1,720,981 research outputs found
Updating a numerical code for the solution of the kompaneets equaation in cosmological context
No full textIn this report we describe the fundamental approach and, in par-
ticular, the recent update to recent NAG versions of a numerical code, KYPRIX,
specifically written for the solution of the Kompaneets equation in cosmologi-
cal context, first implemented in the years 1989-1991, aimed to the very accu-
rate computation of the cosmic microwave background spectral distortions under
quite general assumptions. Specifically, we discuss the main subdivisions of the
code and the most relevant aspects about technical specifications and code imple-
mentation. After a presentation of the equation formalism and of the boundary
conditions added to the set of ordinary differential equations derived from the
original parabolic partial differential equation, we provide details on the adopted
space (i.e. dimensionless frequency) grid, on the output results, on the accuracy
parameters, and on the used integration routines. The problem of introducing the
time dependence of the ratio between electron and photon temperatures and of
the radiative Compton scattering term, both of them introducing integral terms
in the Kompaneets equation, is addressed in the specific context of the recent
NAG versions. Finally, we describe the introduction of the cosmological constant
in the terms controlling the general expansion of the universe, in agreement with
the fundamental discoveries of the last years
Cosmological applications of a numerical code for the solution of the kompaneets equation
No full textAccurancy and performance of a numerical code for the solution of the kompaneets equation in cosmological context
No full textIn this report we present some of the tests we carried out to ver-
ify the accuracy, reliability, and performance of a recent update to recent NAG
versions of a numerical code, KYPRIX, specifically written for the solution of
the Kompaneets equation in cosmological context, first implemented in the years
1989-1991, aimed to the very accurate computation of the cosmic microwave back-
ground (CMB) spectral distortions under quite general assumptions. After a brief
introduction on general aspects concerning the global computational time and the
impact of the various aspects of the code on it and on the accuracy of the numeri-
cal integration, we focus on some dedicated tests. First we compare the results of
the update version of the code with those obtained with the original one, for some
representative cases. Then we discuss to specific quantitative tests: the energy
conservation and the time behaviour of the electron temperature. Finally we fo-
cus on some properties of the free-free distortions relevant for the long wavelength
region of the CMB spectrum. All the tests support the very good accuracy and
reliability of the new code version
Foreground Implications in the Scientific Exploitation of CMB Data
No full textThe study of the Cosmic Microwave Background (CMB) represents one of the main sources of information on which the modern cosmology is based. The observables characterizing the CMB are: its own photon distribution function, the temperature anisotropies and its polarization. Any of these is affected by astrophysical foregrounds: spurious signals that contaminate the CMB observations. The level of contamination depends on the frequency of observation and on the region of the sky observed. Full-sky observation must face with high level of contamination, because of the strong Galactic emission in microwave bands.
The first part of my thesis work focus on the CMB photon distribution function. In particular, I show the implementations and the updating phases characterizing a numerical integration code (KYPRIX) for the solution of the Kompaneets equation in cosmological context. The updating is mainly related to the formalism that must be used in order to include FORTRAN libraries necessary for the integral quantities computation and to the platform transfer of the code itself. Physical implementations were also performed: the introduction of the cosmological constant in the equations dedicated to compute the evolution of the primordial Universe; the choice of the primordial chemical abundances of H and He is now possible; the ionization fractions for the species involved in the physical processes were introduced; it was created an optional interface that links KYPRIX with codes, like RECFAST, in order to calculate a recombination history of the ionization fraction of H and He. A general gain in the performances of the code was obtained and some test on the accuracy of the code are shown. All of the physical implementations contributed to perform more realistic simulation of the spectral distortion of the CMB. Some of the highlighted case are related to the contribution of the cosmological constant for the generation of spectral distortions in late epochs (like reionization induced distortions) and to the more precise estimate of the spectral distortions that could occur just before the recombination. In the last case, a recombination history, instead of an instantaneous recombination, plays a fundamental role for precise spectral simulations.
After a brief review on the past, on-going and future CMB dedicated experiments, the thesis focus on the importance of foregrounds in CMB experiment, paying attention on their description and the way they affect all the CMB osservables.
In order to subtract the foregrounds from sky maps, their morphological characteristics and their spectral behavior must be know as better as possible. The Planck Sky Model (PSM) is a complete and versatile set of programs and data, to be used for the simulation or the prediction of sky emission in the frequency range of typical CMB experiments, and in particular of the upcoming Planck sky mission (the 10-1000 GHz range). It is being developed as part of the activities of Planck Working Group 2 (WG2) on component separation, and of the AD AMIS team at APC.
During my second stage at APC I performed several tests on the PSM. The tests involved the latest two release of Galactic emission model, the Galactic foreground template derived by WMAP data and a clean CMB anisotropy map. For what concerns the PSM polarization prediction of the Galactic emission processes, the tests showed a clear improvement, at all the frequencies tested (the five WMAP bands), both for Q and U Stokes parameters. The last release of the PSM total intensity prediction of the Galactic processes showed results consistent with the previous ones for almost all the frequencies tested, while it still needs some tuning at 23 GHz, where synchrotron emission and free-free emission are more prominent. In order to recover the CMB signal, it is necessary to disentangle the mixed signals that a receiver collect looking at the sky. Component separation technics provide the tools to do it. In the thesis are exposed the main features of the component separation methods most used in CMB context, focusing on a particular tool: SMICA. I started using SMICA during my first stage at APC, in 2007. I used SMICA, and another filter (FFT filter) I developed, for a reprocessing of the IRIS mapset. Being already a reprocessing of the IRAS maps at 12, 25, 60 and 100 microm, the IRIS mapset still suffered from a non-optimal subtraction of the Zodical Light Emission (ZLE) residuals. The oscillations induced by these residuals affect any large scale statistical analysis of the mapset. Some preliminary operations had to be performed on the maps, like the subtraction of point sources and the masking Galactic plane and other relevant compact regions. The first phase of the reprocessing I performed consists in recovering the ZLE residuals pattern and power through SMICA, at all the IRIS frequencies. After several code runs and a continuos tuning of the maps and the code, the ZLE residuals pattern was clearly detected at 12,25 and 60 microm, while at 100 microm its contribution resulted to be totally negligible. The recovered component was then subtracted from the maps, but in some confined regions the subtraction wasn't optimal. A FFT filter was developed for this purpose and I used the filter only on localized regions, not on the full-sky maps. The dramatic improvements obtained on the IRIS maps are clearly visible just by eye. Anyway, a statistical analysis is in progress and preliminary results are showed in the thesis
A numerical code for the solution of the Kompaneets equation in cosmological context
No full textContext. After fundamental ground-based,
balloon-born, and space experiments, and, in particular, after the
COBE/FIRAS results, confirming that only very small deviations from a
Planckian shape can be present in the CMB spectrum,
current and future CMB absolute temperature experiments
aim at discovering very small distortions
such as those associated with the cosmological reionization process
or that could be generated by different kinds of earlier processes.
Aims. Interpretation of future data calls for a continuous improvement in
the theoretical modeling of CMB spectrum.
In this work we describe the fundamental approach
and, in particular, the update to recent NAG versions
of a numerical code, KYPRIX,
specifically written to solve the Kompaneets
equation in a cosmological context. It was first implemented in the
years 1989-1991 to accurately compute
the CMB spectral distortions under general assumptions.
Methods. Specifically, we describe the structure and the main subdivisions of
the code and discuss the most relevant aspects of its technical
implementation. After a presentation of the
equation formalism and of the boundary conditions added
to the set of ordinary differential equations derived from
the original parabolic partial differential equation,
we provide details on the adopted space variable (i.e. dimensionless
frequency) and space discretization,
on time variables, on the output results, on the
accuracy parameters, and
on the used auxiliary integration routines. The problem with introducing
the time dependence of the ratio between electron and photon temperatures
and of the radiative Compton scattering term, both of them
introducing integral terms into the Kompaneets equation,
is addressed in the specific context of the recent NAG versions.
We describe the introduction of the cosmological constant
in the terms controlling the general expansion of the Universe
in agreement with the current concordance model,
of the relevant chemical abundances, and on the ionization history,
from recombination to cosmological reionization.
The global computational time, the impact of the various aspects of the
code on it, and the accuracy of the numerical integration are also
discussed.
Results. We present some of fundamental tests we carried out to
verify the accuracy, reliability, and performance
of the code.
We focus on some quantitative tests of energy
conservation and the time behavior of electron temperature.
A comparison of the results obtained with the update and the
original version of the code is presented for some representative cases.
Finally, we focus on some properties of the free-free distortions
relevant for the long wavelength region of the CMB spectrum.
Conclusions. All the tests demonstrate the reliability and versatility
of the new code version and its accuracy and
applicability to the scientific analysis of current CMB spectrum data and of much more precise measurements that will be
available in the future.
The recipes and tests
described in this work can also be useful for implementing accurate
numerical codes for other scientific purposes using
the same or similar numerical libraries or for verifying the validity
of different codes aimed at the same problem or similar ones
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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