1,720,989 research outputs found
“GNSS Multifrequency receivers in urban environment: Theoretical analysis”
No full textIn this paper, a theoretical approach for the analysis of synchronization performances in GNSS receivers adapted to reduce errors, especially caused by multipath fading, in a urban environment is proposed. In particular, two kinds of bi-frequency receivers based on data fusion methods are analyzed. The performances have been evaluated by comparison of simulated results in a real case and theoretical values based on the dispersion of the S-curve, the characteristic curve output of the DLL. One way to cope with multipath effects is equipping receivers with software modules able to reduce multipath effects. This paper explains two different methods based on data fusion and in particular on fusion between different frequencies. It is shown that improvement is possible if and when the multipath can be considered independent for two frequencies properly spaced in the frequency domain. A theoretical analysis has been carried on together with computer simulation. The signal channel model has been developed with Galileo in mind to show how data fusion techniques can be applied exploiting the frequency diversity. The receiver modules taken into account are the Equal Gain Combining (EGC) and the Adaptive Gain Combining (AGC). Starting from the statistical model of a classical DLL code-tracking system, a theoretical model for both EGC and AGC is derived. To verify the correctness of the theoretical model, a simulation environment has been set up, with the possibility of varying different parameters. The multipath model is referred to an urban environment. Resells are shown both for EGC and AGC receivers. Correct decision probability in the considered cases has confirmed the results in the simulated cases
Neural Networks Based Approach For Fine Tracking in Satellite Navigation Systems
No full textIn this paper a novel method to solve the fine synchronization problem in GNSS receivers is presented. In fact the extended evolution of GNSS-based applications will imply the growth of fast and precise navigation systems. The aim of this study is to found an alternative solution to the classical non-coherent Delay Lock Loop. In particular, the proposed method, based on Self Organizing Map (SOM) a particular type of Neural Networks, allows to improve the performances in multipath channel
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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