6,173 research outputs found
Uso da Capacidade de suporte de carga como prevenção da compactação subsuperficial de um argissolo cultivado com cana-de-açúcar.
Os Argissolos cultivados com cana-de-açúcar nos Tabuleiros Costeiros nordestinos, geralmente, são favorecidos por topografia plana e profundidade adequada. No entanto, o tráfego intenso de máquinas agrícolas pesadas, utilizadas nas operações de colheita e tratos culturais, pode causar compactações subsuperficiais prejudicando o aprofundamento das raízes das plantas, o que pode comprometer a produtividade e longevidade das lavouras. O presente trabalho teve como objetivo estimar a capacidade de suporte de carga (CSC) do horizonte AB de um Argissolo Amarelo cultivado com cana-de-açúcar, por meio da pressão de pré-compactação (σp) e da resistência à penetração em laboratório (RPL), como alternativa para planejamento de operações motomecanizadas e prevenção da compactação do solo em subsuperfície. O estudo foi realizado na Fazenda Progresso da Usina Coruripe, Alagoas. Foram considerados como tratamentos cinco áreas cultivadas com cana-de-açúcar representando diferentes tempos de uso e dois tipos de cultivo: 4 anos cultivo de inverno (4 anos I); 14 anos cultivo de inverno (14 anos I); 14 anos cultivo de verão (14 anos V); 30 anos cultivo de inverno (30 anos I); 30 anos cultivo de verão (30 anos V) e uma área de mata (Mata) que foi considerada como testemunha padrão. Por meio dos resultados obtidos, concluímos que o horizonte AB do Argissolo estudado teve sua σp e RPL aumentadas, revelando a compactação na profundidade entre 0,20 e 0,30 m devido ao tráfego de máquinas nas lavouras de cana; a CSC pode ser estimada pela RPL, com objetivo de planejamento de operações mecanizadas para evitar compactações adicionais em subsuperfície; outros estudos sobre a interface pneu-solo devem ser realizados para determinar modelos que considerem as condições da camada de solo subjacente ao horizonte subsupercicial, além da pressão de inflação dos pneus e carga sobre os rodados.bitstream/item/33372/1/bp-64.pd
Quantifying the Drivers of Star Formation on Galactic Scales. I. The Small Magellanic Cloud
We use the star formation history of the Small Magellanic Cloud (SMC) to
place quantitative limits on the effect of tidal interactions and gas infall on
the star formation and chemical enrichment history of the SMC. The coincident
timing of two recent (< 4 Gyr) increases in the star formation rate and
SMC/Milky Way(MW) pericenter passages suggests that global star formation in
the SMC is driven at least in part by tidal forces due to the MW. The Large
Magellanic Cloud (LMC) is the other potential driver of star formation, but is
only near the SMC during the most recent burst. The poorly constrained LMC-SMC
orbit is our principal uncertainty. To explore the correspondence between
bursts and MW pericenter passages further, we model star formation in the SMC
using a combination of continuous and tidally-triggered star formation. The
behavior of the tidally-triggered mode is a strong inverse function of the
SMC-MW separation (preferred behavior ~ r^-5, resulting in a factor of ~100
difference in the rate of tidally-triggered star formation at pericenter and
apocenter). Despite the success of these closed-box evolutionary models in
reproducing the recent SMC star formation history and current chemical
abundance, they have some systematic shortcomings that are remedied by
postulating that a sizable infall event (~ 50% of the total gas mass) occured
about 4 Gyr ago. Regardless of whether this infall event is included, the
fraction of stars in the SMC that formed via a tidally triggered mode is > 10%
and could be as large as 70%.Comment: Accepted for publication in Ap
Refraction of Electromagnetic Energy for Wave Packets Incident on a Negative Index Medium is Always Negative
We analyze refraction of electromagnetic wave packets on passing from an
isotropic positive to an isotropic negative refractive index medium. We
definitively show that in all cases the energy is always refracted negatively.
For localized wave packets, the group refraction is also always negative.Comment: 5 pages, 3 figure
Thermal performance of fly ash geopolymeric mortars containing phase change materials
This paper reports experimental results on the thermal performance of fly ash-based
geopolymeric mortars containing different percentages of phase change materials
(PCMs). These materials have a twofold eco-efficient positive impact. On one hand,
the geopolymeric mortar is based on industrial waste material. And on the other
hand, the mortars with PCM have the capacity to enhance the thermal performance
of the buildings. Several geopolymeric mortars with different PCM percentages
(10%, 20%, 30%) were studied for thermal conductivity and thermal energy storageinfo:eu-repo/semantics/publishedVersio
Avalanches, Scaling and Coherent Noise
We present a simple model of a dynamical system driven by externally-imposed
coherent noise. Although the system never becomes critical in the sense of
possessing spatial correlations of arbitrarily long range, it does organize
into a stationary state characterized by avalanches with a power-law size
distribution. We explain the behavior of the model within a time-averaged
approximation, and discuss its potential connection to the dynamics of
earthquakes, the Gutenberg-Richter law, and to recent experiments on avalanches
in rice piles.Comment: 17 pages, 4 Postscript figures, written in LaTeX using RevTeX and
epsfig.st
Population Synthesis in the Blue IV: Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations
[Abridged] We present new model predictions for 16 Lick absorption line
indices from Hdelta through Fe5335, and UBV colors for single stellar
populations (SPs) with ages ranging between 1 and 15 Gyr, [Fe/H] ranging from
-1.3 to +0.3, and variable abundance ratios. We develop a method to estimate
mean ages and abundances of Fe, C, N, Mg, and Ca that explores the sensitivity
of the various indices to those parameters. When applied to high-S/N Galactic
cluster data, the models match the clusters' elemental abundances and ages with
high precision. Analyzing stacked SDSS spectra of early-type galaxies brighter
than Lstar, we find mean luminosity-weighted ages of the order of ~ 8 Gyr and
iron abundances slightly below solar. Abundance ratios, [X/Fe], are higher than
solar, and correlate positively with galaxy luminosity. Nitrogen is the element
whose abundance correlates the most strongly with luminosity, which seems to
indicate secondary enrichment. This result may impose a lower limit of 50-200
Myr to the time-scale of star formation in early-type galaxies. Unlike in the
case of clusters, in galaxies bluer Balmer lines yield younger ages than Hbeta.
This age discrepancy is stronger for lower luminosity galaxies. We examine four
scenarios to explain this trend. The most likely is the presence of small
amounts of a young/intermediate-age SP component. Two-component models provide
a better match to the data when the mass fraction of the young component is a
few %. This result implies that star formation has been extended in early-type
galaxies, and more so in less massive galaxies, lending support to the
``downsizing'' scenario. It also implies that SP synthesis models are capable
of constraining not only the mean ages of SPs in galaxies, but also their age
spread.Comment: To appear in the Astrophysical Journal Supplement Series. 55 Pages,
using emulateapj5.sty. Full version, containing all (enlarged) figures can be
found at http://www.astro.virginia.edu/~rps7v/Models/ms.pdf . A number of
useful tables in the Appendix can be obtained in advance of publication by
request to the autho
Rhodium(II)-catalyzed stereocontrolled synthesis of dihydrofuran-3-imines from 1-Tosyl-1,2,3-triazoles
Rhodium(II) acetate catalyzes the denitrogenative transformation of 5-substituted and 4,5-disubstituted 1-sulfonyl-1,2,3-triazoles with pendent allyl and propargyl ether motifs to oxonium ylides that undergo [2,3]-sigmatropic rearrangement to give substituted dihydrofuran-3-imines in high yield and diastereoselectivity
Zoneamento Agroclimático para a Cultura da Soja no Leste do Estado do Pará.
In order to determine reasonable planting time and zoning for soybean in the regions of Northeast and Southeast Pará, water ballance simulation and a zoning approach were conduced. Water balance was analysed by using combinations of 12 planting time, soil available water and two crop varieties. In adition, field informations related to soil texture, plant phenology and crop water consumption were also analysed. From water balance several paramaters were determined including the moisture satisfaction index (HNSI) and climatic risks. The zoning approach was based on two aspects: the climatic risks as an indicator to determine the climatic suitability classes for soybean and the geographic system analyses(GIS) for spatial analysis. The overall results show 72 zoning maps indicanting favorable planting time and suitable areas for soybean crop
Time dependence of breakdown in a global fiber-bundle model with continuous damage
A time-dependent global fiber-bundle model of fracture with continuous damage
is formulated in terms of a set of coupled non-linear differential equations. A
first integral of this set is analytically obtained. The time evolution of the
system is studied by applying a discrete probabilistic method. Several results
are discussed emphasizing their differences with the standard time-dependent
model. The results obtained show that with this simple model a variety of
experimental observations can be qualitatively reproduced.Comment: APS style, two columns, 4 figures. To appear in Phys. Rev.
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