14,251 research outputs found
Future dynamics in f(R) theories
The gravity theories provide an alternative way to explain the current
cosmic acceleration without invoking dark energy matter component. However, the
freedom in the choice of the functional forms of gives rise to the
problem of how to constrain and break the degeneracy among these gravity
theories on theoretical and/or observational grounds. In this paper to proceed
further with the investigation on the potentialities, difficulties and
limitations of gravity, we examine the question as to whether the future
dynamics can be used to break the degeneracy between gravity theories by
investigating the future dynamics of spatially homogeneous and isotropic dust
flat models in two gravity theories, namely the well known gravity and another by A. Aviles et al., whose motivation comes
from the cosmographic approach to gravity. To this end we perform a
detailed numerical study of the future dynamic of these flat model in these
theories taking into account the recent constraints on the cosmological
parameters made by the Planck team. We show that besides being powerful for
discriminating between gravity theories, the future dynamics technique
can also be used to determine the fate of the Universe in the framework of
these gravity theories. Moreover, there emerges from our numerical
analysis that if we do not invoke a dark energy component with
equation-of-state parameter one still has dust flat FLRW solution
with a big rip, if gravity deviates from general relativity via . We also show that FLRW dust solutions with do not
necessarily lead to singularity.Comment: 12 pages, 8 figures. V2: Generality and implications of the results
are emphasized, connection with the recent literature improved, typos
corrected, references adde
Obtenção da evapotranspiração em escala regional com o uso da equação de Penman-Monteith.
Informações agrometeorológicas do Polo Petrolina, PE/Juazeiro, BA - 1963 a 2009.
bitstream/item/31579/1/SDC233.pd
Balanço de energia na cultura da bananeira no primeiro ciclo de produção.
O objetivo desse trabalho foi quantificar a partição da energia solar disponÃvel ao cultivo de bananeira, noprimeiro ciclo de produção, propagada por micropropagação, em diferentes estágios de desenvolvimento e dedemanda evaporativa da atmosfera. Pretendeu-se que os resultados sirvam para subsidiar o manejo de água dacultura em condições semelhantes de cultiv
Caracterizações e tendências de parâmetro do balanço hÃdrico em larga escala no semiárido brasileiro.
Nos últimos anos, a região semiárida do Brasil vem se destacando como um importante centro produtor agrÃcola, principalmente nos municÃpios de Petrolina-PE e Juazeiro-BA. Como uma consequência, a rápida substituição da vegetação natural por culturas irrigadas em conjunto com cenários de mudanças climáticas globais podem afetar diferencialmente a disponibilidade hÃdrica em várias escalas espaço-temporais. O objetivo da presente pesquisa foi a delimitação das condições médias e das tendências dos parâmetros envolvidos no balanço hÃdrico durante o perÃodo de 2003 a 2012. Enquanto que em Petrolina ocorreram precipitações e taxas evapotranspiratórias mais elevadas que para Juazeiro, uma redução da demanda atmosférica ao longo dos anos é constatada no primeiro municÃpio, enquanto que no segundo ocorreu um acréscimo médio desta demanda. De acordo com as condições termo hidrológicas, Petrolina apresenta oportunidades bem superiores para a atividade agrÃcolas dependente de chuvas que em Juazeiro. Entretanto, ao longo do ano, as condições de aridez aumentaram em ambos os municÃpios. Os parâmetros quantificados e analisados em diferentes escalas temporais e espaciais, em conjunto com outras caracterÃsticas ecológicas, podem subsidiar um manejo racional do uso dos recursos hÃdricos em condições de mudanças de uso da terra e climáticas no semiárido brasileiro
Determination of surface resistance to evapotranspiration by remote sensing parameters in the semi-arid region of Brazil for land-use change analyses.
Field energy balances frorn irrigated crops (vineyards and mango orchard) and natural vegetation (caatinga) together with a net of agro-rneteorological stations were used to develop a model for lhe surface resistance (r,) to evapotranspiration at the basin scale in the serni-arid region of Brazil for land-use change analyses. It was done to make a historical picture at the municipal-district levei ofvegetation replacement in Pernambuco (PE) and Bahia (BA), Brazil. Although Petrolina, PE and Juazeiro, BA presented the biggest irrigated areas, the incrernents throughout the years (2002-2006) were smaller (213 and 171%) than those for Santa Maria, PE (275%) and for Lagoa Grande da Boa Vista, PE (260%)
Determinação da produção de biomassa e da evapotranspiração em larga escala na bacia do Submédio São Francisco.
Determining regional actual evapotranspiration ofirrigated crops and natural vegetation in the São Francisco river basin (Brazil) using remote sensing and Penman-Monteith equation.
To achieve sustainable development a nd to ensure water availability in hydrological basins, water managers need tools to determine the actual evapotranspiration (ET) on a large scale. Field energy balances fr om irrigated and natura l ecosystems together with a net of agro-meteorological stations were used to develop two models for ET quantification at basin scale, based on the Penman-Monteith equation. The first model (PM1) uses the resistances to the latent heat fluxes estimated from satellite measurements, while the second one (PM2) is based on the ratio of ET to the refere nce evapotranspiration (ET0) and its relation to remote sensing parame ters. The models were applied in the Low-Middle São Francisco river basin in Brazil and, after comparison against field results, showed good agreements with PM1 and PM2 explaining, respectively, 79% and 89% of the variances and mean square errors (RMSE) of 0.44 and 0.34 mm d?1. Even though the PM1 model was not chosen for ET calculatio ns, the equation for surface resistance (rs) was applied to infer the soil moisture conditions in a simplified vegetation classification. The maximum values of rs were for natural vegetation?c aatinga (average of 1,937 s m?1). Wine grape and mango orchard presented similar values around 130 s m?1, while table grape presented the lowest ones, averaging 74 s m?1. Petrolina and Juazeiro, in Pernambuco (PE) and Bahia (BA) states, respectively, were highlighted with the biggest irrigated areas. The highest increments are for vineyards and mango orchards. For the first crop the maximum increment was verified between 2003 and 2004 in Petrolina-PE, when the cultivated area increased 151%. In the case of mango orchards the most significant period was from 2005 to 2006 in Juazeiro-BA (129%). As the best performance was for PM2, it was selected and used to analyse the regional ET at daily and annual scales, making use of Landsat images and a geograp hic information system for different soil moisture conditions. Considering the daily rates of the regional ET, pixels with values lower than 1.0 mm d?1 occurred outside the rainy season, representing the caatinga species. Values from 1.0 to 5.0 mm d-during the driest conditions of the year coincided with irrigated crops, being the highest values for table grapes. The highest accumulated ET values during 2006 were for mango orchards, being around 500–1,300 mm yr?1. Vineyards presented lower values, ranging from 450–800 mm yr?1, while in caatinga they were between 200 and 400 mm yr ?1. It could be concluded that irrigated mango orchards and vineyards in that year consumed more water than caatinga by factors of 3 and 2, respectively. The mango orchards and vineya rd areas, representing 19.4 and 8.2% of the total irrigated area, respec tively, resulting in a total evaporative depletion of 0.22 km 3 yr?1in the growing regions comprised of the agro-meteorological stations
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