1,720,963 research outputs found
Feasibility analysis of the performance of low-cost GNSS receivers in monitoring dynamic motion
Get PDFThe development of low-cost GNSS receivers broadens their applications, such as deformation monitoring, which have been performed routinely by survey-grade GNSS receivers. To evaluate the performance of low-cost GNSS receivers, we assessed the precision of low-cost multi-GNSS receivers in monitoring dynamic motion and developed methods of using a closely-spaced dual low-cost GNSS receivers’ system to enhance their performance. In this study, both the survey-grade and low-cost GNSS receiver/antennas were mounted on a circular rotating device executing controlled periodic rotation. It was shown that the precision of the low-cost GNSS receivers could be enhanced to the level of 2–4 mm, by using multi-GNSS observations and limiting the noise level based on error modelling and filtering of the closely–spaced low-cost GNSS receivers. Finally, from the experiments and a real bridge monitoring application, it was proved that low-cost GNSS receivers could accurately define modal frequencies of ∼0.362 Hz and ∼1.680 Hz, respectively
Signal-to-Noise ratio (SNR) data of GNSS satellites based on simulations and real experimental measurements to model the multipath effect for antenna vibration
No full textThe impact of multipath effect on GNSS measurements is well-known. Based on this dataset of signal-to-noise ratio (SNR) of GNSS satellites which derived from simulation and experimental measurements in controlled environment, it is evaluated whether the multipath effect can be modelled for the case of an antenna which is vibrated and whether the characteristics of the antenna vibration can be defined
1Hz GPS Japan network (GEONET) data for Tohoku-Oki Mw9.0 2011 earthquake
No full textThe GNSS network of Japan, which is known as GNSS Earth Observatoin Network System (GEONET-Japan) and operated by the Geospatial Information Authority of Japan, consists of more than 1200 continuously observing GNSS stations, covering the Japanese land area with 20 km average distance between neighborouring GNSS sites. The Mw9.0 earthquake of Tohoku on 2011 March 11 was fully recorded by GEONET and GPS records of 847 GEONET stations of 15-hour duration and 1 Hz sampling rate, covering the period of the earthquake, were available. The GPS records have been processed using the scientific Bernese GPS Software 5.2 in post-process Precise Point Positioning mode using a priori information of highest quality from the Center of Orbit Determination in Europe (CODE). This dataset is the 1 Hz GPS coordinate time-series, as the result of the post-process solution, in north, east and up components. The 1 Hz GPS time-series cover 7-hour period prior, during and after the Tohoku Mw9.0 2011 earthquake
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
Documentation of the potential of GPS and RTS to measure oscillations of rigid structures: experimental, analytical approach and application
No full textThe present study focuses on the documentation of the high perfomance of GPS and RTS in monitoring of rigid structures, as those with main modal frequencies higher than 1Hz. The developed methodology was based on experimental assessment of the performance of GPS and RTS, on upgrade of the instruments and development of analytical techniques for the process of GPS and RTS time series. The experiments were based on an experimental device which produces pre-adjusted oscillations of known characteristics (of amplitude 0.5-3cm and frequency 0.05-4Hz), which were simultaneously recorded by GPS and RTS. Based on analysis of GPS and RTS records the time series of the oscillations derived. For the analysis of the oscillation time series techniques (i.e. Normperiod code for the spectral analysis) were developed in order to overpass problems of the instruments records (gaps of data, uncontinious data). Based on these techniques the amplitude and the frequency of the time series were estimated and in sequence were compared with the real, pre-adjusted values. From the comparison was proved that GPS can define accurately the oscillation frequency (deviation <0.05Hz for frequency up to 4Hz) and RTS can define accurately the oscillation amplitude (deviation <2mm for amplitude 5mm). RTS measurements were more accurate than GPS, but GPS records accurately the oscillation waveform due to the higher recording frequency. The instruments and the adopted methodology were for the monitoring of the response of two rigid structures: the Steel Railway Bridge of Gorgopotamos and a steel pedestrian bridge in Athens. In both bridges was proved that GPS data can define the waveform of the dynamic response of the bridges and their main modal frequencies (up to 5Hz), while RTS define accurately the amplitude of the dynamic (4-5mm) and semistatic (3-4mm) response of the bridges. Thus, the combination of the time series of GPS and RTS can define the kinematic response of a rigid structure and its main dynamic characteristics.Η παρούσα διατριβή στοχεύει στη αξιολόγηση της απόδοσης του GPS και του ρομποτικού θεοδόλιχου (RTS) στην καταγραφή των ταλαντώσεων δύσκαμπτων κατασκευών, δηλαδή κατασκευών με κύριες ιδιοσυχνότητες μεγαλύτερες του 1Hz. Η μεθοδολογία που ακολουθήθηκε για την αξιολόγηση αυτή στηρίχθηκε σε πειραματική διερεύνηση, αναβάθμιση των οργάνων και ανάπτυξη τεχνικών ανάλυσης δεδομένων. Τέλος η μεθοδολογία και τα όργανα εφαρμόστηκαν σε κατασκευές. Η πειραματική διερεύνηση έγινε με χρήση πειραματικής συσκευής ελεγχόμενων ταλαντώσεων γνωστών χαρακτηριστικών (εύρους 0.5-3cm και συχνότητας 0.05- 4Hz) οι οποίες κατεγράφησαν από το GPS και RTS ταυτόχρονα. Με ανάλυση των μετρήσεων των οργάνων προέκυψαν χρονοσειρές που περιέγραφαν τις ταλαντώσεις. Χρησιμοποιήθηκαν τεχνικές (π.χ. κώδικας Normperiod φασματικής ανάλυσης) για την ανάλυση των χρονοσειρών με τις οποίες ξεπεράστηκαν προβλήματα των καταγραφών (π.χ. κενά στις καταγραφές, ανισαπέχοντα δεδομένα). Με την χρήση των τεχνικών αυτών προσδιορίστηκαν το εύρος και η συχνότητα ταλάντωσης των καταγραφών και συσχετίστηκαν με τις πραγματικές τιμές. Από την συσχέτιση αυτή προέκυψε ότι με τις χρονοσειρές του GPS προσδιορίζεται αξιόπιστα κυρίως η συχνότητα ταλάντωσης (απόκλιση <0.05Hz ακόμα και για συχνότητα ταλάντωσης 4Hz) ενώ με τις χρονοσειρές του RTS προσδιορίζεται το εύρος ταλάνωσης (απόκλιση <2mm ακόμα και για εύρος 5mm). Αυτό οφείλεται στο ότι η κυματομορφή της ταλάντωσης καταγραφόταν πιο αξιόπιστα από το GPS, ενώ οι μετρήσεις του RTS είχαν μεγαλύτερη ακρίβεια όμως λόγω της μικρότερης συχνότητας δειγματοληψίας δεν καταγραφόταν εξίσου αξιόπιστα η κυματομορφή της ταλάντωσης. Τα όργανα και οι μεθοδολογία αυτή δοκιμάστηκαν σε δύο δύσκαμπτες κατασκευές: την Σιδηροδρομική Γέφυρα του Γοργοποτάμου και μία μεταλλική πεζογέφυρα στην Αθήνα. Και στις δύο γέφυρες διαπιστώθηκε ότι οι καταγραφές του GPS προσδιόρισαν την κυματομορφή της δυναμικής κίνησης της γέφυρας και τις ιδιοσυχνότητες της (μέχρι και 5Hz), ενώ οι καταγραφές του RTS προσδιόρισαν με ακρίβεια το εύρος των δυναμικών (έως και 4-5mm) και των ημιστατικών (έως και 3-4mm) μετακινήσεων. Ο συνδυασμός των χρονοσειρών των δύο οργάνων μας δίνει την πλήρη εικόνα της κινηματικής κατάστασης μίας δύσκαμπτης κατασκευής και των κύριων δυναμικών χαρακτηριστικών της
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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