1,720,960 research outputs found
A three-dimensional QP imaging of the shallowest subsurface of Campi Flegrei offshore caldera, southern Italy
Full text linkTo improve the knowledge of the shallowest subsurface of Campi Flegrei caldera, a 3-D P wave attenuation tomography of the area was performed. We analyzed about 18,000 active seismic traces, which provided a data set of 11,873 Δt* measurements, e.g., the differential travel times to quality factor ratios. These were inverted through an adapted tomographic inversion procedure. The 3-D tomographic images reveal an average QP about 70, interpreted as water-saturated volcanic and marine sediments. An arc-like, low-QP structure at 0.5–1 km depths was interpreted as a densely fractured, fluid-saturated rock volume, well matching the buried rim of Campi Flegrei caldera. The spatial distribution of high- and low-QP bodies in the inner caldera is correlated with low-Vp values and may reflect either the differences in the percentage of fluid saturation of sediments or the presence of vapor state fluids beneath fumarole manifestations
Three-dimensional attenuation imaging of the Irpinia fault zone (Southern Italy): inferences on the fluid storage and earthquake related processes
No full textIn this study we propose to integrate velocity and attenuation tomographic images for a comprehensive seismic interpretation of the 1980 Irpinia earthquake fault zone that uses well established rock physical laws to retrieve information about porosity and the type of permeating fluids from seismic attributes
Potential of ambient seismic noise cross-correlation to characterise the hydrogeology of a clayey landslide : application to Mas D'Avignonet landslide in Trieves region (France)
Full text linkLAUREA MAGISTRALEQuesto lavoro presenta uno studio multidisciplinare su una frana in argilla (“Mas d’Avignonet”) nelle Alpi Francesi, 40 km a sud di Grenoble monitorata permanentemente dal 2007 da OMIV (Ente per l’osservazione delle instabilità di versante). Dopo un’analisi iniziale degli studi messi in campo in passato e delle misurazioni ambientali (idrometeorologiche e geofisiche) effettuate da strumenti di monitoraggio dislocati in una zona particolarmente attiva della frana, il lavoro verte sull’applicazione del metodo di cross correlazione di rumore sismico ambientale. Questo metodo permette di ritrovare le variazioni temporali di velocità sismiche (dv/V) che vengono in seguito correlate principalmente con misure piezometriche (livello di falda superficiale) e indirettamente con le misurazioni meteorologiche (pluviometria, pressione e temperatura), topografiche (GPS), idrogeologiche (SP e TDR) e geofisiche con l’applicazione di metodi di resistività elettromagnetici (EM31) ed elettrici (ERT) precedentemente elaborate.
Il metodo, inizialmente basato sulla cross correlazione di rumore sismico (registrato su tre componenti per stazione) di una coppia di stazioni, è stato successivamente esteso cross correlando componenti differenti di una medesima stazione. Questo processo ha permesso, soprattutto per il primo caso, di ritrovare variazioni di velocità sismiche coerenti con le variazioni di falda superficiale per una determinata banda di frequenza delle onde di Rayleigh.
In seguito, abbiamo studiato il ruolo della saturazione dei fluidi nelle variazioni di velocità sismiche applicando la teoria poroelastica di Biot-Gassmann che considera il terreno un mezzo poroelastico con fase fluida. In particolare, abbiamo applicato leggi di omogeneizzazione della fase fluida, descrivendo l’influenza dell’acqua nella propagazione delle onde di Rayleigh. Il metodo permette infine la valutazione delle variazioni di velocità sismiche rispetto alla frequenza (considerando che il rumore sismico sia composto per lo più da onde di Rayleigh) spiegando quantitativamente i risultati ottenuti con la cross correlazione.
Il seguente lavoro mostra in prima analisi come il metodo di cross correlazione sia un valido strumento di monitoraggio non distruttivo permettendo di descrivere dinamiche idrogeologiche di frane in argilla. Tuttavia la complessità dei risultati suggerisce che la presenza di più stazioni consentirebbe davvero di raggiungere dei risultati soddisfacenti.This work focuses on the study of “Mas d’Avignonet” landslide, a slow moving clayey landslide located in French Western Alps, which benefits from a multi-parameter monitoring implemented by OMIV (Multidisciplinary observatory landslide) since 2007. After an analysis of the several studies carried out and after data acquisition from environmental measurements (meteorological, hydrogeological and geophysical), we apply cross-correlation of ambient seismic noise. This method allows the retrieval of seismic velocity variations over time. We assess its potential mainly through the correlation with piezometrical measurements (water table variations). However, we consider also meteorology (pluviometry, air temperature and pressure), geodesy (GPS), hydrogeology (SP and TDR) and geophysics with the implementation of electromagnetic (EM31) and electric (ERT) resistivity method.
Initially based on the cross-correlations of seismic noise between a pair of stations (each station records three components signal), we extend this method to a single station by cross-correlating the different signal’s components. This processing allows obtaining local velocity changes. Particularly, we find that water table changes are consistent with seismic velocity variations for a specific frequency band of Rayleigh waves’ signal.
In addition, we studied the role of fluid saturation on seismic velocity changes by using the Biot-Gassmann poroelastic theory. We focus on the influence of the water in Rayleigh waves’ propagation considering a poroelastic medium with a fluid phase and by applying fluid substitution mixture laws. This approach allows assessing the amplitude of the velocity changes according to frequency (assuming the seismic noise being composed of Rayleigh waves) and to quantitatively explain cross-correlation results.
This work shows that cross correlation of ambient seismic noise method represents an effective non-destructive monitoring tool able to describe landslide hydrogeology in order to predict its dynamics. The results suggest that the method works but the complexity of the landslide could be completely explained by increasing the stations’ number
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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