1,636 research outputs found
Late time cosmological approach in mimetic gravity
In this paper, we investigate the late-time cosmic acceleration in mimetic
gravity with Lagrange multiplier and potential in a Universe
containing, besides radiation and dark energy, a self-interacting (collisional)
matter. We obtain through the modified Friedmann equations, the main equation
that can describe the cosmological evolution and with several models from
and the well known particular model , we perform an analysis of
the late-time evolution. We examine the behavior of the Hubble parameter, the
dark energy equation of state and the total effective equation of state and we
compare in each case the resulting picture with the non-collisional matter
(assumed as dust) and also with the collisional matter in mimetic
gravity. The results obtained are in good agreement with the observational data
and show that in presence of the collisional matter the dark energy
oscillations in mimetic f(R, T) gravity can be damped.Comment: 18 pages, 2 figure
Late time cosmological approach in mimetic gravity
In this paper, we investigate the late-time cosmic acceleration in mimetic
gravity with Lagrange multiplier and potential in a Universe
containing, besides radiation and dark energy, a self-interacting (collisional)
matter. We obtain through the modified Friedmann equations, the main equation
that can describe the cosmological evolution and with several models from
and the well known particular model , we perform an analysis of
the late-time evolution. We examine the behavior of the Hubble parameter, the
dark energy equation of state and the total effective equation of state and we
compare in each case the resulting picture with the non-collisional matter
(assumed as dust) and also with the collisional matter in mimetic
gravity. The results obtained are in good agreement with the observational data
and show that in presence of the collisional matter the dark energy
oscillations in mimetic f(R, T) gravity can be damped.Comment: 18 pages, 2 figure
Testing some f(R,T) gravity models from energy conditions
We consider theory of gravity, where is the curvature scalar
and the trace of the energy momentum tensor. Attention is attached to the
special case, and two expressions are assumed for the
function , and ,
where , , , , , , , and are input
parameters. We observe that by adjusting suitably these input parameters,
energy conditions can be satisfied. Moreover, an analyse of the perturbations
and stabilities of de Sitter solutions and power-law solutions is performed
with the use of the two models. The results show that for some values of the
input parameters, for which energy conditions are satisfied, de Sitter
solutions and power-law solutions may be stables.Comment: 25 pages, 6 figures. Accepted for publication in Journal of Modern
Physcis (JMP
Onset of phase correlations in YBa2Cu3O{7-x} as determined from reversible magnetization measurements
Isofield magnetization curves are obtained and analyzed for three single
crystals of YBa2Cu3O{7-x}, ranging from optimally doped to very underdoped, as
well as the BCS superconductor Nb, in the presence of magnetic fields applied
both parallel and perpendicular to the planes. Near Tc, the magnetization
exhibits a temperature dependence \sqrt{M} [Ta(H)-T]^m. In accordance with
recent theories, we associated Ta(H) with the onset of coherent phase
fluctuations of the superconducting order parameter. For Nb and optimally doped
YBaCuO, Ta(H) is essentially identical to the mean-field transition line Tc(H).
The fitting exponent m=0.5 takes its mean-field value for Nb, and varies just
slightly from 0.5 for optimally doped YBaCuO. However, underdoped YBCO samples
exhibit anomalous behavior, with Ta(H)>Tc for H applied parallel to the c axis,
suggesting that the magnetization is probing a region of temperatures above Tc
where phase correlations persist. In this region, the fitting exponent falls in
the range 0.5 < m < 0.8 for H\parallel c, compared with m~0. for $H\parallel ab
planes. The results are interpreted in terms of an anisotropic pairing symmetry
of the order parameter: d-wave along the ab planes and s-wave along the c axis.Comment: 5 pages, 4 figure
Influência de aléias de leguminosas arbóreas na infestação de bicho-mineiro em cafeeiro.
O bicho-mineiro, Leucoptera coffeella (Guérin - Mèneville, 1842) (Lepidoptera: Lyonetiidae), é talvez a principal praga do cafeeiro (Coffea spp.) na atualidade, principalmente nas regiões de temperaturas mais elevadas e de maior déficit hídrico. Vários estudos indicam que a abundância e diversidade de insetos dentro de um campo podem estar intimamente relacionadas com a natureza da vegetação circundante. Considerando o exposto, foi objetivo deste trabalho observar o efeito de espécies de leguminosas arbóreas utilizadas como quebra-ventos (aléias) sobre os aspectos fitossanitários do cafeeiro. As leguminosas utilizadas foram: o Guandu (Cajanus cajan Millsp.), Bracatinga (Mimosa scabrella Benth.), Leucena (Leucaena leucocephala (Lam.) De Wit) e Acácia (Acacia mangium Willd.), plantadas perpendiculares ao sentido dos ventos predominantes. Os resultados parciais, obtidos em 2003, 2004, 2005 e 2006, mostram que a menor porcentagem de folhas com minas intactas foi observada nos cafeeiros sob Leucena e Guandu e também a menor porcentagem de minas predadas. Os cafeeiros sob Leucena e Guandu apresentaram nível de controle (NC) para o bicho-mineiro (30% de folhas minadas sem sinais de predação) no final de agosto enquanto que aqueles sob Acácia e Bracatinga foram semelhantes à testemunha e apresentaram NC bem mais cedo, no mês de junho
Categorização funcional de sequências expressas envolvidas na defesa do cafeeiro a doenças.
O entendimento dos mecanismos de defesa e da interação do cafeeiro com patógenos pode ser útil no desenvolvimento de novas alternativas para um controle eficiente das doenças. Tem sido demonstrado, em diferentes espécies de plantas, que genes R, responsáveis pelo reconhecimento dos patógenos, apresentam domínios conservados, como NBS (Nucleotide Binding Site) e LRR (Leucine Rich Repeat). Dessa forma, nesse trabalho, seqüências do Projeto Brasileiro do Genoma Café, previamente identificadas como contendo domínios NBS e LRR, foram funcionalmente categorizadas. A categorização foi realizada em 140 EST-contigs, sendo que 99 foram classificados em pelo menos uma das categorias funcionais do Gene Ontology. Essa categorização permitiu associar os produtos preditos das EST-Contigs com os processos biológicos que incluíram resposta de defesa e apoptose e com funções moleculares como ligação a nucleotídeo e atividade de transdutor de sinais. Esses e outros termos encontrados são comprovadamente relacionados com a atuação de genes de resistência no mecanismo de defesa da planta
Sustainable Horticulture: A bibliometric Study
This paper examines the scientific researches regarding "sustainable horticulture" to identify research flows with potential for future investigation. Through a bibliometric and content analysis for the 2011-2015 periods and the 2016 first semester, 12 articles, according and relevant to the theme, were selected. The results obtained from the analysis demonstrated the importance of the subject for both academic research and for the practice, since it elucidated scientific production and trends, impact factor, relevant scientific periodicals, contribution by countries and its institutions, methods and research tools, keywords. It stands out that the theme "sustainable horticulture" is used in most cases to address only the environmental dimension and, in a few cases, in the economic and social dimensions. Based in the analysis of the keywords, the terms production, systems and sustainability formed the main research clusters, attracting great attention during the study period
Observation of anisotropic diamagnetism above the superconducting transition in iron-pnictide Ba_(1-x)K_xFe2As2 single crystals due to thermodynamic fluctuations
High resolution magnetization measurements performed in a high quality
Ba_(1-x)K_xFe2As2 single crystal allowed to determine the diamagnetism induced
above the superconducting transition by thermally activated Cooper pairs. These
data, obtained with magnetic fields applied along and transverse to the crystal
ab layers, demonstrate experimentally that the superconducting transition of
iron pnictides may be explained at a phenomenological level in terms of the
Gaussian Ginzburg-Landau approach for three-dimensional anisotropic
superconductors.Comment: Final version with minor corrections. 6 pages, 4 figure
- …