1,721,143 research outputs found
TUFFACEOUS DEPOSITS IN THE SEDIMENTARY COVER OF THE STRONA-CENERI ZONE AND IN THE VILLAFORTUNA-TRECATE OIL SYSTEM: PETROLOGICAL, GEOCHEMICAL AND GEOCHRONOLOGICAL CHARACTERIZATION
No full textIn the western sector of the Southern Alps, tuffaceous levels are occasionally found in Triassic sedimentary sequences and the age of the related magmatism is still matter of debate. The few available geochronological data on these tuffites (M. San Giorgio area, Lugano, CH) yield Triassic ages (245±1 Ma; U-Pb zircon [1]), which are slightly older than the stratigraphic position. The precise definition of the tuffite age is, however, important for the Triassic evolution of the western Alps. In particular, if the magmatism is synchronous with their stratigraphic position, tuffites might be linked to the Triassic magmatism documented by the Finero area (NE Ivrea-Verbano Zone [2]). However, it cannot be presently excluded that they are the product of erosion and re-deposition of the Permian acid volcanics located at the base of the Mesozoic sedimentary cover [3].In this work, we have considered the tuffaceous deposits occurring within a late Anisian-Ladinian succession in the Mesozoic sedimentary cover of the Strona-Ceneri Zone in the Borgosesia area [3,4] and the tuffites at the same stratigraphic position found in some wells of the Villafortuna-Trecate oil system field (western Po Plain, Piedmont region, NW Italy) [5]. These tuffaceous deposits are constituted by a variable mixture of magmatic and sedimentary components. Available chamical data on the magmatic component suggests a calc-alkaline affinity. Zircons have been separated with conventional methods from four samples, mounted in epoxy resin and characterised under cathodoluminescence (CL). Based on colour, morphology and internal structure, zircons have been divided in two populations. One group is constituted by light-pink coloured zircons with prismatic habits and tight osciscillatory zoning suggesting growth under magmatic conditions. Zircons from the second group are colourless, rounded in shape and with only relics of magmatic zoning. They most likely suffered metamorphic recrystallization.Ongoing ELA-ICP-MS characterizations of both trace elements composition and U-Pb age of these zircons is expected to provide valuable constraints on the geodynamic evolution of the Southern Alps Domain in Permo-Triassic times.References. [1] Mundil, R., Brack, P., Meier, M., Rieber, H., Oberli, F. (1996): Earth and Planetary Science Letters, 141, 137-151; [2] Peressini, G., Mazzucchelli, M., Rivalenti, G., Hofmann, A.W. (2004): Geophysical Research Abstracts, 6, 05072, SRef-ID: 1607-7962/gra/EGU04-A-05072; [3] Carraro, F., Fiora, L. (1974): Riv. It. Paleont. Strat., 80, 167-191; [4] Fantoni, R., Decarlis, A., Fantoni, E. (2004): Atti Tic. Sc. Terra, 44, 97-110; [5] Fantoni, R., Bello, M., Ronchi, P., Scotti, P. (2002): Extended Abstracts Book EAGE Conference Florence
Laser induced fluorescence applied to diagnosis in calcareous stones
No full textThe Laser Induced Fluorescence (LIF) technique has been already proved to be a powerful diagnostic tool for artworks. The aim of this work is to validate LIF measurements to detect the different detrimental effects of the environmental conditions on the stone materials and to discriminate among different biofilms and crust from smog or pollutants, in order to optimize the restorers’ interventions. A scanning LIF system at 266 nm excitation wavelength has been employed. The line scanning system has operated in two operating mode: reflectance and fluorescence. Reflectance measurements are made by performing a scan while the laser is off and the sample is exposed to the light emitted by a NIST traceable lamp. The result gives for each pixel of the scanned area the reflectance spectrum, from which the CIE/lab coordinates can be computed once the system is calibrated against a reference surface. The samples were placed on a holder for LIF measurements. The acquisition system was placed at than 3.5 m distance from the target and several images acquired with a spatial resolution of approximately 0.0025 m. The most relevant spectral features of crusts are identified by Principal Component analysis. Three groups of samples can be detected: a) samples with blue false color in the images, that are mainly formed by biocrust, b) samples mainly composed with crust and deposits with yellow or green colour, c) samples with no difference between faces. These classifications of samples are mainly according to the results obtained by morphometric techniques. LIF and reflectance measures seems a very powerful technique in this preliminary results, to discriminate the presence of biocrust and crusts/deposits with more sensitive that a naked-eye at 2.5 m of monuments. © 2014 Taylor & Francis Group, London
Paleobathymetry of the Southalpine foreland basin (Cenozoic, NE Italy) inferred from micropaleontological and geometrical data
No full textLaser spectroscopy and imaging applications for the study of cultural heritage murals
No full textLaser induced fluorescence (LIF) associated with imaging scanning techniques has already proved to be a powerful diagnostic tool for artworks. The aim is to assess on-site and remote sensing systems and imaging measurements on murals in order to detect vulnerability and weathering forms due to the effects of environmental conditions. It also seeks to identify treatments in order to optimize interventions by restorers. Four murals (16-18th centuries) were studied using a LIF prototype remotely operating in reflectance and fluorescence mode. Relevant spectral features are identified using principal component analysis and a spectral angle mapper to assess surfaces using imaging applications. The combination of these methods makes possible to identify bio-crust, fissures and the presence of different treatments. © 2015 Elsevier Ltd. All rights reserved
Wertheim perturbation theory: Thermodynamics and structure of patchy colloids
No full textWe critically discuss the application of the Wertheims theory to classes of complex associating fluids that can be today engineered in the laboratory as patchy colloids and to the prediction of their peculiar gas-liquid phase diagrams. Our systematic study, stemming from perturbative version of the theory, allows us to show that, even at the simplest level of approximation for the inter-cluster correlations, the theory is still able to provide a consistent and stable picture of the behaviour of interesting models of self-assembling colloidal suspension. We extend the analysis of a few cases of patchy systems recently introduced in the literature. In particular, we discuss for the first time in detail the consistency of the structural description underlying the perturbative approach and we are able to prove a consistency relationship between the valence as obtained from thermodynamics and from the structure for the one-site case. A simple analytical expression for the structure factor is proposed
Laser Induced Breakdown Spectroscopy in archeometry: A review of its application and future perspectives
No full textLaser Induced Breakdown Spectroscopy (LIBS) in the last decades has been more and more applied to the field of Cultural Heritage with great results obtained either alone or in combination with complementary laser techniques. Its ability to analyze, with a minimal loss, different kinds of materials in laboratory, in situ and even in hostile environments has been highly appreciated. The main aim of this paper is to present a review of LIBS applications in the interdisciplinary field of archeometry. The LIBS technique is shortly described both from a theoretical and practical point of view, discussing the instrumental setup, also in comparison with typical features of laser induced fluorescence (LIF) and Raman spectroscopy apparata. The complementary with multivariate analysis, a method that can help in reducing data set dimensions and in pulling out effective information, is stressed. In particular the role of LIBS in Cultural Heritage material characterization, recognition of fakes and indirect dating is described, reporting general considerations and case studies on metal alloys, mural paintings, decorated ceramics, glasses, stones and gems. © 2014 Elsevier B.V
Applications of laser induced breakdown spectroscopy for cultural heritage: A comparison with XRF and PIXE techniques
No full textWith the aim to establish advantages and limitations of techniques commonly employed for material characterization of Cultural Heritage objects, we performed comparative measurements by LIBS, X-ray Fluorescence (XRF) and Particle Induced X-ray Emission (PIXE) on four typologies of materials. The samples include: 1) egg tempera pigments on gypsum ground; 2) oil paints on gypsum ground with light or dark imprimitura; 3) fragments of decorated glazed ceramic, and 4) ancient Roman coins. The optimal choice of an analytical instrument depends also on the sample type, its dimensions and transportability, and for these reasons our measurements involved two types of instruments per technique. The LIBS probing was done by a table-top instrument (on coins and ceramics) and by a stand-off system at distance of 9.5 m (on pigments). The XRF measurements involved a laboratory micro-XRF system (on coins) and a portable instrument (on pigments and ceramics). The PIXE analyses were obtained by TOP-IMPLART accelerator at ENEA Frascati, using a low energy line that produces the proton beam with adjustable energy between 3 and 7 MeV (used for the pigments and ceramics), and by INFN-LABEC system with proton energy of 3 MeV and complemented by Elastic Backscattering Spectrometry (EBS), for coin samples. Results relevant to quantitative analysis of major sample constituents, identification of trace components, and stratigraphy are reported and discussed for the examined typologies of samples. © 2018 Elsevier B.V
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Thermodynamic instabilities of a binary mixture of sticky hard spheres
No full textThe thermodynamic instabilities of a binary mixture of sticky hard spheres (SHS) in the modified mean spherical approximation (mMSA) and the Percus–Yevick (PY) approximation are investigated using an approach devised by Chen and Forstmann [J. Chem. Phys. 97, 3696 (1992)]. This scheme hinges on a diagonalization of the matrix of second functional derivatives of the grand canonical potential with respect to the particle density fluctuations. The zeroes of the smallest eigenvalue and the direction of the relative eigenvector characterize the instability uniquely. We explicitly compute three different classes of examples. For a symmetrical binary mixture, analytical calculations, both for mMSA and for PY, predict that when the strength of adhesiveness between like particles is smaller than the one between unlike particles, only a pure condensation spinodal exists; in the opposite regime, a pure demixing spinodal appears at high densities. We then compare the mMSA and PY results for a mixture where like particles interact as hard spheres (HS) and unlike particles as SHS, and for a mixture of HS in a SHS fluid. In these cases, even though the mMSA and PY spinodals are quantitatively and qualitatively very different from each other, we prove that they have the same kind of instabilities. Finally, we study the mMSA solution for five different mixtures obtained by setting the stickiness parameters equal to five different functions of the hard sphere diameters. We find that four of the five mixtures exhibit very different type of instabilities. Our results are expected to provide a further step toward a more thoughtful application of SHS models to colloidal fluids
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