1,720,962 research outputs found
Harmonics of the AC susceptibility as probes to differentiate the various creep models
No full textWe measured the temperature dependence of the first and the third harmonics of the AC magnetic susceptibility on some type II superconducting samples at different AC field amplitudes, hAC. In order to interpret the measurements, we computed the harmonics of the AC susceptibility as function of the temperature T, by integrating the non-linear diffusion equation for the magnetic field with different creep models, namely the vortex glass-collective creep (single-vortex, small bundle and large bundle) and Kim–Anderson model. We also computed them by using a non-linear phenomenological I–V characteristics, including a power law dependence of the pinning potential on hAC. Our experimental results were compared with the numerically computed ones, by the analysis of the Cole–Cole plots. This method results more sensitive than the separate component analysis, giving the possibility to obtain detailed information about the contribution of the flux dynamic regimes in the magnetic response of the analysed samples
Flux Dynamics and Critical State in YBCO by AC Harmonic Susceptibility
No full textThe temperature dependences of the third harmonics of the AC susceptibility, χ3′(T) and χ3′′(T), have been used to study the vortex dynamics in Melt Textured YBCO. The experimental curves measured at different AC field amplitudes and frequencies, have been compared with the simulations of χ3′(T) and χ3′′(T) obtained by considering the diffusion of the magnetic flux in the presence of different dynamic regimes. The comparison made as function of the AC field frequency shows that, at low frequencies, the magnetic response is mainly described in terms of a Bean critical state model. As the frequency is increased, the contributions coming from the flux dynamic regimes become predominant. Nevertheless, at the highest frequencies, contrary to what was expected, the curves appear again very similar to the ones simulated in terms of a pure Bean critical state model
Detection of a “vortex glass phase” in YBCO polycrystalline samples by ac magnetic measurements
No full textTransition between the Bragg glass and the disordered phase in Nb3Sn detected by third harmonics of the ac magnetic susceptibility.
No full textWe report on experimental evidence of the presence of a universal behavior in the field-temperature phase diagram of type II superconductors, characterized by a phase transition in the vortex matter between the disordered and the Bragg glass phase. The experimental detection of a peak effect phenomenon has been proved to be strictly connected to the existence of this phase transition. In this paper, we show an observation of a peak effect in the compound Nb3Sn, by using first harmonics of the ac magnetic susceptibility. Peak effect has been detected at fields between 3 and 13 T, whereas it is not observable at higher fields. This seems to be in contrast with the theoretical predictions of such a phase transition at all fields and, therefore, with the predicted universality in the magnetic behavior of the type II superconductors. Nevertheless, by measuring the third harmonics of the ac susceptibility, this phase transition has been detected up to our highest available field (19 T), thus demonstrating the necessity of the higher harmonics analysis in studying these topics and moreover proving the validity of the theoretical predictions
Vortex dynamics in type-two superconductors analysed by Cole-cole plots of the AC magnetic susceptibility 1st and 3rd Harmonics
No full text
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
- …
