1,721,007 research outputs found
Rotation of the Italian peninsula from aeromagnetic evidence
No full textPalaeomagnetic data have been used extensively in order to study the geodynamical history of a region. Similar information can be obtained by analysing the shape of aeromagnetic anomalies and the direction of the total magnetization vector of the anomaly sources. We can suppose that the direction of the Earth's magnetic induction vector is almost constant with time along a N-S direction. If a significant directional difference between total magnetization and induction vector is observed, we can argue that the anomaly sources were affected by conspicuous rotational movements. In the central Southern Tyrrhenian area, the anomaly shape is generally normal i.e., N-S, except for several anomalies which have a maximum-minimum direction parallel to the Italian coast, that is, NW-SE rather than N-S. This feature, and the location of these anomalies on the border of the bathyal plain, seems to be in agreement with the anticlockwise rotation movements suggested in some geodynamical models of the region. © 1988
The Role of Remanent Magnetization In the Southern Italian Crust From Aeromagnetic Anomalies
No full textInduced magnetization in the intermediate to deep crust is insufficient to justify regional magnetic anomalies. This is an unresolved problem, that cannot be completely explained by induced and viscous magnetization. In this context, the contribution of remanent magnetization in the Southern Italian Region has been investigated from a study of long-wavelength magnetic anomalies. By means of a shape analysis, several anomalies were found which indicate a total magnetization vector direction different from the induced one. From the good correspondence between these deduced declinations with palaeomagnetic and palaeotectonic data, we infer a remarkable manifestation of remanent magnetization in the intermediate-crust
Shape analysis of aeromagnetic anomalies in the Southern Italian Region for the evaluation of crustal block rotations
No full textAn extensive analysis of aeromagnetic data from the Italian region is presented, regarding the evaluation of the azimuthal direction of the total-magnetization vector. A method based on the Zietz and Andreasen (1967) correlation between anomaly shape and direction of the total magnetization vector was used. A discussion related to possible traps in using this method is presented, with the aid of several tests on synthetic anomalies. The analysis points out a number of anomalies revealing abnormal directions, either SW-NE or SE-NW, which were used to divide the investigated area into five regions with different trends. Finally, assuming elevated Koenigsberger ratios for the source-rocks, the declinations of the remanent magnetization vector were judged very similar to those estimated for the total-magnetization vector. Thus, by comparing these values with the normal declination of the area, rotation values of the crustal blocks related to the investigated anomalies were proposed. Finally, these were compared with the available geological and palaeomagnetic information and significant correspondences were found. © 1990
Space-frequency analysis and reduction of potential field ambiguity
No full textAmbiguity of depth estimation of magnetic sources via spectral analysis can be reduced representing its field via a set of space-frequency atoms. This is obtained throughout a continuous wavelet transform using a Morlet analyzing wavelet. In the phase-plane representation even a weak contribution related to deep-seated sources is clearly distinguished with respect a more intense effect of a shallow source, also in the presence of a strong noise. Furthermore, a new concept of local power spectrum allows the depth to both the sources to be correctly interpreted. Neither result can be provided by standard Fourier analysis. Another method is proposed to reduce ambiguity by inversion of potential field data lying along the vertical axis. This method allows a depth resolution to gravity or the magnetic methods and below some conditions helps to reduce their inherent ambiguity. Unlike the case of monopoles, inversion of a vertical profile of gravity data above a cubic source gives correct results for the cube side and density
2.5D modelling of Somma-Vesuvius structure by aeromagnetic data
No full textThis paper deals with the analysis of aeromagnetic data on the Sonma-Vesuvius area. An inverse 2.5D method is used, its main features being a variable strike length and a data set relative to a vertical plane. This last provides a depth resolution, so that the result consists in a magnetic tomography along a vertical section. The magnetic model shows that magnetized rocks extend up to carbonate basement depths (about 2 km). The stronger magnetizations (>6 A/m) are concentrated in the emerged part of the volcano, but high magnetizations are still present down to about 1800 m b.s.l. The magnetization distribution found is then compared to the distribution of;he hypocenters of Vesuvian earthquakes and for shallow depth a positive correlation is noted. At depths greater than about 2 km, i.e. at the level where a geothermal well started to encounter dolomites, the model shows no magnetization, while hypocenters form a nearly continuous vertical belt. This pattern leads to the conclusion that this evidence may be considered as being due to a small volume of the feeding system at these depths or eventually as an indication of strong alteration processes of magnetic rocks. (C) 1998 Elsevier Science B.V. All rights reserved
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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