1,721,034 research outputs found
Planetary analogue study using microseismic analysis for near-surface lava tube detection and exploration
No full textThe paper presents new results from microseismic data analysis for the detection and delineation of near-surface lava tubes. Single-station, free-field seismic noise data were collected at the Corona Volcano area (Lanzarote, Canary Islands) as part of the PANGAEA-X 2017 European Space Agency (ESA) astronaut training campaign. The site was selected as it represents a suitable analogue for lunar maria and provided the opportunity to cross-validate and ground truth seismic and other geophysical studies. In this paper, we present our observations on the distribution of frequencies and amplitudes of standing waves generated by microtremors in the space between the ground surface and underground cavities by averaging amplitude spectra of microseismic records. This study shows that the frequency of the vertical component peaks is a relatively good indicator of presence, lateral extent and approximate dip of the cavities. However, only the vertical component peaks with a frequency either equal to or close to central to high amplitude (3.1–8.5) horizontal-to-vertical (H/V) peaks are related to lava tubes. If the P-wave velocities in the rocks overlying the lava tubes are known, then these frequencies can also be used to estimate the depth of such cavities. This study also identified some important pitfalls that may limit the use and accuracy of our approach. These include layering of rocks overlying the lava tubes, lateral changes in thickness, lateral variations of the P-wave velocity, and the presence of shallow void-rich zones. Overall, the results of this study confirmed that microseismic data are suitable for cavity detection. It is also, to our knowledge, one of the first studies dealing with microseismic data from near-surface lava tubes. With the recent increase in planetary exploration, this method can be easily adapted to support the geophysical exploration of volcanic terrains on the Moon and Mars
Tectonically-driven mud volcanism since the late Pliocene on the Calabrian accretionary prism, central Mediterranean Sea
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ERT data collected at the Corona volcano (Lanzarote, Canary Islands) during the European Space Agency (ESA) testing campaign PANGAEA-X 2017
No full textDetection, imaging and analysis of lava tubes for planetary analogue studies using electric methods (ERT)
No full textThis paper presents new field and synthetic modelling results of Electrical Resistivity Tomography (ERT) surveys for the identification and detection of lava tubes with the particular aim of using ERT techniques for stratigraphic investigations of planetary volcanic analogues. These geophysical surveys were undertaken at the Corona volcano (Lanzarote, Canary Islands), as part of the PANGAEA-X 2017 campaign, which formed part of the European Space Agency's (ESA) astronaut training program. ERT profiles were acquired at two test sites located along the main Corona lava tube system. During the campaign a variety of experimental setups were tested. This provided an ideal opportunity to cross-validate geophysical results with ground truth provided by partial surface exposure of the lava tubes and laser scanner mapping of the lava tube system in the subsurface. It also permitted an assessment of the usability of ERT in detecting lava tubes in a heterogeneous volcanic setting. Our experiments showed that a combination of different electrode arrays and their joint inversion resulted in good detectability of the lava tubes with a large size with respect to the electrode spacing. The dipole-dipole array configuration provided more accurate models for lava tubes of a size in the same order of magnitude as the electrode spacing. This study showed that the main drawbacks of ERT in heterogeneous volcanic settings are linked to lava tube-related high-resistivity anomalies which appear larger and shallower and may also be laterally shifted with respect to their true location. For lava tubes with a small size with respect to the electrode spacing our synthetic data modelling results show the difficulty in distinguishing single lava tubes from in contact lava tubes, and distinguishing lava tubes in general from void-rich zones. Overall, ERT surveys were successful in detecting lava tubes, providing a good definition of the main boundaries between different volcanic units and highlighting the presence of close, near-parallel unexplored lava tubes
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
Methane Seepage on Mars: Looking for analogues from submarine fluid flow systems on Earth
No full textMethane Seepage on Mars: Looking for analogues from submarine fluid flow systems on Eart
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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