Dark matter from cosmic defects on galactic scales?

We discuss the possible dynamical role of extended cosmic defects on galactic scales, specifically focusing on the possibility that they may provide the dark matter suggested by the classical problem of galactic rotation curves. We emphasize that the more standard defects (such as Goto-Nambu strings) are unsuitable for this task, but show that more general models (such as transonic wiggly strings) could in principle have a better chance. In any case, we show that observational data severely restricts any such scenarios.Comment: Submitted to Phys. Rev. D (Brief Reports). v2: Reference added and some typos corrected, matches published versio

Cosmological constant constraints from observation-derived energy condition bounds and their application to bimetric massive gravity

Among the various possibilities to probe the theory behind the recent accelerated expansion of the universe, the energy conditions (ECs) are of particular interest, since it is possible to confront and constrain the many models, including different theories of gravity, with observational data. In this context, we use the ECs to probe any alternative theory whose extra term acts as a cosmological constant. For this purpose, we apply a model-independent approach to reconstruct the recent expansion of the universe. Using Type Ia supernova, baryon acoustic oscillations and cosmic-chronometer data, we perform a Markov Chain Monte Carlo analysis to put constraints on the effective cosmological constant $\Omega^0_{\rm eff}$. By imposing that the cosmological constant is the only component that possibly violates the ECs, we derive lower and upper bounds for its value. For instance, we obtain that $0.59 < \Omega^0_{\rm eff} < 0.91$ and $0.40 < \Omega^0_{\rm eff} < 0.93$ within, respectively, $1\sigma$ and $3\sigma$ confidence levels. In addition, about 30\% of the posterior distribution is incompatible with a cosmological constant, showing that this method can potentially rule it out as a mechanism for the accelerated expansion. We also study the consequence of these constraints for two particular formulations of the bimetric massive gravity. Namely, we consider the Visser's theory and the Hassan and Roses's massive gravity by choosing a background metric such that both theories mimic General Relativity with a cosmological constant. Using the $\Omega^0_{\rm eff}$ observational bounds along with the upper bounds on the graviton mass we obtain constraints on the parameter spaces of both theories.Comment: 11 pages, 4 figures, 1 tabl

Effect of Species Horizontal Distribution on Defoliation of Ryegrass-Clover Swards Grazed by Sheep

Defoliation events on labelled white clover (Trifolium repens) growing points or ryegrass (Lolium perenne) tillers were measured during grazing tests by sheep with swards consisting of mixed ryegrass-clover (MIX) or alternate strips of clover and ryegrass (STRIP). Sward surface height was maintained at 6.4 cm by lawnmower cuts in order to obtain a similar surface height for both species. On average, during 13 grazing tests in STRIP and 11 in MIX swards, clover was the more defoliated species : 23.3% of the growing points in STRIP and 26.5% in MIX swards were defoliated compared to 16.2% and 12.5% of the tillers. No difference of clover defoliation probability occurred between STRIP and MIX swards, nor between clover growing points in different neighbourhoods in STRIP sward, indicating that the horizontal distribution of clover does not affect its pattern of defoliation by sheep

Desempenho produtivo de cultivares de girassol (Helianthus annuus L.) sob condições irrigadas no Rio Grande do Norte.

Este trabalho teve como objetivo avaliar o desempenho produtivo de cultivares de girassol em regime de irrigação. O ensaio foi conduzido na Estação Experimental da EMPARN, (Ipanguaçu,RN, 05º37? S 36º50? W , 70 m). O solo foi é um Neossolo de alta fertilidade, com adubação de 50-20-20 kg/ha + 2kg de Boro.. Utilizou-se irrigaçãoi por sulco e durante o ciclo da cultura foram aplicados 510 mm de água.. Foram avaliadas 26 cultivares, sendo 24 híbridos e 02 variedades em foi blocos ao acaso, com 04 repetições. As médias de rendimentos de grãos (aquênios) variaram de 2.110 kg/ha a 4.120 kg/ha, com média de 3.218 kg/ha. Sobressaíram-se os híbridos GRIZZLY, T 700, MG 52, NEON, HLS 03 e o HÉLIO 358, com respectivamente, 4.120 kg/ha, 4.097kg/ha, 3.705kg/ha, 3.638 kg/ha, 3.633 kg/ha e 3.610 kg/ha. Os maiores rendimentos de óleo foram obtidos com os genótipos MG 52, HÉLIO 358, HLS 03 e BRS-Gira 11, acima de 1.500kg/ha