680 research outputs found
Compact source detection in multi-channel microwave surveys: from SZ clusters to polarized sources
In this paper we describe the state-of-the art status of multi-frequency
detection techniques for compact sources in microwave astronomy. From the
simplest cases where the spectral behaviour is well-known (i.e. thermal SZ
clusters) to the more complex cases where there is little a priori information
(i.e. polarized radio sources) we will review the main advances and the most
recent results in the detection problem.Comment: 13 pages, 4 figures. Accepted for publication in the Special Issue
"Astrophysical Foregrounds in Microwave Surveys" of the journal Advances in
Astronom
Statistics of the fractional polarisation of compact radio sources in Planck maps
In this work we apply the stacking technique to estimate the average
fractional polarisation from 30 to 353 GHz of a primary sample of 1560 compact
sources - essentially all radio sources - detected in the 30 GHz Planck all-sky
map and listed in the second version of the Planck Catalogue of Compact Sources
(PCCS2). We divide our primary sample in two subsamples according to whether
the sources lay (679 sources) or not (881 sources) inside the sky region
defined by the Planck Galactic mask (fsky ~ 60 per cent) and the area around
the Magellanic Clouds. We find that the average fractional polarisation of
compact sources is approximately constant (with frequency) in both samples
(with a weighted mean over all the channels of 3.08 per cent outside and 3.54
per cent inside the Planck mask). In the sky region outside the adopted mask,
we also estimate the {\mu} and {\sigma} parameters for the log-normal
distribution of the fractional polarisation, finding a weighted mean value over
all the Planck frequency range of 1.0 for {\sigma} and 0.7 for {\mu} (that
would imply a weighted mean value for the median fractional polarisation of 1.9
per cent).Comment: 12 pages, 7 figures, 2 tables, MNRAS in pres
Criptosporidiosis
La criptosporidiosis es una enfermedad parasitaria que afecta tanto a animales como al hombre y que es reconocida como una de las causas más importantes de diarrea a nivel mundial. Está producida por especies del género Cryptosporidium, un protozoo descubierto hace más de cien años que infecta las células intestinales y que se puede transmitir tanto de persona a persona como de animal a persona y también mediante ingestión de alimentos o agua contaminada.
La sintomatología de la enfermedad incluye normalmente una diarrea acuosa abundante y en ocasiones dolor abdominal, aunque es también frecuente que curse de forma asintomática, sobre todo en pacientes inmunocompetentes. A pesar de que puede afectar a cualquier género, a cualquier edad y de no tener una zona endémica concreta, es especialmente considerada de mayor riesgo en algunos grupos específicos como son pacientes inmunocomprometidos y niños, donde en algunos casos puede llegar a ser mortal.
Por este motivo, en este trabajo se estudia la prevalencia de esta enfermedad en uno de estos grupos, más concretamente en niños que acuden a guarderías donde la transmisión del parásito mediante la vía fecalZoral es de gran importancia. Para llevarlo a cabo se tomaron muestras fecales de cada uno de los niños y se analizaron en el laboratorio. El número de muestras fue de 112, para su análisis se utilizó el método de tinción de ZiehlZNeelsen modificado o Kinyoun y posteriormente se observaron al microscopio para evaluar la presencia de ooquistes de Cryptosporidium sp en cada una de las muestras tomadas.Universidad de Sevilla. Grado en Farmaci
Statistics of the fractional polarisation of extragalactic dusty sources in Planck HFI maps
We estimate the average fractional polarisation at 143, 217 and 353 GHz of a
sample of 4697 extragalactic dusty sources by applying stacking technique. The
sample is selected from the second version of the Planck Catalogue of Compact
Sources at 857 GHz, avoiding the region inside the Planck Galactic mask (fsky ~
60 per cent). We recover values for the mean fractional polarisation at 217 and
353 GHz of (3.10 \pm 0.75) per cent and (3.65 \pm 0.66) per cent, respectively,
whereas at 143 GHz we give a tentative value of (3.52 \pm 2.48) per cent. We
discuss the possible origin of the measured polarisation, comparing our new
estimates with those previously obtained from a sample of radio sources. We
test different distribution functions and we conclude that the fractional
polarisation of dusty sources is well described by a log-normal distribution,
as determined in the radio band studies. For this distribution we estimate
{\mu}_{217GHz} = 0.3 \pm 0.5 (that would correspond to a median fractional
polarisation of {\Pi}_{med} = (1.3 \pm 0.7) per cent) and {\mu}_{353GHz} = 0.7
\pm 0.4 ({\Pi}_{med} = (2.0 \pm 0.8) per cent), {\sigma}_{217GHz} = 1.3 \pm 0.2
and {\sigma}_{353GHz} = 1.1 \pm 0.2. With these values we estimate the source
number counts in polarisation and the contribution given by these sources to
the CMB B-mode angular power spectrum at 217, 353, 600 and 800 GHz. We conclude
that extragalactic dusty sources might be an important contaminant for the
primordial B-mode at frequencies > 217 GHz.Comment: arXiv admin note: text overlap with arXiv:1703.0995
Biparametric Adaptive Filter: detection of compact sources in complex microwave backgrounds
In this article we consider the detection of compact sources in maps of the
Cosmic Microwave Background radiation (CMB) following the philosophy behind the
Mexican Hat Wavelet Family (MHWn) of linear filters. We present a new
analytical filter, the Biparametric Adaptive Filter (BAF), that is able to
adapt itself to the statistical properties of the background as well as to the
profile of the compact sources, maximizing the amplification and improving the
detection process. We have tested the performance of this filter using
realistic simulations of the microwave sky between 30 and 857 GHz as observed
by the Planck satellite, where complex backgrounds can be found. We demonstrate
that doing a local analysis on flat patches allows one to find a combination of
the optimal scale of the filter R and the index of the filter g that will
produce a global maximum in the amplification, enhancing the signal-to-noise
ratio (SNR) of the detected sources in the filtered map and improving the total
number of detections above a threshold. We conclude that the new filter is able
to improve the overall performance of the MHW2, increasing the SNR of the
detections and, therefore, the number of detections above a 5 sigma threshold.
The improvement of the new filter in terms of SNR is particularly important in
the vicinity of the galactic plane and in the presence of strong galactic
emission. Finally, we compare the sources detected by each method and find that
the new filter is able to detect more new sources than the MHW2 at all
frequencies and in clean regions of the sky. The BAF is also less affected by
spurious detections, associated to compact structures in the vicinity of the
galactic plane.Comment: 17 pages, 15 figures and 3 tables. Accepted for publication in MNRA
Detection/estimation of the modulus of a vector. Application to point source detection in polarization data
Given a set of images, whose pixel values can be considered as the components
of a vector, it is interesting to estimate the modulus of such a vector in some
localised areas corresponding to a compact signal. For instance, the
detection/estimation of a polarized signal in compact sources immersed in a
background is relevant in some fields like astrophysics. We develop two
different techniques, one based on the Neyman-Pearson lemma, the Neyman-Pearson
filter (NPF), and another based on prefiltering-before-fusion, the filtered
fusion (FF), to deal with the problem of detection of the source and estimation
of the polarization given two or three images corresponding to the different
components of polarization (two for linear polarization, three including
circular polarization). For the case of linear polarization, we have performed
numerical simulations on two-dimensional patches to test these filters
following two different approaches (a blind and a non-blind detection),
considering extragalactic point sources immersed in cosmic microwave background
(CMB) and non-stationary noise with the conditions of the 70 GHz \emph{Planck}
channel. The FF outperforms the NPF, especially for low fluxes. We can detect
with the FF extragalactic sources in a high noise zone with fluxes >=
(0.42,0.36) Jy for (blind/non-blind) detection and in a low noise zone with
fluxes >= (0.22,0.18) Jy for (blind/non-blind) detection with low errors in the
estimated flux and position.Comment: 11 pages, 5 figure
Extragalactic Source Counts and Contributions to the Anisotropies of the Cosmic Microwave Background. Predictions for the Planck Surveyor mission
We present predictions for the counts of extragalactic sources, the
contributions to fluctuations and their spatial power spectrum in each channel
foreseen for the Planck Surveyor (formerly COBRAS/SAMBA) mission. The
contribution to fluctuations due to clustering of both radio and far--IR
sources is found to be generally small in comparison with the Poisson term;
however the relative importance of the clustering contribution increases and
may eventually become dominant if sources are identified and subtracted down to
faint flux limits. The central Planck frequency bands are expected to be
``clean'': at high galactic latitude (|b|>20), where the reduced galactic noise
does not prevent the detection of the extragalactic signal, only a tiny
fraction of pixels is found to be contaminated by discrete extragalactic
sources. Moreover, removal of contaminating signals is eased by the substantial
difference between their power spectrum and that of primordial fluctuations.Comment: 10 pages, Latex, mn.sty, 8 figures included, MNRAS, in the press.
Minor changes in the text. Sections 3.1 and 3.2 have been expanded. Source
counts in Table 2 have been slightly changed. Figure 1,2,7 and 8 have been
replaced by new version
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