1,720,978 research outputs found
Component separation for all-sky CMB temperature maps
Full text linkThe work described in this Thesis is related to the PLANCK mission, scheduled for launch in 2008, which will observe the microwave sky with unprecedent resolution and sensitivity. The PLANCK collaboration involves hundreds of scientists and profits from the contributions of research groups in many countries. Among them, an Italian collaboration has a key role on component separation. This is a crucial step of the data reduction process, aimed at disentangling the Cosmic Microwave Background (CMB) and all the astrophysical components which are mixed in the nine observational channels of PLANCK The most important diffuse components are, besides the CMB, synchrotron, free-free and thermal dust emissions due to our own Galaxy. Moreover, the PLANCK maps will contain radio and infrared extragalactic sources as well as the Sunyaev-Zel'dovich effects from clusters of galaxies. All the components which mix with the CMB are referred to as ``foregrounds'', as they are placed between the CMB and the observer.
The main goal of component separation is to provide a map of the CMB, from which the relevant cosmological information will be derived, clean from foreground contamination. On the other hand, maps of astrophysical components are of great interest per se. The accuracy of the component separation process will ultimately set that of the final results PLANCK will provide.
Our work was mainly focused on the development and testing of a new method for the separation of diffuse foregrounds, the Correlated Component Analysis (CCA), proposed by Bedini et al. (2005). This technique exploits second-order statistics to estimate the ``mixing matrix'', which contains the frequency behavior of the components mixed in the data. It is necessary to adopt a model for such components, i.e. to parametrize their frequency scaling in a suitable way. Our approach is to estimate the mixing matrix separately in different regions of the sky, where the spectral dependencies of foregrounds can be assumed to be constant.
Once the mixing matrix is known, several methods are available to perform component separation, such as Wiener Filtering (WF), Maximum Entropy Method (MEM) or other Bayesian inversion techniques.
After having suitably implemented the CCA method, we tested its performances on simulated PLANCK data.
In Bonaldi et al. (2006) we applied the method to different sets of simulated PLANCK channels and estimated the errors on the mixing matrix with a Monte Carlo approach. The simulations included realistic diffuse foregrounds, with spatially varying spectral properties, and Gaussian noise at the nominal level for the PLANCK satellite.
This test showed that the method is efficient and that the errors on the mixing matrix estimation produce a minor contribution to the errors on the CMB power spectrum.
We then partecipated in a blind comparative test of component separation methods coordinated by the PLANCK working group on ``component separation''.
The test used a more sophisticated simulation of PLANCK data, which included, besides diffuse foreground emissions, also point sources and extragalactic background and a more realistic treatment of the noise. On these data, we tested CCA combined with harmonic Wiener Filtering. We focused on the reconstruction of the CMB map and on the power spectrum estimation, and obtained in both cases very good results, highly competitive with those provided with the best methods developed so far. We also got satisfactory reconstructions of Galactic dust emission, which is the dominant foreground in the highest resolution (high frequency) PLANCK channels.
In Bonaldi et al. (2007b) we tested the same strategy on real data i.e. the first three years of WMAP data. Our results are generally compatible with the result published by the WMAP team. We investigated the presence in the data of the so-called "microwave anomalous emission", an additional foreground component which could dominate in the lowest frequency WMAP channel (23 GHz). This component, revealed by cross correlations of microwave data with IR maps, appears to be correlated with thermal dust emission and has been interpreted as emission due to spinning dust grains (Draine & Lazarian 1998) or, alternatively, as synchrotron emission from dusty active star-forming regions (Hinshaw et al. 2006). We adopted various models for the frequency scaling of such component, whose properties are still poorly known.
We then applied several quality tests to the maps reconstructed for each model and selected a subset of models having a good compatibility with the data. We also managed to get the first, albeit preliminary, template of the anomalous emission over about 90% of the sky.
We then estimated how our imperfect knowledge of the foreground components affects the CMB power spectrum. To this end we compared the CMB power spectra obtained adopting different foreground models that passed our quality tests. A significant spread has been found for the largest scales, where anomalies of the WMAP power spectrum compared to the expectations from the best fit cosmological model have been reported. Taking into account modelization errors, we find no large scale power spectrum anomalies significant at > 1.5 sigma, except for the excess power at l=40,
which is significant at around the 4 sigma level.
A minor part of this Thesis was devoted to the study of the Sunyaev-Zel'dovich (SZ) effect, due to inverse Compton scattering of CMB photons by hot electrons in the astrophysical plasmas bound to the cosmic structures. PLANCK is expected to provide a big sample of galaxy clusters observed through the SZ effect. One exploitation of the PLANCK cluster sample is related to the study of the physics of the intra-cluster (IC) gas. In Bonaldi et al. (2007a) we investigated
the observable effects of different modeling of the physics of the IC gas.
Another research field related to the SZ effect concerns the study of the Large Scale Structure of the Universe. In Dolag et al. (2006) we analysed the SZ emission due to the so-called cosmic web, the network of filamentary structures which is now believed to connect galaxy clusters. The signal is too weak to be detected but its presence may bias the observed properties of galaxy clusters both in the X-ray band and in the microwaves
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Sunyaev–Zel'dovich profiles and scaling relations: modelling effects and observational biases
No full textWe use high-resolution hydrodynamic resimulations to investigate the
properties of the thermal Sunyaev-Zel'dovich (SZ) effect from galaxy
clusters. We compare results obtained using different physical models
for the intracluster medium (ICM), and show how they modify the SZ
emission in terms of cluster profiles and scaling relations. We also
produce realistic mock observations to verify whether the results from
hydrodynamic simulations can be confirmed. We find that SZ profiles
depend marginally on the modelled physical processes, while they exhibit
a strong dependence on cluster mass. The central and total SZ emission
strongly correlates with the cluster X-ray luminosity and temperature.
The logarithmic slopes of these scaling relations differ from the
self-similar predictions by less than 0.2; the normalization of the
relations is lower for simulations including radiative cooling. The
observational test suggests that SZ cluster profiles are unlikely to be
able to probe the ICM physics. The total SZ decrement appears to be an
observable much more robust than the central intensity, and we suggest
using the former to investigate scaling relations
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
