1,720,972 research outputs found
Effects of volcanic seismic events on the Stromboli stability by finite difference numerical modeling
No full textThe effect of seismic activities is one of the crucial issues that needs to be analyzed in evaluating the stability of a volcanic edifice. The seismicity can be related to tectonic activity or due to magma migration mechanisms. The aim of this work is to analyze the effects of seismic events associated to magma migration mechanisms on the stability of the Stromboli volcano flanks, coupling the dynamic analysis with the effects of the magma pressure in the feeding conduits. It was performed by two-dimensional finite difference numerical modeling (FLAC 5.0, Itasca). The dynamic input was applied on both sides of the magmatic conduit, extended vertically below the active crater zone. In accordance with the evidences provided by the geophysical data, the dynamic source has been located between 300 and 700 meters. The effects of the dynamic perturbation are analyzed in terms of displacements vectors, strain increments and pore pressure variations
Valutazione delle condizioni di stabilità di una discarica di R.S.U. eseguita mediante metodi numerici alle differenze finite (FLAC 5, Itasca): Il collasso della discarica di RSU sita in località La Torre, nel comune di Teramo.
No full textAMMASSI ROCCIOSI FRATTURATI: MODELLAZIONE DEL RETICOLO DI FRATTURAZIONE, EFFETTI SULLA CIRCOLAZIONE IDRICA E SULLA STABILITÀ.
Full text linkRock joint characterization is a very complex task due to the heterogeneity and spatial variability of the fracture parameters. This PhD thesis is aimed to model a discrete fracture network and assess the effects of fracture properties on fluid flow and rock mass stability. Data were collected on a quartz rock mass well exposed both on surface and underground, along a well developed network of mining tunnels.
A large number of structural and geomechanical data were collected and analysed by statistical procedures. Distribution and probability density function of fracture parameters were derived from row data. Geostatistical interpolation methods were used to reproduce the spatial variability of the rock features, such as the variation of fracture spacing, aperture and orientation. A stochastic simulation of the discrete fracture network was then developed using FracMan software package, and a flow model, based on the dual porosity approach, was developed to assess the water inflow into the tunnel system. A review of the fracture permeability assessment is also discussed and applied for the definition of the model properties. The fracture parameters were validated using backfitting methods until the obtained results were consistent with the hydrogeological and mechanical conditions of the study site.
Block stability was then evaluated considering the blocks defined by the intersections between the discrete fracture network and the tunnels. Kinematics of instability were analyzed for the identified blocks; the factor of safety and the volume of stable and unstable blocks were also evaluated
Understanding Etna flank instability through numerical models
No full textShallow and deep deformations, mainly associated with both eruptive and seismic events, are concentrated along recognised fracture and fault systems, mobilising the eastern and south-eastern flank of the volcano. Several interacting causes were postulated to control the phenomenon, including gravity force, magma ascent along the feeding system, and a very complex local and/or regional tectonic activity. Nevertheless, the complexity of such dynamics is still an open subject of research and being the volcano flanks heavily urbanised, the comprehension of the gravitative dynamics is a major issue for public safety and civil protection. The present research explores the effects of the main geological features (in particular the role of the subetnean clays, interposed between the Apennine–Maghrebian flysch and the volcanic products) and the role of weakness zones, identified by fracture and fault systems, on the slope instability process. The effects of magma intrusions are also investigated. The problem is addressed by integrating field data, laboratory tests and numerical modelling. A bi- and tri-dimensional stress–strain analysis was performed by a finite difference numerical code (FLAC and FLAC3D), mainly aimed at evaluating the relationship among geological features, volcano-tectonic structures and magmatic activity in controlling the deformation processes. The analyses are well supported by dedicated structural–mechanical field surveys, which allowed to estimate the rock mass strength and deformability parameters. To take into account the uncertainties which inevitably occur in a so complicated model, many efforts were done in performing a sensitivity analysis along a WNW–ESE section crossing the volcano summit and the Valle del Bove depression. This was mainly devoted to evaluate the effect of topography, geometry and rheological behaviour of the structural units. The 3D numerical model, extended 40 × 60 km, was implemented to simulate the volcano deformation pattern. First, the role of the Pleistocene subetnean clays was investigated, then, two “structural weakness zones” – the Pernicana Fault system and the NE rift – were introduced and their effects on the flank instability evaluated. Two extreme hydrogeological conditions, drained and undrained, were analysed. The results are expressed in terms of stress–strain field, displacement pattern, plasticity states and shear strain increments. Two main instability mechanisms were identified: one at shallow depth, with the sliding surface located inside the subetnean Quaternary clay, and another deep-seated mechanism with a not continuous and less evident sliding surface, developed inside the Apennine–Maghrebian Chain flysch, bordered by active structures. Both mechanisms contribute to explain the present deformation pattern and some of the main structures of the Etna flank. The effect of magma pressure exerted on the active dyke walls during eruptions was then simulated and relations between magmatic activity and flank instability were preliminarily investigated
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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