1,721,481 research outputs found
The search for primordial B-modes in the polarization of the cosmic microwave background with LSPE/SWIPE and LiteBIRD
No full textThe most ambitious challenge in Experimental Cosmology today is the preci- sion measurement of the polarized signal of the Cosmic Microwave Background (CMB). CMB was discovered in 1967 by Penzias and Wilson. It is a snapshot of the primordial universe and represents an essential source of information about all epochs of the universe. This experimental thesis concerns the study of polarization measurement techniques and the development of a new superconducting magnetic bearing to continuously rotate a cryogenic half-wave plate (HWP). The chapter 1 of this thesis focuses on the fundamentals of the cold dark matter model (ΛCDM) which is a parametrization of the Big Bang cosmo- logical model. It describes the constituents and the evolution of the universe. The ΛCDM model can be extended by adding cosmological inflation, a short period of exponential expansion in the very early universe. Inflation’s basic predictions regarding the universe large-scale geometry and structure have been borne out by cosmological measurements to date. Inflation makes an additional prediction as the existence of a background of gravitational waves, or tensor mode perturbations. At the recombination epoch, the inflationary gravitational waves (IGW) contribute to the anisotropy of the CMB in both total intensity and linear polarization, discussed deeply in the second part of the first chapter. The amplitude of tensors is conventionally parameterized by r, the tensor-to-scalar ratio at a fiducial scale, and its trace in the CMB polarization is a direct measure of the energy scale of inflation. Theoretical predictions of the value of r cover a very wide range. Conversely, a measurement of r can discriminate between models of inflation. The current upper limit is r < 0.06 at 95% confidence. The chapter 2 presents the Large-Scale Polarization Explorer (LSPE), an experiment composed of two instruments (the ground-based telescope STRIP and the balloon-borne counterpart SWIPE) which aims to measure the polarization of the CMB at large angular scale with a goal of r = 0.01. This thesis is mainly focused on the development of few important subsystems of SWIPE balloon. The detection of this tiny signal requires a very large array of polarization-sensitive detectors coupled to an imaging optical system, to obtain a wide field of view, thus maximizing the mapping speed. SWIPE will focus the incoming radiation on two large curved focal planes (at a temperature of 0.3 K) hosting 326 multi-mode pixels with Transition Edge Sensor (TES) thermistors, divided in the 3 frequency bands: 145GHz (30% bandwidth), 210GHz (20% bandwidth) and 240GHz (10% bandwidth). Chapter 3 describes the tests performed on the multi-mode pixel assembly. A custom cryogenic neoprene absorber was developed to reduce the background on the detector at a level similar to the one expected in flight, allowing to measure the main beam of the pixel assembly. The measured FWHM of the pixel assembly is 21°, slightly narrower than the expected one (24°), due to vignetting produced by the filters stack. Unfortunately this CMB polarization signal is well below the level of un- polarized foregrounds. This makes systematic errors due to temperature-to-polarization leakage particularly detrimental. Polarization modulators offer a solution to separate the polarized signal of interest from these unpolarized foregrounds. Many polarization modulation schemes exist, and a rapidly-rotating half-wave plate (HWP) is one of the most promising. The working principle of a polarimeter is discussed in chapter 4, where there is also an analysis of the main systematics introduced by a rotating HWP, particularly focused on HWP spurious signals and HWP wobbling. Chapter 5 is focused on the SWIPE polarization modulator unit which op- erates at 1.6 K to reduce the background on the detector produced by the HWP emission. On the other hand rotating an object at cryogenic temperature is not trivial, in particular because the dissipation becomes an issue. The technology adopted is based on a superconducting magnetic bearing (SMB) which can significantly reduce the friction. After introducing the basics of superconductivity, the baseline design is described. A large number of tests were performed on a room temperature mockup to optimize the motor configuration while room and cryogenic temperature tests were performed on the clamp mechanism (necessary to hold the bearing at room temperature and release it below the superconductive transition). The total heat load expected from the polarization modulator unit is < 25 mW. This value has to be confirmed during cryogenic test of the whole system which is not performed yet due to delays in the cryostat fabrication. The expected heat load from the polarization modulator represents less than 15% of the total heat load on the superfluid He reservoir, and is fully compatible with the operation of the instrument. Finally, chapter 6 presents LiteBIRD mission and the development of both polarization modulators of the medium and high frequency instruments. LiteBIRD is the next generation spacecraft [5], expected to be operative in ∼ 10 years, and will map CMB polarization 20 times deeper than Planck, with a total error of δr < 0.001, conservatively assuming equal contributions of statis- tical error, systematic error, and margin. The use of 3 continuously rotating HWPs (for the 3 telescopes of LiteBIRD) mitigates important systematic errors already observed in Planck data. Their development is more challenging than for SWIPE due to the spacecraft requirements and the Technology Readiness Level (TRL) required. A scaled baseline design and an optimized configuration are discussed. We find that the optimized one will meet the power budget with a 100% of margin
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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