1,720,963 research outputs found
Marine magnetic anomalies and plate motions in the central Atlantic region during the Oligocene and early Miocene
No full textAlthough the plate kinematics associated with the opening of the central Atlantic ocean after the break-up of Pangaea has been the subject of several studies since the late 1960s, there are still open problems and debated solutions to the tectonic evolution of this area. In particular, the initial fit of Pangaea, the spreading directions during the early stages of opening, the existence of ridge jumps, and the entity of intraplate deformation processes in northwest\ud
Africa are still subject to different interpretations by different research groups. The objective of this study is a reassessment of the central Atlantic plate kinematics since the early Jurassic through a re-examination of marine magnetic anomalies, fracture zone trends and geologic data.\ud
A total of 215 magnetic ship-tracks from the NGDC GEODAS database for the time interval from 1964 through 1994, in the area comprised between the Atlantis FZ and the Azores\ud
triple junction, were analyzed. The data quality was assessed through an examination of Kp indices. Magnetic data collected during disturbed days were filtered away. Thus, 29 reliable magnetic profiles were extracted having an azimuth that differed from the fracture zones trend\ud
by less than 30° and did not cross any fracture zone. The ship-track segments were projected onto flow lines that parallel existing fracture zones in order to avoid shape distortion and possible misinterpretation of the magnetic anomalies. Finally, the magnetic data were high-pass\ud
filtered to remove trends.\ud
A new advanced software tool for the analysis and interpretation of the anomalies was used improving the reliability of magnetic anomaly identifications.\ud
The main result of this work has been the assessment that an independent Moroccan plate existed during the Oligocene and early Miocene, which moved eastward relative to\ud
northwest Africa. This event has significant implications for the fit of central Pangea during the early Mesozoic.\ud
A new map of the magnetic lineations in the central Atlantic is proposed, which is based on an analysis of magnetic anomaly profiles and fracture zone geometry in the zone north of the Atlantis FZ. This map overcomes the flaws of previous compilations, even if it retains much of\ud
the classic works.\ud
The structural pattern that results from this study evidences that: 1) the whole set of North American isochrons are shifted to the west in the area north of the Atlantis FZ with respect to the classical compilations; 2) a unique spreading direction existed during the early and middle Jurassic, and until the M25 – M21 time interval in the late Jurassic. Such a spreading direction is compatible with that proposed in a recent model of opening of the proto-Atlantic, but extends the trend well beyond the early Jurassic
Trench curvature and the state of stress of subducting slabs
No full textViene descritta la relazione esistente tra lo stato di stress laterale all’interno di uno slab in subduzione ed il piegamento della litosfera al corrispondente margine attivo. Dato un raggio di curvatura della zona di trench, per valori sempre maggiori dell’angolo di piegamento questa relazione implica una piccola componente di stress compressivo a profondità non elevate, ed una considerevole deformazione laterale estensionale quando l’angolo di piegamento supera il valore di equilibrio. Lo studio della geometria di 35 zone di subduzione attuali, accompagnata dall’analisi del pattern di strain dei corrispondenti slab in subduzione, mostra che la litosfera di circa la metà di queste placche è in uno stato di stress laterale di tipo estensionale, mentre gli slab rimanenti supportano una compressione laterale. Un’analisi statistica dei meccanismi focali di terremoti inclusi nel catalogo Harvard CMT mostra che per 27 placche su 35 la componente di momento sismico cumulativo associata a stress laterale aumenta linearmente con lo strain previsto teoricamente quando questa quantità non supera l’1%. Comunque, per otto slab lo strain laterale che è necessario per accomodare la subduzione supera questa soglia. In questo caso il momento sismico cumulativo per unità di area lungo la zona di Wadati-Benioff è approssimativamente costante ed indipendente dallo strain laterale teorico legato al piegamento. Ciò suggerisce che il massimo strain che può essere associato a slip sismico in uno slab in subduzione è vicino all’1%. Infine, otto slab su 35 manifestano un comportamento anomalo, caratterizzato da valori elevati del momento sismico associato a strain laterale
Design, Control and Prototyping of a Bidirectional Dual Active Bridge Converter for integrating a Sodium Metal Halide Battery into a Telecom Station
No full textThe paper presents the design, control and prototyping of a Dual Active Bridge converter (DAB) devoted to interface a Sodium Metal Halide Battery (SMHB) to the DC grid of a telecom station. The design process is accomplished starting from telecom DC supply and SMHB specifications, especially power and voltage ratings and their corresponding variation ranges. Furthermore, DAB components are selected carefully based on an extensive performance analysis to maximise the energy efficiency, by enabling Zero-Voltage Switching (ZVS) over wide power and voltage operating ranges. The effectiveness of the proposed configuration is guaranteed also by a nested PI-based control system, which avoids unsuitable DC-bias current components by a proper management of phase-shift variations. Both simulations and experiments are presented and discussed, which corroborate the validity of all the design solutions
Reply to comments by C. Labails and W. Roest on ‘Breakup of Pangaea and plate kinematics of the central Atlantic and Atlas regions’
No full textIn their comment, Labails and Roest have raised several points against the kinematic model of Schettino and Turco for the central Atlantic region, which requires the existence of an independent Moroccan Plate during the Oligocene and the early Miocene. We thank these authors for giving us the opportunity to clarify some controversial points, but disagree with most of their objections and show that they are based either on a different interpretation of existing data or a distortion of the facts presented by Schettino and Turco
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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