1,721,016 research outputs found
New insights on the porosity and grain features of Al Haggounia 001, an impact-melt meteorite
No full textIn the frame of a broader study on impact effects on meteorites microstructures and mineralogy, we studied the internal structures and grain features of Al Haggounia 001 meteorite, a very interesting EL3 impact melt characterized by a strong porosity. The study was carried out using a 3D reconstruction obtained by micro-Computed x-ray Tomography (μ-CT) supported by chemo-mineralogical characterization obtained by SEM-EDS. The fragments examined consist of a matrix of enstatite, plagioclase, with minor phases such as sulfides, oxides, and phosphides. Only one relict chondrule was observed that consists of a radial pyroxene with enstatite composition, Na plagioclase and silica mesostasis. SEM-EDS analyses reveal that the average composition of pyroxene and plagioclase is (En98.4 Fs0 Wo1.6) and (Ab80 An12 Or8), respectively. The minor phases found are daubréelite, schreibersite, oldhamite, troilite, graphite, tiny kamacite grains survived to the weathering, and N-bearing oxide. In addition to primary phases, terrestrial products as jarosite and halite were found. Kamacite appears variably oxidized. HR-SEM images reveal resorption features as well as rounded etch pits on the surfaces of daubréelite, holes on plagioclase and scalloped enstatite crystals. The μ-CT measurements show an uneven porosity with an average percentage of about 15% that consists averagely of open pores (12%) and closed pores (3%) with irregular to round shapes. The methodological approach based on volumetric investigation provides information about the spatial distribution, volume percentage and shape of voids and mineralogical phases with different density and adds new elements about the origin of porosity in this meteorite
The terminal velocity of volcanic particles with shape obtained from 3D X-ray microtomography
Full text linkNew experiments of falling volcanic particles were performed in order to define terminal velocity models applicable in a wide range of Reynolds number Re. Experiments were carried out with fluids of various viscosities and with particles that cover a wide range of size, density and shape. Particle shape, which strongly influences fluid drag, was measured in 3D by High-resolution X-ray microtomography, by which sphericity Φ3D and fractal dimension D3D were obtained. They are easier to measure and less operator dependent than the 2D shape parameters used in previous papers. Drag laws that make use of the new 3D parameters were obtained by fitting particle data to the experiments, and single-equation terminal velocity models were derived. They work well both at high and low Re (3 × 10− 2 < Re < 104), while earlier formulations made use of different equations at different ranges of Re. The new drag laws are well suited for the modelling of particle transportation both in the eruptive column, where coarse and fine particles are present, and also in the distal part of the umbrella region, where fine ash is involved in the large-scale domains of atmospheric circulation. A table of the typical values of Φ3D and D3D of particles from known plinian, subplinian and ash plume eruptions is presented. Graphs of terminal velocity as a function of grain size are finally proposed as tools to help volcanologists and atmosphere scientists to model particle transportation of explosive eruptions
Percutaneous edge-to-edge repair as a bailout option to treat Iatrogenic leaflet perforation
No full textAn 80-year-old man was referred to our center for heart failure and severe degenerative mitral regurgitation (MR). Transesophageal echocardiography revealed severe MR due to anterior leaflet prolapse, mainly in its central portion (A2) in the context of fibroelastic deficiency
Long-term hazard of pyroclastic density currents at Vesuvius (Southern Italy) with maps of impact parameters
No full textThe hazard of pyroclastic density currents (PDCs) at Vesuvius is investigated by analysing deposits from past eruptions. No specific eruption was chosen as representative of the hazard of PDCs, and the analysis is extended to all the eruptions that left substantial deposits on the ground. Based on the stratigraphic evidence, we assume that at Vesuvius the currents are bipartite, with a highly concentrated basal part, which was fed from the collapse of the eruptive fountain on the ground, and an overlying part generated by the expulsion of gas and fine particulate matter that fed a dilute and turbulent shear flow. Dynamic pressure, particle volumetric concentration, temperature, and flow duration are hazardous characteristics of PDCs that can impact buildings and population and are defined here as impact parameters. They have been calculated by means of an implementation of the PYFLOW code, which uses the deposit particle characteristics as input. The software searches for the probability density function of impact parameters. The 84th percentile has been chosen as a safety value of the expected impact in the long term (50 years). There is no correlation between eruption size and impact parameters. Maps have been constructed by interpolation of the safety values calculated at various points over the dispersal area, and they show how impact parameters change as a function of distance from the volcano. The maps are compared with the red zone, which is the area that the National Department of the Italian Civil Protection has declared to be evacuated under conditions of an impending eruption. The capacity of currents to damage buildings and population is discussed for both the highly concentrated part and the diluted one
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
The grain size dependency of vesicular particle shapes strongly affects the drag of particles. First results from microtomography investigations of Campi Flegrei fallout deposits
No full textAcknowledging the grain size dependency of shape is important in volcanology, in particular when dealing with tephra produced and emplaced during and after explosive volcanic eruptions. A systematic measurement of the tridimensional shape of vesicular pyroclasts of Campi Flegrei fallout deposits (Agnano-Monte Spina, Astroni 6 and Averno 2 eruptions) varying in size from 8.00 to 0.016 mm has been carried out by means of X-Ray Microtomography. Data show that particle shape changes with size, especially for juvenile vesicular clasts, since it is dependent on the distribution and size of vesicles that contour the external clast outline. Two drag laws that include sphericity in the formula were used for estimating the dependency of settling velocity on shape. Results demonstrate that it is not appropriate to assume a size-independent shape for vesicular particles, in contrast with the approach commonly employed when simulating the ash dispersion in the atmosphere.Acknowledging the grain size dependency of shape is important in volcanology, in particular when dealing with tephra produced and emplaced during and after explosive volcanic eruptions. A systematic measurement of the tridimensional shape of vesicular pyroclasts of Campi Flegrei fallout deposits (Agnano-Monte Spina, Astroni 6 and Averno 2 eruptions) varying in size from 8.00 to 0.016 mm has been carried out by means of X-Ray Microtomography. Data show that particle shape changes with size, especially for juvenile vesicular clasts, since it is dependent on the distribution and size of vesicles that contour the external clast outline. Two drag laws that include sphericity in the formula were used for estimating the dependency of settling velocity on shape. Results demonstrate that it is not appropriate to assume a size-independent shape for vesicular particles, in contrast with the approach commonly employed when simulating the ash dispersion in the atmosphere. (C) 2018 Elsevier B.V. All rights reserved
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
PYFLOW_2.0: a computer program for calculating flow properties and impact parameters of past dilute pyroclastic density currents based on field data
Full text linkThis paper presents PYFLOW_2.0, a hazard tool for the calculation of the impact parameters of dilute pyroclastic density currents (DPDCs). DPDCs represent the dilute turbulent type of gravity flows that occur during explosive volcanic eruptions; their hazard is the result of their mobility and the capability to laterally impact buildings and infrastructures and to transport variable amounts of volcanic ash along the path. Starting from data coming from the analysis of deposits formed by DPDCs, PYFLOW_2.0 calculates the flow properties (e.g., velocity, bulk density, thickness) and impact parameters (dynamic pressure, deposition time) at the location of the sampled outcrop. Given the inherent uncertainties related to sampling, laboratory analyses, and modeling assumptions, the program provides ranges of variations and probability density functions of the impact parameters rather than single specific values; from these functions, the user can interrogate the program to obtain the value of the computed impact parameter at any specified exceedance probability. In this paper, the sedimentological models implemented in PYFLOW_2.0 are presented, program functionalities are briefly introduced, and two application examples are discussed so as to show the capabilities of the software in quantifying the impact of the analyzed DPDCs in terms of dynamic pressure, volcanic ash concentration, and residence time in the atmosphere. The software and user’s manual are made available as a downloadable electronic supplement
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