Viscosity of andesite melts and its implication for magma mixing prior to Unzen 1991-1995 eruption

The viscosity of an iron-bearing melt with composition similar to Unzen andesite was determined experimentally in the high (109-1010.5 Pa·s) and low (5-1000 Pa·s) viscosity range using a parallel plate viscometer and the falling sphere method, respectively. Falling sphere experiments were carried out in an internally heated argon pressure vessel and in a piston cylinder apparatus at 1323 to 1573 K and 200 to 2000 MPa. Creep experiments were performed in the temperature range of 747 - 845 K at 300 MPa. The water content of the melt varies from nominally dry to 6.2 wt% H2O. The Fe2+/Fetot ratio was determined for each sample in the quenched glass using a colorimetric method. Pressure has minor influence on the viscosity compared with the effect of temperature, water content (main compositional parameter controlling the viscosity) or with the Fe2+/Fetot ratio (especially important at low water content of the melt). Based on our new viscosity data and literature data with measured Fe2+/Fetot ratio we propose a new empirical equation to estimate the viscosity η (in Pa·s) of andesitic melts as a function of temperature T (in K), water content w (in wt%) and Fe2+/Fetot ratio. The derived relationship reproduces the experimental data (87 in total) in the viscosity range from 100.5 to 1013 Pa·s with a 1σ standard deviation of 0.17 log units. However, application of this calculation model is limited to Fe2+/Fetot>0.3 and to temperatures above Tg. Moreover, in the high viscosity range the variation of viscosity with water content is constrained only by few experimental data and needs verification by additional measurements. The viscosity data are used to interpret mixing processes in the Unzen magma chamber prior to 1991-1995 eruption. We demonstrate that the viscosities of the rhyolite and andesite melts from the two end-member magmas are nearly identical prior and during mixing, enabling efficient magma mixing

The viscosity of shoshonitic melts (Vulcanello Peninsula, Aeolian Islands, Italy): insight on the magma ascent in dikes

The viscosity of shoshonitic melts from Vulcanello Peninsula (Vulcano Island, Italy) is experimentally determined at temperatures between 733 K and 1673 K. The water content of the melts varies from 0.03 to 4.75 wt% H2O. The micropenetration technique is employed at ambient pressure in the high viscosity range (109-1012 Pa·s). Falling sphere(s) experiments are performed at 500 and 2000 MPa in the low viscosity range (100.5-103 Pa·s). Results show a decrease of about 2 orders of magnitude in viscosity if ~ 3 wt% of water is added to the dry melt at 1300 K. At high temperature the viscosity of Vulcanello melts is intermediate between that of andesitic and basaltic melts. In contrast, at low temperatures (≤1050 K), the shoshonitic melt is characterized by a lower viscosity with respect to the two previous melts. Based on our new data set, a calculation model is proposed to predict the viscosity of the shoshonitic melts as a function of temperature and water content. The viscosity data are used to constrain the ascent velocity of shoshonitic magmas from Vulcanello within dikes. Using petrological data (temperature and crystal content of the magma) and volcanological information (geometrical parameters of the eruptive fissure and depth of magma storage), we estimate the time scale for the ascent of magma from the main reservoir to the surface. Results show time scales in the order of hours to few days. We conclude that the rapid ascent of poorly evolved melts from Moho depths should be taken into account for the hazard assessment of Vulcano Island

Atropisomerism in Hindered Naphthyl Sulfoxides: Structure, Stereodynamics, and Chiral Resolution.

Barriers for the EZ interconversion of atropisomers of 1-naphthyl sulfoxides (ArSOR) having a methyl group at position 2 of the naphthalene moiety were measured by variable-temperature NMR. Their values were found to cover the range 10.6-18.4 kcal mol-1, the extreme values corresponding to derivatives 1 (R = Me) and 4 (R = Bu(t)), respectively. NOE and LIS measurements indicated that the Z atropisomer is more stable than the E but that the absence of the methyl group at position 2 of the naphthalene moiety reverses this trend, rendering E more stable than Z. Solid-state NMR and X-ray diffraction of 4 established that only the more stable atropisomer (Z) is present in the crystalline state. Molecular mechanics calculations suggest that the Z,E interconversion process might occur by a rotation pathway having an opposite direction in the case of the more hindered derivatives 3 and 4 (R = Pr(i) and Bu(t), respectively) with respect to the less hindered 1 and 2 (R = Me and Et, respectively). The enantiomers, which are due to the presence of the asymmetric sulfur atom, were resolved on a chiral stationary phase (DACH-DNB) having an SS configuration. Asymmetric oxidation reactions were employed to assign the absolute R configuration to the more retained enantiomers of alkyl aryl sulfoxides. The opposite trend (S being retained longer) was observed for diaryl sulfoxides such as 5 (R = Ph). In the case of the derivative with the largest interconversion barrier, sulfoxide 4, it was also possible to resolve (at -35-degrees-C) the two enantiomeric forms and their associated atropisomers. The use of on-line CD detection and the knowledge of the NMR assignments allowed us to unambiguously assign the elution order of the four species as ES, ER, ZS, ZR

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

A general viscosity model of Campi Flegrei (Italy) melts

Viscosities of shoshonitic and latitic melts, relevant to the Campi Flegrei caldera magmas, have been experimentally determined at atmospheric pressure and 0.5 GPa, temperatures between 840 K and 1870 K, and H2O contents from 0.02 to 3.30 wt%. The concentric cylinder technique was employed at atmospheric pressure to determine viscosity of nominally anhydrous melts in the viscosity range of 101.5 - 103 Pa·s. The micropenetration technique was used to determine the viscosity of hydrous and anhydrous melts at atmospheric pressure in the high viscosity range (1010 Pa·s). Falling sphere experiments were performed at 0.5 GPa in the low viscosity range (from 100.35 to 102.79 Pa·s) in order to obtain viscosity data of anhydrous and hydrous melts. The combination of data obtained from the three different techniques adopted permits a general description of viscosity as a function of temperature and water content using the following modified VFT equation: where η is the viscosity in Pa·s, T the temperature in K, w the H2O content in wt%, and a, b, c, d, e, g are the VFT parameters. This model reproduces the experimental data (95 measurements) with a 1σ standard deviation of 0.19 and 0.22 log units for shoshonite and latite, respectively. The proposed model has been applied also to a more evolved composition (trachyte) from the same area in order to create a general model applicable to the whole compositional range of Campi Flegrei products. Moreover, speed data have been used to constrain the ascent velocity of latitic, shoshonitic, and trachytic melts within dikes. Using petrological data and volcanological information (geometrical parameters of the eruptive fissure and depth of magma storage), we estimate a time scale for the ascent of melt from 9 km to 4 km depth (where deep and shallow reservoirs, respectively, are located) in the order of few minutes. Such a rapid ascent should be taken into account for the hazard assessment in the Campi Flegrei area

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

the secondary alcohol and aglycone metabolites of doxorubicin alter metabolism of human erythrocytes

Anthracyclines, a class of antitumor drugs widely used for the treatment of solid and hematological malignancies, cause a cumulative dose-dependent cardiac toxicity whose biochemical basis is unclear. Recent studies of the role of the metabolites of anthracyclines, i.e., the alcohol metabolite doxorubicinol and aglycone metabolites, have suggested new hypotheses about the mechanisms of anthracycline cardiotoxicity. In the present study, human red blood cells were used as a cell model. Exposure (1 h at 37ºC) of intact human red blood cells to doxorubicinol (40 µM) and to aglycone derivatives of doxorubicin (40 µM) induced, compared with untreated red cells: i) a ~2-fold stimulation of the pentose phosphate pathway (PPP) and ii) a marked inhibition of the red cell antioxidant enzymes, glutathione peroxidase (~20%) and superoxide dismutase (~60%). In contrast to doxorubicin-derived metabolites, doxorubicin itself induced a slighter PPP stimulation (~35%) and this metabolic event was not associated with any alteration in glutathione reductase, glutathione peroxidase, catalase or superoxide dismutase activity. Furthermore, the interaction of hemoglobin with doxorubicin and its metabolites induced a significant increase (~22%) in oxygen affinity compared with hemoglobin incubated without drugs. On the basis of the results obtained in the present study, a new hypothesis, involving doxorubicinol and aglycone metabolites, has been proposed to clarify the mechanisms responsible for the doxorubicin-induced red blood cell toxicity

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

Intrinsic solidification behaviour of basaltic to rhyolitic melts: a cooling rate experimental study

Dynamic cooling-induced solidification experiments were run using six silicate glasses along the basalt - rhyolite join (B100= 100 wt % of basalt, R100= 100 wt % of rhyolite), i.e. B100, B80R20, B60R40, B40R60, B20R80 and R100; the glasses directly quenched from 1300 °C after a dwell of 120 minutes (experiment E0) contain 50-400 ppm H2O, << 1 area% μm-sized bubble, and Fe2+/Fetot between 0.34 and 0.46. Experiments were performed in Pt capsules at room pressure and fO2 of air, between 1300 and 800 °C using three different cooling rates of 0.0167, 3 and 30 °C/min; these cooling rates were run two times: E1-E2 experiments at 0.0167°C/min, S1-E3 at 3 °C/min, and E4-E5 at 30 °C/min. In experiments E1 to E5, samples were annealed for 120 minutes at 1300 °C, whereas in the experiment S1 the samples were firstly heated for 30 minutes at 1400 °C followed by a dwell time of 2400 minutes at 1300°C before cooling. In the experiments a preferential crystallization was not observed at the melt/gas interface. B100, B80R20 and B60R40 run-products have a low tendency to preferentially crystallize on Pt walls, while B40R60, B20R80 and R100 are not affected by the presence of Pt substrata. All run-products show very homogeneous textures, except for B60R40 and B40R60 at 0.0167°C/min in the E1 experiment. The duplicates of B40R60 and B60R40 at 0.0167°C/min and B100 at 30 °C/min show relatively large differences in crystal content (> 4 and < 14 area%). B40R60 and B60R40 duplicated run-products have the same amount of earlycrystallized clinopyroxene and spinel, but different contents in lately-formed plagioclase. The run-products with the same starting composition from E3-S1 (3 °C/min) show a high reproducibility in terms of crystal shape, size, and amount (< 4 area%). This demonstrates that the crystallization path is not affected by the different heat treatment above the liquidus temperature, i.e. the time scale of structural re-equilibration (relaxation) and chemical rehomogenization are shorter than our experimental time scale. Possible chemicalheterogeneities on a length scale of several micrometers for R100 and several hundreds of micrometers for B100 can be removed at 1300 °C within 120 minutes. A heat treatment at 1300 °C for 120 minutes significantly reduces the amount of μm-sized bubbles, potentially responsible for the onset of nucleation and unreveals the intrinsic solidification of silicate melts. The experimental reproducibility is low when the cooling path intersects the tip of the time-temperature-transformation (TTT) curves, i.e. when the nucleation rate is near its maximum (Imax). In that case, even small thermal variations in cooling rate and local composition can have large effects on phase abundance and crystal size. Dynamic crystallization experiments can be properly interpreted and compared only if they are texturally homogeneous and the physico-chemical state of the superheated silicate liquid is known. The solidification conditions used in this study mirror those of aphyric lavas and dikes emplaced at shallower crustal levels