1,721,262 research outputs found
Observation of the Cosmic Microwave Background Brightness and Polarization with BOOMERanG
No full textIn this thesis I describe \boom
(Balloon Observation Of Microwave Extragalactic
Radiation ANd Geophysics),
a telescope mounted on a long duration stratospheric
balloon, devoted to the measurement of extragalactic radiation
in the microwave band of the electromagnetic spectrum.
This work is not a complete description of the experiment,
rather it is a presentation of a part of the research work
done during my doctorate. A full description of the
experiment and of the results obtained with
it in the last years are given in the several referred
articles and collaborators Ph.D. theses.
\boom is an experiment of wide scientific interest, which gave
in year 2000 a main contribution to cosmology,
crossing for the first time what was considered a
knowledge {\it frontier} in the field:
to obtain a high signal to noise ratio maps of the
cosmic background radiation. From those maps
was possible to measure the value of the
total energy density of the Universe,
, with important consequences
on the description of our Universe.
In this work I particularly treat the 2003 setup of \boomn,
which flew in January of that year from Antarctica,
measuring cosmic background
temperature and polarization anisotropy.
In the cosmic microwave background
a level of linear polarization of the order of 1-5\%
of the temperature anisotropy intensity is expected.
The angular power spectrum of that polarized signal should
be characterized by
features strictly linked to the cosmological model.
Observation of the angular power spectrum of polarization
can confirm the model and improve the precision
in the measurement of the cosmological parameters, the
numbers that quantitatively describe the evolution of the Universe.
The work is experiment-oriented because such was
my research work, even if space is given to
description of data analysis tasks.
In Chapter~\ref{chap:cmb} I introduce the cosmic
background radiation science, particularly
focusing on information obtainable from
polarization measurements and on the relevant
physical observables. In Chapter~\ref{chap:instrument}
I describe the instrument, in a general
view and in detail, component by component.
In Chapter~\ref{chap:flight} I present the pre-flight
calibration measurements performed at ground to characterize
the instrumental sensitivity to a polarized signal.
To make that possible,
a custom apparatus was built, in order to
illuminate the telescope with a linearly polarized
plane wave. In the same chapter I briefly describe
the flight, hiding stress and emotions of those
15 days.
In Chapter~\ref{chap:pointing} I describe the
techniques used to obtain the pointing solution: the
measure, for each data sample, of the direction
in sky observed by each detector. I particularly
worked on this aspect of the
raw-data analysis, in which data are treated
to be used in map-making and power spectrum estimation procedures.
Main steps in the raw-data analysis are the
pointing solution, data deglitching and deconvolution, calibration,
and beam measurement for each receiver.
The pointing solution technique adopted is fully described.
It is based on the Kalman filter, an optimal method
of data integration.
In this Chapter, the problem is presented, together
with the involved geometry, the optimal method and the
developed algorithms. Results are shown.
Finally I describe the power spectrum extraction
problem and techniques and I present preliminary
results and compare them to the data realized by other experiments
Long Duration Stratospheric Balloon flights: a unique opportunity for mm and sub-mm astronomy
No full textEstimating Interstellar Medium Dust Temperature And Spectral Index In The Far-infrared And Submillimeter
No full textDust temperature and spectral index are evidenced to be anti-correlated from observations in the far-infrared and millimeter wavelengths and from laboratory experiments. However, uncertainties in flux measurements combined with calibration errors and other source of systematic errors, affect the results of the spectral energy distribution (SED) fit. An inverse correlation between dust temperature and spectral index naturally arises from the spectral model assumed for the fit combined with data noise and systematic uncertainties. When the spectral coverage do not sample the whole SED but only a limited range of it, it is even more difficult to get reliable results on dust physical properties. We developed a method to fit the inverse relationship between the temperature and spectral index with Bayesian statistics taking properly into account both the statistics and the systematic errors. We simulate observations of one-component Interstellar Medium (15 K < T < 25 K), and of two-components sources both warm (HII regions) and cold (cold cores) in the Herschel PACS and SPIRE spectral bands (70-500 um). We also include some ancillary simulated data from Planck-HFI, IRAS and MIPS to better sample the SEDs
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
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