A new test for equilibrium based on clinopyroxene-melt pairs: Clues on the solidification temperatures of Etnean alkaline melts at post-eruptive conditions

We have performed new global regression analyses to calibrate a model of equilibrium between clinopyroxene and co-existing melt. Then we have applied this model to a restricted but important range of clinopyroxene and melt compositions from Mt. Etna volcano. The degree of disequilibrium is determined through the comparison between components “predicted” for clinopyroxene via regression analyses of clinopyroxene-liquid pairs in equilibrium conditions, with those “measured” in the analyzed crystals. The model is tested using compositions not included into the calibration dataset, i.e., clinopyroxene-melt pairs obtained from equilibrium and cooling rate experiments conducted at ambient pressure on an Etnean trachybasalt. The experiments were duplicated at the NNO+1.5 and QFM oxygen buffering conditions estimated for magmas at Mt. Etna. Both equilibrium and disequilibrium clinopyroxene-melt pairs from the experiments were also used as input data for one of the most recent thermometers based on the Jd-DiHd exchange reaction. Results from calculations indicate that, under rapid cooling rate conditions, clinopyroxenes do not equilibrate with the melt. Consequently, the thermometers predict higher crystallization temperatures compared to the final experimental temperature, prior to rapid quenching of the experiment. The systematic difference between expected and measured compositions and temperatures allows us to calibrate a model that describes undercooling based on disequilibrium exchange reactions. We use this new tool to estimate the thermal history of naturally cooled lava flows and dikes at Mt. Etna volcano

COMPORTAMENTO AD ALTA PRESSIONE DI TRASDUTTORI PIEZOELETTRICI PER APPLICAZIONI DI GEOFISICA SPERIMENTALE

L’investigazione del comportamento acustico di campioni di roccia implica l’uso di trasduttori piezoelettrici [Spinelli et al., 2009], sia in uso attivo (eccitazione e rilevazione) che passivo (rilevazione delle onde elastiche generate da fenomeni di fratturazione). In alcuni casi vengono imposte elevate pressioni per simulare le condizioni di sconfinamento del campione di roccia in profondità, utilizzando un liquido o un gas. La natura dei trasduttori piezoelettrici suggerisce che essi non debbano soffrire molto in ambienti in cui la variazioni di pressione o la pressione di esercizio sia un elemento non trascurabile e possono essere utilizzati in tali condizioni senza particolari precauzioni con evidenti vantaggi nella semplificazione del set-up sperimentale. Questa nota è la descrizione delle misure condotte per caratterizzare dei trasduttori piezoelettrici, nell’intervallo di pressione di interesse (0 - 1000 atm), da utilizzare per scopi sperimentali nell’ambito del progetto europeo ERC Starting Grant Project GLASS InteGrated Laboratories to investigate the mechanics of ASeismic vs. Seismic faulting. Per fare ciò due trasduttori sono stati incollati direttamente tra loro in modo da realizzare un quadripolo, con una porta d’ingresso e una di uscita, e ne è stata rilevata la caratteristica ingresso – uscita al variare della frequenza. Per il rilevamento delle caratteristiche elettriche sono stati usati differenti strumenti di misura: un generatore di segnali, un oscilloscopio e un analizzatore di reti vettoriale. Per imporre sui campioni una pressione controllata è stato allestito un apparato meccanico dedicato, formato da un insieme pistone-cilindro all’interno del quale viene alloggiata la coppia di trasduttori incollati. Nel cilindro viene inserito olio (adeguatamente incomprimibile ed elettricamente isolante) come vettore di pressione; la spinta sul pistone viene esercitata attraverso una pressa idraulica. Una particolare cura è stata posta nella costruzione del passacavo a tenuta per alte pressioni. Nei paragrafi che seguono verranno dapprima descritti i trasduttori usati per gli esperimenti e l’apparato meccanico, quindi si passerà alla presentazione delle misure effettuate in varie condizioni e con i vari strumenti

On the relevance of uncorrelated Lorentzian pulses for the interpretation of turbulence in the edge of magnetically confined toroidal plasmas

Recently, it has been proposed that the turbulent fluctuations measured in a linear plasma device could be described as a superposition of uncorrelated Lorentzian pulses with a narrow distribution of durations, which would provide an explanation for the reported quasi-exponential power spectra. Here, we study the applicability of this proposal to edge fluctuations in toroidal magnetic confinement fusion plasmas. For the purpose of this analysis, we introduce a novel wavelet-based pulse detection technique that offers important advantages over existing techniques. It allows extracting the properties of individual pulses from the experimental time series, and quantifying the distribution of pulse duration and energy, as well as temporal correlations. We apply the wavelet technique to edge turbulent fluctuation data from the W7-AS stellarator and the JET tokamak, and find that the pulses detected in the data do not have a narrow distribution of durations and are not uncorrelated. Instead, the distributions are of the power law type, exhibiting temporal correlations over scales much longer than the typical pulse duration. These results suggest that turbulence in open and closed field line systems may be distinct and cast doubt on the proposed ubiquity of exponential power spectra in this context.Comment: 10 pages, 4 figure

Metasomatism induced by alkaline magma in the upper mantle of northern Victoria Land (Antarctica): an experimental approach

Magma generation in the Ross Sea system is related to partial melting of strongly metasomatised mantle sources where amphibole most probably plays a crucial role. In this context, metasomatism induced by a mela-nephelinite melt in lithospheric mantle of the Mt. Melbourne Volcanic Province (northern Victoria Land – NVL, Antarctica) was investigated experimentally studying the effects of melt interaction with lherzolite at 1.5-2.0 GPa and T=975-1300°C, and wehrlite at 1.0 GPa and T=1050-1250°C. The experiments were designed to induce melt infiltration into the ultramafic rocks. The observed modifications in minerals are compared with those found in mantle xenoliths from NVL. The effects of metasomatic modifications are evaluated on the basis of run temperature, distance from the infiltrating melt and on the diffusion rates of chemical components. Both in lherzolite and wehrlite, clinopyroxene exhibits large compositional variations ranging from primary diopside to high Mg-Cr-(Na) augitic and omphacitic clinopyroxenes in lherzolite, and to low Mg and high Ti-Al-Fe-Na augites in wehrlite. Olivine (in wehrlite) and spinel (in lherzolite) also result compositionally modified, the former shows enrichments in Fe, the latter displays a higher Cr/(Cr+Al) ratio. The systematic variations in mineral compositions imply modifications of the chemistry of the infiltrating melt as recorded by the glass veinlets and patches observed in some charges. In experiments involving wehrlite paragenesis, the glass composition approaches that of melt patches associated to both amphibole-free and amphibole-bearing natural samples, and is related to olivine+clinopyroxene crystallisation coupled with primary clinopyroxene dissolution at the contact between the metasomatising melt and the solid matrix. Even if amphibole crystallisation was not attained in the experiments, we were able to explain the occurrence of amphibole in the natural system considering that in this case a hot metasomatising melt infiltrates a cooler matrix

Respiratory inhibition of isolated mammalian mitochondria by salivary antifungal peptide histatin-5

Histatin-5 is a peptide secreted in the human saliva, which possesses powerful antifungal activity. Previous studies have shown that this peptide exerts its candidacidal activity, through the inhibition of both mitochondrial respiration and the formation of reactive oxygen species. The purpose of the present study was to investigate the biological consequences of histatin-5 action on mammalian mitochondria to verify if the toxic mechanism exerted on mitochondria from Candida albicans is an exclusive for fungal cells. Moreover, hypothesising that the damage exerted on mitochondria may induce programmed cellular death pathways, we evaluated two main markers of apoptosis: the mitochondrial membrane potential (DeltaPsi) and the release of cytochrome c. The results obtained show that exposure of isolated mammalian mitochondria to histatin-5 determines: (i) a large inhibition of the respiratory chain at the level of complex 1, (ii) a slight decrease in the mitochondrial membrane potential, and (iii) no release of cytochrome c. (C) 2003 Elsevier Inc. All rights reserved

Motor and higher‐order functions topography of the human dentate nuclei identified with tractography and clustering methods

Deep gray matter nuclei are the synaptic relays, responsible to route signals between specific brain areas. Dentate nuclei (DNs) represent the main output channel of the cerebellum and yet are often unexplored especially in humans. We developed a multimodal MRI approach to identify DNs topography on the basis of their connectivity as well as their microstructural features. Based on results, we defined DN parcellations deputed to motor and to higher-order functions in humans in vivo. Whole-brain probabilistic tractography was performed on 25 healthy subjects from the Human Connectome Project to infer DN parcellations based on their connectivity with either the cerebral or the cerebellar cortex, in turn. A third DN atlas was created inputting microstructural diffusion-derived metrics in an unsupervised fuzzy c-means classification algorithm. All analyses were performed in native space, with probability atlas maps generated in standard space. Cerebellar lobule-specific connectivity identified one motor parcellation, accounting for about 30% of the DN volume, and two non-motor parcellations, one cognitive and one sensory, which occupied the remaining volume. The other two approaches provided overlapping results in terms of geometrical distribution with those identified with cerebellar lobule-specific connectivity, although with some differences in volumes. A gender effect was observed with respect to motor areas and higher-order function representations. This is the first study that indicates that more than half of the DN volumes is involved in non-motor functions and that connectivity-based and microstructure-based atlases provide complementary information. These results represent a step-ahead for the interpretation of pathological conditions involving cerebro-cerebellar circuits

Vector casting for noise reduction

We report a new method for the reduction of noise from spectra. This method is based on casting vectors from one data point to the following data points of the noisy spectrum. The noise‐reduced spectrum is computed from the casted vectors within a margin that is identified by an envelope‐finder algorithm. We compared here the presented method with the Savitzky–Golay and the wavelet transform approaches for noise reduction using simulated Raman spectra of various signal‐to‐noise ratios between 1 and 25 dB and experimentally acquired Raman spectra. The method presented here performs well compared with the Savitzky–Golay and the wavelets‐based denoising method, especially at small signal‐to‐noise ratios and furthermore relies on a minimum of human input requirements

Carbonate assimilation in magmas: a reappraisal based on experimental petrology

The main effect of magma-carbonate interaction on magma differentiation is the formation of a silica-undersaturated, alkali-rich residual melt. Such a desilication process was explained as the progressive dissolution of CaCO3 in melt by consumption of SiO2 and MgO to form diopside sensu stricto. Magma chambers emplaced in carbonate substrata, however, are generally associated with magmatic skarns containing clinopyroxene with a high Ca-Tschermak activity in their paragenesis. Data are presented from magma-carbonate interaction experiments, demonstrating that carbonate assimilation is a complex process involving more components than so far assumed. Experimental results show that, during carbonate assimilation, a diopside-hedenbergite-Ca-Tschermak clinopyroxene solid solution is formed and that Ca-Tschermak/diopside and hedenbergite/diopside ratios increase as a function of the progressive carbonate assimilation. Accordingly, carbonate assimilation reaction should be written as follows, taking into account all the involved magmatic components: CaCO3solid+SiO2melt+MgOmelt+FeOmelt+Al2O3melt → (Di-Hd-CaTs)sssolid+CO2fluid The texture of experimental products demonstrates that carbonate assimilation produces three-phases (solid, melt, and fluid) whose main products are: i) diopside-hedenbergite-Ca-Tschermak clinopyroxene solid solution; ii) silica-undersaturated CaO-rich melt; and iii) C-O-H fluid phase. The silica undersaturation of the melt and, more importantly, the occurrence of a CO2-rich fluid phase, must be taken into account as they significantly affect partition coefficients and the redox state of carbonated systems, respectively

CO2 bubble generation and migration during magma-carbonate interaction

We conducted quantitative textural analysis of vesicles in high temperature and pressure carbonate assimilation experiments (1200 °C, 0.5 GPa) to investigate CO2 generation and subsequent bubble migration from carbonate into magma. We employed Mt. Merapi (Indonesia) and Mt. Vesuvius (Italy) compositions as magmatic starting materials and present three experimental series using (1) a dry basaltic-andesite, (2) a hydrous basaltic-andesite (2 wt% H2O), and (3) a hydrous shoshonite (2 wt% H2O). The duration of the experiments was varied from 0 to 300 s, and carbonate assimilation produced a CO2-rich fluid and CaO-enriched melts in all cases. The rate of carbonate assimilation, however, changed as a function of melt viscosity, which affected the 2D vesicle number, vesicle volume, and vesicle size distribution within each experiment. Relatively low-viscosity melts (i.e. Vesuvius experiments) facilitated efficient removal of bubbles from the reaction site. This allowed carbonate assimilation to continue unhindered and large volumes of CO2 to beliberated, a scenario thought to fuel sustained CO2-driven eruptions at the surface. Conversely, at higher viscosity (i.e. Merapi experiments), bubble migration became progressively inhibited and bubble concentration at the reaction site caused localised volatile over-pressure that can eventually trigger short-lived explosive outbursts. Melt viscosity therefore exerts a fundamental control on carbonate assimilation rates and, by consequence, the style of CO2-fuelled eruptions

CO2 bubble generation and migration during magma–carbonate interaction

We conducted quantitative textural analysis of vesicles in high temperature and pressure carbonate assimilation experiments (1200 °C, 0.5 GPa) to investigate CO2 generation and subsequent bubble migration from carbonate into magma. We employed Mt. Merapi (Indonesia) and Mt. Vesuvius (Italy) compositions as magmatic starting materials and present three experimental series using (1) a dry basaltic-andesite, (2) a hydrous basaltic-andesite (2 wt% H2O), and (3) a hydrous shoshonite (2 wt% H2O). The duration of the experiments was varied from 0 to 300 s, and carbonate assimilation produced a CO2-rich fluid and CaO-enriched melts in all cases. The rate of carbonate assimilation, however, changed as a function of melt viscosity, which affected the 2D vesicle number, vesicle volume, and vesicle size distribution within each experiment. Relatively low-viscosity melts (i.e. Vesuvius experiments) facilitated efficient removal of bubbles from the reaction site. This allowed carbonate assimilation to continue unhindered and large volumes of CO2 to be liberated, a scenario thought to fuel sustained CO2-driven eruptions at the surface. Conversely, at higher viscosity (i.e. Merapi experiments), bubble migration became progressively inhibited and bubble concentration at the reaction site caused localised volatile over-pressure that can eventually trigger short-lived explosive outbursts. Melt viscosity therefore exerts a fundamental control on carbonate assimilation rates and, by consequence, the style of CO2-fuelled eruptions