1,721,160 research outputs found
Magma-carbonate interaction under dynamic conditions: experimental insights on crystallization kinetics and multiphase rheology
No full textMagma-carbonate interactions within volcanic plumbing systems are pivotal in shaping the chemical and physical properties of erupted magmas, with far-reaching implications for magma transport dynamics, crystallization, and eruption processes. This research focuses on the Somma-Vesuvius volcanic system (Italy), where assimilation of carbonate lithologies (e.g., limestone and dolostone) introduces CaO and MgO into magmatic melts, significantly altering their rheological behavior. Through a comprehensive experimental approach, this study investigates the effects of carbonate assimilation on melt viscosity, rheological evolution, and crystallization kinetics under varying thermal and deformation conditions. In the first phase, viscosity measurements were conducted on a phonotephritic melt from the 472 CE Pollena eruption, doped with CaO and CaO+MgO to simulate carbonate assimilation. High-temperature (1150–1400 °C) and low-temperature (640–760 °C) viscosity experiments were performed using concentric cylinder viscometry, micropenetration techniques, and differential scanning calorimetry. The experimental results revealed a pronounced viscosity reduction with CaO doping, exceeding the effects of CaO+MgO, highlighting the dominant role of CaO in modifying melt rheology. A viscosity/temperature crossover was observed: above 750 °C, doped melts exhibited significantly lower viscosities than the pristine melt, while below this threshold, the trend reversed, with doped melts becoming more viscous than the undoped counterpart. The formation of nanoheterogeneities, detected during low-temperature experiments, emerged as a critical factor influencing rheological behavior. Raman spectroscopy, integrated with viscosity data, provided detailed insights into the structural changes within the melt, allowing for the quantification of the impact of these heterogeneities on viscosity. Additionally, Brillouin spectroscopy was employed to refine the prediction of high-temperature viscosities, offering a more robust alternative to empirical viscosity models, which consistently failed to reproduce the experimental data for melts with higher levels of carbonate contamination. These findings provide a framework for understanding the impact of carbonate assimilation on key processes in volcanic plumbing systems. The changes in viscosity caused by CaO and CaO+MgO doping influence magma mobility and the potential for hybrid magma formation, with implications for the mixing versus mingling behavior of magmas.. The second phase explored the combined effects of carbonate assimilation and shear strain rate on the rheological evolution of phonotephritic melts, incorporating isothermal static and deformation experiments and flash differential scanning calorimetry. The results demonstrated that carbonate assimilation promotes crystallization and the development of a mineral framework under dynamic conditions. Textural analyses revealed that residual glasses from undoped and low-doped melts resembled juvenile materials from Somma-Vesuvius eruptions, while highly doped samples resembled those from skarn xenoliths. Crystallization kinetics and residual glass viscosity were better characterized using a novel calorimetry-based approach, which proved more reliable than chemical-based models. Distinct deformation regimes were identified: viscous flow in undoped melts, indicative of uniform deformation, and non-homogeneous flow in doped melts, marked by shear localization, stress drops, and brittle rupture. Increasing shear rates and carbonate assimilation amplified the development of crystal networks, leading to non-Newtonian behavior. Mechanical heterogeneities introduced by crystal networks disrupted uniform flow, promoting localized stress and premature crack formation. This resulted in narrower viscosity ranges compared to pure viscous models, emphasizing the complexity of rheological behavior under stress conditions. The interplay between carbonate assimilation and deformation facilitated the recycling of skarn shells and enhanced magma contamination at the margins of magma chambers. This dissertation advances the understanding of magma-carbonate interactions by linking compositional, thermal, and rheological properties to physical processes in volcanic systems
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
How complex is the obscuration in active galactic nuclei? new cluesfrom the suzaku monitoring of the x-ray absorbers in ngc 7582
No full textWe present the results of a Suzaku monitoring campaign of the Seyfert 2galaxy, NGC 7582. The source is characterized by very rapid (ontimescales even lower than a day) changes of the column density of aninner absorber, together with the presence of constant componentsarising as reprocessing from a Compton-thick material. The best-fittingscenario implies important modifications to the zeroth-order view ofUnified Models. While the existence of a pc-scale torus is needed inorder to produce a constant Compton reflection component and an ironKa-emission line, in this Seyfert 2 galaxy this is not viewed along theline of sight. On the other hand, the absorption of the primarycontinuum is due to another material, much closer to the black hole,roughly at the distance of the broad-line region, which can produce theobserved rapid spectral variability. On top of that, the constantpresence of a 10(22) cm(-2) column density can be ascribed to thepresence of a dust lane, extended on a galactic scale, as previouslyconfirmed by Chandra. There is now mounting evidence that complexity inthe obscuration of active galactic nuclei (AGNs) may be the rule ratherthan the exception. We therefore propose to modify the UnificationModel, adding to the torus the presence of two furtherabsorbers/emitters. Their combination along the line of sight canreproduce all the observed phenomenology
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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