1,721,086 research outputs found
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
Spin wave excitation in ferromagnetic nanowire - Conferenza internazionale
No full textRecently, excitation of persistent magnetization precession in a nanowire with a point-contact for spin-polarized current injection has been demonstrated. [1] Here we present a complete numerical study of current-driven magnetization dynamics in an extended Permalloy nanowire (x-direction)
with the width of 100nm (y-direction) and a thickness of 6nm (z-direction). The spin-polarized current is injected from a square 20-nm-thick CoFe 100x100 nm2 point-contact located in the middle of the nanowire. We focus on the dynamics at low in-plane bias field (parallel to the nanowire axis) where the magnetization of the polarizer forms an off-center vortex.
First, we study the magnetization dynamics excited by direct current: the Hopf bifurcation is found at the critical current. There is a current range where a limit cycle and a fixed point of dynamics (static state) co-exist. As expected, the self-oscillation frequencies are smaller than the ferromagnetic
resonance (FMR) frequency of 7.95 GHz , while the oscillation output power is found to be nearly constant. The off-center vortex configuration we studied is promising for application
where zero-field signal emission is required. The zero-field off-center vortex configuration may be achieved via exchange biasing of the pinned layer in low annealing field [2].
We also study the properties of spin-waves excited by a microwave spin-polarized current in this
system. a peak amplitude is observed at the
frequencies of long-wavelength spin-wave modes. We have found two interesting results: 1) the presence
of a jump in the curve of the wave vector vs. the microwave frequency near the FMR-frequency accompanied by a change of slope of the curve from positive to negative 2) the existence of a narrow range of frequencies where the group velocity is negative. The first result can be due to the
change of nature of the spin-wave mode excited (from surface to volume mode), while the second
one is in agreement with the fact that, in this region, a backward volume spin-wave is excited. The
backward nature of these spin-waves excited by spin-polarized current can be identified experimentally by means of the inverse Doppler effect.[3]
[1] C. Boone, J. A. Katine, J. R. Childress, J. Zhu, X. Cheng, I. N. Krivorotov, Phys. Rev. B, 79, 140404(R), (2009).
[2] A. Hoffmann, J. Sort, K. S. Buchanan, J. Nogués, IEEE Trans. on Magn. 44(7), 1968 (2008).
[3] D. D. Stancil, B. E. Henty, A. G. Cepni, J. P. Van’t Hof, Phys. Rev. B, 74, 060404(R), (2006)
Influence of the Cut Angle and Grain Size on the Behavior of Non-Oriented Magnetic Steels
No full text
Modeling of hysteresis in magnetic multidomains
No full textIn this paper, the analysis of multi-domain nanostructures is made by means of numerical approaches. The Landau-Lifshitz-Gilbert LLG equation is used to compute the magnetic hysteresis loops for different alternate scalar polarizations. The data computed are then used to identify the parameters of a phenomenological model, based on the extension of the Preisach model in 2-D. The identification in this case is the evaluation of the size and the position of the hysterons in the H-plane. Each hysteron is associated to a domain of the nanostructure and the assembly of hysterons reproduces with satisfactory accuracy the hysteretic behavior of the nanostructure computed by the LLG equation with an extremely reduced computational time. Some possible relationships between the magnetization nanostructure and the parameters of the hysteron are suggested. These relationship should be used for a "blind" prediction of the magnetization state of much larger magnetic structures, whose computation using the LLG equation is not possible in practice due to the enormous computational time, supposing that magnetic structures with the same aspect ratio exhibit a similar distribution of magnetic domains. The theory is applied here to an example of Permalloy nanostructure
Spreading sequences for fast switching process in spin-valve nanopillars
No full textA detailed study of the effects of binary spreading sequences (BSS) excitation in the magnetization dynamics of exchange-biased spin-valves driven by spin-transfer-torque has been carried out by full micromagnetic modeling. We show that the use of BSS allows to trigger the magnetization reversal by exciting its main precession modes. We compared our numerical results with the experimental ones reported by [Cui etal, Phys. Rev. B 77, 214440 (2008)], attaining quantitative agreement. Advantages of BSS as microwave source with respect to a sinusoidal signal are also reported and discussed
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