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Search Results: 1 - 10 of 200663 matches for " P. Mazzetti "
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Preface Earth System Science Data access, distribution and use for education and research
L. Bigagli, S. Nativi,P. Mazzetti
Advances in Geosciences (ADGEO) , 2006,
Abstract: We address the problem of data and information interoperability in the Earth System Science information domain. We believe that well-established architectures and standard technologies are now available to implement data interoperability. In particular, we elaborate on the mediated approach, and present several technological aspects of our implementation of a Mediator-based Information System for Earth System Science Data. We highlight some limitations of current standard-based solutions and introduce possible future improvements.
Current noise in high Tc granular superconductors under non-stationary conditions of current and magnetic field
P. Mazzetti,P. Tura,A. Masoero,A. Stepanescu
Physics , 2003, DOI: 10.1117/12.490199
Abstract: We present a set of experimental results concerning the power spectrum of current noise, detected on a granular high Tc superconductor submitted either to a slowly varying magnetic field or to a varying current intensity. Experiments were performed on a YBCO specimen suitably treated in order to weaken the weak links without affecting the oxygen content of grains. The weakening of the intergrain region allowed the use of very small magnetic fields and currents to induce the resistive transition of the specimen and to observe current noise. The induced noise is of the 1/f^2 type and will be interpreted in terms of two different models. One of the model is based on the enhancement of the noise due to the clustering of the resistive transition of the weak links, produced by correlation effects related to the strong nonlinearity of their Josephson type I-V characteristics. This model has been the object of a computer simulation based on a 3D-network of Josephson-like elements and seems suitable to explain the noise produced by current variation. The second model explains the excess noise as produced by discontinuous penetration of the magnetic flux inside the intergrain region. This discontinuity is related to the field screening effect of rings made of several superconducting weak links connecting different grains, which are alternatively broken and restored by the current induced during flux variation, and seems suitable to explain the larger noise produced by a varying magnetic field.
Barkhausen-like conductance noise in polycrystalline high Tc superconductors immersed in a slowly varying magnetic field
A. Masoero,P. Mazzetti,I. Puica,A. Stepanescu,P. Tura
Physics , 2001,
Abstract: Analysis of the resistive transition of a polycristalline YBCO specimen produced by an a.c. magnetic field, reveals the presence of a large conductance noise signal which is repetitive over subsequent magnetization cycles. It is shown that the noise arises from avalanche effects produced by the simultaneous resistive transition of large groups of weak links. Owing to its repeatability, the noise signal may be considered a sort of signature of the weak links critical current distribution, making it an interesting new tool for the study of high Tc ceramic superconductors, as reported measurements of noise hysteresis show.
Electrical anisotropy in high-Tc granular superconductors in a magnetic field
D. Daghero,P. Mazzetti,A. Stepanescu,P. Tura,A. Masoero
Physics , 2002, DOI: 10.1103/PhysRevB.66.184514
Abstract: We propose an analytical model devoted to explain the anisotropy of the electrical resistance observed below the critical temperature in granular high-Tc superconductors submitted to a magnetic field H. Reported experimental results obtained on a YBCO sample show that the superconducting transition occurs in two stages, with a steep drop of the resistance at Tc and a subsequent, smoother decrease. In this second stage, the resistance vs. temperature curve is strongly dependent not only on the field intensity, but also on the angle between H and the macroscopic current density j. We start from the assumption that the resistance below Tc is mainly due to the weak links between grains. In the model, weak links are thought of as flat surface elements separating adjacent grains. We calculate the probability for a weak link to undergo the transition to the resistive state, as a function of the angles it makes with the external magnetic field H and the macroscopic current density j. In doing this, an important role is given to the strong non-uniformity of the local magnetic field within the specimen, due to the effect of the screening supercurrents flowing on the surface of the grains. Finally, we calculate the electrical resistance of the sample in the two cases where H is parallel and perpendicular to j, respectively. The predictions of this simple model turn out to be in reasonable agreement with reported experimental results obtained on a YBCO granular specimen.
A Spatial Data Infrastructure for the Global Mercury Observation System
Cinnirella S.,D’Amore F.,Mazzetti P.,Nativi S.
E3S Web of Conferences , 2013, DOI: 10.1051/e3sconf/20130128001
Abstract: The Global Mercury Observation System (GMOS) Project includes a specific Work Package aimed at developing tools (i.e. databases, catalogs, services) to collect GMOS datasets, harvest mercury databases, and offer services like search, view, and download spatial datasets from the GMOS portal (www.gmos.eu). The system will be developed under the framework of the Infrastructure for Spatial Information in the European Community (INSPIRE) Directive and the Directive 2003/4/EC on public access to environmental information, which both aim to make relevant, harmonized, high-quality geographic information available to support the formulation, implementation, monitoring, and evaluation of policies and activities that have a direct or indirect impact on the environment. Three databases have been proposed (on emissions, field data and model results), and each will be equipped with state-of-the-art, open-source software to allow for the highest performance possible. Web-based user-interfaces and prototype applications will be developed to demonstrate the potential of blending different datasets from different servers for environmental assessment studies. Several services (i.e. catalog browsers, WMS and WCS services, web GIS services) will be developed to facilitate data integration, data re-use, and data exchange within and beyond the GMOS project. Different types of measurement and model datasets provided by project partners and other sources will be integrated into PostgreSQL-PostGIS, harmonized by creating INSPIRE-compliant metadata and made available to a larger community of stakeholders, policy makers, scientists, and NGOs (as well as to other public and private institutions, as dictated by the Directive 2003/4/EC). Since interoperability is a central concept for the Global Earth Observation System of Systems (GEOSS), the Global Monitoring for Environmental and Security (GMES) and the INSPIRE Directive, guidelines developed in these three frameworks will be adopted. The use of standards will be a key concern throughout the encoding process. We will use the international standards for data and spatial schemas (ISO19107, ISO14825), for metadata (ISO19115:2003, ISO/DTS19139:2005, ISO15836) and for services (WMS 1.1.1, WFS 1.0, SLD 1.0, GML 3.1). On the other side, we will use XML for data exchange, together with SOAP, XSD, J2EE (for applications development) and W3C (for standard interfaces). With specific reference to GMES, the global database on mercury monitoring and the GMOS model outputs will be made available through a series of monitoring, forecast and re-an
Generalized Theory of Electrical Conductivity and Current Noise for Discontinuous Metal Films Over a Wide Range of Temperatures
M. Celasco,A. Masoero,P. Mazzetti,A. Stepanescu
Active and Passive Electronic Components , 1980, DOI: 10.1155/apec.7.39
Abstract:
The GEOSS Common Infrastructure for the heavy metal pollution community applications
Mazzetti P.,Nativi S.,Santoro M.,Boldrini E.
E3S Web of Conferences , 2013, DOI: 10.1051/e3sconf/20130118002
Abstract:
Array of Josephson junctions with a non-sinusoidal current-phase relation as a model of the resistive transition of unconventional superconductors
A. Carbone,M. Gilli,P. Mazzetti,L. Ponta
Physics , 2009, DOI: 10.1063/1.3525984
Abstract: An array of resistively and capacitively shunted Josephson junctions with nonsinusoidal current-phase relation is considered for modelling the transition in high-T$_c$ superconductors. The emergence of higher harmonics, besides the simple sinusoid $I_{c}\sin\phi$, is expected for dominant \emph{d}-wave symmetry of the Cooper pairs, random distribution of potential drops, dirty grains, or nonstationary conditions. We show that additional cosine and sine terms act respectively by modulating the global resistance and by changing the Josephson coupling of the mixed superconductive-normal states. First, the approach is applied to simulate the transition in disordered granular superconductors with the weak-links characterized by nonsinusoidal current-phase relation. In granular superconductors, the emergence of higher-order harmonics affects the slope of the transition. Then, arrays of intrinsic Josephson junctions, naturally formed by the CuO$_2$ planes in cuprates, are considered. The critical temperature suppression, observed at values of hole doping close to $p=1/8$, is investigated. Such suppression, related to the sign change and modulation of the Josephson coupling across the array, is quantified in terms of the intensities of the first and second sinusoids of the current-phase relation. Applications are envisaged for the design and control of quantum devices based on stacks of intrinsic Josephson junctions.
Resistive transition in granular disordered high-T$_c$ superconductors: a numerical study
L. Ponta,A. Carbone,M. Gilli,P. Mazzetti
Physics , 2009, DOI: 10.1103/PhysRevB.79.134513
Abstract: The resistive transition of granular high-T$_c$ superconductors, characterized by either weak (YBCO-like) or strong (MgB$_2$-like) links, occurs through a series of avalanche-type current density rearrangements. These rearrangements correspond to the creation of resistive layers, crossing the whole specimen approximately orthogonal to the current density direction, due to the simultaneous transition of a large number of weak-links or grains. The present work shows that exact solution of the Kirchhoff equations for strongly and weakly linked networks of nonlinear resistors, with Josephson junction characteristics, yield the subsequent formation of resistive layers within the superconductive matrix as temperature increases. Furthermore, the voltage noise observed at the transition is related to the resistive layer formation process. The noise intensity is estimated from the superposition of voltage drop elementary events related to the subsequent resistive layers. At the end of the transition, the layers mix-up, the step amplitude decreases and the resistance curve smoothes. This results in the suppression of noise, as experimentally found. Remarkably, a scaling law for the noise intensity with the network size is argued. It allows to extend the results to networks with arbitrary size and, thus, to real specimens.
CDI/THREDDS interoperability in the SeaDataNet framework
S. Nativi, P. Mazzetti, M. Santoro, E. Boldrini, G. M. R. Manzella,D. M. A. Schaap
Advances in Geosciences (ADGEO) , 2010,
Abstract: SeaDataNet is an EU funded project aiming to create and operate a pan-European, marine data infrastructure for managing the large and diverse datasets (i.e. temperature, salinity current, sea level, chemical, physical and biological properties) collected by the oceanographic fleets and the new automatic observation systems. In order to make the SeaDataNet system compliant with the INSPIRE Implementing Rules for discovery service, an ISO 19139 encoding of the SeaDataNet Common Data Index (CDI) metadata model was defined. Moreover, the problem of heterogeneous data sources has been addressed. In fact, a widely used system of SeaDataNet partners and oceanographic-marine community is THREDDS/OPeNDAP; this raises up the problem of federating into SeaDataNet framework THREDDS/OPeNDAP systems as well. In this paper we describe an interoperability framework to access resources (i.e. data and services) that are available through CDI and THREDDS/OPeNDAP services. The proposed solution implements a common catalog interface to discover and access the two heterogeneous resources in a common way. This catalog service is fully distributed and implements international standards as far as geospatial information discovery and query are concerned. The developed solution is called GI-cat and was experimented in the framework of the SeaDataNet European project.
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