1,721,190 research outputs found
Testing discrete symmetries with the cosmic microwave background: current constraints and Planck forecasts
No full textAnisotropy and polarization of the CMB are probing cosmological models with unprecedented precision. The WMAP satellite data are largely consistent with concordance ACDM cosmology. However, intriguing flukes are known to exist that may pinpoint at physics beyond the standard model. Constraining the violations of discrete symmetries in the CMB pattern is a promising mean to investigate these discrepancies. In this paper we constrain the Parity and CPT symmetries through CMB datasets. We describe the basic formalism, the relevant estimators and the overall analysis strategy. We provide marginal evidence for large scale Parity anomaly in the WMAP data that may be soon confirmed or discarded by the Planck satellite. Planck is currently measuring CMB anisotropies and their polarization with a level of precision that will remain unparalleled for many years to come. We also show how the CMB can be used to constrain fundamental symmetry violations in the photon sector through the so-called cosmological birefringence phenomenon. Finally, we provide forecasts for Planck and we discuss how emission from a specific diffuse foreground component arising within the Solar System needs to be kept under strict control to avoid incurring into false positive detections
The Planck Mission: Recent Results, Cosmological and Fundamental Physics Perspectives
No full textWe provide a description of the latest status and performance of the Planck satellite, focusing on the final predicted sensitivity of Planck. The optimization of the observational strategy for the additional surveys following the nominal 15 months of integration (about two surveys) originally allocated and the limitation represented by astrophysical foreground emissions are presented. An outline of early and intermediate astrophysical results from the Planck Collaboration is provided. A concise view of some fundamental cosmological results that will be achieved by exploiting Planck's full set of temperature and polarization data are presented. Finally, the perspectives opened by Planck in answering some key questions in fundamental physics, with particular attention to parity symmetry analyses, are described
In-flight main beam reconstruction for Planck-LFI
No full textIn-flight measurements of the shape of the antenna main beam is a crucial input to the data analysis pipeline of each high resolution Cosmic Microwave Background (CMB) anisotropy experiment. We study the main beam reconstruction achievable by the PLANCK Low Frequency Instrument (LFI) through the observation of external planets. Although we restrict our analysis to the 30 GHz LFI channel, the method can be easily extended to all the PLANCK frequency channels and to other CMB anisotropy experiments. We show that it is possible to fit the time ordered data from the external planets (mainly Jupiter and Saturn) to obtain an accurate, robust, simple and fast reconstruction of the main beam properties under very general conditions, almost independently of the calibration accuracy. In addition, we find that a bivariate Gaussian approximation of main beam shapes represents a significant improvement with respect to a symmetric representation. The impact of the most relevant systematic effects is also addressed. We demonstrate that by combining the recovery of the maximum signal at the planet transit with accurate in-flight calibration, it is possible to measure the intrinsic planet temperatures at millimetric wavelengths with <1% accuracy. This work is based on PLANCK-LFI activities
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
The Planck mission: From first results to cosmology
Get PDFPlanck is a ESA satellite, currently in operation, whose main objective is to accurately image the anisotropies of the Cosmic Microwave Background Radiation in intensity and polarization. Benefiting from an unprecedented combination
of sensitivity, angular resolution, and frequency leverage, Planck will provide high quality data to be mined in cosmology and astrophysics. The first Planck results have been released in January 2011 and include both Galactic and extragalactic source catalogues, a list of galaxy clusters selected by the Sunyaev-Zel’dovich effect, and a cold cores catalogue. The first cosmological data products are awaited for early 2013. Planck has a wide list of scientific targets. Here we focus on one specific aspect which is also of interest to the high energy physics community: constraining the Parity and CPT symmetries through CMB datasets. We describe the basic formalism, the relevant estimators and the overall analysis strategy. We provide
marginal evidence for large scale Parity anomaly in the WMAP data that may be soon confirmed or discarded by the Planck satellite. Planck is currently measuring CMB anisotropies and their polarization with a level of precision that will remain unparalleled for many years to come. We also show how the CMB can be used to constrain fundamental symmetry violations in the photon sector through the so-called cosmological birefringence phenomenon
Removing 1/f noise stripes in cosmic microwave background anisotropy observations
Get PDFRemoval of systematic effects is crucial in present and future CMB experiments mapping large fraction of the sky. Accurate CMB measurements ask for multi-feed array instruments observing the sky with a redundant scanning strategy covering the same sky region on different time scales and with different detectors for a better control of systematic effects. We investigate the capability to suppress 1/f noise features in Time Ordered Data (TOD) by using the destriping technique described in Maino et al. (1999), under realistic assumptions for crossing condition between different scan circles and sky signal fluctuations on small angular scales. We perform, as a working case, PLANCK-LFI simulated observations with few arcminutes pixel size convolved with LFI beam resolutions. In the noiseless case for crossing condition based on pixels with side larger than the input one, the destriping algorithm inserts extra-noise in the final map of the order of ∼μK in rms and few μK in peak-to-peak amplitude at 30 GHz. However including instrumental noise (white and 1/f noise) in the TOD, the impact of the sky signal on the destriping is found to be very small. In addition, for crossing condition based on pixels with side half of the one of the final map (typically ∼1/3 of the FWHM), we find only a small improvement (∼1% level) in the destriping quality with respect to the case when crossings are searched on pixels with same size of the final map one. We can conclude that the receiver noise is the driver for destriping quality. We extend the analysis to high values of the knee frequency and find that, although significantly suppressed by destriping, the residual additional noise rms is ∼31% larger than the pure white noise rms at fk = 1 Hz which could be a critical issue in the extraction of CMB angular power spectrum. We verified that the approximation of the 1/f noise on averaged scan circles as a single baseline still works well even for these high values of the knee frequency. Furthermore, by comparing simulations with different noise levels and different sampling rates, we find that the destriping quality does not significantly depend on the receiver sensitivity whereas it improves proportionally to the improvement of sampling rate. Therefore given a noise level, the higher the sampling rate, the better the destriping quality. This paper is based upon PLANCK-LFI activities
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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