1,721,037 research outputs found
Analytical and numerical solution to the nonlinear cubic Duffing equation: An application to electrical signal analysis of distribution lines
Full text linkThe Duffing oscillator represents an important model to describe mathematically the non- linear behaviour of several phenomena occurring in physics and engineering. In this paper, analytical and numerical solutions to the nonlinear cubic Duffing equation governing the time behaviour of an electrical signal are found as a function of the magnitude and of the sign of the nonlinear parameter, of the damping parameter and for different values of the forcing term. A stability analysis of the Duffing equation in the absence of the forcing term is also performed as a function of the sign and magnitude of the nonlinear param- eter. A fitting procedure of the Duffing solution to the current signal flowing in different distribution lines allows us to determine the degree of nonlinearity of the electrical signal suggesting a potential way to quantify the nonlinear behaviour of current electrical signals
Micromagnetic Study of Electrical-Field-Assisted Magnetization Switching in MTJ Devices
No full textPerpendicular MgO-based magnetic tunnel junctions are optimal candidates as building blocks of spin-transfer torque (STT) magnetoresistive memories. However, up to now, the only STT is not enough to achieve switching current density below A/cm . A recent work has experimentally demonstrated the possibility of performing magnetization switching assisted by an electric-field at ultralow current density. Theoretically, this switching has been studied using a macrospin approach only. Here, we show a full micromagnetic study. We found that the switching occurs via a complex nucleation process including the nucleation of magnetic vortexes
Seasonal signal analysis of distribution lines in smart grids via Hilbert-Huang transform
No full textThe increase of grid-connected renewable energy
sources represents a hot topic for the operation and management
of a smart grid, because the power injected into the grid by the
most of them is unpredictable. Some constraints depend on the
environmental condition, while some others depend on the need
to guarantee stability, security and power quality of the grid.
This implies that the power signals of distribution lines having
distributed generators are typically a-periodic, non-stationary
and nonlinear. Thus, mathematical tools usually adopted to
analyze the electrical behavior of a distribution line can be
inaccurate and reductive. This paper compares the seasons-based
results obtained by applying the Fast Fourier Transform (FFT)
and the Hilbert-Huang Transform (HHT) to the active and
reactive powers of three different distribution lines belonging to a
smart grid, highlighting remarkable differences. That analysis
shows that the HHT is able to extract more accurate information
than the FFT
Skyrmion motion induced by spin-Hall current in constrained geometries
No full textMagnetic skyrmions are topologically protected spin textures typical of chiral magnets characterized
by a special kind of exchange interaction known as Dzyaloshinkii-Moriya interaction (DMI).
In the last years growing interest has been addressed to the study of these topological defects both
from a fundamental point of view and for its several technological applications like for instance
their usage as information carriers [1]. Great attention has been also given to skyrmion nucleation,
stability and motion in confined magnetic systems under the influence of a spin-current [2,3].
Recently, the effect of confinement has been studied in the presence of spin-polarized current [2],
but there are not yet studies focusing on the skyrmion motion driven by SHE in constrained
geometries.
Here, we solve analytically Thiele’s equation in the presence of spin-Hall effect (SHE) with no
external field and by taking into account confinement. The spin-Hall current injected in the heavy
metal along the x direction (see Fig.1 (a)) combined with the interfacial DMI favors the Néel skyrmion
(hedgehog-like) nucleation in a thin magnetized stripe. We model confinement effects by
introducing a potential V(r) which arises at the boundaries of the magnetic stripe. This potential can
be thought of as a positive barrier having a repulsive nature associated to the static magnetization
rotation at the stripe borders. The Nèel skyrmions is interpreted as a quasi-particle which interacts
repulsively with this barrier. As a result, its trajectory is deviated
Topological skyrmion dynamics driven by spin-transfer torque
No full textVery recently, an important class of magnetic solitons called magnetic skyrmions has been widely
studied [1,2]. The stability of these topological defects has been analyzed in the presence of intrinsic
dissipation both as a function of Dzyaloshinskii–Moriya interaction (DMI) and as a function of
a spin-polarized current (SPC).
Here, we show that in a spin-valve consisting of Pt(5 nm)/Co(0.6 nm)/Cu (4 nm)/CoPt(4 nm) a
perpendicular spin current, in the presence of the DMI [3,4] and strong perpendicular anisotropy,
induces the rotation of the spins from the hedgehog-like to the vortex-like texture in the topological
droplet state and excites low-frequency topological modes. The SPC is injected locally in the Co
giving rise to the local excitation of the magnetization. The Pt heavy metal adds a further degree of
freedom, the interfacial DMI, to the effective field of the Co. The FL has a square cross section of
400 x 400 nm2, while the point contact has a diameter of 70 nm. Both FL and polarizer have out-ofplane
magnetic state at zero bias field. The “topological droplet” state (integer skyrmion number)
arises and its dynamical response, namely a “topological mode” (TM), can be excited and sustained
by a SPC. The low-frequency TM is linked to a continual conversion from hedgehog-like (Néel
skyrmion) to vortex-like (Bloch skyrmion) state, preserving the topology represented by the skyrmion
number S = -1. A negative current (J < 0) flows from the free layer (Co) to the fixed (nanocontact,
CoPt) layer. The topological character of these spin-wave excitations results from the
synchronized dynamics between the 360o rotation of the spin of the outer droplet domain and the
expansion/shrinking of the droplet core.
A quantitative description of topological droplet modes is given according to an analytical model
based on the linearization of the equations of motion including intrinsic positive Gilbert damping
and negative damping related to the spin-transfer torque. The analytical frequency of the topological
droplet mode is expressed as the solution of a second-order algebraic equation written in terms
of the magnetic parameters including the intrinsic and extrinsic damping
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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