5,040 research outputs found

    ATLAS RPC offline monitoring and data quality assessment

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    In this work several aspects of ATLAS RPC offline monitoring and data quality assessment are illustrated with cosmics data selected by RPC trigger. These correspond to trigger selection, front-end mapping, detection efficiency and occupancy, which are studied in terms of low level quantities such as: RPC off-line hits and standalone tracks. The tools and techniques presented are also extended to the forthcoming LHC p-p beam collisions.Comment: Poster section at ICHEP08, Philadelphia, USA, July 2008. 3 pages, LaTeX, 3 eps figure

    Magma degassing episodes and volcanic unrest periods in quiescent volcanoes

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    Long time series of fumarolic chemical and isotopic compositions, at Solfatara (Campi Flegrei) and Vulcano highlight the occurrence of mixing processes among magmatic and hydrothermal fluids. At Solfatara temperatures of about 360°C of the hydrothermal system are inferred by methane chemical-isotopic geoindicators and by the H2/Ar geothermometer. These high temperatures are representative of a deep zone where magmatic gases flash hydrothermalliquid forming a gas pIume where the kinetically fast reactive species (H2 and CO) re-equilibrate at temperatures of 200240°C. The stable isotope compositions of the two dominant species, i.e, H20 and C02, shows that sampled effluents are mixture between magmatic fluids and the vapor generated at about 360°C by the vaporization of hydrothermalliquids of meteotic origino Similar mixing processes between magmatic fluids and a hydrothermal component of marine origin have been recognized at Vulcano high temperature fumaroleso In both the system a typical 'andesitic' water type composition and high C02 contents characterizes the magmatic component. Our hypothesis is that pulsing injections of these C02-rich magmatic fluids at the bottom of the hydrothermal systems trigger the bradyseismic crises, periodically affecting Campi Flegrei, and the periodical volcanic unrest periods of Vulcano. At Campi Flegrei a strong increase of the fraction of the magmatic component, marked in fact the bradyseismic crisis of 1982-84 and four minor episodes occurred in 1989, 1994 and 2000 and 2006. Increases of the magmatic component in the fumaroles of Vulcano were recorded in 1979-1981, 1985, 1988, 1996, 2004 and 2005 concurrently with anomalous seismic activity localized in the erater area. Physical-numerical simulations of the injection of hot, C02 rich fluids at the base of a hydrothermal system, asses the physical feasibility the processo Ground deformations, gravitational anomalies and seismic crisis can be well explained by the complex fluid dynamic processes caused by magma degassing episodes. Data on the fumaroles of other volcanoes, for example Vesuvio, Panarea, Nisyros (Greece), Mammoth (California), suggest that magma degassing episodes frequently occur in dormant volcanoes causing volcanic unrest processes not necessarily linked to magma movement but rather to pulsating degassing processes from deep pressurized, possibly stationary, magma bodies

    Le Fumarole di Vulcano

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    In tempi storici l’Isola di Vulcano è stata interessata da numerose eruzioni. Come già detto l’ultima attività vulcanica è avvenuta fra il 1888 e il 1890. Da allora l’attività del vulcano è caratterizzata dalla presenza di numerose aree fumarolizzate..

    SnO<sub>2</sub> nanoparticles in silica: nanosized tools for femtosecond-laser machining of refractive index patterns

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    We show that SnO2 nanoclusters in silica interact with ultrashort infrared laser pulses focused inside the material generating a hydrostatic compression and photoelastic response of the surrounding glass. This effect, together with the laser-induced nanocluster amorphization, gives rise to positive or negative refractive-index changes, up to 10–2, depending on the beam-power density. This result points out a wide tuning of the refractive index patterns obtainable in silica-based optical technology

    MODELING OF GAS COMPOSITION AND GRAVITY SIGNALS AT THE PHLEGREAN FIELDS CALDERA

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    Hydrothermal systems are known to play an important role in the evolution of active calderas: these volcanic systems periodically undergo dramatic unrest crises, commonly involving ground deformation, seismic activity and important changes in several geophysical and geochemical parameters monitored at the surface. These unrest crises may, or may not, culminate with a renewal of the eruptive activity, but in any case they bear important consequences in densely populated regions. Early warning and a prompt evaluation of the state of evolution of the volcanic system are therefore essential to ensure proper mitigation measures. A proper interpretation of monitoring data, however, is only achieved within the framework of a robust conceptual model of the system. Recent research work carried out at the Phlegrean Fields shows that the recent evolution of the caldera is consistent with the presence of a pulsating magmatic source, periodically discharging CO2-enriched fluids into a shallow hydrothermal system. Such pulsating degassing affects the amount of heat and fluids entering the hydrothermal system, the distribution of fluid phases throughout the system, and their composition. As a consequence, degassing controls not only the composition of fluids discharged at the surface, but also ground displacement and gravity residuals. In this work, the TOUGH2 code has been applied to study how different degassing scenarios could affect the composition of discharged fluids and the gravity signals recorded at the surface

    Numerical model of gas dispersion emitted from volcanic sources

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    An Eulerian model for passive gas dispersion based on the K-theory for turbulent diffusion, coupled with a mass consistent wind model is presented. The procedure can be used to forecast gas concentration over large and complex terrains. The input to the model includes the topography, wind measurements from meteorological stations, atmospheric stability information and gas flow rate from the ground sources. Here, this model is applied to study the distribution of the CO2 discharged from the hot sources of the Solfatara Volcano, Naples, Italy, where the input data were measured during a 15 day campaign in June 2001 carried out to test an Eddy Covariance (EC) station by Osservatorio Vesuviano-INGV, Naples

    Carbon Dioxide Diffuse Emission from the Soil at Vesuvio and Campi Flegrei (Pozzuoli): Ten Years of Observations

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    Carbon dioxide flux from the soil is regularly monitored in selected areas of Vesuvio and Solfatara (Campi Flegrei, Pozzuoli) with the main aim of investigating if the surface phenomena could provide information about the processes occurring at depth. Surveyed areas include 15 fixed points around the rim of Vesuvio and 71 fixed points in the floor of Solfatara crater, where soil CO2 flux is measured since 1998, at least once a month. In addition, two automatic permanent stations, located at Vesuvio and Solfatara, continually measure the CO2 flux and some environmental parameters that can potentially influence the CO2 diffuse degassing. We analysed, with statistical procedures, the feature of the acquired signals, evaluating the spatial and temporal variations of the CO2 degassing process. Series acquired by continuous stations are characterized by an annual periodicity that is related to the typical periodicities of some meteorological parameters (e.g., air temperature, air humidity, etc.). Such a kind of signal permits to define the “reference” level of the CO2 degassing process that diffusely affects the flanks and the base of the volcanoes. Conversely, series of CO2 flux data arising from periodic measurements over the arrays of Vesuvio and Solfatara, are less dependent on external factors such as meteorological parameters, local soil properties (porosity, hydraulic conductivity) and topographic effects (high or low ground). Therefore we argue that the longterm trend of this signal contains the “best” possible representation of the endogenous signal related to the upflow of deep hydrothermal fluids. At Vesuvio and Solfatara, the variations of these series have shown some correspondence with other physical changes of the volcanic systems

    VOLCANIC CO2 FLUX MEASUREMENTS BY TUNABLE DIODE LASER ABSORPTION SPECTROSCOPY

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    Introduction In the last decades, the use of near-infrared room-temperature diode lasers for gas sensing has grown significantly. The use of these devices, for instance in combination with optical fibers, is particularly convenient for volcanic monitoring applications [1,2]. Here, we report on the first results of the application of an open-path infrared tunable laser-based at Campi Flegrei (Southern Italy). Such Diode-laser-based measurements were performed, during two field campaigns (october 2012, and january 2013), in the attempt to obtain novel information on the current degassing unrest of Solfatara and Pisciarelli fumarolic fields. Results and Discussion At each site, we used an ad-hoc designed measurement geometry, using a TDLS (a Gas Finder unit) and several differently positioned retroreflectors (mirrors), to scan the fumaroles’ plume from different angles and distances. From post-processing of the data (acquired at 1 hz), we derived tomographic maps of CO2 concentrations in the plume and, by integration and combination with plume transport speed (from video cameras), we inferred the CO2 flux directly. The so-calculated fluxes, the first ever obtained at Campi Flegrei, average of 500 tons/day, and support a significant contribution of fumaroles to the total CO2 budget. The cumulative (fumarole [this study] +soil [3]) CO2 output from Campi Flegrei is finally evaluated at 1600 tons/day. [1] Gianfrani L. et al. (2000). Appl. Phys. B-Rapid Common. 70, 467-470. [2] Richter D. et al (2002), Optics and Lasers in Engineering, Volume 37, Issues 2–3, Pages 171-186. [3] Chiodini G. et al. (2010), Journal of Geophysical Research, Volume 115, B03205, doi:10.1029/2008JB006258

    On the Unruh effect in de Sitter space

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    We give an interpretation of the temperature in de Sitter universe in terms of a dynamical Unruh effect associated with the Hubble sphere. As with the quantum noise perceived by a uniformly accelerated observer in static space-times, observers endowed with a proper motion can in principle detect the effect. In particular, we study a "Kodama observer" as a two-field Unruh detector for which we show the effect is approximately thermal. We also estimate the back-reaction of the emitted radiation and find trajectories associated with the Kodama vector fields are stable.Comment: 8 pages; corrected typos; sections structure revise
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