1,721,048 research outputs found
Effect of age on Pine wood microstructure studied by micro-MRI and diffusion-NMR
No full textWood is a natural complex material widely used from men in the past to create artworks. One of its main anatomical elements is the annual ring that varies according to the species, the weather conditions under which the tree has grown and to possible adversities. To observe the anatomy of waterlogged archaeological wood could be complicated because of its degradation. However, knowing the state of conservation is very important for the future restoration. In this work a non-destructive approach based on the combined use of MRI and diffusion on the modern and ancient pine wood is presented. Micro-MR images allow to observe the diagnostic features. The molecular NMR diffusion analysis, with the estimation of the pores diameter and the tortuosity, provide important information about the effect of age on the wood microstructure. At the end of the analysis the unaltered sample can be repositioned in its original location on the artwork
Molecular diffusion and perfusion of biological water quantified by MRI for the diagnosis of pathological human placentas
No full textThe study aimed to find biomarkers to characterize and differentiate healthy and pathological placentas using the nuclear magnetic resonance diffusion weighted imaging (DWI) technique. Fetal and maternal placentas tissues are characterized by a different diffusion behavior. Diffusion and perfusion can be quantified using intravoxel-incoherent-motion (IVIM) model of DWI signal acquired using a specific acquisition sequence. The dataset is divided into two groups: 33 healthy subjects and 15 pathological subjects classified as Fetal Growth Restriction (FGR) by an ultrasound investigation. The perfusion fraction f has a significant difference between fetal and maternal side which is connected to the role of the villi involved in the exchange of nutrients between fetal and maternal blood. It also discriminates healthy and FGR placentas. In conclusion, diffusion and perfusion of water quantified by DWI is a powerful non-invasive, radiation-free tool for prenatal diagnosis
Effetti del superfluidificante sull’idratazione del silicato tricalcico studiati tramite Risonanza Magnetica Nucleare
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Stone structure properties determination by Nuclear Magnetic Resonance Imaging and relaxation
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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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The γ parameter of the stretched-exponential model is influenced by internal gradients: Validation in phantoms
No full textIn this paper, we investigate the image contrast that characterizes anomalous and non-Gaussian diffusion images obtained using the stretched exponential model. This model is based on the introduction of the gamma stretched parameter, which quantifies deviation from the mono-exponential decay of diffusion signal as a function of the b-value. To date, the biophysical substrate underpinning the contrast observed in gamma maps, in other words, the biophysical interpretation of the gamma parameter (or the fractional order derivative in space, beta parameter) is still not fully understood, although it has already been applied to investigate both animal models and human brain. Due to the ability of gamma maps to reflect additional microstructural information which cannot be obtained using diffusion procedures based on Gaussian diffusion, some authors propose this parameter as a measure of diffusion heterogeneity or water compartmentalization in biological tissues. Based on our recent work we suggest here that the coupling between internal and diffusion gradients provide pseudo-superdiffusion effects which are quantified by the stretching exponential parameter gamma. This means that the image contrast of M gamma maps reflects local magnetic susceptibility differences (Delta chi(m)), thus highlighting better than T-2*; contrast the interface between compartments characterized by Delta chi(m). Thanks to this characteristic, M gamma imaging may represent an interesting tool to develop contrast-enhanced MRI for molecular imaging.The spectroscopic and imaging experiments (performed in controlled micro-beads dispersion) that are reported here, strongly suggest internal gradients, and as a consequence Delta chi(m), to be an important factor in fully understanding the source of contrast in anomalous diffusion methods that are based on a stretched exponential model analysis of diffusion data obtained at varying gradient strengths g. (C) 2012 Elsevier Inc. All rights reserved
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