836 research outputs found

    When Do Adolescents Accept or Defy to Maternal Prohibitions? The Role of Social Domain and Communication Style.

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    Drawing upon both Social-Cognitive Domain Theory and Self-Determination Theory, the goal of the present multi-informant study was to test whether the correlates of maternal prohibitions depend on what is prohibited (i.e., the content of the social domain involved), thereby contrasting moral with friendship prohibitions, as well on how the prohibition is communicated, thereby contrasting an autonomy-supportive with a controlling communication style. In a sample of adolescents (N = 196; mean age = 13.9 years; 63 % female) and their mothers (N = 185; mean age = 44 years), we first examined mean-level differences between the two domains in terms of mothers' degree and style of prohibition, as well as on a number of developmental outcomes (i.e., adolescents' legitimacy perceptions, internalization, and oppositional defiance). Both adolescents and mothers reported more maternal involvement in the moral domain (e.g., higher scores for degree of prohibition and controlling communication style). In addition, adolescents reported greater perceived legitimacy and less oppositional defiance in the moral domain (as compared to the friendships domain). Second, we tested whether associations between degree and style of prohibition and the developmental outcomes were moderated by social domain. Whereas associations between degree of prohibition and developmental outcomes either were non-significant or moderated by domain, the associations with communication style were more domain-invariant, with an autonomy-supportive style generally yielding an adaptive pattern of correlates and with a controlling style relating to maladaptive outcomes. The discussion focuses on similarities and differences in the characteristics and correlates of both types of prohibitions

    Direct excitation of propagating spin waves by focused ultrashort optical pulses

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    An all-optical experiment long utilized to image phonons excited by ultrashort optical pulses has been applied to a magnetic sample. In addition to circular ripples due to surface acoustic waves, we observe an X-shaped pattern formed by propagating spin waves. The emission of spin waves from the optical pulse epicenter in the form of collimated beams is qualitatively reproduced by micromagnetic simulations. We explain the observed pattern in terms of the group velocity distribution of Damon-Eshbach magnetostatic spin waves in the reciprocal space and the wave vector spectrum of the focused ultrafast laser pulse

    Chiral symmetry breaking of magnetic vortices by sample roughness

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    Finite-element micromagnetic simulations are employed to study the chiral symmetry breaking of magnetic vortices, caused by the surface roughness of thin-film magnetic structures. An asymmetry between vortices with different core polarizations has been experimentally observed for square-shaped platelets. E.g., the threshold fields for vortex core switching were found to differ for core up and down. This asymmetry was however not expected for these symmetrically-shaped structures, where both core polarizations should behave symmetrically. Three-dimensional finite element simulations are employed to show that a small surface roughness can break the symmetry between vortex cores pointing up and down. A relatively small sample roughness is found sufficient to reproduce the experimentally observed asymmetries. It arises from the lack of mirror-symmetry of the rough thin-film structures, which causes vortices with different handedness to exhibit asymmetric dynamics

    Efficient magneto-optical trapping of a metastable helium gas

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    This article presents a new experiment aiming at BEC of metastable helium atoms. It describes the design of a high flux discharge source of atoms and a robust laser system using a DBR diode coupled with a high power Yb doped fiber amplifier for manipulating the beam of metastable atoms. The atoms are trapped in a small quartz cell in an extreme high vacuum. The trapping design uses an additional laser (repumper) and allows the capture of a large number of metastable helium atoms (approximately 10910^9) in a geometry favorable for loading a tight magnetostatic trap.Comment: 12 pages, 7 figures, Late

    The importance of the weak: Interaction modifiers in artificial spin ices

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    The modification of geometry and interactions in two-dimensional magnetic nanosystems has enabled a range of studies addressing the magnetic order, collective low-energy dynamics, and emergent magnetic properties, in e.g. artificial spin ice structures. The common denominator of all these investigations is the use of Ising-like mesospins as building blocks, in the form of elongated magnetic islands. Here we introduce a new approach: single interaction modifiers, using slave-mesospins in the form of discs, within which the mesospin is free to rotate in the disc plane. We show that by placing these on the vertices of square artificial spin ice arrays and varying their diameter, it is possible to tailor the strength and the ratio of the interaction energies. We demonstrate the existence of degenerate ice-rule obeying states in square artificial spin ice structures, enabling the exploration of thermal dynamics in a spin liquid manifold. Furthermore, we even observe the emergence of flux lattices on larger length-scales, when the energy landscape of the vertices is reversed. The work highlights the potential of a design strategy for two-dimensional magnetic nano-architectures, through which mixed dimensionality of mesospins can be used to promote thermally emergent mesoscale magnetic states.Comment: 17 pages, including methods, 4 figures. Supplementary information contains 16 pages and 15 figure

    Polarisation selective magnetic vortex dynamics and core reversal in rotating magnetic fields

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    A magnetic vortex occurs as an equilibrium configuration in thin ferromagnetic platelets of micron and sub-micron size and is characterised by an in-plane curling magnetisation. At the centre, a magnetic singularity is avoided by an out-of-plane magnetisation core. This core has a gyrotropic excitation mode, which corresponds to a circular motion of the vortex around its equilibrium position, where the rotation sense is determined by the direction of the vortex core magnetisation, its polarisation. Unlike linear fields or spin polarised currents, which excite both polarisation states, an in-plane rotating field can selectively excite one of the polarisation states. Here we report the observation of vortex dynamics in response to rotating magnetic fields, imaged with time-resolved scanning X-ray microscopy. We demonstrate that the rotating field only excites the gyrotropic mode if the rotation sense of the field coincides with the vortex gyration sense and that such a field can selectively reverse the vortex polarisation

    Motivating learners through information literacy

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    This paper is included in the Information Literacy: Key to an Inclusive Society, the proceedings of the European Conference on Information Literacy, 2016. The paper introduces a model for creating information literacy learning activities that motivate students. The model draws from informed learning, an approach to information literacy that emphasizes the role that information plays in fostering learning about a subject. Self-determination theory, a motivational theory that focuses on enabling self-determined learners, is applied within the informed learning framework. The results of the investigation outline characteristics of motivating learning activities that enable learning subject content through engagement with information. The model is intended to be used by librarians when working with classroom teachers to foster greater student learning gains through creative and reflective engagement with information
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