1,721,051 research outputs found
The Planck-LFI : a Study of Instrumental and Astrophysical Effects
No full textThis thesis aims to address some aspects of the Low Frequency Instrument (LFI) on board
the PLANCK satellite. As for any CMB experiment a great attention has to be devoted
to all the possible systematic effects. Previous experiences in CMB experiments have in
fact demonstrated that the more and the larger are systematic effects which contaminate
the data and which have to be scrubbed in the data analysis, the less robust the final
results will be. It is therefore of great importance, for not degrading the nominal angular
resolution and sensitivity per resolution element, to carefully address and quantify all
potential systematic effects. Through accurate and realistic simulations of PLANCK-LFI
observations we study how LFI performances are affected by some of these systematic
effects and how to control and further reduce these effects.
This thesis is organized as follows. We give a brief overview of the origin of microwave
sky fluctuations, including CMB anisotropy, foreground contaminations originated
within our Galaxy (synchrotron, free-free and dust emission) and extra-galactic
foregrounds (Sunyaev-Zel'dovich effect and point sources fluctuations). Since accurate
simulations are needed, they must include complete and realistic simulated microwave sky
at the various observing frequencies. Unfortunately our present knowledge of foreground
emissions (both galactic and extra-galactic) is far from complete and approximations have
to be made. All these problems are discussed in Chapter 2.
A presentation of the PLANCK mission and its scientific capabilities is reported in
Chapter 3: §3.2 reports on the selected orbit and scanning strategy; §3.3 describes the
adopted telescope configuration and actual focal plane arrangement; §3.4 briefly outlines
the LFI instrument and §3.5 reports LFI scientific capabilities. An introduction to the
systematic effects addressed in this thesis is in §3.6 and the Flight Simulator code is
presented in §3. 7. .
The rest of the work deals with the results from different kinds of PLAN9K-LFI :?imulations.
The off-axis position of the LFI instrument, as in the present baseline, results in
optical aberrations in the angular response function of the instrument. The effect of these
distortions (usually called main-beam distortions since they affect the very central part
of the response function) on the nominal angular resolution is addressed in Chapter 4,
firstly considering a pure CMB sky, and then a more realistic sky including galactic emission.
§4.l uses approximated response functions while "real" optical simulated ones are
considered in §4.4. The effective angular resolution is derived and the loss in capabilities
of cosmological parameters extraction properly quantified. The angular response function of the LFI instrument at large angles out of the central
part is extremely complex and depends not only on the telescope design but also on
the whole optical system (shields, supporting structures, focal plane assembly). Signal
and signal variations entering at large angles from the true direction of observation may
produce errors on CMB measurem~nts. Chapter 5 addresses this issue using a simulated
full pattern of the response function and considering signal coming from our Galaxy (§5.1
and §5.2). The level of this contamination and its spatial distribution on the sky are
discussed in §5.4.
As described in Chapter 2, PLANCK is a spinning space-craft with 1 minute period.
Instrumental drifts occurring on time scales less than the spinning period are possible
sources of systematic artifacts in final data. In general they produce "stripes" in the
final maps. Chapter 6 considers typical instrumental drifts which are mainly due to gain
fluctuations in the LFI amplifiers. A de-striping code for removing these artifacts is
described in §6.6; its performances and possible residual striping are evaluated in §6. 7.
Finally, Chapter 7 overviews simulations results and their implication on the optimization
of the PLANCK design
The Needlet CMB Trispectrum
No full textWe propose a computationally feasible estimator for the needlet trispectrum, which develops earlier work on the bispectrum by Donzelli et al. (2012). Our proposal seems to enjoy a number of useful properties, in particular a) the construction exploits the localization properties of the needlet system, and hence it automatically handles masked regions; b) the procedure incorporates a quadratic correction term to correct for the presence of instrumental noise and sky-cuts; c) it is possible to provide analytic results on its statistical properties, which can serve as a guidance for simulations. The needlet trispectrum we present here provides the natural building blocks for the efficient estimation of nonlinearity parameters on CMB data, and in particular for the third order constants g(N) (L) and tau(N) (L)
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
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
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