3,592 research outputs found
Gyrofluid simulations of collisionless reconnection in the presence of diamagnetic effects
No full textInternational audienceThe effects of the ion Larmor radius on magnetic reconnection are investigated by means of numerical simulations, with a Hamiltonian gyrofluid model. In the linear regime, it is found that ion diamagnetic effects decrease the growth rate of the dominant mode. Increasing ion temperature tends to make the magnetic islands propagate in the ion diamagnetic drift direction. In the nonlinear regime, diamagnetic effects reduce the final width of the island. Unlike the electron density, the guiding center density does not tend to distribute along separatrices and at high ion temperature, the electrostatic potential exhibits the superposition of a small scale structure, related to the electron density, and a large scale structure, related to the ion guiding-center density
I prelievi coattivi. Procedibilità, competenza ed attribuzione. Accelerazione dei processi. Interventi in materia di libertà personale
No full textil contributo riguarda le novità normative introdotte con la legge sull'omicidio stradale, con particolare riferimento all'introduzione dei prelievi coattivi di materiale biologico finalizzate all'accertamento dei reati di lesioni personali stradali e omicidio stradale. Vengono altresì analizzate le nuove disposizioni in materia di libertà personale riguardanti l'introduzione del potere di arresto in flagranza obbligatorio e facoltativo per i reati di nuova introduzione, come pure le disposizioni in tema di accelerazione delle indagini e dell'esercizio dell'azione penale per i reati in questione
Lo spirito del naturale e il sentimento del tempo
No full textSi tratta di una introduzione agli articoli pubblicati da Roberto Tassi sul quotidiano "La Repubblica", su cui Tassi ha scritto per una ventina d'anni, sino alla morte (1996) e si concentra sulle due linee tematiche principali affrontate da Tassi nella sua lettura delle arti visive: la natura e il tempo
Introduzione alla Finanza Matematica. Concetti di base, tassi e obbligazioni
No full textI principi fondamentali della Finanza Matematica. Leggi di capitalizzazione, tassi d'interesse, arbitraggi, obbligazioni, contratti a termin
Submarine gas burst at Panarea Island (southern Italy) on 3 November 2002: A magmatic versus hydrothermal episode
No full textOn 3 November 2002, fishermen observed the sudden appearance at the sea surface of three large whitish plumes 3 km offshore of Panarea Island (Aeolian Islands, southern Italy) caused by the uprising from the seafloor of huge columns of gas bubbles, mixed with sediments and colloidal sulfur. The degassing event partly superimposed an already existing gentle-degassing fumarolic field. Since 12 November 2002, a discontinuous geochemical monitoring program of these new discharging fluids have been carried out. The submarine emissions collected on November 2002 were an emulsion made by a CO2-dominated continuous gas phase with suspended sediments, colloidal sulfur, and water condensate microdroplets acidified by dissolution of compounds such as SO2, HCl, and HF. In the gas phase, light-unsaturated hydrocarbons also occurred, possibly related to relatively high temperature and oxidizing conditions due to local input of magmatic fluids at depth, whose occurrence was also supported by the relative high values of 3He/4He isotopic ratio (R/Rair = 4.62) with respect to previously measured values (R/R air < 4.2). The flux of the submarine emissions significantly decreased in a couple of months together with the almost complete disappearance of the magmatic chemical markers and the decrease of the helium isotopic ratio. Thus the most striking feature of the temporal and spatial evolution in the chemical and isotopic compositions of the submarine fumaroles was the relatively rapid restoration, since January 2003, of the precrisis conditions, i.e., typical of a stationary hydrothermal system. Copyright 2007 by the American Geophysical Union
A joint communication and computing resource management scheme for pervasive grid networks
No full textThe last years have been characterized by an increasing interest in the grid and cloud computing that allow the implementation of high performance computing structures in a distributed way by exploiting multiple processing resources. The presence of mobile terminals has extended the paradigm to the so called pervasive grid networks, where multiple heterogeneous devices are interconnected to form a distributed computing resource. In such a scenario, there is the need of efficient techniques for providing reliable wireless connections among network nodes. This paper deals with the proposal of a suitable resource management scheme relying on a routing algorithm able to perform jointly the resource discovery and task scheduling for implementing an efficient pervasive grid infrastructure in a wireless ad hoc scenario. The proposed solutions have been considered within two different parallelization processing schemes, and their effectiveness has been verified by resorting to computer simulations. Copyright (c) 2011 John Wiley & Sons, Ltd
A novel routing algorithm for mobile pervasive computing
No full textThe interest towards real-time computing has lead an even more interest in grid computing. While in the past the implementation of grid computing has been done on high performance computers, in the recent years there is an increasing interest in the pervasive grid scenarios, where multiple devices can be used for a distributed computing. The most challenging idea is to use mobile devices connected among them with wireless connections for setting up pervasive grid environments. In this context, it is a crucial problem the optimization of the routing algorithms among the processing nodes, in order to satisfy the performance requirements of a distributed computing. Aim of this paper is the design of specific routing algorithms for different pervasive grid applications with a particular attention to time sensitive scenarios
Reply to Dahlman et al. No association of reported functional protein tyrosine phosphatase 1B 3'UTR gene polymorphism with features of the metabolic syndrome in a Swedish population
No full textSANS/VSANS investigation of the porosity microstructure in rocks from a natural CO2 reservoir
No full textSequestration of CO2 in deep geological reservoirs represents one of the potential methods to reduce anthropogenic emissions into the atmosphere. In the long term the injected CO2 dissolves into the local formation of rocks and, when present, in saline deep aquifers, participating to a variety of geochemical reactions. The overall impact of these processes produces changes in mineralogy, texture, permeability and porous structure of the rocks, to a level which depends on the different lithologies present in the rocks.
Mineralogical changes can be investigated by considering what occurs in rocks and minerals with natural CO2 accumulations, as analogues for geological sequestration. Also computer simulations, based on thermodynamics, kinetics and geochemical modeling [1, 2], can be beneficial. On the other hand, reliable data concerning the porous structure, which is so important to trap CO2, can be hardly extracted from computer simulations.
In this context a valuable help can be provided by Small and Very Small Angle Neutron Scattering techniques (SANS and VSANS, respectively): they have been indeed demonstrated to be powerful tools for the determination of the microstructure and porosity of rocks from Ångstrom to millimeter sizes [3], proofing also the existence of fractal dimensions for the volume and surfaces interfaces between pores and rocks.
Here we present the preliminary results of a SANS/VSANS investigation on rocks pertaining to a geological context (located in Eastern Tuscany, Central Italy) featured by a deep geological gas reservoir. The former reservoir was intercepted by a bore-well drilled in ’80 by ENI and is presently hosting 700 bar of supercritical CO2. Texture and mineralogy of volcanic rocks samples, from drill cores corresponding to the top of the reservoir, were found to be heavily modified by the interaction with CO2-rich fluids.
The combined neutron experiments, performed using the PAXE and G5bis diffractometers at LLB (Saclay, F), allowed to approximately investigate pore sizes ranging from ∼ 60 nm to ∼ 6 μm. Samples of host rocks (from drill core) and a selection of possible analogues of the same volcanic rocks, unaffected by CO2 presence, were chosen for the experiments together with samples of rocks, from outcrops, corresponding to the geological layers the characteristics of geological layers overlying the reservoir. Globally these rocks are representative of a wide spectrum of different lithologies (as limestones, marls, evaporitic deposits bearing gypsum and volcanic rocks with intermediate-acid composition).
The information provided by these experiments must still be fully analyzed and integrated with other data (e.g. chemical composition of rocks and fluids [4]) in order to get a better understanding of: i) the role and the possible effects of CO2 in determining the micro-porosity of these host rocks, and ii) the sealing effect of the sedimentary rocks overlying the reservoir which act as a barrier with respect to the CO2-rich gases.
References
[1] Zhu C. and Anderson G., 2002 Environmental Applications of Geochemical Modeling, Cambridge University Press, Cambridge, UK, 284 pp.
[2] Cantucci B, Montegrossi G., Vaselli O., Tassi F., Quattrocchi F., and Perkins E.H., 2009 Geochemical modelling of CO2 storage in deep reservoirs: The Weyburn Project (Canada) case study. Chemical Geology, 265 (1), 181-197.
[3] A.P. Radlinski, 2006 and reference therein, in Neutron Scattering in Earth Sciences, Reviews in Mineralogy & Geochemistry, 63, pp. 363-397.
[4] Bicocchi G., Montegrossi G., Ruggieri G., Buccianti A. and Vaselli O. (2011). Modeling composition of Ca-Fe-Mg carbonates in a natural CO2 reservoir. In: Egozcue, J.J., Tolosana-Delgado, R. and Ortego, M.I. (eds.). Codawork11 Proceedings, 16 p
Geochemistry of the magmatic-hydrothermal fluid reservoir of Copahue volcano (Argentina): insights from the chemical and isotopic features of fumarolic discharges
No full textThis study present the chemical (inorganic and organic) and isotopic compositions (d13C-CO2, d15N, 3He/4He, 40Ar/36Ar, d13C-CH4, dD-CH4, and dD-H2O and d18O-H2O) of gases from fluid discharges located at the foot of Copahue volcano. Gas samples were collected during 6 campaigns carried out from 1976 to 2012. Gas composition is typical of hydrothermal fluids from volcanic areas, since it consists of dominant CO2 and relatively high concentrations of H2S, H2, CH4 and N2. The isotopic ratios of He are the highest observed for a Southern American volcano to date (R/Ra up to 7.94). This feature is not common for gases from a classic arc-like setting, and is possibly related to an extensional regime subdued to asthenospheric thinning. The CO2/3He ratios (from 1.4 to 8.8×109) slightly exceeding that of MORB gases, and the d15N values (+5.3 to +5.5 ? vs. air) point to an occurrence of an additional crustal source for CO2 and N2. Gas discharges of the northern sector of the volcanic edifice are likely produced by mixing of hydrothermal gases with fluids from a shallow source permeating through local fault systems. Gas geothermometry based on chemical reactions characterized by slow kinetics, such as those involving the CO2-CH4 redox pair, are quenched at temperatures (~260 °C) and redox conditions [log(XH2/XH2O) = -2.8)] consistent with those measured in the goethermal wells. On the contrary, the C3H6-C3H8 pair, H2 and CO tend to re-adjust at decreasing temperatures and more oxidizing conditions [log(XH2/XH2O) ≤ -3.4] in the uprising vapor phase. The hydrothermal reservoir is mainly recharged by meteoric water whose isotopic signature is modified by water-rock interactions. The N2/He ratios measured in 2006-2007 were significantly lower than those of 2012, possibly due to variations of N2-bearing species in sediments interacting with the magmatic source. Considering that the R/Ra values of the 2006-2007 period were significantly higher than those measured in 2012, such compositional variation may also be explained by the injection of fresh N2and 3He-rich magma that triggered the 2000 eruption. This hypothesis, although speculative since no geochemical data of fumaroles are available from 1997 to 2006, implies that a geochemical monitoring of inert gas compounds discharged from the hydrothermal emissions could be used to detect the occurrence at depth of injections of new magma batches.Fil: Tassi, Franco. Università degli Studi di Firenze; ItaliaFil: Agusto, Mariano Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Vaselli, Orlando. Università degli Studi di Firenze; ItaliaFil: Chiodini, Giovanni. Istituto Nazionale di Geofisica e Vulcanologia; Itali
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