1,721,160 research outputs found
Integrating ambient noise with GIS for a new perspective on volcano imaging and monitoring: The case study of Mt. Etna
Full text linkThe timely estimation of short- and long-term volcanic hazard relies on the availability of detailed 3D geophysical images of volcanic structures. High-resolution seismic models of the absorbing uppermost conduit systems and highly-heterogeneous shallowest volcanic layers, while particularly challenging to obtain, provide important data to locate feasible eruptive centres and forecast flank collapses and lava ascending paths. Here, we model the volcanic structures of Mt. Etna (Sicily, Italy) and its outskirts using the Horizontal to Vertical Spectral Ratio method, generally applied to industrial and engineering settings. The integration of this technique with Web-based Geographic Information System improves precision during the acquisition phase. It also integrates geological and geophysical visualization of 3D surface and subsurface structures in a queryable environment representing their exact three-dimensional geographic position, enhancing interpretation. The results show high-resolution 3D images of the shallowest volcanic and feeding systems, which complement (1) deeper seismic tomography imaging and (2) the results of recent remote sensing imaging. The study recovers a vertical structure that divides the pre-existing volcanic complexes of Ellittico and Cuvigghiuni. This could be interpreted as a transitional phase between the two systems. A comparison with recent remote sensing and geological results, however, shows that anomalies are generally related to volcano-tectonic structures active during the last 17 years. We infer that seismic noise measurements from miniaturized instruments, when combined with remote sensing techniques, represent an important resource to monitor volcanoes in unrest, reducing the risk of loss of human lives and instrumentation.Fil: Guardo, Roberto Antonino. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: De Siena, L.. University Of Aberdeen; Reino Unid
Does innovation drive resilience? The case study of the Italian provinces
No full textL’innovazione è considerata una variabile chiave nel determinare la resistenza economica regionale. Tuttavia, sono stati condotti finora pochissimi studi sulla relazione tra innovazione
e resilienza regionale nelle sue varie dimensioni. Il nostro paper mira a colmare
questa lacuna indagando la capacità di ‘resistere’ alla crisi economico-finanziaria mostrata delle province italiane (NUTS3) nel periodo di recessione economica che va dal 2008 al 2014. La nostra analisi statistica rivela come l’innovazione, misurata in termini di tasso di variazione di individui impiegati nei settori ad alta tecnologia, sia chiaramente non associata alla ‘resistenza’ a livello regionale. Altre variabili come un’elevata diversità di attività economiche a livello regionale, il tasso di variazione del Prodotto Interno Lordo, la densità
della popolazione e la posizione geografica sono effettivamente associate ad un più alto grado di resistenza, mentre la related variety mostra una correlazione inversa e statisticamente
significativa.Innovation is considered a key variable for determining regional economic resistance.
However, a very few studies aiming to determine the existence of a relationship between innovation and regional resilience – in its various dimensions – have been carried out until now. Our paper aims at narrowing the gap in this regard by looking at the ability of ‘resistance’ showed by the Italian provinces (NUTS3 level) in the 2008-2014 recessionary period. Our statistical analysis reveals that innovation, proxied by employment variation rate in high tech sectors, is not clearly associated with ‘resistance’ at the regional level. Other variables such as diversity of regional economic activities, GDP variation rate, population density and geographical location are actually associated with a higher degree of resistance, while related variety shows an inverse and statistically significant correlation
Semi-Automated Inversion-Specific Data Selection for Volcano Tomography
Full text linkActive seismic experiments allow reconstructing the subsurface structure of volcanoes with unprecedented resolution and are vital to improve the interpretation of volcanic processes. They require a quality assessment for thousands of seismic waveforms recorded at hundreds of stations in the shortest amount of time. However, the processing necessary to obtain reliable images from such massive datasets demands signal processing and selection strategies specific to the inversions attempted. Here, we present a semi-automated workflow for data selection and inversion of amplitude-dependent information using the original TOMODEC2005 dataset, recorded at Deception Island (Antarctica). The workflow is built to tomographic techniques using amplitude information, and can be generalised to passive seismic imaging. It first selects data depending on standard attributes, like the presence of zeroes across all seismic waveforms. Then, waveform selections depend on inversion-specific attributes, like the delay of the maximum amplitude of the waveform or the quality of coda-wave decays. The automatic workflow and final visual selections produce a dataset reconstructing anomalies at a node spacing of 2 km, imaging a high-attenuation anomaly in the centre of the Deception Island bay, consistent with previously-published maps. Attenuation models are then obtained at a node spacing of 1 km, highlighting bodies of highest attenuation scattered across the island and a NW-SE trend in the high-attenuation anomaly in the central bay. These results show the effect of the local extension regime on volcanic structures, providing details on the eruptive history and evolution of the shallow magmatic and hydrothermal systems. The selection workflow can be easily generalised to other amplitude-dependent tomographic techniques when applied to active seismic surveys. Image improvements from the original dataset are minor when selecting data using standard attributes, like signal-to-noise ratios. Tomographic maps become drastically more stable and consistent between different frequencies and resolutions when data selection targets attributes specific to the inversion
Agglomeration economies in the Italian ICT sector: The structural features
No full textIl presente articolo analizza le caratteristiche strutturali del settore dell’ICT in Italia, assieme alla presenza di economie di agglomerazione. L’adozione dell’analisi delle componenti
principali (ACP) ha permesso di evidenziare le specificità del settore all’interno del
contesto italiano. Nello specifico, il nostro studio fornisce un quadro delle caratteristiche dell’ICT nelle province italiane e in particolare in quelle urbanizzate. Inoltre, lo studio rivela l’esistenza di province caratterizzate da un alto livello di concorrenza, là dove le nuove imprese tendono a localizzarsi. Infine, in linea con la precedente letteratura, l’analisi empirica mostra come le province urbanizzate siano caratterizzate da specializzazione e da un
alto tasso di nascita di nuove imprese nel settore ICT.This paper aims to analyse the structural features of the ICT sector in Italy, along with the presence of agglomeration economies. The adoption of principal component analysis (PCA) enabled us to highlight the specificities of the ICT sector in Italy. In particular, our study provides a picture of the features of the ICT sector in Italy as a whole, especially
in the urbanized provinces. Moreover, this study reveals the existence of provinces
characterized by a high level of competition where new firms tend to be localized. Finally, in line with previous literature on the topic, our empirical analysis shows that urbanized provinces in Italy are characterized by specialization in the ICT sector as well as a higher
level of new firm birth
Multi-scale reasonable attenuation tomography analysis (MuRAT): An imaging algorithm designed for volcanic regions
No full textThe attenuation of body-wave amplitudes with propagation distance can be used to provide detailed tomographic images of seismic interfaces, fluid reservoirs, and melt batches in the crust. The high sensitivity of body-wave energies to high-scattering structures becomes an obstacle when we try to apply attenuation tomography to small-scale volcanic media, where we must take into account the complexities induced by strong heterogeneous scattering, topography, and uncertain source modeling in the recorded wave-fields. The MuRAT code uses a source- and site-independent coda-normalization method to obtain frequency-dependent measurements of P-to-coda and S-to-coda energy ratios. The code inverts these data for both the geometrical spreading factor and the spatially-dependent quality factors (Q), providing additional attenuation information in the regions where velocity tomography is available. The high sensitivity of coda-waves to highly heterogeneous structures highlights zones of anomalous scattering, which may corrupt amplitude-dependent attenuation measurements, and where basal assumptions of linear optics may go unfulfilled. A multi-step tomographic inversion increases the stability of the results obtained in regions of high heterogeneity (e.g., the volcanic edifice) by the inclusion of data corresponding to either sources or stations located in regions of lower heterogeneity. On the other hand, a mere increase in the number of rays entirely contained in the heterogeneous structures affects both the stability and the effective resolution of the results. We apply the code to two small waveform datasets recorded at an active (Mount St. Helens) and at a quiescent (Mount Vesuvius) volcano. The results show that the seismicity located inside or under the volcanic edifice produces an increase of the low-frequency energy ratios with travel time in both areas. In our interpretation, the anomalous concentration of energy which affects any waveform recorded on the cone, produced inside the volcanic edifice or in the feeding system of the volcano is due to seismic source- or medium-dependent resonance. The results also provide spatial and frequency limits on the feasibility of attenuation tomography in these two regions with larger datasets. © 2014 Elsevier B.V
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
Three-dimensional kernel-based coda attenuation imaging of caldera structures controlling the 1982-84 Campi Flegrei unrest
No full textCoda-wave attenuation imaging has risen as a state-of-the-art technique to depict volcanic structures using their dispersion effects. The 1982–84 seismic and deformation unrest at Campi Flegrei caldera (Italy) is a unique example of non-eruptive volcanic activity in a structured caldera. Here, we propose the first application of 3D coda-attenuation kernels to image caldera structures at multiple frequencies during unrest. Using sensitivity kernels is necessary to assess the effective resolution of coda imaging in highly heterogeneous volcanoes. The technique relies on the solution of Paasschens' equations in the framework of radiative transfer theory. The results map coda attenuation in the 3D space without need of pre-existent velocity models. The resolution and stability of the inversion solutions were examined by changing the damping parameters and outputting the corresponding images, inverting for different node spacings and performing checkerboard tests. These tests show that the resolution of the multiple-scattering model is much lower than that provided by a standard isotropic-scattering and/or single scattering technique. The best resolution in our model is obtained between depths of 1 km and 3 km in the centre of the model, between Pozzuoli town and Solfatara crater. The results are discussed at a frequency of 3 Hz, due to both longer coda durations and broader kernel illumination: in this frequency range, coda-based 3D imaging had so far failed to provide stable results. The interpretation is performed based on the extensive geological and geophysical knowledge of the caldera. High-attenuation anomalies below Solfatara and Monte Nuovo mark areas either saturated with water or enriched in molten rocks, feeding the respective fumarole fields. The flattening and horizontal elongation of these anomalies below 2 km depth is a manifestation of the blocking and spreading around of the rising hot magmatic fluids below a previously-inferred high-velocity, low-attenuation and highly-deforming caprock. This caprock is not uniform, likely due to the remnants of erupted structure. A SW-to-NE-trending low-attenuation and high-velocity anomaly deeps down to 3 km under Pozzuoli. We infer that the high seismicity in the region is a consequence of the stress sustained by the caprock from a 4-km-deep deformation source in 1983–84. On top of this source, high coda attenuation corresponds to high Vp/Vs ratios and high direct-wave attenuation. The region's characteristics are likely due to the accumulation of magmatic fluids above a magmatic sill
- …
