9,182 research outputs found
The synchrotron foreground and CMB temperature-polarization cross correlation power spectrum from the first year WMAP data
We analyse the temperature-polarization cross-correlation in the Galactic
synchrotron template that we have recently developed, and between the template
and CMB temperature maps derived from WMAP data. Since the polarized
synchrotron template itself uses WMAP data, we can estimate residual
synchrotron contamination in the CMB angular spectrum. While
appears to be contamined by synchrotron, no evidence for
contamination is found in the multipole range which is most relevant for the
fit of the cosmological optical depth.Comment: Accepted for pubblication on MNRAS Lette
PC1643+4631A,B: The Lyman-Alpha Forest at the Edge of Coherence
This is the first measurement and detection of coherence in the intergalactic
medium (IGM) at substantially high redshift (z~3.8) and on large physical
scales (~2.5 h^-1 Mpc). We perform the measurement by presenting new
observations from Keck LRIS of the high redshift quasar pair PC 1643+4631A, B
and their Ly-alpha absorber coincidences. This experiment extends multiple
sightline quasar absorber studies to higher redshift, higher opacity, larger
transverse separation, and into a regime where coherence across the IGM becomes
weak and difficult to detect. We fit 222 discrete Ly-alpha absorbers to
sightline A and 211 to sightline B. Relative to a Monte Carlo pairing test
(using symmetric, nearest neighbor matching) the data exhibit a 4sigma excess
of pairs at low velocity splitting (<150 km/s), thus detecting coherence on
transverse scales of ~2.5 h^-1 Mpc. We use spectra extracted from an SPH
simulation to analyze symmetric pair matching, transmission distributions as a
function of redshift and compute zero-lag cross-correlations to compare with
the quasar pair data. The simulations agree with the data with the same
strength (~4sigma) at similarly low velocity splitting above random chance
pairings. In cross-correlation tests, the simulations agree when the mean flux
(as a function of redshift) is assumed to follow the prescription given by
Kirkman et al. (2005). While the detection of flux correlation (measured
through coincident absorbers and cross-correlation amplitude) is only
marginally significant, the agreement between data and simulations is
encouraging for future work in which even better quality data will provide the
best insight into the overarching structure of the IGM and its understanding as
shown by SPH simulations.Comment: 15 pages, 11 figures; accepted for publication in Astronomical
Journa
Estimativa de parâmetros biofísicos em plantio de sorgo com aplicação de técnicas de sensoriamento remoto.
Atualmente, o sorgo é um dos grãos mais produzidos no mundo, superado apenas pela soja, milho, trigo e arroz (Simões, 2008). No Brasil, a área cultivada com sorgo tem se expandido, com plantio em sucessão à soja, principalmente quando é maior o risco climático da escolha pela cultura de milho (Casela, 2002). Segundo o IBGE (2009), a safra de sorgo 2009/10 terá acréscimo de 1,1%, com produção estimada em 1.869.419 toneladas. Ao considerar a análise espacialmente explícita de parâmetros biofísicos da cultura, torna-se fundamental a aplicação de técnicas de sensoriamento remoto nas quais possuem como vantagem a possibilidade de extração de informações da produção agrícola de forma rápida e menos onerosa (Papa, 2009). Informações de sensores remotos têm alimentado diversos modelos e algoritmos para obtenção de parâmetros biofísicos da superfície da terra (Andrade et al., 2009). O SEBAL (Surface Energy Balance Algorith for Land) é um algoritmo que tem como vantagem a obtenção de alguns parâmetros biofísicos com poucos dados observacionais de forma efetiva e econômica. Diante do exposto, este trabalho objetivou estimar parâmetros biofísicos em plantio de sorgo com aplicação do algoritmo SEBAL e imagem do sensor TM do satélite Landsat 5
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