1,720,966 research outputs found
Eruption History and Depositional Processes of the Campanian Ignimbrite Based on its Lithofacies Architecture
No full textLarge ignimbrites are the product of high-temperature pyroclastic density currents (PDCs) spreading over vast regions and representing one of the most devastating natural catastrophes in human history. We present a detailed examination of the ignimbrite sequence, emplaced from 10 to 80 km from the source area, of the Campanian Ignimbrite (CI) eruption, a caldera-forming Plinian event, occurred 39 ka ago, whose PDC spread over a huge area from Campi Flegrei (Italy). The CI sequence comprises seven lithofacies based upon the different sedimentary structures: 1) massive tuff or lapilli tuff; 2) diffuse-stratified tuff; 3) fines-poor lithic lapilli tuff; 4) pumice-rich lapilli tuff; 5) lenses of pumice lapilli; 6) cross-stratified tuff; 7) accretionary lapilli-bearing. Three main vertical facies association have been identified: a) fines-poor lithic lapilli to diffuse stratified or massive or inverse graded; b) cross-stratified or diffuse stratified to massive or normal- to inverse-graded; c) massive to inverse graded. These vertical variations define a dominant trend during which the concentration into the boundary layer was progressively increasing, at a fixed point, and records the increasing importance of fluid-escape condition with time. Distribution of lithofacies in the different units shows a remarkable lack of lateral variation at regional scale. This suggests an overall uniform behavior of the PDC. A temporal evolution, from traction- to granular- or fluid-escape- dominated mechanisms, records unsteadiness conditions and contrast with persistent lateral facies reflecting an overall uniform behavior of the current. Stratigraphical and chemical evidences indicate the presence of a bypass zone around the caldera
Dynamics of large pyroclastic currents inferred by the internal architecture of the Campanian Ignimbrite
No full textLarge ignimbrites are the product of devastating explosive eruptions that have repeatedly impacted climate and life on global scale. The assemblage of vertical and lateral lithofacies variations within an ignimbrite sheet, its internal architecture, may help to determine how the parental pyroclastic current evolves in time and space. The 39 ka Campanian Ignimbrite eruption, vented from Campi Flegrei caldera, laid down a thick ignimbrite over an area of thousands of km2. A detailed reconstruction of the vertical and lateral variation of the seven lithofacies recognised in the ignimbrite medial sequence constrains the behaviour of this event. The pyroclastic current flowed over a wide area around Campi Flegrei without depositing (bypass zone), and inundated a huge area during most of the paroxysmal, waxing phase, emplacing a mainly incipiently- to strongly- welded ignimbrite. Following this waxing phase, the leading edge of the current retreated back towards the source as the current waned, impacting a progressively smaller area and leaving an unconsolidated ash and lapilli deposit, later lithified. Our study illustrates how large pyroclastic currents can evolve in time and space and the importance of both internal (eruptive and transport mechanisms) and external (topography, surficial water and rain) factors in governing their behaviour
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Pompeii to Stabiae: downwind versus substrate-induced variations of the AD 79 Vesuvius fall deposits and their impact on human settlements
No full textThe AD 79 Vesuvius eruption destroyed the famous towns of Pompeii and Herculaneum located 5 and 10 km from the vent, respectively. A more distant town, Stabiae, where Pliny the Elder found his death, was also buried by pyroclastic material. Recent excavations carried out in collaboration with the Archaeological Park of Pompeii, both in Pompeii and in the imposing Stabian villas, have shown the products of the AD 79 eruptive sequence that covered these Roman settlements. During the excavation phases, ephemeral sections are exposed and then removed as the excavation proceeds. The presence on the excavation sites of a team of volcanologists allows the acquisition and evaluation of all stratigraphic and sedimentological data. The discovery of thick sequences of reworked material accumulated during previous excavations, testifies for the presence of underground tunnels dug for the Royal House of Bourbon. The deposit of pumice lapilli which forms the lower part of the pyroclastic succession, was studied in detail to define the downwind variations of its sedimentological features and how these were influenced by urban structures. At Pompeii, the AD 79 fall deposit consists of a lower white to grey pumice lapilli bed (units A and B) showing a remarkable thickness variation ranging from 0 to 4.5 metres. Two ash layers (units C1 and C2) are interstratified at the top of unit B. The internal structure of the pumice lapilli fall deposit is weakly stratified, showing sub-horizontal layering when observed in open areas (peristyles), or appearing strongly stratified with coarse to fine layering when the pumice lapilli deposit forms piles with steep layers. At Stabiae, this deposit ranges in thickness from 0 to 2 metres and is not interstratified by ash horizons. Its internal structure shows the same types of stratification observed at Pompeii. Several roofing-tiles, either intact or in fragments, were recovered at various stratigraphic heights in the lapilli deposit at Pompeii and Stabiae. This study shows that downwind variations in lapilli fall deposits are strongly influenced by an articulated substrate like that of urban structures. During the first phase of the AD 79 eruption, several roof collapses occurred, as evidenced by abundant debris and tiles found in the lapilli fall deposit. The presence of steep roofs allowed the falling pumice clasts to roll and slide down and then accumulate in the impluvium areas and in the alleys, attaining greater thicknesses with respect to deposits accumulated in open areas. This rolling produced a selection by size and density of the pyroclasts, thus forming a well-stratified deposit. At the same time, under the canopies the fall deposit thins dramatically towards the sheltered corridors. It is evident that the urban structures affect the structure of the deposit much more than the variations induced by the increase in the distance from the eruptive vent
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