1,721,009 research outputs found
Single-sided NMR Analysis on Model Systems for the Evaluation of in situ Measurements on Cultural Heritage Materials
No full textNMR relaxometry and IR thermography to study ancient cotton paper bookbinding
No full textDefects related to degradation were observed in an ancient book paperboard cover through nuclear magnetic resonance relaxometry and infrared thermography. Data collected with this combined method allowed identifying areas with moisture content and thermal diffusivity anomalies within the front board, corresponding to the different conservation status of the cellulose-based material. Non-destructive testing analytical procedures provide comprehensive knowledge for preserving precious library archives
Pore-size evaluation by single-sided nuclear magnetic resonance measurements: Compensation of water self-diffusion effect on transverse relaxation
No full textThe determination of penetration depth and distribution of water at surfaces is essential to knowledge of the state of conservation of Cultural Heritage items and materials, such as frescoes, stone, brick, wood, and paper. Water can penetrate the surface of an object, coming from either an external or an internal source, and in general the moisture content of the surface region is the cause of various decay phenomena such as microfractures and disintegration. The nuclear magnetic resonance (NMR) approach can be very powerful for the evaluation of the state of fine arts materials. Not only the water saturation and?or the porosity of the material can be evaluated but also information on material pore-size distributions can be obtained by monitoring the distributions of relaxation times of the transverse (T2) and longitudinal (T1) components of the magnetization of the trapped water. The drawback is that generally the sample does not fit into standard NMR magnets, and for in situ application, single-sided NMR devices have to be used. Therefore, the standard methods to get NMR parameters are not always valid, and some alternative procedures have to be performed. For example, in strongly inhomogeneous magnetic fields due to the geometrical features of single-sided NMR devices, the transverse relaxation is greatly influenced by the molecular self-diffusion even at the shortest interpulse time available for a Carr–Purcell–Meiboom–Gill (CPMG) sequence. In this paper we show how the dephasing effect due to molecular self-diffusion can be corrected by using the “constant echo time method.” We report an attempt to recover the corrected T2 distribution in well-characterized porous materials saturated with water, with data acquired in the highly inhomogeneous magnetic field of a single-sided NMR device. The results are discussed and compared with those acquired on the same samples in the highly homogeneous magnetic field of a traditional NMR instrument
Two-dimensional longitudinal and transverse relaxation times correlation as a low-resolution nuclear magnetic resonance characterization of ancient ceramics
No full textPore-size evaluation by single-sided nuclear magnetic resonance measurements: compensation of water self-diffusion effect on trasverse relaxation
No full textA portable NMR sensor for moisture monitoring of wooden works of art, particularly of painting on wood
No full textIt is proposed the use of a mobile device based on a NMR single-sided sensor for in situ non-invasive determination of the moisture content (MC) of wood items, especially items of Cultural Heritage interest. The MC is obtained through the moisture volume fraction, which is an appropriate quantity for the sensor and corresponds to the fraction of its measurements sensitive volume occupied by water. The device has been used here to track changes in MC of wood specimens caused by changes over time of the environmental relative humidity. The kinetics of water adsorption has been related to results obtained with the gravimetric method. Measurements on an old painting, the Pietà (1516–1517), oil on a poplar wood panel by Sebastiano del Piombo (1485 Venice, 1547 Rome), Civic Museum, Viterbo, Italy, have shown, conclusively, the good sensitivity of the sensor and its capability to behave as a non-invasive and in situ utilizable device. Results of in situ painting measurements show that the NMR sensor can track moisture fluctuations that are outside the sensitivity range and precision of electro-hygrometric approach
Dense fluid displacement in wet porous media by spin relaxation selective contrast
No full textLow field Magnetic Resonance Imaging is used to study oil diffusion in a wet soil model. A complete discrimination between oil and water has been obtained by using Inversion-Recovery pulse sequence. The time evolution of the oil image gives the parameters which describe the dense fluid diffusion rate in the whole space directions. © 1993 Springer
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
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