1,720,978 research outputs found
RECURRENCE QUANTIFICATIONANALYSIS OF ACOUSTIC EMISSION TIME SERIES IN THE PETEROA VOLCANO AREA (ARGENTINA).
No full textNon linear time series techniques are largely being applied in different disciplines, such as Earth Sciences, Astrophysics, Engineering, Economy, Physiology, and Neurosciences. One, in particular, Recurrence Quantification Analysis (RQA), appears quite promising for the analysis of complex systems [1]. Moreover, it has recently been applied to investigate both acoustic emissions from rocky specimens [2] and the dynamics of complex seismic processes [3].
Whenever two objects are put in contact and let them slide with respect to each other, friction induced vibrations may occur. Examples are represented by active faults within seismogenic zones, narrow-banded noise of train wheels running along tight curves, friction in bearings, and micro-scale events in molecular physics.
In this framework, the paper describes the application of RQA to the Passive Acoustic Emission (AE) signal released, at ultrasonic frequencies, by stressed rocks in the Earth’s crust above a given threshold (event). The data record is represented by AE time series gathered, with 30 sec. of sampling rate, at the Peteroa Volcano monitoring station (Argentinean Andes). In these site AE data were collected by piezoelectric transducers, working at two ultrasonic frequencies, stuck to a rock [4, 5, 6]. This way, a huge amount of data is available but the AE signal amplitude varies with to the acoustic impedance, related to local rocks stress conditions and particularly sensitive to fracture density and water content. In order to investigate the evolution characteristics of the quiescence and activation status of the crustal system, the application of the RQA method to the AE time-series is focused to pinpoint peculiar recurrence patterns, without taking into account the amplitude. RQA is a quite simple processing technique that introduces few parameters descriptive of the global complexity of a signal, which are computed from the so-called “Recurrence Plot” [7]. In particular, it is possible to monitor quantitative changes in dynamics of temporal distribution [2], loss of synchronization of dynamic mechanism or spatial irregularities occurring in time. The aim of this work is to identify few descriptors that can explain the main characteristics of the AE signals and identify anomalies to be related to crustal stress modifications or, as in the Peteroa case study, paroxysmal volcanic activities or Earth’s tides imprints [5, 6]
Earlier appraisal of seismic and volcanic events by means of recurrence quantification analysis of AE time-series: preliminary results
No full textRecurrence Quantification Analysis (RQA) appears one of most promising non linear time series techniques for
the analysis of complex systems [1]. Recently, it has been applied to investigate acoustic emissions from both
rocky samples [2] and complex seismic processes dynamics [3].
Friction induced vibrations may occur whenever two objects, once put in contact, slide with respect to each other.
Typical examples are active faults inside seismogenic zones, train wheels running along tight curves with their
narrow-banded noise, friction in bearings, and events at microscopic scale in molecular physics.
Within this context, the application of RQA to Passive Acoustic Emission (AE) signals released, at ultrasonic
frequencies, by stressed rocks in the Earth’s crust beyond a specific threshold (event) is presented. The data
records are constituted by AE time-series collected nearby active tectonic and volcanic sites in Italy, Greece and
Argentina. The AE data were gathered, with 30 sec of sampling rate, by piezoelectric transducers, operating at
two ultrasonic frequencies (typically 25 and 150 kHz), fixed to a rock [4, 5, 6]. Usually, the data set is very huge
and the AE signal amplitude changes with to the acoustic impedance, associated with local rock stress conditions
and particularly sensitive to fracture density and water content. The evolution features of the quiescence and
activation status of the crustal structure is examined by applying the RQA method to the AE time-series focusing
on characteristic recurrence patterns, disregarding the signal amplitude. RQA is a quite simple processing method
which considers few parameters describing the whole complexity of a signal. The RQA parameters are simply
reckoned from the so-called “Recurrence Plot” [7] and are used to monitor quantitative changes in dynamics of
temporal distribution [2], loss of synchronization of dynamic mechanism or spatial irregularities occurring along
time [8]. In particular, this work aims at defining few descriptors that are able to explain the main characteristics
of the AE signals and identifying anomalies to be related to crustal stress modifications or paroxysmal volcanic
activities in the monitored seismic and volcanic areas [4,5]
Comparison of Classification Methods on Geomorphometric Data of Peteroa Volcano Area
No full textFour different geomorphometric classifications of local topographic gradients for the Peteroa Volcano area are introduced and compared. The compared methods are Isodata, Tandem Analysis on correlation and covariance matrices, and the segmentation following a Hierarchical Factorial Classification of gradients. Input data are obtained by processing a raster Digital Elevation Model extracted from ASTER stereo-pairs. The resulting maps show the spatial distribution of homogeneous landform units, highlighting the impact of erosional and tectonic processes on the whole relief. Moreover, each class is being described by either mean gradient values or mean topographic attributes such as elevation, slope and aspect. Next, these data are interpreted in terms of morphological setting
Morpho-Structural Comparison of Latin American Volcanoes.
No full textThe geomorphometric classifications of local topographic gradients of two groups of Andean volcanoes situated in the Andes Cordillera are introduced and compared. Input data are eight topographic gradients obtained by processing each volcano raster Digital Elevation Models extracted from ASTER stereo-pairs. Based on these data, the pixels have been classified into 17 classes through a clustering procedure applied to coordinates resulting from Principal Component
Analysis. The resulting thematic colour maps show the spatial distribution of homogeneous landform units, highlighting the impact of erosional and tectonic processes on the whole relieves.
The comparison of the corresponding classes of the different volcanoes may be interpreted as similarity among the volcanoes
Relationship between Topographic Relief and Ground Deformation at Cephalonia Island (Greece)
No full textRelief is a major element for portraying a landscape, while even slight changes in its shape are frequently identified as a result of deformation. Both are strictly related to the morphological setting of a given area that is often represented as a raster data set, the Digital Elevation Model (DEM). In particular, morpho-units can be discriminated by applying classification methods to topographical attributes, usually derived by processing DEMs, while deformation rates are pinpointed by elaborating Synthetic Aperture Radar (SAR) data by means of Interferometric techniques. The main goal of this work is to relate the morphological information gathered by classifying terrain units of Cephalonia
Island (Greece), on the basis of a DEM, with the observed deformation resulting from SAR interferometry, not disregarding the geo-structural setting of the area
Comparison of three Andean volcanic complexes through Multidimensional Analyses of geomorphometric data
No full textThe geomorphometric classifications of local topographic gradients for three volcanoes situated in the Andes Cordillera, Parinacota, Socompa, and Tata Sabaya, are introduced and compared.. Input data are eight topographic l gradients obtained by processing raster Digital Elevation Models extracted from ASTER stereo-pairs. Based on these data, the pixels have been classified through a clustering procedure applied to coordinates resulting from Principal
Component Analysis. The resulting thematic colour maps show the spatial distribution of homogeneous landform units, highlighting the impact of erosional and tectonic processes on the whole reliefs. Moreover, each class is described by both mean gradient values and mean topographic attributes such as elevation, slope and aspect. An unexpected result concerns the high similarity among the three volcanoes concerning the classes of pixels oriented toward SE, S, and SW: this suggests some common trigger phenomenon
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
VOLCANO-TECTONIC SCENARIO OF VULSINI VOLCANOS (CENTRAL ITALY) FROM LANDSAT-MSS IMAGES AND DIGITAL ELEVATION DATA
No full textThrough the analysis of LANDSAT-MSS images and Digital Elevation Model (DEM) from the Vulsini Volcanic District (VVD), Central Italy, 62 lineaments have been detected. All data sets have been converted into thematic maps showing the correspondence of the lineaments with geological limits, geophysical anomalies trends, mineral hot water locations, eruptive fractures and volcanic centres. Lastly, some lineaments have been correlated with basement tectonics and magma composition. © 1990
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
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