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

Application Protocols enabling Internet of Remote Things via Random Access Satellite Channels

Nowadays, Machine-to-Machine (M2M) and Internet of Things (IoT) traffic rate is increasing at a fast pace. The use of satellites is expected to play a large role in delivering such a traffic. In this work, we investigate the use of two of the most common M2M/IoT protocols stacks on a satellite Random Access (RA) channel, based on DVB-RCS2 standard. The metric under consideration is the completion time, in order to identify the protocol stack that can provide the best performance level

Leading-order nucleon self-energy in relativistic chiral effective field theory

We apply thermal field theory methods to compute microscopically the nucleon self-energy arising from one-pion exchange in isospin-symmetric nuclear matter and neutron matter. A self-consistent numerical scheme is introduced and its convergence is demonstrated. The repulsive contribution from the Fock exchange diagram to the energy per nucleon in symmetric nuclear matter is obtained.Comment: v3: matches published version, 8 pages, 6 figures. Removed discussion of saturation, changed title to reflect the shortened content. v1: 9 pages, 7 figures, v2: minor amendment

The Detailed Chemical Abundance Patterns of M31 Globular Clusters

We present detailed chemical abundances for $>$20 elements in $\sim$30 globular clusters in M31. These results have been obtained using high resolution ($\lambda/\Delta\lambda\sim$24,000) spectra of their integrated light and analyzed using our original method. The globular clusters have galactocentric radii between 2.5 kpc and 117 kpc, and therefore provide abundance patterns for different phases of galaxy formation recorded in the inner and outer halo of M31. We find that the clusters in our survey have a range in metallicity of $-2.2<$[Fe/H]$<-0.11$. The inner halo clusters cover this full range, while the outer halo globular clusters at R$>$20 kpc have a small range in abundance of [Fe/H]$=-1.6 \pm 0.10$. We also measure abundances of alpha, r- and s-process elements. These results constitute the first abundance pattern constraints for old populations in M31 that are comparable to those known for the Milky Way halo.Comment: XII International Symposium on Nuclei in the Cosmos August 5-12, 2012 Cairns, Australia. To appear in Proceedings of Scienc