1,721,007 research outputs found
Analytical and Micromagnetic Study of Nonlinear Amplitude Modulation in Spintronic Modulators
No full textA previous universal model of "combined" frequency-amplitude nonlinear modulation has been used to describe the spin-wave dynamics observed in spin-transfer oscillators. In that case, it was shown that it is not possible to obtain a pure frequency modulation process because the strict nonlinear relationship existing between the characteristic parameters of the oscillator yields a non-negligible amplitude modulation process to take place simultaneously. Here, we demonstrate that there exists a particular configuration in which a spin-torque oscillator behaves as a "pure" nonlinear amplitude modulator. For the case of a nano-contact geometry, for example, such a condition implies the usage of an external out-of-plane bias field directed along the critical angle at which the frequency tunability coefficient T = partial derivative f/partial derivative I vanishes. In all those cases in which this coefficient is not zero, the previous combined process takes place. The phenomenon is first analyzed by developing an analytical model which describes the structure of the frequency spectrum of a nonlinearly amplitude modulated signal. Results of this approach are finally compared with those of micromagnetic investigations, carried out in time and frequency domains, deriving an excellent agreement
Eckhaus instability of stationary patterns in hyperbolic reaction–diffusion models on large finite domains
Full text linkWe have theoretically investigated the phenomenon of Eckhaus instability of stationary patterns arising in hyperbolic reaction–diffusion models on large finite domains, in both supercritical and subcritical regime. Adopting multiple-scale weakly-nonlinear analysis, we have deduced the cubic and cubic–quintic real Ginzburg–Landau equations ruling the evolution of pattern amplitude close to criticality. Starting from these envelope equations, we have provided the explicit expressions of the most relevant dynamical features characterizing primary and secondary quantized branches of any order: stationary amplitude, existence and stability thresholds and linear growth rate. Particular emphasis is given on the subcritical regime, where cubic and cubic–quintic Ginzburg–Landau equations predict qualitatively different dynamical pictures. As an illustrative example, we have compared the above-mentioned analytical predictions to numerical simulations carried out on the hyperbolic modified Klausmeier model, a conceptual tool used to describe the generation of stationary vegetation stripes over flat arid environments. Our analysis has also allowed to elucidate the role played by inertia during the transient regime, where an unstable patterned state evolves towards a more favorable stable configuration through sequences of phase-slips. In particular, we have inspected the functional dependence of time and location at which wavelength adjustment takes place as well as the possibility to control these quantities, independently of each other
Dryland vegetation pattern dynamics driven by inertial effects and secondary seed dispersal
Full text linkThis manuscript tackles the study of vegetation pattern dynamics driven by inertial effects and secondary seed dispersal. To achieve this goal, an hyperbolic extension of the classical parabolic Klausmeier model of vegetation, generally used to predict the formation of banded vegetation along the slopes of semiarid environments, has been here considered together with an additional advective term mimicking the downslope motion of seeds. Linear stability analyses have been carried out to inspect the dependence of the wave instability locus on the model parameters, with particular emphasis on the role played by inertial time and seed advection speed. Moreover, periodic travelling wave solutions are taken into account to better characterize modulus and direction of the migration speed of striped vegetation patterns. Theoretical predictions are corroborated by numerical Investigations and ecological implications are also discussed. In particular, it is highlighted how the hyperbolic nature of the model may provide possible justifications about some controversial field observations
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
Magnetic Signature Analysis of the Propulsor of a Military Ship
No full textThe analysis of magnetic signature and the consequent identification of
mitigation strategies are crucial issues in naval applications. The possibility to
evaluate the magnetic signature of some essential components and structures during
the design phase, represents an interesting opportunity to enhance ship design in
terms of stealth capabilities. The current paper focuses on the assessment of the
magnetic signature produced by a propulsor from a military ship with a fiberglass
hull. The propulsor largest and heaviest components, which contribute most to the
MS, were considered in the analysis. The numerical analysis carried out by means
of a finite-element method technique was based on a simple theoretical model
involving the concepts of averaged magnetization and of averaged permeability. The
developed investigation is aimed at comparing the magnetic signature of a
traditional propulsor with the one achievable by replacing the original ferromagnetic
materials with weakly ferromagnetic ones and with a non-magnetic material, such
as Aluminum, in the coating of the electric motor. The magnetic signature produced
in the underwater region nearby the propulsor is consistently reduced and it is
proved that the effect of Aluminum used in place of Cast iron is remarkable in
determining this reduction. Therefore, the selection of suitable materials for the most
critical parts in terms of magnetization and permeability, represents an effective yet
simple strategy to improve the stealth properties of military ships. The possibility to
use a simple model to evaluate the magnetic signature during the design phase is,
therefore, essential to support a convenient selection of materials
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-transfer torque switching in magnetic multilayers
No full textIn this paper, we point out how the magnetization switching depends on the nanostructure geometry and on the material parameters. The micromagnetic study is carried out on multilayer nanodevices constituted by Permalloy(Py)/Cu/Py and Co/Cu/Co with different cross-sections. Results show that the switching time is strongly dependent on the magnetization of the materia
Spin-transfer torque switching in magnetic multilayers
No full textIn this paper, we point out how the magnetization switching depends on the nanostructure geometry and material parameters. The micromagnetic study is carried out on multilayer nanodevices of Permalloy (Py)/CU/Py and Co/Cu/Cu with different cross section. Results show that the switching time is strongly dependent on the magnetization saturation of the materia
- …
