5,550 research outputs found
Post-correlation radio frequency interference classification methods
We describe and compare several post-correlation radio frequency interference
classification methods. As data sizes of observations grow with new and
improved telescopes, the need for completely automated, robust methods for
radio frequency interference mitigation is pressing. We investigated several
classification methods and find that, for the data sets we used, the most
accurate among them is the SumThreshold method. This is a new method formed
from a combination of existing techniques, including a new way of thresholding.
This iterative method estimates the astronomical signal by carrying out a
surface fit in the time-frequency plane. With a theoretical accuracy of 95%
recognition and an approximately 0.1% false probability rate in simple
simulated cases, the method is in practice as good as the human eye in finding
RFI. In addition it is fast, robust, does not need a data model before it can
be executed and works in almost all configurations with its default parameters.
The method has been compared using simulated data with several other mitigation
techniques, including one based upon the singular value decomposition of the
time-frequency matrix, and has shown better results than the rest.Comment: 14 pages, 12 figures (11 in colour). The software that was used in
the article can be downloaded from http://www.astro.rug.nl/rfi-software
A Search for the Most Massive Galaxies. II. Structure, Environment and Formation
We study a sample of 43 early-type galaxies, selected from the SDSS because
they appeared to have velocity dispersion > 350 km/s. High-resolution
photometry in the SDSS i passband using HRC-ACS on board the HST shows that
just less than half of the sample is made up of superpositions of two or three
galaxies, so the reported velocity dispersion is incorrect. The other half of
the sample is made up of single objects with genuinely large velocity
dispersions. None of these objects has sigma larger than 426 +- 30 km/s. These
objects define rather different relations than the bulk of the early-type
galaxy population: for their luminosities, they are the smallest, most massive
and densest galaxies in the Universe. Although the slopes of the scaling
relations they define are rather different from those of the bulk of the
population, they lie approximately parallel to those of the bulk "at fixed
sigma". These objects appear to be of two distinct types: the less luminous
(M_r>-23) objects are rather flattened and extremely dense for their
luminosities -- their properties suggest some amount of rotational support and
merger histories with abnormally large amounts of gaseous dissipation. The more
luminous objects (M_r<-23) tend to be round and to lie in or at the centers of
clusters. Their properties are consistent with the hypothesis that they are
BCGs. Models in which BCGs form from predominantly radial mergers having little
angular momentum predict that they should be prolate. If viewed along the major
axis, such objects would appear to have abnormally large sigma for their sizes,
and to be abnormally round for their luminosities. This is true of the objects
in our sample once we account for the fact that the most luminous galaxies
(M_r<-23.5), and BCGs, become slightly less round with increasing luminosity.Comment: 21 pages, 19 figures, accepted for publication in MNRA
Avaliação do crescimento de videiras irrigadas utilizando um polímero hidrorretentor de umidade em diferentes lâminas de irrigação.
O objetivo deste trabalho foi avaliar o efeito de um polímero hidrorretentor de umidade em diferentes lâminas de irrigação por microaspersão sobre o crescimento de videiras irrigadas no submédio São Francisco.bitstream/CNPS/11840/1/circ132002avalcrescvideiras.pd
A Search for the Most Massive Galaxies. III. Global and Central Structure
We used the Advanced Camera for Surveys on board the Hubble Space Telescope
to obtain high resolution i-band images of the centers of 23 single galaxies,
which were selected because they have SDSS velocity dispersions larger than 350
km/s. The surface brightness profiles of the most luminous of these objects
(M_i<-24) have well-resolved `cores' on scales of 150-1000 pc, and share
similar properties to BCGs. The total luminosity of the galaxy is a better
predictor of the core size than is the velocity dispersion. The correlations of
luminosity and velocity dispersion with core size agree with those seen in
previous studies of galaxy cores. Because of high velocity dispersions, our
sample of galaxies can be expected to harbor the most massive black holes, and
thus have large cores with large amounts of mass ejection. The mass-deficits
inferred from core-Sersic fits to the surface-brightness profiles are
approximately double the black-hole masses inferred from the M_bh-sigma
relation and the same as those inferred from the M_bh-L relation. The less
luminous galaxies (M_i>-23) tend to have steeper `power-law' inner profiles,
higher-ellipticity, diskier isophotes, and bulge-to-total ratios of order 0.5
-- all of which suggest that they are `fast-rotators' and rotational motions
could have contaminated the velocity dispersion estimate. There are obvious
dust features within about 300 pc of the center in about 35% of the sample,
predominantly in power-law rather than core galaxies.Comment: 27 Pages, 22 Figures, 2 Tables, Accepted for Publication in MNRA
Comparação de técnicas analíticas para a determinação de cálcio, magnésio e alumínio trocáveis em amostras de solos.
Comparação de métodos titulométrico e espectrofotométrico de emissão ótica por plasma indutivamente acoplado (ICP-OES) para a determinação de Ca, Mg e Al trocáveis em amostras de solos de referência, oriundas do Programa de Análise de Qualidade de Laboratórios de Fertilidade (PAQLF) que utilizam o método Embrapa. Comparação de métodos titulométrico e espectrofotométrico de emissão ótica por plasma indutivamente acoplado (ICP-OES) para a determinação de Ca, Mg e Al trocáveis em amostras de solos de referência, oriundas do Programa de Análise de Qualidade de Laboratórios de Fertilidade (PAQLF) que utilizam o método Embrapa.bitstream/CNPS/11581/1/circtec21_2003_comparacao.pd
Regimento interno dos núcleos temáticos da Embrapa Pecuária Sudeste.
bitstream/item/38168/1/Documentos92.pd
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