1,720,976 research outputs found
Evidence of the Early Holocene eruptive activity of Volcán de Colima and the 8.2 kyr global climatic event in lacustrine sediments from a debris avalanche-dammed lake
Full text linkVolcán de Colima, one of the most active volcanoes in Mexico, experienced at least nine flank failures
during the last 30 000 years, with catastrophic effects on the environment that implies the formation of temporary
dams where lacustrine sediments accumulated for hundreds of years. These lacustrine sequences
preserve an exceptional record from which to reconstruct the effect of subsequent volcanic eruptions and, eventually,
contemporary environmental and climatic conditions. Here we analyse an Early Holocene lacustrine
sequence, named ‘Gypsum King’, which accumulated in a short-lived temporary lake, likely formed by
emplacement of the 10 755–11 230 cal years BP Mesa-Yerbabuena debris avalanche. Through detailed analysis
of the 1.8 m thick lacustrine sequence (14C ages, sulfur content, grain size), it was possible to identify the 8.2 kyr
global climate event and better constrain the Early Holocene main sub-plinian to plinian eruptions of Volcán de
Colima. The results presented here highlight the potential to explore sulfur content and abrupt change in grain
size in lacustrine sediments as additional proxies to better constrain eruptive phases in volcanic environments.
Finally, the Gypsum King sequence provides the first evidence of the 8.2 kyr global climate event along the
Eastern tropical Pacific Coast
Paleoproterozoic andesitic volcanism in the southern Amazonian craton, the Sobreiro Formation: New insights from lithofacies analysis of the volcaniclastic sequences
No full textThe Sobreiro Formation (SF) records one excellent and well-preserved example of subaerial Precambrian (ca. 1.88 Ga) volcanism on earth. It is located in the Sao Felix do Xingu region (SFX), in the eastern part of Path State, southern Amazonian craton, northern of Brazil. The high-K calcalkaline composition of the Sobreiro rocks indicates that this formation likely generated in an ocean-continent convergent margin. This paper documents the architecture of a series of basaltic-andesite to andesite and minor dacite lava flows and associated volcaniclastic rocks. These rocks are divided into primary and secondary lithotypes, depending if they resulted from a direct volcanic activity (pyroclastic) or reworked processes and massive to stratified, depending on the different transport and emplacement mechanisms. Primary lithofacies is formed of pyroclastic flow and surge deposits, volcanic breccias and welded ignimbrites; secondary volcaniclastic lithofacies consist of reworked debris. Mass-flows, hyperconcentrated flows and stream floods are interpreted as fluvial/alluvial deposits representing periods of stream and river reworking and re-establishment after an eruptive phase or an edifice failure event. These different lithofacies record the volcanic history of the Sobreiro Formation. A complex volcanic environment is thought to have existed with emission of large lava flows and explosive eruptions. The modern volcanological approach used here can serve as a model for the evolution of Precambrian volcano-sedimentary basins. Our approach sheds new light on the different processes operating on volcanic edifices and to constrain the depositional environment and thus geodynamic setting of Precambrian continental volcanic belts. (C) 2016 Elsevier B.V. All rights reserved
Ordering the res gestae: observations on the relationship between texts and images in Roman ‘historical’ representations
No full textThe purpose of this chapter is to examine the relationship between images and texts in the Roman ‘historical’ narrative. A letter that Lucius Verus addressed to Fronto about his Parthian war and the shipping of paintings and epistulae from the battlefield to Rome by Septimius Severus and Maximinus Thrax suggest a fruitful dialogue between the texts written by commanders on the field and the picturae commissioned by them to immediately celebrate their victories. Cicero’s epistulae to the Senate (Fam. 15.1–2) and a letter (Fam. 15.4) to Cato that the orator wrote when he was leading his only military campaign in Cilicia are the only surviving texts that really allow us to compare this type of swift and rhetorically less elaborate form of communication from the battlefield with the ‘historical’ friezes of the imperial age. They show remarkable commonalities with
figurative representations of wars such as the reference to suovetaurilia at the beginning of the campaign and the emphasis on challenging the ‘barbarian’ landscape. Indeed, the brevitas of these texts (litterae laureatae and the less sophisticated commentarii) also left much space for a strong figurative redevelopment of the storytelling, especially in the case of a carefully planned monument such as Trajan’s column. Moreover, in front of a monument like this, the observer was also free to follow different reading strategies in reconstructing his own ordo of the res gestae, as suggested by the importance of the vertical axis on the column itself or by Josephus’ description or, more correctly, by his perception of the ‘historical’ pegmata during the Jewish triump
Emplacement temperature estimation of the 2015 dome collapse of Volcán de Colima as key proxy for flow dynamics of confined and unconfined pyroclastic density currents
No full textThe recent 10th–11th of July 2015 Volcán de Colima eruption involved the collapse of the summit dome that breached to the south generating pyroclastic density currents (PDCs) along the Montegrande ravine on the southern flank of the volcano. Trees within the valley were buried, uprooted and variably transported by the PDCs, while the trees on the edges of the valley and on the overbanks, were mainly burned and folded. The emplacement temperature of valley confined and overbank PDC deposits were reconstructed using Partial Thermal Remanent Magnetization (pTRM) analysis of lithic clasts and Charcoal Reflectance analysis (Ro %) applied to the charred wood. A total of 13 sites were sampled for the pTRM study and 39 charcoaled wood fragments were collected for the charcoal optical analysis along the entire deposit length in order to detect temperature variation from proximal to distal zone. The result overlap from both data sets display a T max from ≃345°–385 °C in valley-confined area (from 3.5 to 8.5 km from the vent) and ≃170°–220 °C (from 8.0 to 10.5 km from the vent) in unconfined distal area. The emplacement temperature pattern along the 10.5 km long deposit appears related to the degree of topography confinement: valley confined and unconfined. In particular the valley confined setting is very conservative in terms of temperature, while the major drop occurs in a very narrow space where the PDC expanded over unconfined flat topography just at the exit of the main valley. This study represents the first attempt in determining the relationship between PDCs flow dynamics variation and topographic confining using deposit emplacement temperature as key proxy
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
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