1,720,974 research outputs found
Effetti dell’intrusione superficiale del magma sulla stabilità della Sciara del Fuoco (Stromboli).
No full textModelling the instability phenomena on the NW flank of Stromboli Volcano (Italy) due to lateral dyke intrusion
No full textThe aim of the paper is to provide quantitative elements on the mechanisms that controlled the slope instabilities occurred after two major recent eruptions at Stromboli volcano (i.e. 2002–2003 and 2007). After a brief description of the geological setting and of the largest well documented instability phenomena on volcano flanks, the main objective is pursued using three-dimensional stress-strain analyses for modelling the effects of the magma intrusion on the stability of the volcano flank. Modelling is based on the results of an extensive geotechnical characterization of the volcaniclastic and lava materials. The numerical analyses investigate the influence of different paths and geometry of magma intrusion as well as the spatial variation of mechanical properties. As a result, favourable conditions for specific failure modes are identified. The stress-strain analyses show that magma intrusion can cause both a local failure of a wedge immediately downslope from the dyke or deepseated movement involving large part of the slope; these two mechanisms were consistent with the deformative patterns observed during the 2007 and 2002–2003 eruptions, respectively. The magma thrust induces shear strains up to levels associated to appreciable grain crushing even below the sea level, where flow liquefaction can be invoked to explain the occurrence of past submarine slides. The submarine landslide is analysed by a combined finite element – limit equilibrium approach that demonstrates that instability conditions can develop if the loading exerted by the upper portion of the slope is sufficiently fast to produce undrained conditions. The analyses also support the hypothesis that at the 2002 subaerial failure occurred, due to combined effects of a magma mild thrust and the removal of the toe support caused by the preceding submarine slide
Un approccio integrato per la valutazione prestazionale della stabilità delle spalle di dighe ad arco
Full text linkLa nota presenta un metodo per valutare le prestazioni sismiche di cunei in roccia alle spalle di una diga ad arco, secondo un approccio agli spostamenti di tipo Newmark opportunamente modificato per includere le forze trasmesse dalla diga e tutti i possibili cinematismi tridimensionali del cuneo all’interno della nicchia di distacco. Nell'ipotesi di blocco rigido e assenza di rotazioni, il metodo è in grado di tenere conto delle tre componenti dell'input sismico, il progressivo distacco del blocco dai piani di appoggio del giunto, l'eventuale recupero del contatto e anche il temporaneo distacco completo del blocco attraverso una fase di volo libero. Oltre alle azioni inerziali gravitazionali e sismiche, sono incluse nell’analisi le forze statiche e dinamiche esercitate al contatto diga-cuneo, comprese quelle relative all'interazione inerziale con l'invaso. Il metodo viene applicato per la verifica sismica della diga ad arco-gravità di Ridracoli (Italia), fondata su una formazione rocciosa fittamente stratificata di origine turbiditica. In particolare, la spalla destra viene verificata rispetto alla formazione di cunei adagiati su piani di strato con caratteristiche di resistenza particolarmente scadenti
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
Computation of irreversible seismic displacements of rock wedges: an application to dam abutment safety assessment
No full textThe paper discusses a method to assess the seismic performance of rock wedges in contact with arch-dam abutments based on the Newmark displacement approach, conveniently modified to include all possible three-dimensional failure mechanisms and forces transmitted by the structure. Under rigid-block and no-rotations assumptions, the method allows to consider the three components of the seismic input, the progressive detachment of the block from the supporting discontinuity planes, the possible recover of the contact, and the temporary complete detachment of the block from the rock mass. In addition to gravitational and seismic inertial actions, static and dynamic forces exerted at the dam-wedge contact, including those related to the inertial interaction with the reservoir, are included in the analyses. A case study is presented, referred to the seismic verification of the Ridracoli arch-gravity dam (Italy), founded on a marly-arenaceous formation. In particular, the right abutment is thoroughly investigated against wedge sliding involving bedding planes of particularly poor resistance. The results in terms of maximum wedge displacements are compared with the corresponding factor of safety obtained with a limit equilibrium approach, indicating that even a wedge resulting unstable with limit equilibrium analyses shows relatively small displacements at the end of the seismic excitement
Damping formulations for finite difference linear dynamic analyses: performance and practical recommendations
Full text linkAn in-depth study is presented on some numerical formulations used to reproduce damping of motion in solid continua. The focus is addressed in particular to those formulations that in the finite difference geotechnical code FLAC can be exploited to perform linear analyses. The numerical investigations are performed through a simple 1D model of a homogeneous soil deposit interested by a shear wave motion coming from the bedrock, and a gravity dam model subjected to seismic excitations in presence of dam-water-foundation interaction. The Rayleigh damping method is tested in particular to find an appropriate choice of the control frequency in order to minimize the problems of high-frequency overdamping. The analyses also investigate two other formulations (the local damping and its variant, the combined damping) that present the major advantages in providing a frequency independent action and in needing not significant computational resources. Limits and principal drawbacks of their possible use are highlighted
Buckling of high natural slopes: The case of Lavini di Marco (Trento-Italy),
No full textLayered limestones with marly–clayey interbeds are widespread in mountain regions. Where tectonics has
not changed the original structure they frequently form homocline slopes, that since the last deglaciation
have evolved through planar block slides along bedding joints. A typical dip slope showing this evolution is
represented by the left flank of the Adige River valley south of Rovereto (North-Eastern Italy). Even though
layers never daylight at the slope toe, the exceptional persistence and weakness of bedding joints allows
buckling of layers, which occasionally collapse causing rock avalanches. Before monitoring started,
deformations were believed to be no longer active, this conviction being strengthened by the high safety
factors provided by limit equilibrium analyses. SAR satellite interferometry performed between 1990 and
2002 and probe inclinometer measures indicate that the slabs located uphill from the buckle folds are slowly
sliding. Since some doubts have been raised about rock mass behaviour, slope geometry and hydraulic
conditions assumed in the analyses, buckling was back-analysed using the Distinct Element Method (DEM)
and the Discontinuous Deformation Analysis (DDA). These treat the rock mass as a discontinuum and
account for deformation and failure of the rock material. To perform numerical analyses, rock mass structure,
strength and stiffness were determined through extensive in situ and laboratory investigations. For this
purpose field surveys, borehole core logging and geophysical surveys were performed and laboratory
geotechnical tests on the rock material, clayey interbeds and bedding joints were conducted. Discontinuous
analyses confirmed that buckling deformations are definitely possible if some conditions are present (high
water pressure, minor flexures). Modelling also indicate that buckling deformations may evolve into failures
and should therefore be taken into account in evaluating long term stability of the slope
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