1,720,966 research outputs found
Forecasting TV audience:a consulting project with the Italian public television
No full textA statistical marketing consulting project financed by RAI, the public Italian television, is illustrated. Two alternative models have first been used, a statistical regression model and a data mining one, of a more empirical nature. Then the two models are hybridised in a third model, a compromise useful for applications. Finally, some real forecasting examples are illustrated
Stam inequality on Z(n)
Full text linkWe prove a discrete version of Stam inequality for random variables taking values on Z(n
Detecting multi-dimensional threats: A comparison of solution separation test and uniformly most powerful invariant
No full textIntegrity for GNSS (Global Navigation Satellite Systems) at user level is monitored by means of RAIM (Receiver Autonomous Integrity Monitoring) algorithms. Most RAIM algorithms are based on detection tests, which are able to detect and identify possible anomalies in the measurements and eventually exclude suspected measurements from the position solution or forward a warning to the pilot. In this paper the two most commonly used tests, the standard Uniformly Most Powerful Invariant (UMPI) test and the Solution Separation (SS) test, are compared and differences are pointed out, both from a general statistical point of view and a more specifically integrity point of view. The detection regions of the two methods are compared and a numerical example is provided. The results show that the two methods are equivalent in case the anomaly or threat model has only one dimension, whereas differences arise in case of multi-dimensional threats.Geoscience & Remote SensingCivil Engineering and Geoscience
GNSS-based receiver autonomous integrity monitoring for aircraft navigation
No full textNowadays, GNSS-based navigation is moving more and more to critical applications. Global Navigation Satellite Systems (GNSS), which in the past used to be represented by the American GPS and the Russian GLONASS are now growing in number and performance. The European systemGalileo and the Chinese systemBeidou are being deployed, while GPS and GLONASS are being modernized. The availability of a larger number of satellites to provide measurements, together with a new frequency dedicated to civil use, are strongly increasing the application potential of GNSS technology. To be used in aviation, in particular during critical phases of flight as approach and landing, satellite navigation shall provide a very high level of service. Correctness—within tight bounds—of the position solution, shall be guaranteed to extremely high levels of probability. In operating an aircraft, the risk for so-called HazardouslyMisleading Information (HMI) due to the navigation systemis typically budgeted at the 10−7 to 10−9 level. These extremely tight requirements constitute a guarantee of safety, which is called integrity. More formally, integrity is about the trust that a user can have in the navigation service (and more specifically, the indicated position information). The trust is measured by the probability of HMI (or integrity risk), which is the probability that the position error exceeds a certain tolerance, without being detected and an Alert being raised in time.Commonly, a distinction is made between system-level integrity and user-level integrity. At system level, integrity is monitored directly by the GNSS control segment and can be monitored by additional external augmentation systems. At user level, integrity is monitored directly by the user via statistical methods. This dissertation focuses on user-level integrity monitoring, also called Receiver Autonomous IntegrityMonitoring (RAIM). In a RAIM method, integrity ismonitored by exploiting the redundancy of theGNSS signals as collected at the receiver. Calculations are performed within the user equipment itself to check the measurements’ consistency. RAIM computations are possible as long as a number of satelliteslarger than the minimumnecessary for a position fix (four in case of single constellation) is visible.RAIM algorithms have been investigated since the late 1980s, starting with publications by Lee, Brown and Brenner. As main representative and reference of the first generation RAIM algorithms we cite the Weighted RAIM algorithm, also referred to as Least-Squares-Residuals (LS) RAIM, proposed by Walter and Enge. This algorithm is still in use today, typically implemented in aviation grade GPS receivers, to provide low-precision lateral integrity only. As of today no RAIM implementation exists for any application requiring integrity in the vertical plane (i.e. precision approaches), which has more stringent certification requirements. To serve this scope second generation RAIMalgorithms are nowbeing developed and tested, as for instance the Advanced RAIM(ARAIM), proposed by the Stanford group.Different approaches being around show that the community has not reached convergence on the subject of integrity of GNSS for aviation yet, especially on RAIM. The Least Squares residuals RAIM, was the staple of the first generation RAIM: its algorithmwas found to be not completely flawless from a theoretical point of view and is not designed to deal with a multi-constellation system. The ARAIM is currently being tested but has not reached yet a definitive shape and has not fully convinced the community because of its high computational load, its convoluted structure and supposed approximations. New alternative approaches are also being proposed.This dissertation offers to the community a critical review of the most popular RAIM algorithms currently available or under development (in particular LS RAIMand ARAIM), and highlights their major strengths and shortcomings. Furthermore it reviews the DIA procedure, a well-established method for gross error detection in geodesy developed by TU Delft, and proposes its application to the RAIMproblem. A connection is made fromthe DIA concept of reliability to integrity risk and a method to evaluate RAIM performance parameters (False Alarm and HMI rates) for a multi-step exclusion/adaptation procedure is proposed (by means of the concept of worst-case bias). The study performed shows the viability ofthe DIA procedure as an alternative RAIMprocedure, and its competitive performance compared to the algorithms currently in use or under development in aviation (LS RAIM and ARAIM). Simulation results show that in several scenarios the DIA method performs significantly better than the others. Points of improvement are nevertheless individuated, also in the DIA, and recommendations are given for the development of the RAIMof the future.In particular, as a result of the algorithms review and the simulation results, it is concluded that all RAIM algorithms discussed, including the DIA procedure, have room for improvement. Both ARAIM and DIA show safe performance (i.e. risk is never larger than required/announced), but some of the approximations employed in ARAIM seem rather conservative and its exclusionmechanismseems not particularly effective. At the sametimealso the DIA exclusion mechanismdoes not appear to performoptimally, fromthe integrity maximization point of view. From a reliability analysis point of view — i.e. prior computation of the probability of HMI (PHMI) based on the satellite geometry alone — the DIA performs better than ARAIM, i.e. can guarantee higher availability (and higher continuity in a faulty scenario). On the other hand one of the mainweaknesses of the RAIMalgorithms analyzed is the Exclusion (or Adaptation) mechanism. Both ARAIM and DIA procedures recognize that in many geometries—given a requirement on the continuity—attempting exclusion introduces more risk than just declaring Alert. This suggests that further investigation is required to develop a more robust and reliable exclusion method for integrity
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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