the stochastic process that corresponds to this dynamics in the standard pair approximation. Using the fact that the nodes of a pair are unlikely to share neighbors, we derive the master equation for this process and obtain from the system size expansion the power spectrum of the fluctuations in the quasi-stationary state. We show that whenever the pair approximation deterministic equations give an accurate description of the behavior of the system in the thermodynamic limit, the power spectrum of the fluctuations measured in long simulations is well approximated by the analytical power spectrum. If this assumption breaks down, then the cluster approximation must be carried out beyond the level of pairs. We construct an uncorrelated triplet approximation that captures the behavior of the system in a region of parameter space where the pair approximation fails to give a good quantitative or even qualitative agreement. For these parameter values, the power spectrum of the fluctuations in finite systems can be computed analytically from the master equation of the corresponding stochastic process.Comment: the notation has been changed; Ref. [26] and a new paragraph in Section IV have been adde

Divergência genética entre linhagens de melão do grupo Inodorus.

O presente trabalho teve como objetivo estimar a divergência genética entre linhagens Pele de Sapo e entre linhagens Honey Dew. Foram avaliadas dez linhagens de melão Pele de Sapo e dez linhagens de melão Honey Dew, em experimentos separados, conduzidos em blocos casualizados com três repetições. A divergência genética foi estimada pela distância de Mahalanobis. Foram utilizados os métodos de Tocher e UPGMA para o agrupamento das linhagens. Para as linhagens Pele de Sapo, constatou-se divergência genética com a formação de quatro e cinco grupos conforme os métodos de agrupamento de Tocher e UPGMA, respectivamente. Sugere-se cruzamento das linhagens PS-01, PS-05 e PS-7 entre si ou com as demais linhagens do grupo I. Para as linhagens Honey Dew, verificou-se a formação dos mesmos três grupos nos métodos de agrupamento de Tocher e UPGMA. O grupo II formado pelas linhagens OF-01 e OF-02; o grupo III pela linhagem OF-03 e o primeiro grupo pelas demais linhagens. Com relação às linhagens Honey Dew, recomenda-se os cruzamentos das linhagens OF-01 ou OF-02, com as demais linhagens avaliadas. A linhagem OF-03, com características semelhantes às linhagens OF-01 ou OF-02 pode ser cruzada com as linhagens do grupo I

Implicações da interação genótipos x ambientes sobre ganhos com a seleção em meloeiro.

O objetivo do presente trabalho foi estudar o efeito da interação genótipos por ambientes sobre a avaliação de famílias de meloeiro. Foram avaliadas 144 famílias na geração S6, em quatro municípios, Mossoró, Baraúna, Assu e Alto do Rodrigues, em um látice simples 12x12. As características avaliadas foram: produtividade, peso médio do fruto, proporção da cavidade interna, espessura da polpa, firmeza da polpa e teor de sólidos solúveis. Constatou-se efeito significativo de famílias nos quatro ambientes de avaliação e na análise conjunta para todas as características. A interação famílias x locais foi acentuada, sendo a estimativa do componente de variância da interação superior àquele da variância genética entre famílias. Ocorreu superioridade na contribuição da parte complexa em relação à simples da interação para todas as características. A interação famílias x ambientes teve reflexo na seleção, pois a resposta correlacionada pela seleção em um ambiente e ganho em outro sempre foi inferior ao ganho da seleção direta. As estimativas de coeficiente de variação genética e variância genética entre famílias foram superestimadas pelo componente da interação famílias x locais, sendo necessárias avaliações em ambientes diferentes. A seleção com base no comportamento médio das famílias foi eficiente, pois proporcionou maiores ganhos de seleção do que aqueles obtidos com base na seleção no ambiente individual

New sources of resistance to Myrothecium roridum and Podosphaeria xanthii in yellow melon.

The aim of this study was to identify sources of resistance to Myrothecium roridum and Podosphaeria xanthii. Initially, 86 inbred lines of the crossing AM-04 x Goldex, 91 inbred lines of the crossing AM-12 x Rochedo, and 75 inbred lines of the crossing ACP x AF-646 were evaluated. The trials were carried out in a greenhouse in a randomized block design with five replications. Seventeen inbred lines were identified as resistant to M. roridum. These inbred lines, as well as the parents and seven differential cultivars (checks) were evaluated for the reaction to P. xanthii. Ten inbred lines were selected as moderately resistant to M. roridumand resistant to P. xanthii

A Frustrated 3-Dimensional Antiferromagnet: Stacked J1−J2J_{1}-J_{2} Layers

We study a frustrated 3D antiferromagnet of stacked $J_1 - J_2$ layers. The intermediate 'quantum spin liquid' phase, present in the 2D case, narrows with increasing interlayer coupling and vanishes at a triple point. Beyond this there is a direct first-order transition from N{\' e}el to columnar order. Possible applications to real materials are discussed.Comment: 11 pages,7 figure

Temperature effects on dislocation core energies in silicon and germanium

Temperature effects on the energetics of the 90-degree partial dislocation in silicon and germanium are investigated, using non-equilibrium methods to estimate free energies, coupled with Monte Carlo simulations. Atomic interactions are described by Tersoff and EDIP interatomic potentials. Our results indicate that the vibrational entropy has the effect of increasing the difference in free energy between the two possible reconstructions of the 90-degree partial, namely, the single-period and the double-period geometries. This effect further increases the energetic stability of the double-period reconstruction at high temperatures. The results also indicate that anharmonic effects may play an important role in determining the structural properties of these defects in the high-temperature regime.Comment: 8 pages in two-column physical-review format with six figure