1,721,288 research outputs found
Structure and rheology of lithosphere in Italy and surrounding
No full textWe define the structure and rheology of the lithosphere in Italy and surrounding, combining the cellular velocity models derived from nonlinear tomographic inversion with the distribution vs. depth of hypocentres to assess the brittle properties of the Earth’s crust. We average, over cells sized 1×1 degree, the mechanical properties of the uppermost 60 km of the Earth, along with seismicity, grouping hypocentral depths in 4-km intervals. For most of the cells, the earthquake energy is concentrated in the upper crust (4–12 km). For some regions, where orogenic processes occur, the release of earthquake energy is shallower and limited to the uppermost 10 km of the crust. Ambiguities in the structural models are minimized considering the hypocentral distribution, mainly to define the location of the Moho boundary, when its identification, based on shear-wave velocities, is not straight- forward
Surface waves tomography and non-linear inversion in the southeast Carpathians.
No full textA set of shear-wave velocity models of the lithosphere–asthenosphere system in the southeast Carpathians is determined by the non-linear inversion of surface wave group velocity data, obtained from a tomographic analysis. The local dispersion curves are assembled for the period range 7–150 s, combining regional group velocity measurements and published global Rayleigh wave dispersion data. The resolution of the tomography data is improved using a priori information about the shallow crustal velocity structure. The lithosphere–asthenosphere velocity structure is reliably reconstructed to depths of about 250 km for 27 cells with size 1◦ ×1◦. The adopted non-linear inversion method computes a set of acceptable velocity models for each cell. Local smoothness optimization (LSO) is applied to select the representative cellular structures and the three-dimensional shear-wave velocity model of the studied region is assembled. Interpretation of the obtained structure shows that the thickness of the lithosphere in the region varies from about 90 km to 170 km and the asthenosphere can be as deep as about 150 km. Mantle seismicity concentrates where the high-velocity lid is detected just below the Moho. The obtained results are in agreement with recent seismic refraction, receiver function, and travel time P-wave tomography investigations in the region. The similarity among the results obtained from different kinds of structural investigations (including the present work) highlights some new features of the lithosphere–asthenosphere system in southeast Carpathians, such as the relatively thin crust under Transylvania basin and in the Vrancea zone
The shear-wave velocity structure of the lithosphere-asthenosfhere system in the Iberian area and surroundings
No full textThe S-wave velocity model, to the depth of 300 km for the Iberian area and surroundings, is obtained with the non-linear inversion of Rayleigh wave tomographic data in the period range from 5 to 150 s. The three-dimensional model of the region is assembled from 74 juxtaposed one-dimensional cellular structures, sized 1° 9 1°, by means of a local smoothing optimisation. The S-wave velocity model shows the almost constant velocity (*4.40 km/s) in the upper mantle beneath the Iberian Massif, the well- developed low-velocity zones in the Valencia Trough and under northwest Africa, and specific features of the upper mantle layering in the zone of the Iberian range. The thickness of the crust varies between 25 and 35 km with exceptions in the zones of the Valencia Trough (11–18 km) and Pyrenees (35–45 km). Our Vs models are well correlated with the geological structure along Transmed I and evidence several features of the lith- osphere–asthenosphere system in the Betic–Rif domain: quite distinct Iberian, Alboran and Meseta crustal domains; relatively thin, well-developed lithosphere under the Rif system; and clearly defined boundary between the upper and lower asthenosphere. The cellular velocity model of the Betics, where ultrapotassic lamproitic magmatism is observed, has features similar to those of other three areas in the western Mediterranean where ultra- potassic lamproitic magmatism of different age is observed. The crust and upper mantle models in these four areas can be correlated with the age of the magmatism and the local heat flow, and outline how, starting from a naturally quite undifferentiated mantle where magma genesis is currently in progress, the differentiation in lithosphere and asthenosphere can take place in time
PanORAMa: Oblivious RAM with Logarithmic Overhead
Full text linkWe present PanORAMa, the first Oblivious RAM construction that achieves communication overhead for a database of blocks and for any block size while requiring client memory of only a constant number of memory blocks. Our scheme can be instantiated in the ``balls and bins model in which Goldreich and Ostrovsky [JACM 96] showed an lower bound for ORAM communication.
Our construction follows the hierarchical approach to ORAM design and relies on two main building blocks of independent interest: a \emph{new oblivious hash table construction} with improved amortized communication overhead for security parameter and , assuming its input is randomly shuffled; and a complementary \emph{new oblivious random multi-array shuffle construction}, which shuffles blocks of data with communication when the input has a certain level of entropy. We combine these two primitives to improve the shuffle time in our hierarchical ORAM construction by avoiding heavy oblivious shuffles and leveraging entropy remaining in the merged levels from previous shuffles. As a result, the amortized shuffle cost is asymptotically the same as the lookup complexity in our construction
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
Upper mantle flow in the western Mediterranean
No full textTwo cross-sections of the western Mediterranean Neogene-to-present back-arc basin are presented, in which geological and geophysical data of the TRANSMED Project are tied to a new shear-wave tomography. Major results are i) the presence of a well stratified upper mantle beneath the older African continent, with a marked low-velocity layer between 130–200 km of depth; ii) the dilution of this layer within the younger western Mediterranean back-arc basin to the north, and iii) the easterly raising of a shallower low-velocity layer from about 140 km to about 30 km in the Tyrrhenian active part of the back-arc basin. These findings suggest upper mantle circulation in the western Mediterranean back-arc basin, mostly easterly-directed and affecting the boundary between upper asthenosphere (LVZ) and lower asthenosphere, which undulates between about 180 km and 280 km
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