1,720,977 research outputs found
Geophysical surveys for the characterization of periglacial mountain environments
No full textThe degradation of mountain permafrost is well documented at many Alpine areas. During the last decades, geophysical techniques have been intensively used to monitor these sites, since thawing permafrost is a proxy of climate change and global warming but also a possible source of slope instabilities and triggering of mass movements. Consequently, the development of new reliable geophysical methods to study Alpine mountain permafrost areas have both an economic and scientific interest. This PhD project has been focused on the application and optimization of different geophysical techniques, data acquisition and processing, for the characterization of several periglacial mountain environments in the Alps and Apennines. The works that have been realized during the PhD period can be divided into four different categories: i) evaluation and optimization of the contact resistances between electrodes and debris-blocky surfaces during electrical resistivity tomography (ERT) measurements, with the application of conductive textile sachets as substitute of traditional stainless steel rod electrodes; ii) application of different electromagnetic instruments in the frequency domain (FDEM) to rapidly verify the presence in the subsurface of the frozen layer and its thickness; iii) optimization of two joint inversion methods, structurally-coupled and petrophysical-coupled joint inversions, applied to seismic refraction (RST) and ERT datasets to improve the structural interpretation of the inverted models, thanks to sharper boundaries between the different layers, and the evaluation of ice, water, and air fractions in the subsurface; iv) evaluation of the hydraulic behaviour of the active layer and the frozen layer in a mountain permafrost area with an infiltration experiment combined with ERT time-lapse measurements
The Use of Textile Electrodes for Electrical Resistivity Tomography in Periglacial, Coarse Blocky Terrain: A Comparison With Conventional Steel Electrodes
No full textBrief communication: On the potential of seismic polarity reversal to identify a thin low-velocity layer above a high-velocity layer in ice-rich rock glaciers
Full text linkSeismic refraction tomography is a commonly used technique to characterise rock glaciers, as the boundary between unfrozen and ice-bearing layers represents a strong impedance contrast. In several rock glaciers, we observed a reversed polarity of the waves refracted by an extended ice-bearing layer compared to direct-wave arrivals. This phase change may be related to the presence of a thin low-velocity layer (LVL), such as fine- to coarse-grained sediments, above a thicker ice-rich layer. Our results are confirmed by the modelling and analysis of synthetic seismograms to demonstrate that the presence of a low-velocity layer can produce a polarity reversal on the seismic gather
Brief communication: Use of lightweight and low-cost steel net electrodes for electrical resistivity tomography (ERT) surveys performed on coarse-blocky surface environments
No full textERT is a widely used geophysical technique for characterizing various mountainous environments where land surfaces consist of coarse blocks and debris, such as landslide deposits or rock glaciers. In this situation, installing the common steel spike electrodes is both challenging and time-consuming, and achieving galvanic contact between the electrodes and the surface is difficult. In this work, we have successfully tested an alternative electrode that is tougher, lighter and cheaper than the recently proposed conductive textile electrode. A thin stainless-steel net and sponges are used to create small bags that can be easily inserted between the blocks, and then removed
Surface wave tomography using dense 3D data around the Scrovegni Chapel in Padua, Italy
Full text linkThis collection includes all raw shot gathers collected around the Scrovegni Chapel the 29th October 2020 (data are in SEGD format). This dataset is the result of the collaboration between the University of Padova, that performed the data acquisition, and STRYDE, that provided the seismic nodes and the technical support
Mountain permafrost acts as an aquiclude during an infiltration experiment monitored with ERT time-lapse measurements
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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
Advances in Soil Compaction Characterization Through Applied Geophysics
No full textSoil compaction is a rather complex phenomenon, with spatial variability and temporal dynamics dependent on several factors. Its side effects have a significant impact on the soil ecosystem, particularly on hydrological regulation and agronomic production, resulting in significant ecological and economic damage to the entire society. Therefore, a correct understanding and characterization of the processes involved are necessary for prevention and to address future global challenges of sustainability and food security. Geophysics has several strengths to create added value in providing an answer to agriculture challenges of our time, such as improving management of soils and more sustainable approaches in general and consequently preventing the compaction phenomenon. Due to their non-invasive nature, near-surface geophysical methods support the investigation of soil properties, characteristics, and variables. In this work, we present the ability of electric and electromagnetic geophysical methods, i.e. Electrical Resistivity Tomography and Frequency-domain Electromagnetic Method, and recent applications of active seismic methods, i.e. Seismic Refraction Tomography and Multichannel Analysis of Surface Waves, to assess the effects of compaction on agricultural soil. The purpose is to show pros & cons of all techniques and their resolution and ability in characterizing compacted areas with good confidence
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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