1,720,957 research outputs found
New magnet design for fast-field-cycling nuclear magnetic resonance
Get PDFA new magnet design for fast-field-cycling nuclear magnetic resonance is described. A topic of interest is the compensation of the magnetic field homogeneity during the generation of the pulsed magnetic field. In contrast with previous solutions, the magnet system here discussed can be electronically controlled. In Kelvin-type magnets used today, the homogeneity of the field is set-up through a current density distribution along the air-cored cylinders that compose the magnet coil. A common feature of this type of magnets is that the magnetic field value and its homogeneity are affected by thermo-mechanical stress during the strong current pulses applied to the coil. In the new design here presented, the problem can be circumvented through a multicoil arrangement driven by individual current sources, allowing an automatic correction of the magnetic field drift and the homogeneity.Fil: Kruber, Stephan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Farrher, German David. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Anoardo, Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin
Air core notch-coil magnet with variable geometry for fast-field-cycling NMR
Get PDFIn this manuscript we present details on the optimization, construction and performance of a wide-bore (71 mm) α-helical-cut notch-coil magnet with variable geometry for fast-field-cycling NMR. In addition to the usual requirements for this kind of magnets (high field-to-power ratio, good magnetic field homogeneity, low inductance and resistance values) a tunable homogeneity and a more uniform heat dissipation along the magnet body are considered. The presented magnet consists of only one machined metallic cylinder combined with two external movable pieces. The optimal configuration is calculated through an evaluation of the magnetic flux density within the entire volume of interest. The magnet has a field-to-current constant of 0.728 mT/A, allowing to switch from zero to 0.125 T in less than 3 ms without energy storage assistance. For a cylindrical sample volume of 35 cm3 the effective magnet homogeneity is lower than 130 ppm.Fil: Kruber, Stephan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Resonancia Magnética Nuclear; ArgentinaFil: Farrher, German David. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Resonancia Magnética Nuclear; ArgentinaFil: Anoardo, Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Resonancia Magnética Nuclear; Argentin
New Trends in Field-Cycling NMR Technology
No full textThis chapter discusses different aspects related to the evolution and current state of fast field-cycling NMR technology. Technical advances affect NMR in two main ways: by extending and improving the capabilities and performance of machines and consequently, increasing the quality and reliability of measurements in a broader range, with a direct impact on the significance of the derived results. But it also opens up unexplored possibilities for new applications and experimental conditions that were previously unattainable owing to technical limitations. Field-cycling apparatus provides excellent platforms for engineering research, from magnet technology to control and power electronics and low-noise sensing, among others. Both the historical frame and the state of the art are considered. The chapter focuses on selected topics where the group in Córdoba has concentrated its efforts in recent years, but also considers the remarkable work done by other colleagues worldwide. Finally, a future scenario for the field-cycling technique is ventured.Fil: Anoardo, Esteban. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Kruber, Stephan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Forte, Guillermo Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Dominguez, Gabriela Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin
Comparative study of helical-cut notch–coil magnets for fast-field-cycling nuclear magnetic resonance
Get PDFIn this manuscript we describe an -helical-cut notch–coil magnet system designed for fast switching of the magneticfield. An attempt was made to determine the extent to which such a magnet configuration can be efficiently used for fast-field-cycling (FFC) nuclear magnetic resonance (NMR) instruments. In addition to the typical technical requirements (high field-to-power ratio, adequate electric performance for fast-switching of the magnetic field and NMR-compatible magnetic fieldhomogeneity), a tunable homogeneity within the sample volume and more uniform heat dissipation along the magnet body areincluded. A helical-cut notch–coil machined in metallic cylinders with external movable pieces was found to fit these require-ments very well. A key factor for the optimization of the magnet parameters is the use of a novel calculation procedure based ona more realistic model that consider a magnet geometry with broken azimuthal symmetry. The aim of this paper is to theoret-ically compare the proposed geometry with other existing designs. No particular prototype is presented here. A clear under-standing of the notch–coil performance was found to be an essential step for its further consideration as a potential autoadaptive(electronically controlled) magnet system for FFC applications.Nous décrivons ici un système magnétique, comportant une bobine avec une coche hélicoïdale, destiné a`unecommutation cyclique rapide du champ magnétique. Nous tentons de déterminer si cette configuration serait efficace dans uninstrument de résonance magnétique nucléaire (RMN) a`cycle rapide du champ. En plus des exigences techniques habituelles(haut rapport champ/puissance, bonne performance électrique dans la commutation rapide du champ magnétique et unehomogénéité de champ compatible avec des mesures de RMN), nous incluons une homogénéité ajustable du champ magnétiquedans le volume de l’échantillon et une dissipation plus uniforme de la chaleur le long de l’aimant. Nous trouvons qu’une bobineavec une coche hélicoïdale usinée dans des cylindres métalliques avec pièces extérieures déplaçables remplit très bien cesexigences. Un facteur clé dans l’optimisation des paramètres de l’aimant est l’utilisation d’une nouvelle procédure de calculbasée sur un modèle réaliste qui considère une géométrie d’aimant dont la symétrie azimutale est brisée. Notre objectif ici estde comparer théoriquement la géométrie que nous proposons avec d’autres existant déja`. Nous ne présentons aucun prototype.Une compréhension claire de la performance d’une bobine avec coche est une étape essentielle pour évaluer son potentielcomme système magnétique.Fil: Kruber, Stephan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Farrher, German David. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Anoardo, Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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