1,721,022 research outputs found
Structural and lithological guidance on speleogenesis in quartz–sandstone: Evidence of the arenisation process
No full textAbstract A detailed petrographic, structural and morphometric investigation of different types of caves carved in the quartz–sandstones of the “tepui” table mountains in Venezuela has allowed identification of the main speleogenetic factors guiding cave pattern development and the formation of particular features commonly found in these caves, such as funnel-shaped pillars, pendants and floor bumps. Samples of fresh and weathered quartz–sandstone of the Mataui Formation (Roraima Supergroup) were characterised through \{WDS\} dispersive X-ray chemical analyses, picnometer measurements, \{EDAX\} analyses, \{SEM\} and thin-section microscopy. In all the caves two compositionally different strata were identified: almost pure quartz–sandstones, with content of silica over 95% and high primary porosity (around 4%), and phyllosilicate-rich quartz–sandstone, with contents of aluminium over 10% and low primary porosity (lower than 0.5%). Phyllosilicates are mainly pyrophyllite and kaolinite. \{SEM\} images on weathered samples showed clear evidence of dissolution on quartz grains to different degrees of development, depending on the alteration state of the samples. Grain boundary dissolution increases the rock porosity and gradually releases the quartz grains, suggesting that arenisation is a widespread and effective weathering process in these caves. The primary porosity and the degree of fracturing of the quartz–sandstone beds are the main factors controlling the intensity and distribution of the arenisation process. Weathering along iron hydroxide or silt layers, which represent inception horizons, or a strata-bounded fracture network, predisposes the formation of horizontal caves in specific stratigraphic positions. The loose sands produced by arenisation are removed by piping processes, gradually creating anastomosing open-fracture systems and forming braided mazes, geometric networks or main conduit patterns, depending on the local lithological and structural guidance on the weathering process. This study demonstrates that all the typical morphologies documented in these quartz–sandstone caves can be explained as a result of arenisation, which is guided by layers with particular petrographic characteristics (primary porosity, content of phyllosilicates and iron hydroxides), and different degrees of fracturing (strata-bounded fractures or continuous dilational joints)
Analisi morfologica tramite software 3D del sistema carsico dei Piani Eterni nel Parco Nazionale Dolomiti Bellunesi, Veneto, Italia
Full text linkNegli ultimi anni lo sviluppo di software per la resa vettoriale 3D dei sistemi carsici
e per la costruzione di modelli geologici, ha permesso di ampliare notevolmente le potenzialità
delle analisi di controllo strutturale e litologico dei vuoti carsici. L’analisi tridimensionale dei
condotti, in cavità topografate per almeno 5 km di sviluppo spaziale (sistemi di dimensione non
locale), permette di individuare le zone di maggiore carsificazione dei massicci carbonatici e di
metterle in relazione al contesto geologico della zona. Le caratteristiche morfologiche dei sistemi
carsici epigenetici sono controllate da fattori direttamente connessi con l’assetto strutturale
dei massicci, le litologie e l’evoluzione paleogeografica dell’area. Grazie ai software di resa 3D
è possibile individuare inception horizons da analisi statistiche della distribuzione dei vuoti,
ricostruire in tre dimensioni particolari orizzonti stratigrafici e desumere le successive fasi di
stazionamento della tavola d’acqua nel sistema carsico.
Lo studio tramite metodologie 3D del Sistema dei Piani Eterni, nelle Dolomiti Bellunesi, ha evidenziato
le varie fasi di stazionamento del livello di base, le relazioni tra le paleo-tavole d’acqua
con le superfici di controllo stratigrafico e tettonico, fornendo interessanti spunti sull’evoluzione
paleogeografia e morfotettonica dell’intero massiccio
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
DeepLandforms: A Deep Learning Computer Vision Toolset Applied to a Prime Use Case for Mapping Planetary Skylights
Full text linkThematic map creation is a meticulous process that requires several steps to be accomplished regardless of the type of map to be produced, from data collection, through data exploitation and map publication in print, image, and GIS format. Examples are geolithological, and geomorphological maps in which most of the highest time-consuming tasks are those related to the discretization of single objects. Introducing also interpretative biases because of the different experience of the mappers in identifying a set of unique characteristics that describe those objects. In this setting, Deep Learning Computer Vision techniques could play a key role but lack the availability of a complete set of tools specific for planetary mapping. The aim of this work is to develop a comprehensive set of ready-to-use tools for landforms mapping based on validated Deep Learning methodologies and open-source libraries. We present DeepLandforms, the first pre-release of a toolset for landform mapping using Dee..
Prototyping of Lunar surface geological sampling tools for Moon spacewalk simulations by ESA
No full textApollo Lunar missions returned to scientists on Earth the first collection of geological extra-terrestrial planetary
samples, other than meteorites. Scientists around the world are still studying rocks and soil samples that were
collected, by the Apollo 11 through 17 missions, using modern equipment, methods and technologies. The return of samples has allowed the field of planetary science to advance in ways unthinkable with the restrictions of in-situ analysis and remote observations.
As for every other aspect of the Apollo programme, the design and manufacturing of the tools utilized by
astronauts for sample collection had to meet rigorous planetary protection requirements, whilst respecting stringent environmental and operability constraints. Many of those tools went through various redesign efforts, based on feedback from the very skillful and resourceful astronauts using them. In future planetary exploration missions, geological and geo-microbiological sampling will be a key to further development of our understanding of the evolution of the solar system, and to develop successful technologies for in-situ resource utilization and 3D printing. Designing and manufacturing technologies and ergonomics have developed since the 1960s, and so have chemical and biological hazard containment protocols, and analytical tools. Whilst it is important to solidly build on the lessons learned in the Apollo era, there is a serious opportunity for innovative design solutions. The European Space Agency (ESA) Neutral Buoyancy Facility (NBF) based in the European Astronaut Centre (EAC) in Cologne has a large experience in performing 0g simulations for ISS (International Space Station) Extra Vehicular Activities (EVA), and has recently engaged in simulations of Lunar surface operations, replicating reduced gravity and mobility constraints, in order to prepare future human and robotics surface operations. One of the main objectives within this area is prototyping and testing new geological sampling tools which could be used in future human surface Lunar missions. The tools are being developed in cooperation with the team of planetary geologists of the PANGAEA project (Planetary ANalogue Geological and Astrobiological Exercise for Astronauts), and field tested during the PANGAEA Space Analogue test campaigns.
This paper discusses the requirements and objectives to be met while developing such tools, the challenges
related to EVA suits and Lunar environment which impact the astronauts’ mobility and tools performance. It presents the status of development achieved during NBF and PANGAEA analogue field testing. The examples include a variety of sample collectors, containers, markers and the outcome of test performed in various mission scenarios
A Novel Method for Hidden Natural Caves Characterization and Accessibility Assessment From Spaceborne VHR SAR Images
No full textCaves are one of the last frontiers of human exploration on Earth. They are very relevant scientific targets as they host significant biodiversity and unique geologic formations. The presence of underground passages accessible for human or robotic exploration are revealed by localized collapse of the near-surface ceiling of a cave system (skylight). Remote sensing systems are a valuable tool for skylights detection as these features are often located on very remote and often inaccessible regions of the Earth. However, with the available remote sensing techniques and data analysis methodologies, it is very difficult to determine whether a skylight is providing access to a cave continuation or it represents only a closed depression with no extensions. In this article we propose a methodology, based on very high-resolution (VHR) orbital synthetic aperture radar (SAR) imaging systems, to estimate both caves geometric characteristics and accessibility information in the proximity of a skylight. To test our methodology, we acquired radar data over different Earth's location by exploiting the Capella Space X-band microsatellite radar constellation. The experimental results show that our methodology effectively determines the caves geometric characteristics and accessibility under a variety of surface conditions. We also detected several unknown and unexplored large cave systems located near Volcan Wolf and Ecuador, Isla Isabela, Galapagos. The presented work has relevant implications for the field of geological studies, ecology, and space exploration research since optical imaging shows the evidence of potential cave systems accessible from skylights on other planetary bodies such as Mars
A Method for the Characterization of the Interior of Pits from Single Spaceborne SAR Images
Full text linkPits are depressions in the ground that occur due to the collapse of the surface layer. The characterization from the orbit of their internal structure using optical images is challenging due to uncontrolled illumination geometry. In this letter, we propose a methodology for the characterization of pits' interiors by exploiting Synthetic Aperture Radar (SAR) images. The methodology analyzes the amplitude and range of the radar echoes originating from the pit's interior to determine its geometric characteristics through data inversion. The experimental results demonstrate that a set of bright reflections in the radar image can be attributed to the response of pits' vertical walls and floor. By applying the proposed methodology and interpreting the radar reflections, we are able to derive a geometric characterization (e.g., depth) of a given pit. The retrieved geometric parameters from SAR data of a terrestrial pit denoted as Well of Barhout align well with the ground truth. The findings of this study have implications for both Earth observation and planetary exploration
- …
