1,720,966 research outputs found
Modeling clinopyroxene and plagioclase growth kinetics at Mt. Etna and Stromboli: a time-integrated, polybaric and polythermal perspective
Full text linkBasaltic volcanoes (e.g., Mt. Etna, Stromboli, Hawaii, etc.) are characterized by a range of effusive to explosive activities with variable intensity, which can pose different type of threats to local populations. Challenges in modern volcanology and petrology involve the attempt to constrain pre-eruptive magmatic processes, which provide the basis for volcanic hazard assessment. Although the recent literature has reported constant advancements in this respect, several key questions remain unanswered. Understanding how magma is stored, migrates and feeds eruption is not a trivial task, requiring for renewed improvements over the years. In this context, both textural maturation and compositional variability of minerals crystallizing in basaltic systems represent valuable sources of information to quantify the physio-chemical conditions experienced by magmas upon the effect of changing and complex plumbing system dynamics.
This study aims to provide new insights on the solidification behavior of mafic alkaline magmas erupted at Mt. Etna and Stromboli (Italy). Such open conduit volcanoes are characterized by the ubiquitous stability of clinopyroxene from mantle depths to shallow crustal levels. More evolved magmas are also saturated with plagioclase, especially at lower temperatures, melt-water contents, and pressures. Thus, clinopyroxene and plagioclase crystals represent powerful recorders of the intricate ascent dynamics explored by mafic alkaline magmas during their ascent paths towards the surface. By focusing on textural and chemical features of natural/synthetic clinopyroxene, plagioclase and coexisting glasses, I have provided new tools for interpreting polythermal-polybaric changes of magmas, together with several guidelines and a secure methodology to model pre- and syn-eruptive conditions. The temporal evolution of Etnean and Strombolian magmas has been also tracked via timescale modeling to better constrain the cooling-decompression paths of magmas rising and accelerating through the vertically extended, highly dynamic plumbing systems.
In the first part of this PhD thesis, I have experimentally explored the role of supersaturation and relaxation phenomena on clinopyroxene nucleation and growth processes, which affect the final crystal cargo of variably undercooled magmas. A certain degree of undercooling is pivotal to promote the growth and textural maturation of crystals. With increasing crystallization time, however, the crystal growth rate decreases as the system approaches to near-equilibrium conditions that minimize the effect of melt supersaturation. By quantifying the textural features of synthetic and natural crystals it has been possible to parameterize clinopyroxene growth kinetics under a broad range of isothermal-isobaric, decompression, and cooling conditions representative of crystallization scenarios typically encountered in open-conduit volcanoes. This model parameterization has been combined with the textural analysis of natural clinopyroxene crystals erupted during lava fountain events at Mt. Etna allowing to unlock timescale of growth for microphenocryst and microlite populations. The retrieved temporal information has been used to develop a new conceptual model for the timescale of magma dynamics recorded by the (dis)equilibrium textural evolution of clinopyroxene and for the rapid acceleration of magma ascending within the volcanic conduit, immediately before eruption at the vent.
A more comprehensive work, focusing on plagioclase textural and compositional features, characterized the second part of my PhD thesis with the aim to identify disparate aspects of plagioclase growth scenarios. Following the same approach discussed above, timescale of plagioclase crystallization from mafic alkaline magmas has been parameterized as a function of growth rate by integrating experimental (i.e., isothermal-isobaric, decompression, and cooling experiments) and natural textural data from literature. Timescales of eruptive processes at Mt. Etna and Stromboli volcanoes have been quantified by considering phenocryst/microphenocryst and microlite crystals growing during lava flow and explosive eruptions. Statistical methodologies have been employed to assess the correlation between plagioclase growth rate and other system parameters governing the crystallization process. Special attention has been paid to disambiguate the role of temperature and melt-H2O content on plagioclase chemical zoning patterns at Stromboli and Mt. Etna. By using plagioclase components and major cation substitution mechanisms, I have refined and readapted equilibrium, thermometric, and hygrometric models for future investigations
Kinetic aspects of major and trace element partitioning between olivine and melt during solidification of terrestrial basaltic materials
Full text linkOlivine is an important mineral phase in naturally cooled basaltic rocks. The morphology and composition of olivine are controlled by the cooling kinetics, and the mechanisms controlling the crystal growth directly impact the partitioning of elements. Cations partitioning between two phases may document on the crystallization conditions of rocks. Indeed, the major elements composing a mineral usually affect the chemical equilibrium of a system, while trace elements are sensitive to thermodynamic conditions and record the chemical reactions occurring in the system without modifying the bulk reactions. Therefore, major and trace elements partitioning between olivine and melt is greatly considered by petrologists investigating terrestrial rocks through the use of phases exchange reactions.
In this study I explore the partitioning of major and trace elements between olivine and basaltic melt under conditions encountered by magmas during natural solidification path, and the cation substitution and charge balance mechanisms controlling the cations entrance in the lattice site of olivine crystals. In this context, I have performed undercooling (-ΔT) and cooling rate (CR) experiments under relatively reduced environment (QFM-2) and atmospheric conditions using a tholeiitic basalt from Hawaii. Experiments started from the same superliquidus temperature of 1250 °C and was cooled at the rates of 4, 20, and 60 °C/h to the final temperature of 1175 and 1125 °C (-ΔT = 35 and 85 °C, respectively).
The olivine textural results indicate equilibrium at -ΔT = 35 °C, whereas strong disequilibrium occur at -ΔT = 85 °C. It is verified by the determination of the Fe-Mg exchange between olivine and melt. Indeed, low -ΔT experiments show bulk chemical equilibrium, while local equilibrium occurs at higher -ΔT. The forsterite content decreases as CR increases and a diffusive boundary layer develops in the melt next to the crystal interface. However, the principal cations (Mg, Fe, Mn, and Ca) enter the crystal lattice (M-site) at near-equilibrium, which is compatible with the establishment of a local equilibrium. Ti, Al, and P cations are incorporated in olivine lattice by substituting Si in the T-site. Ti incorporation is controlled by a homovalent substitution [TSi4+] ↔ [TTi4+], while heterovalent substitutions occur for Al and P, following [MMg2+, TSi4+] ↔ [MAl3+, TAl3+], and [2 TSi4+] ↔ [TP5+, TAl3+]. Although Cr is an octahedrally coordinated cation, it shows the same behaviour as cations entering in the T-site. Indeed, Cr is incorporated in the olivine lattice by forming a coupled substitution with a tetrahedrally coordinated cation [MMg2+, TSi4+] ↔ [MCr3+, TAl3+], in order to maintain the charge balance. To preserve the charge balance, disequilibrium incorporation of minor elements is governed by the same mechanisms that occur under equilibrium crystallization, which is consistent with interface local equilibrium
Ovarian carcinoma presenting with axillary lymph node metastasis: a case report
No full textOvarian cancer is usually limited to the abdomen and frequently remains confined. The occurrence of extrabdominal mestastases is unusual. In this report we describe a rare case of axillary involvement at initial presentation of ovarian cancer in a 48-year-old woman. The axillary mass was the only clinical abnormality. Cytological and histological findings, performed on axillary lymph nodes, showed the presence of psammoma bodies and specific immunohistochemical tumor markers (OC-125 and WTI), supporting the evidence of a metastatic axillary lymphadenopathy from ovarian cancer. Subsequently, chest and abdominopelvic computed tomography showed a right ovarian complex mass of 30 x 25 mm and biochemical tests showed high levels of CA 125. Surgical therapy was performed. Histology confirmed the diagnosis, evidencing a poorly differentiated serous-papillary carcinoma of the right ovary. In conclusion, cytological and histological findings can play a crucial role in suggesting the correct origin of a metastatic adenocarcinoma when the clinical presentation is atypical
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
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