Future dynamics in f(R) theories

The $f(R)$ 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 $f(R)$ 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 $f(R)$ gravity, we examine the question as to whether the future dynamics can be used to break the degeneracy between $f(R)$ gravity theories by investigating the future dynamics of spatially homogeneous and isotropic dust flat models in two $f(R)$ gravity theories, namely the well known $f(R) = R + \alpha R^{n}$ gravity and another by A. Aviles et al., whose motivation comes from the cosmographic approach to $f(R)$ 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 $f(R)$ gravity theories, the future dynamics technique can also be used to determine the fate of the Universe in the framework of these $f(R)$ gravity theories. Moreover, there emerges from our numerical analysis that if we do not invoke a dark energy component with equation-of-state parameter $\omega < -1$ one still has dust flat FLRW solution with a big rip, if gravity deviates from general relativity via $f(R) = R + \alpha R^n$. We also show that FLRW dust solutions with $f''<0$ 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

Informações agrometeorológicas do Polo Petrolina, PE/Juazeiro, BA - 1963 a 2009.

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Balanço de energia na cultura da bananeira no primeiro ciclo de produção.

O objetivo desse trabalho foi quantificar a partição da energia solar disponível 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 hídrico em larga escala no semiárido brasileiro.

Nos últimos anos, a região semiárida do Brasil vem se destacando como um importante centro produtor agrícola, principalmente nos municípios 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 hídrica em várias escalas espaço-temporais. O objetivo da presente pesquisa foi a delimitação das condições médias e das tendências dos parâmetros envolvidos no balanço hídrico durante o período 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 município, 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 agrícolas dependente de chuvas que em Juazeiro. Entretanto, ao longo do ano, as condições de aridez aumentaram em ambos os municípios. Os parâmetros quantificados e analisados em diferentes escalas temporais e espaciais, em conjunto com outras características ecológicas, podem subsidiar um manejo racional do uso dos recursos hídricos 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%)

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