1,332 research outputs found
Thick brane models in generalized theories of gravity
This work deals with thick braneworld models, in an environment where the
Ricci scalar is changed to accommodate the addition of two extra terms, one
depending on the Ricci scalar itself, and the other, which takes into account
the trace of the energy-momentum tensor of the scalar field that sources the
braneworld scenario. We suppose that the scalar field engenders standard
kinematics, and we show explicitly that the gravity sector of this new
braneworld scenario is linearly stable. We illustrate the general results
investigating two distinct models, focusing on how the brane profile is changed
in the modified theories.Comment: 8 pages, 8 figures. To appear in PL
First-order formalism for twinlike models with several real scalar fields
We investigate the presence of twinlike models in theories described by
several real scalar fields. We focus on the first-order formalism, and we show
how to build distinct scalar field theories that support the same extended
solution, with the same energy density and the very same linear stability. The
results are valid for two distinct classes of generalized models, that include
the standard model and cover a diversity of generalized models of current
interest in high energy physics.Comment: 9 pages; Version to appear in EPJ
Braneworld solutions for F(R) models with non-constant curvature
This work deal with braneworld scenarios with generalized gravity. We
investigate models where the potential of the scalar field is polynomial or
nonpolynomial. We obtain exact and approximated solutions for the scalar field,
warp factor and energy density, in the complex scenario with no restriction on
the scalar curvature. In particular, we describe the case where the brane may
split, engendering internal structure, with the splitting caused by the same
parameter that controls deviation from standard gravity.Comment: 9 pages, 7 figures; new versio
Telenomus remus Nixon egg parasitization of three species of Spodoptera under different temperatures.
Telenomus remus Nixon is a promising biocontrol agent as an egg parasitoid of Spodoptera spp., but the lack of information on the host?parasitoid interactions in this system precludes its applied use in agriculture. Therefore, we studied the parasitism capacity of T. remus on eggs of Spodoptera cosmioides (Walker), Spodoptera eridania (Cramer), and Spodoptera frugiperda (Smith) in a range of temperatures (19, 22, 25, 28, 31, and 34 ± 1°C) under controlled conditions (70 ± 10% RH and 12 h photophase). Egg masses of Spodoptera spp. were offered to a single-mated T. remus female on a daily basis. More than 80% lifetime parasitism on eggs of S. cosmioides, S. frugiperda, and S. eridania was reached from 1 to 5, 1 to 7, and 1 to 9 days, respectively, at temperatures from 19 to 34°C. More than 80% parasitization was obtained at extreme temperatures for all hosts studied. Lifetime parasitization of S. frugiperda, S. cosmioides, and S. eridania was affected by temperature, with the lowest values for S. frugiperda (34°C) and S. cosmioides (19 and 34°C). Parasitization of S. eridania eggs was reduced around 18% at 28 and 31°C, but dropped more severely at 34°C. Parasitoid longevity was reduced as temperature increased. Thus, our data indicated that T. remus might be suitable as a biocontrol agent against S. eridania, S. cosmioides, and S. frugiperda in geographical areas that fit the temperature range studied here, even though T. remus parasitism was reduced at 34°C
Impact of Increasing Nitrogen Fertilizer Rates upon an Irrigated Tanzania Grass Pasture. 1. Dry Matter Yield
An experiment was carried out with irrigated Tanzania grass (Panicum maximum, Jacq.) pasture receiving five nitrogen (N) rates of (0, 30, 60, 90 and 120 kg N ha-¹ cut-¹) during the growing season. N application increased dry matter yield and Tanzania growth rate linearly (P \u3c 0.05). Responses to nitrogen applications were higher in the first two cuts of the growing season than in the last two cuts. The N fertilizer conversion into herbage dry matter was also higher in the beginning of the growing season
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