Controlled nucleation of topological defects in the stripe domain patterns of Lateral multilayers with Perpendicular Magnetic Anisotropy: competition between magnetostatic, exchange and misfit interactions

Magnetic lateral multilayers have been fabricated on weak perpendicular magnetic anisotropy amorphous Nd-Co films in order to perform a systematic study on the conditions for controlled nucleation of topological defects within their magnetic stripe domain pattern. A lateral thickness modulation of period $w$ is defined on the nanostructured samples that, in turn, induces a lateral modulation of both magnetic stripe domain periods $\lambda$ and average in-plane magnetization component $M_{inplane}$. Depending on lateral multilayer period and in-plane applied field, thin and thick regions switch independently during in-plane magnetization reversal and domain walls are created within the in-plane magnetization configuration coupled to variable angle grain boundaries and disclinations within the magnetic stripe domain patterns. This process is mainly driven by the competition between rotatable anisotropy (that couples the magnetic stripe pattern to in-plane magnetization) and in-plane shape anisotropy induced by the periodic thickness modulation. However, as the structural period $w$ becomes comparable to magnetic stripe period $\lambda$, the nucleation of topological defects at the interfaces between thin and thick regions is hindered by a size effect and stripe domains in the different thickness regions become strongly coupled.Comment: 10 pages, 7 figures, submitted to Physical Review

Further analysis of the connected moments expansion

We apply the connected moments expansion to simple quantum--mechanical examples and show that under some conditions the main equations of the approach are no longer valid. In particular we consider two--level systems, the harmonic oscillator and the pure quartic oscillator.Comment: 19 pages; 2 tables; 4 figure

Intermittency in Hall-magnetohydrodynamics with a strong guide field

We present a detailed study of intermittency in the velocity and magnetic field fluctuations of compressible Hall-magnetohydrodynamic turbulence with an external guide field. To solve the equations numerically, a reduced model valid when a strong guide field is present is used. Different values for the ion skin depth are considered in the simulations. The resulting data is analyzed computing field increments in several directions perpendicular to the guide field, and building structure functions and probability density functions. In the magnetohydrodynamic limit we recover the usual results with the magnetic field being more intermittent than the velocity field. In the presence of the Hall effect, field fluctuations at scales smaller than the ion skin depth show a substantial decrease in the level of intermittency, with close to monofractal scaling.Comment: 10 pages, 8 figure

Block Gauss and anti-Gauss quadrature with application to networks

Approximations of matrix-valued functions of the form WT f(A)W, where A ∈Rm×m is symmetric, W ∈ Rm×k, with m large and k ≪ m, has orthonormal columns, and f is a function, can be computed by applying a few steps of the symmetric block Lanczos method to A with initial block-vector W ∈ Rm×k. Golub and Meurant have shown that the approximants obtained in this manner may be considered block Gauss quadrature rules associated with a matrix-valued measure. This paper generalizes anti-Gauss quadrature rules, introduced by Laurie for real-valued measures, to matrix-valued measures, and shows that under suitable conditions pairs of block Gauss and block anti-Gauss rules provide upper and lower bounds for the entries of the desired matrix-valued function. Extensions to matrix-valued functions of the form WT f(A)V , where A ∈ Rm×m may be nonsymmetric, and the matrices V, W ∈ Rm×k satisfy VT W = Ik also are discussed. Approximations of the latter functions are computed by applying a few steps of the nonsymmetric block Lanczos method to A with initial block-vectors V and W. We describe applications to the evaluation of functions of a symmetric or nonsymmetric adjacency matrix for a network. Numerical examples illustrate that a combination of block Gauss and anti-Gauss quadrature rules typically provides upper and lower bounds for such problems. We introduce some new quantities that describe properties of nodes in directed or undirected networks, and demonstrate how these and other quantities can be computed inexpensively with the quadrature rules of the present paper

Analytical Model of Socio-Technical Sustainability of Dynamic Hypermedia Devices

Este artículo presenta un modelo analítico de sostenibilidad de redes socio-técnicas para la construcción colaborativa de conocimiento en contextos institucionales y organizacionales. El objetivo se centra en fundamentar una perspectiva teórica-metodológica a partir de la noción de “dispositivo hipermedial dinámico” (DHD). En lo metodológico, desde un posicionamiento sociotécnico, se realiza una revisión de los principales debates y perspectivas teóricas sobre la expansión de TIC en relación a la problemática a tratar. Luego se desarrollan propositivamente las componentes del modelo de sostenibilidad-DHD siguiendo sus cuatro dimensiones: social, institucional, tecnológica y textual. El diseño del modelo, no jerárquico y relacional, se estima a su vez beneficioso para orientar el proceso constructivo de este tipo de dispositivos. Además, puede colaborar de manera flexible para analizar transformaciones socio-tecnológicas en diversos contextos situados. Finalmente, la consistencia de los resultados analíticos a alcanzar podría ser efectiva, ya que es posible vincular: el carácter dinámico, relacional e interactivo de las características de una tecnología; las tensiones sociales y políticas existentes en el marco socio-institucional donde se desarrolla; las posibles formas de diseño participativo, en función de los requerimientos de una institución u organización; y la producción colaborativa en red, promoviendo responsabilidades de gestión organizacional.Este artigo apresenta um modelo analítico de sustentabilidade de redes sociotécnicas para a construção colaborativa de conhecimento em contextos institucionais/organizacionais. O objetivo é focado na fundamentação de uma perspectiva teórico-metodológica a partir da noção de “dispositivo hipermedial dinâmico” (DHD). No metodológico, a partir de um posicionamento sociotécnico, é feita uma revisão dos principais debates e perspectivas teóricas sobre a expansão de TIC em relação à problemática a ser tratada. Depois, são desenvolvidos propositivamente os componentes do modelo de sustentabilidade-DHD seguindo suas quatro dimensões: social, institucional, tecnológica e textual. O design do modelo, não hierárquico e relacional, é também considerado propício para orientar o processo construtivo deste tipo de dispositivos. Além disso, pode colaborar de forma flexível para analisar transformações sociais tecnológicas em diversos contextos. Finalmente, a consistência dos resultados analíticos a serem alcançados poderia ser efetiva, pois é possível vincular: o caráter dinâmico, relacional e interativo das características de uma tecnologia; as tensões sociais e políticas existentes no plano social institucional onde é desenvolvido; as possíveis formas de design participativo, em função dos requerimentos de uma instituição ou organização; e a produção colaborativa em rede, promovendo responsabilidades de gestão organizacional.This paper presents an analytical model of sustainable socio-technical networks for the collaborative knowledge building in organizational/institutional contexts. Its objective focuses on supporting a theoretic-methodological perspective based on the idea of a “dynamic hypermedia device” (DHD). With regard to the methodological aspect, from a socio-technical position, the main debates and theoretical perspectives about the expansion of information and communication technologies pertinent to the issue to be discussed are reviewed. Then the components of the sustainability-DHD model are developed proactively, following its four dimensions: social, institutional, technological and textual. The design of the model, nonhierarchical and relational, is considered beneficial to guide the building process of these kinds of devices. In addition, it can collaborate in a flexible way in order to analyze the sociotechnological transformations in diverse situational contexts. Finally, the consistency of the analytical results to be reached could be effective, since it is possible to connect: the dynamic, relational and interactive aspects of the technology’s characteristics; the social and political tensions within the socio-institutional framework in which it develops; the possible ways of participative design, as a function of the institution or organization’s requirements; and the networked collaborative production, promoting organizational management responsibilities.Fil: Andres, Gonzalo Dario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto Rosario de Investigaciones en Ciencias de la Educación. Universidad Nacional de Rosario. Instituto Rosario de Investigaciones en Ciencias de la Educación; ArgentinaFil: San Martin, Patricia Silvana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto Rosario de Investigaciones en Ciencias de la Educación. Universidad Nacional de Rosario. Instituto Rosario de Investigaciones en Ciencias de la Educación; ArgentinaFil: Rodriguez, Guillermo L.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto Rosario de Investigaciones en Ciencias de la Educación. Universidad Nacional de Rosario. Instituto Rosario de Investigaciones en Ciencias de la Educación; Argentin