124,831 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
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
Clinopyroxene Growth and Dissolution Rates: High-Pressure Investigation on a Primitive Alkaline Basalt from the Campi Flegrei Volcanic District (South Italy)
No full textWith the aim to investigate the influence of time, temperature, water content and pressure on clinopyroxene growth and dissolution rate, we performed crystallization and dissolution experiments on a K-basaltic rock from Procida island (Campi Flegrei Volcanic District, south Italy). Crystallization experiments were performed at anhydrous and hydrous (1 ≤ H2O ≤ 4 wt.%) conditions, pressure of 0.8 GPa, temperature between 1030 °C and 1250 °C and dwell time between 0.25 and 9 hours. Crystallization experiments show that time is the factor that most affects the growth rate compared to temperature and water content. Clinopyroxene growth rate, indeed, varies from 10-7 to 10-8 cm/s and it reaches the maximum value in the shortest experiments (0.25 h) while it decreases increasing time (9 h). Comparing our high-pressure growth rates with the low-pressure ones available in literature related to clinopyroxene, it was possible to note that pressure does no affect the growth rate. Indeed, all the considered growth rates show similar values that vary from 10-5 to 10-9 cm/s regardless of pressure but as a function of time. Moreover, partition coefficients based on the crystal-liquid exchange demonstrate that the chemistry of minerals progressively approaches to equilibrium from the shortest to long-lasting experiments, putting forward the latter as representative of the ideal condition of crystallization in a deep magmatic reservoir. Short experiments, instead, could be representative of ascent mechanisms in disequilibrium conditions and quick times. Dissolution experiments, instead, were carried out at high pressure (0.8-2 GPa), superliquidus temperatures and different dwell times by using the seeding technique. Preliminary results show that clinopyroxene dissolution rate varies from 10-2 to 10-7 cm/s, highlighting an influence of temperature and time with respect to pressure
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
Clinopyroxene growth rates at high pressure. Constraints on magma recharge of the deep reservoir of the Campi Flegrei volcanic district (south Italy)
No full textClinopyroxene growth rates were experimentally determined in a K-basaltic rock from Campi Flegrei Volcanic District (south Italy). The primary objective was to provide constraints on the clinopyroxene crystallization kinetics at high pressure: we carried out a series of experiments at 0.8 GPa, 1030–1250 °C, 1 ≤ H2O ≤ 4 wt.%, with durations of 0.25, 3, 6 and 9 h. Overall, growth rate reaches a maximum value in the shortest experiments (~ 3·10−7 cm·s−1), decreasing to ~ 1·10−8 cm·s−1 in the longest duration runs. Temperature and water content do not seem to significantly affect the growth rate. Moreover, partition coefficients based on the crystal-liquid exchange show that mineral chemistry progressively approaches equilibrium with increasing run duration. Furthermore, to estimate the magma recharge of the deep reservoirs, we combined the determined growth rates with data from thermobarometry and from crystal size distribution analyses of clinopyroxenes in the most primitive scoria clasts of the Campi Flegrei Volcanic District (CFVD). We obtained a minimum residence time of ~ 5 months for the larger clinopyroxene population, and an ascent velocity of ~ 0.5·10−4 m·s−1 for the CFVD K-basaltic magma. The smaller clinopyroxene phenocrysts and microlite populations, however, suggest that the late stage of Procida magma crystallization took place in disequilibrium conditions
Figure 5 in Patterns of spatial variability of mobile macro-invertebrate assemblages within a Posidonia oceanica meadow
No full textFigure 5. Percentage pseudo-variance components of mobile macro-invertebrate assemblages of Posidonia oceanica meadow at (a) shallow, (b) intermediate and (c) deep stands.Published as part of Bedini, R., Bedini, M., Bonechi, L. & Piazzi, L., 2015, Patterns of spatial variability of mobile macro-invertebrate assemblages within a Posidonia oceanica meadow, pp. 2559-2581 in Journal of Natural History 49 (41) on page 2574, DOI: 10.1080/00222933.2015.1021872, http://zenodo.org/record/400081
Uncommon K-foiditic magmas. The case study of Tufo del Palatino (Colli Albani Volcanic District, Italy)
Full text linkLeucititic rocks, K-foiditic in composition are volumetrically important in the Colli Albani (also known as Alban Hills)
volcanic district (Central Italy)especially during the most explosive phases of activity (>200 km
3
). The Colli Albani
tephra in distal (>500 km) deposits indicates that K-foiditic magma chambers fed large explosive eruptions
(i.e., tens of km
3
of pyroclastic rocks). Major oxides, trace elements and Raman spectra were measured on the glasses
and minerals occurring in the K-foiditic scoria clasts of the~530 kyr-old Tufo del Palatino, erupted in the Colli Albani
volcanic district. The Colli Albani pre-eruptive magmatic system is characterized by theaH2O<1andhighCO2activity in the melt, as testified by the CO3in the clinopyroxene melt inclusions, by the early crystallization of CO3-bearing
apatite and by the high CO2activity in the free volatile phase that led to crystallization of calcium carbonate in the
scoria clast vesicles. The K-foiditic magmas plot on the Cpx + Lc + melt divariant surface of the Ol-Cpx-Lc-MelH2O-CO2, P≥0.2 GPa andT≤1100 °C. The assimilation of cold carbonate by hot magmas is an important opensystem process allowing the establishment ofaH20< 1 condition in the volatile-rich, Colli Albani magma chambers
where the stabilityfields of the olivine and phlogopite are reduced infavor of clinopyroxene and leucite. Trace element modelling indicates large amount of carbonate assimilation (~12.4 wt%) involved in the differentiation process
that origins the K-foiditic magmas starting from a K-rich, phonotephritic parental magma. The large amount of assimilate carbonate is consistent with the peculiar distribution of the latent heat across the crystallization interval of
the phonotephritic parental magma. The isenthalpic assimilation process is very efficient in the phonotephritic
magma because the crystallization of clinopyroxene and leucite in equilibrium with a K-foiditic melt proceeds
over a relatively large temperature interval (>200 °C) and the K-foiditic melt shows low viscosity (10
4
Pa·s at
1000 °C). Actually, the low melt viscosity, that increases the growth rate, and the large temperature interval of crystallization are intrinsic factors that increase the release ofthe latent heat of crystallization from the phonotephritic
parental magma. Extrinsic factors enhancing the assimilation process efficiency are the thickness (>4 km) and the
depth (down to 5–7 km) of the carbonate substrate in the Colli Albani volcanic distric
Interaction of Quercetin and its conjugate Quercetin 3-b-D-glucoside with Albumin Determined by NMR Relaxation Data
No full textNMR methodology has been developed in order to study phytochemical-macromolecular receptor interactions. This
approach is based on the analysis of proton selective spin–lattice relaxation rate enhancements of the ligand in the
presence of the macromolecule, to calculate an affinity index, [A]
, related to the strength of the interaction process.
This index has been modified by normalization to the relaxation rate of the free ligand, in order to take into account the
effects of motional anisotropies and different proton densities. The normalized affinity index, [A
L
T
N
]
, isolates the contribution
due to a decrease in the ligand dynamics caused by the binding with the protein. This methodology has been applied
to the interaction between two flavonoids (quercetin, 1, and quercetin 3-O-D-glucopyranoside,
2) and bovine serum
albumin (BSA). The calculated values of the affinity indexes and thermodynamic equilibrium constants suggested a
much stronger capacity of 1 to interact with BSA when compared with its glucosylated derivative, 2
Pragmatic Case Studies as a Source of Unity in Applied Psychology
No full textTo unify or not to unify applied psychology: that is the question. In this article we review pendulum swings in the historical efforts to answer this question—from a comprehensive, positivist, “top-down,” deductive yes between the 1930s and the early 60s, to a postmodern no since then. A rationale and proposal for a limited, “bottom-up,” inductive yes in applied psychology is then presented, employing a case-based paradigm that integrates both positivist and postmodern themes and components. This paradigm is labeled “pragmatic psychology” and, its specific use of case studies, the “Pragmatic Case Study Method” (“PCS Method”). We call for the creation of peer-reviewed journal-databases of pragmatic case studies as a foundational source of unifying applied knowledge in our discipline. As one example, the potential of the PCS Method for unifying different angles of theoretical regard is illustrated in an area of applied psychology, psychotherapy, via the case of Mrs. B. The article then turns to the broader historical and epistemological arguments for the unifying nature of the PCS Method in both applied and basic psychology.Peer reviewe
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