Modelling of bubble nucleation in trachy-phonolitic magmas: implications for the dynamics of ash-rich eruptions

Nucleation of water gas bubbles in trachyphonolitic magmatic melts has been investigated integrating theory and numerical modelling with decompression experiments and analysis of natural ash samples of explosive eruptions. Bubble nucleation, considered the natural response of magmas to decompression, is strongly dictated by the gas-melt surface tension. Here, I use an integrated approach to quantify the role of the surface tension in the nucleation process combining high pressure - high temperature nucleation experiments with a numerical modelling based on the gradient theory (Cahn and Hilliard, 1959). This theory, successfully applied in several studies of industrial polymers (Poser and Sanchez, 1981; Harrison et al., 1999; Kahl and Enders, 2000; Enders et al., 2005) was never been used before to study systems of volcanological interest. I show that surface tension is far to be a constant, but it decreases with in- creasing nucleation pressure (i.e. the confining pressure). Entering the values of surface tension into the classical theory of nucleation, I obtain a variable supersaturation pressure triggering nucleation. The decreasing value of the gas-melt surface tension with increasing pressure, facilitate bubble nucleation at high pressure, thus enhancing the explosivity of eruptive events from deeper reservoirs. Instead, the hindered nucleation at relatively low pressure, due to high bubble surface tension, implies that the generation of explosive eruptions from shallow reservoirs requires high decompressions. Finally the vesiculation, in terms of nucleation and growth, of natural samples of ash-rich eruptions has been studied by applying a novel technique able to take 3D measurements of bubbles preserved on ash particle’s surface. The Bubble Size Distributions (BSD), together with the field evidence, suggest that the ash production in these ash-rich eruptions, rather than to magma-water explosive interaction, is related to the high decompression necessary to nucleate bubbles in a shallow reservoir

Modelling of bubble nucleation in trachy-phonolitic magmas: implications for the dynamics of ash-rich eruptions

Nucleation of water gas bubbles in trachyphonolitic magmatic melts has been investigated integrating theory and numerical modelling with decompression experiments and analysis of natural ash samples of explosive eruptions. Bubble nucleation, considered the natural response of magmas to decompression, is strongly dictated by the gas-melt surface tension. Here, I use an integrated approach to quantify the role of the surface tension in the nucleation process combining high pressure - high temperature nucleation experiments with a numerical modelling based on the gradient theory (Cahn and Hilliard, 1959). This theory, successfully applied in several studies of industrial polymers (Poser and Sanchez, 1981; Harrison et al., 1999; Kahl and Enders, 2000; Enders et al., 2005) was never been used before to study systems of volcanological interest. I show that surface tension is far to be a constant, but it decreases with in- creasing nucleation pressure (i.e. the confining pressure). Entering the values of surface tension into the classical theory of nucleation, I obtain a variable supersaturation pressure triggering nucleation. The decreasing value of the gas-melt surface tension with increasing pressure, facilitate bubble nucleation at high pressure, thus enhancing the explosivity of eruptive events from deeper reservoirs. Instead, the hindered nucleation at relatively low pressure, due to high bubble surface tension, implies that the generation of explosive eruptions from shallow reservoirs requires high decompressions. Finally the vesiculation, in terms of nucleation and growth, of natural samples of ash-rich eruptions has been studied by applying a novel technique able to take 3D measurements of bubbles preserved on ash particle’s surface. The Bubble Size Distributions (BSD), together with the field evidence, suggest that the ash production in these ash-rich eruptions, rather than to magma-water explosive interaction, is related to the high decompression necessary to nucleate bubbles in a shallow reservoir

Comparison of Convective Overshooting Models and Their Impact on Abundances from Integrated Light Spectroscopy of Young (<< 3 Gyr) Star Clusters

As part of an ongoing program to measure detailed chemical abundances in nearby galaxies, we use a sample of young to intermediate age clusters in the Large Magellanic Cloud with ages of 10 Myr to 2 Gyr to evaluate the effect of isochrone parameters, specifically core convective overshooting, on Fe abundance results from high resolution, integrated light spectroscopy. In this work we also obtain fiducial Fe abundances from high resolution spectroscopy of the cluster individual member stars. We compare the Fe abundance results for the individual stars to the results from isochrones and integrated light spectroscopy to determine whether isochrones with convective overshooting should be used in our integrated light analysis of young to intermediate age (10 Myr -3 Gyr) star clusters. We find that when using the isochrones from the Teramo group, we obtain more accurate results for young and intermediate age clusters over the entire age range when using isochrones without convective overshooting. While convective overshooting is not the only uncertain aspect of stellar evolution, it is one of the most readily parametrized ingredients in stellar evolution models, and thus important to evaluate for the specific models used in our integrated light analysis. This work demonstrates that our method for integrated light spectroscopy of star clusters can provide unique tests for future constraints on stellar evolution models of young and intermediate age clusters.Comment: 16 pages, accepted for publication in Ap

Detailed Chemical Abundances of Globular Clusters in Local Group Dwarf Galaxies

We present detailed chemical abundances of Fe, Ca and Ba for 17 globular clusters (GCs) in 5 Local Group dwarf galaxies: NGC 205, NGC 6822, WLM, the SMC and LMC. These abundances are part of a larger sample of over 20 individual elements measured in GCs in these galaxies using a new analysis method for high resolution, integrated light spectra. Our analysis also provides age and stellar population constraints. The existence of GCs in dwarf galaxies with a range of ages implies that there were episodes of rapid star formation throughout the history of these galaxies; the abundance ratios of these clusters suggest that the duration of these burst varied considerably from galaxy to galaxy. We find evolution of Fe, Ca, and Ba with age in the LMC, SMC, and NGC 6822 that is consistent with extended, lower-efficiency SF between bursts, with an increasing contribution of low-metallicity AGB ejecta at late times. Our sample of GCs in NGC 205 and WLM are predominantly old and metal-poor with high [Ca/Fe] ratios, implying that the early history of these galaxies was marked by consistently high SF rates.Comment: 2 pages, To appear in the proceedings of the conference "A Universe of Dwarf Galaxies" (Lyon, June 14-18, 2010

Energetical analysis of two different configurations of a liquid-gas compressed energy storage

In order to enhance the spreading of renewable energy sources in the Italian electric power market, as well as to promote self-production and to decrease the phase delay between energy production and consumption, energy storage solutions are catching on. Nowadays, in general, small size electric storage batteries represent a quite diffuse technology, while air liquid-compressed energy storage solutions are used for high size. The goal of this paper is the development of a numerical model for small size storage, environmentally sustainable, to exploit the higher efficiency of the liquid pumping to compress air. Two different solutions were analyzed, to improve the system efficiency and to exploit the heat produced by the compression phase of the gas. The study was performed with a numerical model implemented in Matlab, by analyzing the variation of hermodynamical parameters during the compression and the expansion phases, making an energetic assessment for the whole system. The results show a good global efficiency, thus making the system competitive with the smallest size storage batteries

Rational and boundedly rational behavior in sender-receiver games

We consider a signalling game in which a population of receivers decide on the outcome by majority rule, sender and receivers have conflicting interests, and there is uncertainty about both players’ types. We model players rationality along the lines of recent findings in behavioral game theory. We characterize the structure of the equilibria in the reduced game so obtained. We find that all pure strategy equilibria are consistent with successful attempts to mislead the receivers, and relate them to the message bin Laden sent on the eve of the 2004 US Presidential elections. The same result holds if we allow for some uncertainty about the sign of the correlation between the sender’s and the receivers’ payoffs.