7,315 research outputs found
Non-vascular interventional procedures: effective dose to patient and equivalent dose to abdominal organs by means of dicom images and Monte Carlo simulation
This study evaluates X-ray exposure in patient undergoing abdominal extra-vascular interventional procedures by means of Digital Imaging and COmmunications in Medicine (DICOM) image headers and Monte Carlo simulation. The main aim was to assess the effective and equivalent doses, under the hypothesis of their correlation with the dose area product (DAP) measured during each examination. This allows to collect dosimetric information about each patient and to evaluate associated risks without resorting to in vivo dosimetry. The dose calculation was performed in 79 procedures through the Monte Carlo simulator PCXMC (A PC-based Monte Carlo program for calculating patient doses in medical X-ray examinations), by using the real geometrical and dosimetric irradiation conditions, automatically extracted from DICOM headers. The DAP measurements were also validated by using thermoluminescent dosimeters on an anthropomorphic phantom. The expected linear correlation between effective doses and DAP was confirmed with an R(2) of 0.974. Moreover, in order to easily calculate patient doses, conversion coefficients that relate equivalent doses to measurable quantities, such as DAP, were obtained
Experimental Test of Two-way Quantum Key Distribution in Presence of Controlled Noise
We describe the experimental test of a quantum key distribution performed
with a two-way protocol without using entanglement. An individual incoherent
eavesdropping is simulated and induces a variable amount of noise on the
communication channel. This allows a direct verification of the agreement
between theory and practice.Comment: 4 pages, 3 figure
Opinion formation models based on game theory
A way to simulate the basic interactions between two individuals with
different opinions, in the context of strategic game theory, is proposed.
Various games are considered, which produce different kinds of opinion
formation dynamics. First, by assuming that all individuals (players) are
equals, we obtain the bounded confidence model of continuous opinion dynamics
proposed by Deffuant et al. In such a model a tolerance threshold is defined,
such that individuals with difference in opinion larger than the threshold can
not interact. Then, we consider that the individuals have different
inclinations to change opinion and different abilities in convincing the
others. In this way, we obtain the so-called ``Stubborn individuals and
Orators'' (SO) model, a generalization of the Deffuant et al. model, in which
the threshold tolerance is different for every couple of individuals. We
explore, by numerical simulations, the dynamics of the SO model, and we propose
further generalizations that can be implemented.Comment: 18 pages, 4 figure
Raro caso de tumores adenomatoides mĂşltiples derivados de la tĂşnica vaginal de testĂculo y epidĂdimo
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Numerical modelling of gas-water-rock interactions in volcanic-hydrothermal environment: the Ischia Island (Southern Italy) case study.
Hydrothermal systems hosted within active volcanic systems represent an excellent opportunity to investigate the
interactions between aquifer rocks, infiltrating waters and deep-rising magmatic fluids, and thus allow deriving
information on the activity state of dormant volcanoes. From a thermodynamic perspective, gas-water-rock
interaction processes are normally far from equilibrium, but can be represented by an array of chemical reactions,
in which irreversible mass transfer occurs from host rock minerals to leaching solutions, and then to secondary
hydrothermal minerals. While initially developed to investigate interactions in near-surface groundwater environments,
the reaction path modeling approach of Helgeson and co-workers can also be applied to quantitative
investigation of reactions in high T-P environments.
Ischia volcano, being the site of diffuse hydrothermal circulation, is an ideal place where to test the application
of reaction-path modeling. Since its last eruption in 1302 AD, Ischia has shown a variety of hydrothermal
features, including fumarolic emissions, diffuse soil degassing and hot waters discharges. These are the superficial
manifestation of an intense hydrothermal circulation at depth. A recent work has shown the existence of several
superposed aquifers; the shallowest (near to boiling) feeds the numerous surface thermal discharges, and is
recharged by both superficial waters and deeper and hotter (150-260° C) hydrothermal reservoir fluids.
Here, we use reaction path modelling (performed by using the code EQ3/6) to quantitatively constrain the
compositional evolution of Ischia thermal fluids during their hydrothermal flow. Simulations suggest that
compositions of Ischia groundwaters are buffered by interactions between reservoir rocks and recharge waters
(meteoric fluids variably mixed - from 2 to 80% - with seawater) at shallow aquifer conditions. A CO2 rich
gaseous phase is also involved in the interaction processes (fCO2 = 0.4-0.6 bar). Overall, our model calculations
satisfactorily reproduce the main chemical features of Ischia groundwaters. In the model runs, attainment of
partial to complete equilibrium with albite and K-feldspar fixes the Na/K ratios of the model solutions at values
closely matching those of natural samples. Precipitation of secondary phases, mainly clay minerals (smectite and
saponite) and zeolites (clinoptilolite), during the reaction path is able to well explain the large Mg-depletions
which characterise Ischia thermal groundwaters; while pyrite and troilite are shown to control sulphur abundance
in aqueous solutions. SiO2(aq) contents in model simulations fit those measured in groundwaters and are being
buffered by the formation of quartz polymorphs and Si-bearing minerals. Finally, our simulations are able to
reproduce redox conditions and Fe-depletion trends of natural samples. We conclude that reaction path modelling is an useful tool for quantitative exploration of chemical process within volcano-hosted hydrothermal systems
Quantitative models of hydrothermal fluid–mineral reaction:The Ischia case
The intricate pathways of fluid–mineral reactions occurring underneath active hydrothermal systems are explored in this study by applying reaction path modelling to the Ischia case study. Ischia Island, in Southern Italy, hosts a well-developed and structurally complex hydrothermal system which, because of its heterogeneity in chemical and physical properties, is an ideal test sites for evaluating potentialities/limitations of quantitative geochemical models of hydrothermal reactions. We used the
EQ3/6 software package, version 7.2b, to model reaction of infiltrating waters (mixtures of meteoric water and seawater in variable proportions) with Ischia’s reservoir rocks (the Mount Epomeo Green Tuff units; MEGT). The mineral assemblage and composition of such MEGT units were initially characterised by ad hoc designed optical microscopy and electron microprobe analysis, showing that phenocrysts (dominantly alkali–feldspars and plagioclase) are set in a pervasively altered (with abundant clay minerals and zeolites) groundmass. Reaction of infiltrating waters with MEGT minerals was simulated over a
range of realistic (for Ischia) temperatures (95–260° C) and CO2 fugacities (10 ^-0.2 to 10^0.5) bar. During the model runs, a set of secondary minerals (selected based on independent information from alteration minerals’ studies) was allowed to precipitate from model solutions, when saturation was achieved. The compositional evolution of model solutions obtained in the 95–260°C runs were finally compared with compositions of Ischia’s thermal groundwaters, demonstrating an overall agreement.
Our simulations, in particular, well reproduce the Mg-depleting maturation path of hydrothermal solutions, and have end-of-run model solutions whose Na–K–Mg compositions well reflect attainment of full-equilibrium conditions at run temperature.
High-temperature (180–260° C) model runs are those best matching the Na–K–Mg compositions of Ischia’s most chemically
mature water samples, supporting quenching of deep-reservoir conditions for these surface manifestations; whilst Fe, SiO2 and, to a lesser extent, SO4 contents of natural samples are better reproduced in low-temperature (95°C) runs, suggesting that these species reflect conditions of water–rock interaction in the shallow hydrothermal environment. The ability of model runs to reproduce the compositional features of Ischia’s thermal manifestations, demonstrated here, adds supplementary confidence
on reaction path modelling as a realistic and insightful representation of mineral–fluid hydrothermal reactions. Our results, in particular, demonstrate the significant impact of host rock minerals’ assemblage in governing the paths and trends of hydrothermal fluids’ maturation
Upper Palaeolithic hunter-gatherer subsistence in Mediterranean coastal environments: an isotopic study of the diets of earliest directlyt-dated humans from Sicily
Polar distortions in hydrogen bonded organic ferroelectrics
Although ferroelectric compounds containing hydrogen bonds were among the
first to be discovered, organic ferroelectrics are relatively rare. The
discovery of high polarization at room temperature in croconic acid [Nature
\textbf{463}, 789 (2010)] has led to a renewed interest in organic
ferroelectrics. We present an ab-initio study of two ferroelectric organic
molecular crystals, 1-cyclobutene-1,2-dicarboxylic acid (CBDC) and
2-phenylmalondialdehyde (PhMDA). By using a distortion-mode analysis we shed
light on the microscopic mechanisms contributing to the polarization, which we
find to be as large as 14.3 and 7.0\,C/cm for CBDC and PhMDA
respectively. These results suggest that it may be fruitful to search among
known but poorly characterized organic compounds for organic ferroelectrics
with enhanced polar properties suitable for device applications.Comment: Submitte
Revised seismic classification of the ITACA stations, according to the EC8 and the Italian norms site classes
The activities carried out within Task 2 aim to collect, organize and synthesize geological, geomorphological, geotechnical and geophysical data for the location site of the Accelerometric National Network (RAN) stations in Italy, managed by the Department of Civil Protection, to improve the knowledge about the subsoil (see Delverable D05) and to permit a subsoil and topographic site classification based on EC8 categories.
At the end of the project the subsoil of 695 stations have been classified using an hybrid
approch, based on surface geology, spectral classification and Vs profils from different
recording tecniques (DH, CH, MASW, ESAC).
These activities have been useful to link the ITACA database with the software REXEL to
select natural accelerograms, compatible with Norme Tecniche per le Costruzioni (NTC2008) and EUROCODE 8 (EC8) spectra, which may also reflect characteristics of the source in terms of magnitude and epicentral distance. For 688 station sites have been provided also a topographic classification using a GIS based semiautomatic method with “by-hand” corrections using topographic maps and/or Google Earth software.
A Microsoft Excel Database which also allows to track all changes that have been made since the beginning of the project related to the site classification has been developed
Predominant-period site classification for response spectra prediction equations in Italy
We propose a site-classification scheme based on the predominant period of the site, as determined from the average horizontal-to-vertical (H/V) spectral ratios of ground motion. Our scheme extends Zhao et al.(2006) classifications by adding two classes, the most important of which is defined by flat H/V ratios with amplitudes less than 2. The proposed classification is investigated by using 5%-damped response spectra from Italian earthquake records. We select a dataset of 602 three-component analog and digital recordings from 120 earthquakes recorded at 214 seismic stations within a hypocentral distance of 200 km. Selected events are in the moment-magnituderange 4.0 ≤ Mw ≤ 6.8 and focal depths from a few kilometers to 46 km. We computed H/V ratios for these data and used them to classify each site into one of six classes. We then investigate the impact of this classification scheme on empirical
ground-motion prediction equations (GMPEs) by comparing its performance with that
of the conventional rock/soil classification. Although the adopted approach results in only a small reduction of the overall standard deviation, the use of H/V spectral ratios in site classification does capture the signature of sites with flat frequency-response, as well as deep and shallow-soil profiles, characterized by long- and short-period resonance, respectively; in addition, the classification scheme is relatively quick and inexpensive, which is an advantage over schemes based on measurements of shear wave velocity
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