1,721,025 research outputs found
Signature of negative domain wall mass in soft magnetic materials
No full textMagnetic properties of ferromagnetic materials often originate from domain wall motion, involving different damping mechanisms, an effective mass and various interactions with the surrounding media. In metallic materials, eddy current damping overwhelms inertia and thus the effect of the mass is usually neglected. We have recently reported experimental evidence that in soft metallic ferromagnets eddy currents yield an observable negative contribution to the effective domain wall mass. The weight of this mass is of the order of 10-5 kg/m2, much larger than the positive Doring mass (∼10-9 kg/m2). This negative effective mass is responsible for the leftward asymmetry of Barkhausen noise pulse shapes. In particular, this asymmetry depends on the pulse duration and it is found to encode important information on the characteristic time of the underlying domain wall dynamics. Only on long timescales the pulse shapes are symmetric and show the universal features typical of the Barkhausen effect. This result clarifies the general significance of pulse shape asymmetry commonly observed in systems showing a similar crackling noise, and contributes to better understand the microscopic phenomena responsible of magnetic hysteresis
Rayleigh loops in the random-field Ising model on the Bethe lattice
Full text linkWe analyze the demagnetization properties of the random-field Ising model on the Bethe lattice focusing on the behavior near the disorder induced phase transition. We derive an exact recursion relation for the magnetization and integrate it numerically. Our analysis shows that demagnetization is possible only in the continuous high disorder phase, where at low field the loops are described by the Rayleigh law. In the low disorder phase, the saturation loop displays a discontinuity that is reflected by a nonvanishing magnetization m∞ after a series of nested loops. In this case, at low fields the loops are not symmetric and the Rayleigh law does not hold
Dynamic fracture model for acoustic emission
No full textWe study the acoustic emission produced by micro-cracks using a two-dimensional disordered lattice model of dynamic fracture, which allows to relate the acoustic response to the internal damage of the sample. We find that the distributions of acoustic energy bursts decays as a power law in agreement with experimental observations. The scaling exponents measured in the present dynamic model can related to those obtained in the quasi-static random fuse model. © EDP Sciences, Società Italiana di Fisica, and Springer-Verlag 2003
Loss separation for dynamic hysteresis in ferromagnetic thin films
No full textWe develop a theory for dynamic hysteresis in ferromagnetic thin films, on the basis of the phenomenological principle of loss separation. We observe that, remarkably, the theory of loss separation, originally derived for bulk metallic materials, is applicable to disordered magnetic systems under fairly general conditions regardless of the particular damping mechanism. We confirm our theory both by numerical simulations of a driven random-field Ising model, and by reexamining several experimental data reported in the literature on dynamic hysteresis in thin films. All the experiments examined and the simulations find a natural interpretation in terms of loss separation. The power losses' dependence on the driving field rate predicted by our theory fits satisfactorily all the data in the entire frequency range, thus reconciling the apparent lack of universality observed in different materials
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
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