New insights into the application of the Coulomb model in real-time

The Coulomb model for stress change estimation is considered one of the most powerful physics-based forecasting tools, even though its calculations are affected by uncertainties due to the large number of a priori assumptions needed. The aim of this paper is to suggest a straightforward and reliable strategy to apply the Coulomb model for real-time forecasting. This is done by avoiding all dispensable assumptions, thus reducing the corresponding uncertainties. We demonstrate that the depth at which calculations are made is a parameter of utmost importance and apply the Coulomb model to three sequences in different tectonic regimes: Umbria-Marche (normal), Landers (strike-slip), and Chi-Chi (thrust). In each case the results confirm that when applying the Coulomb model: (i) the depth of calculation plays a fundamental role; (ii) depth uncertainties are not negligible; (iii) the best forecast at a given location is obtained by selecting the maximum stress change over the whole seismogenic depth rang

Microstructure and chemical composition of Roman orichalcum coins emitted after the monetary reform of Augustus (23 B.C.)

A collection of ancient Roman orichalcum coins, i.e., a copper-zinc alloy, minted under the reigns from Caesar to Domitianus, have been characterised using scanning electron microscopy (SEM-EDS) and electron microprobe analysis (EMPA). We studied, for the first time, coins emitted by Romans after the reforms of Augustus (23 B.C.) and Nero (63-64 A.D). These coins, consisting of asses, sestertii, dupondii and semisses, were analysed using non- and invasive analyses, aiming to explore microstructure, corrosive process and to acquire quantitative chemical analysis. The results revealed that the coins are characterized by porous external layers, which are affected by dezincification and decuprification processes. As pictured by the X-ray maps, the elemental distribution of Cu and Zn shows patterns of depletion that in some cases penetrate in deep up to 1 mm. The composition of the un-corroded nucleus is a Cu-Zn alloy containing up to 30% of Zn, typical of coins produced via cementation process

The effect of trivalent cations on the major lower mantle silicates

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2011.Cataloged from PDF version of thesis. Vita.Includes bibliographical references (p. 151-165).I have investigated the effect of composition, especially ferric iron and aluminum, on the equations of state and phase stability of perovskite and post-perovskite. The presence of trivalent cations decreases the bulk modulus of perovskite at pressures corresponding to the upper lower mantle. Ferric iron in perovskite undergoes a spin-pairing transition from the high spin state to low spin in the octahedral site. Ferric iron in the dodecahedral site remains high spin. In the absence of aluminum, the spin transition is gradual between 0 and 55 GPa, and bulk modulus increases at the completion of the spin transition. In the presence of aluminum, there is an abrupt increase in the amount of low spin ferric iron near 70 GPa, likely the result of site mixing. The high compressibility of the structure below 70 GPa results in the volume nearing that of magnesium endmember, MgSiO₃ , perovskite. Concurrent with the spin transition in aluminum-bearing perovskite, the structure stiffens. The increase in density and bulk modulus at -70 GPa results in an increase in bulk sound speed that may be related to heterogeneities in bulk sound speed observed seismically at 1200-2000 km depth in the Earth. The effect of composition on the perovskite to postperovskite phase transition was also investigated. No change in the spin state of ferric iron was found at the perovskite to post-perovskite phase transition: ferric iron is low spin in the octahedral site and high spin in the dodecahedral site. At the phase transition, ferric iron only slightly broadens the perovskite plus post-perovskite mixed phase region while ferrous iron and aluminum were each found to significantly broaden the mixed phase region to hundreds of kilometers thick. The effect of background mineral phases was assessed for a basaltic system, rich in aluminum. The coexisting minerals were found to significantly reduce the effect of the aluminum, producing a boundary that is potentially sharp enough for seismic detection in silicon-rich systems, such as basalt.by Krystle Carina Catalli.Ph.D

“News” e tasso di cambio €/$ in alta frequenza: stime econometriche Garch

Analizzando l’impatto che news scheduled ed unscheduled possono avere sul tasso di cambio €/$ a frequenza oraria per un arco temporale di sei anni, il presente lavoro indica la necessità di utilizzare queste due tipologie di news per spiegare al meglio l’andamento del cambio. Si rileva inoltre come l’ordine in cui gli indicatori macroeconomici scheduled vengono rilasciati all’interno del mese impatta sulla loro diversa significatività. Molto importante è anche la separazione degli eventi tra favorevoli e sfavorevoli per il cambio in esame: si conferma il noto risultato della letteratura finanziaria, secondo cui il mercato reagisce alle news in modo asimmetrico, dando un maggior peso alle bad news piuttosto che alle good news.