137,641 research outputs found
Revision of seismic hazard in emilia-romagna based on a new seismogenic zonation of the northern apennines
No full textRecent events in the Emilia-Romagna region highlighted unexpected large ground motions and this aspect caused criticism to the estimates obtained by probabilistic seismic hazard analyses represented by the national seismic hazard maps MPS04 (Stucchi et al., 2011). For this reason, some regional seismotectonic studies are in progress for this area, and a preliminary version of a new regional seismogenic zonation (see Fig. 1a) has been proposed (Martelli et al., 2014). This new zonation is, in the studied area, intentionally more detailed if compared to the national one (Meletti et al., 2008) that has been conceived to cover the entire Italian territory. The introduction of two SW-NE transfer zones cutting the NW-SE trend of the Apennine zones of the national zonation represents the major novelty for the Emilia-Romagna region. The boxes of Fig. 1a represent the superficial projection of rock volumes characterized by homogeneous deformation inside (in terms of failure mechanisms and geometry of faults: depthrange, strike and dip). In the present work, a probabilistic seismic hazard analysis (PSHA) has been conducted aiming at comparing the seismic hazard estimates based on the new zonation[obtained according to Cornell (1968) in the software formulation of Crisis 2012 (Ordaz et al., 2012)] with the national ones. In agreement with the Italian zonation, also the new seismogenic zones (SZs) have been initially considered in 2D. Successively, a 3D geometry has been defined for the new zones by introducing some seismogenic planes, i.e., 3D surfaces with a geometry in agreement with the tectonic style dominating in the SZ. The new hazard estimates, although very preliminary, show interesting differences with respect to the national ones and point outthe influence of a 3D geometry joint with a proper attenuation model in the expected ground motions on the surface
Navier-stokes simulations of hypersonic flows with coupled graphite ablation
No full textA study of graphite ablation in reentry flows is carried out by a surface ablation approach integrated with a two- dimensional axisymmetric Navier-Stokes solver. The gas-surface interaction model is based on chemical equilibrium ablation with surface mass and energy balances fully coupled with the numerical solver and can account for both surface oxidation and sublimation. The surface temperature is obtained from the steady-state ablation approximation. This numerical procedure can predict aerothermal heating, chemical species concentrations, and carbon material ablation rate over the heat-shield surface of reentry vehicles. Two-dimensional axisymmetric simulations have been performed to numerically reproduce the ablation of a graphite sphere cone that has been tested in the Interaction Heating Facility at the NASA Ames Research Center. The freestream conditions of the selected test case are typical for Earth reentry from a planetary mission. The predicted ablation rate and surface temperature assuming frozen chemistry in the flow show a good agreement with the available experimental data. The agreement is further improved freezing the nitrogen recombination reaction at the surface to be more consistent with experimental observation, which has shown nitrogen atom recombination not to occur at the graphite surface. Copyright © 2010 by D. Bianchi, F. Nasuti, and E. Martelli
Thermochemical erosion analysis for graphite/carbon-carbon rocket nozzles
No full textA study is conducted to predict graphite/carbon-carbon nozzle erosion behavior in solid rocket motors for wide variations of propellant formulations. The numerical model considers the solution of Reynolds-averaged Navier- Stokes equations in the nozzle, heterogeneous chemical reactions at the nozzle surface, variable transport and thermodynamic properties, and heat conduction in the nozzle material.Two different ablation models are considered and compared: a surface equilibrium approach and a finite-rate model. Results show that the erosion rate is diffusion limited for metallized propellants, ensuring sufficiently high wall temperatures, and it is kinetic limited for nonmetallized propellants. For low surface temperatures, the two models are consistent with each other and predict the same erosion rate, while the surface equilibrium model overpredicts the recession at low surface temperatures. The calculated results show an excellent agreement with the experimental data from the ballistic test and evaluation system motor firings, and the finite-rate model actually improves the predictions when the kinetic-limited regime is approached. 2010. Copyright © 2010 by D. Bianchi, F. Nasuti, M. Onofri, and E. Martelli
The inflammatory reflex reloaded
No full textIn their recent paper in Brain, Behavior, and Immunity, Katayama and colleagues outlined the neural pathway of a basic neural reflex responsible for the endogenous inhibition of inflammation (Katayama et al., 2022)
L’analisi del rischio locatario nel mercato immobiliare italiano
No full textLa difficoltà di riallocazione degli immobili che potrebbero essere lasciati vacanti dagli affittuari a causa dell’attuale crisi ha riportato alla luce un rischio spesso sottovalutato in passato dagli operatori: il rischio locatario. Scopo del presente lavoro è l’analisi del rischio tenant degli investimenti immobiliari nel mercato domestico, concentrandosi in modo particolare su tre aspetti specifici: dapprima viene presentata una fotografia del mercato italiano, con l’obiettivo di verificare se la durata “reale” dei contratti sia inferiore a quella pattuita inizialmente per via dell’esercizio delle opzioni di recesso anticipato da parte degli locatari. La seconda parte della ricerca è invece incentrata sulla verifica delle modalità con cui gli investitori professionali gestiscono questa componente aleatoria, al fine di verificare se le diverse asset allocation considerano anche tale fattore di rischio. L’ultima parte dell’analisi, infine, è dedicata all’impostazione di un modello statistico che mira ad individuare eventuali situazioni di tensione, ossia casi in cui le possibilità di abbandono dell’immobile da parte dei locatari sono particolarmente elevate.Difficulties in relocating buildings that occupants could leave vacant due to the current crisis have induced landlords to consider a risk that in the past was in most cases underestimated: the tenant risk. The aim of this study is to analyze the tenant risk in the Italian real estate market, focusing especially on three different aspects: firstly, the study presents an overview of the Italian real estate market, in order to verify whether the effective contract lengths are lower than those ones agreed at the stipulation dates, due to the exercise of break options by tenants. Then the study analyzes in details if and how professional investors manage this kind of risk, in order to determine whether different asset allocations consider this risky factor. Finally, the last part of the study aims to build a statistical model which helps landlords in identifying possible critical situations, i.e. cases where the probability of the break option exercise by tenants is particularly high
Dual view of the 3D Heisenberg model and the Abelian projection
No full textThe Heisenberg model in 3D is studied from a dual point of view. It is shown that it can have vortex configurations, carrying a conserved charge [U(1) symmetry]. Vortices condense in the disordered (demagnetized) phase. A disorder parameter [mu] is defined, dual to the magnetization [(n) over right arrow], which signals the condensation of vortices, i.e., spontaneous breaking of dual U(1) symmetry. This study sheds light on the procedure known as Abelian projection in non-Abelian gauge theories. [S0556-2821(99)03221-X]
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